**2. Compact and electrically small printed multiband monopoles**

The currently available and future commercial wireless systems require antennas having wide bandwidth to support higher data rate and be able to operate at multiple frequency bands defined by various protocols. Compact size printed monopole antennas are important for the wireless applications due to its advantages of easy fabrication, omnidirectional radiation and wide operation bandwidth.

**2.1. Dual band fractal monopole**

spaced lines [3].

is no ground plane.

there is no ground plane.

**1.2.1 Dual band fractal monopole**

such space filling geometry.

Studies show that Minkowski Island geometry is a good candidate for the design of multiband printed monopole antennas. Compared to other fractal geometries such as Hilbert curves, Minkowski Island geometry can work more efficiently with respect to the frequency reduction, due to its meandered-like configuration [3]. As demonstrated in Figure 1, when a Hilbert curve is employed to design a printed monopole antenna, the closely spaced lines can cause a large amount of current cancellation compared to the Minkowski Island geometry, which means that the effective electrical length of the Hilbert Curve antenna cannot benefit much from using

Studies show that Minkowski Island geometry is a good candidate for the design of multiband printed monopole antennas. Compared to other fractal geometries such as Hilbert curves, Minkowski Island geometry can work more efficiently with respect to the frequency reduction, due to its meandered-like configuration [3]. As demonstrated in Figure **1**, when a Hilbert curve is employed to design a printed monopole antenna, the closely spaced lines can cause a large amount of current cancellation compared to the Minkowski Island geometry, which means that the effective

Figure 1: (a) The 2nd iteration of Minkowski Island geometry ; (b) current cancellation of a Hilbert Curve (b) [3].

**Figure 1.** (a) The 2nd iteration of Minkowski Island geometry; (b) current cancellation of a Hilbert Curve (b) [3].

Current Cancellation

http://dx.doi.org/10.5772/58815

59

(a) (b)

Input

In [4], two compact dual-band printed fractal monopoles for WLAN applications were presented. These two monopoles are designed using the 1st and 2nd iteration of the Minkowski Island, as presented in **Figure 2**. **Figure 2**(a) shows the printed monopole based on the 1st iteration Minkowski Island. Its size is 28 mm ×18 mm with a partial ground plane having a width of 35 mm and length of 10 mm on the back side of the substrate. The width of the microstrip line is 0.5 mm. **Figure 2**(b) shows another proposed fractal monopole using the 2nd iteration Minkowski Island. Its size is 21.5 mm ×18 mm and the size of the ground plane is 30 mm ×10 mm. The depth *t*, shown in Figure 1, is 1/4 of the side length (*s*/4) at each iteration for both antennas. The line widths of both antennas were set based on two factors: the antenna input impedance and the fact that the microstrip line needs to be narrow enough to avoid the intersection between adjacent lines. This issue is more significant for fractal of higher iterations. As a result of using a higher iteration fractal, narrower microstrip line needs to be used and the width of the microstrip line is reduced to 0.25 mm. Both of the proposed antennas are printed on the top side of the substrate, 0.813 mm thick Roger 4003 with relative permittivity εr=3.38, while the ground plane is printed at the bottom side. Behind the antenna elements, there

In [4], two compact dual-band printed fractal monopoles for WLAN applications were presented. These two monopoles are designed using the 1st and 2nd iteration of the Minkowski Island, as presented in Figure 2. Figure 2(a) shows the printed monopole based on the 1st iteration Minkowski Island. Its size is 28 mm ×18 mm with a partial ground plane having a width of 35 mm and length of 10 mm on the back side of the substrate. The width of the microstrip line is 0.5 mm. Figure 2(b) shows another proposed fractal monopole using the 2nd iteration Minkowski Island. Its size is 21.5 mm ×18 mm and the size of the ground plane is 30 mm ×10 mm. The depth *t*, shown in Figure 1, is 1/4 of the side length (*s*/4) at each iteration for both antennas. The line widths of both antennas were set based on two factors: the antenna input impedance and the fact that the microstrip line needs to be narrow enough to avoid the intersection between adjacent lines. This issue is more significant for fractal of higher iterations. As a result of using a higher iteration fractal, narrower microstrip line needs to be used and the width of the microstrip line is reduced to 0.25 mm. Both of the proposed antennas are printed on the top side of the substrate, 0.813 mm thick Roger 4003 with relative permittivity εr=3.38, while the ground plane is printed at the bottom side. Behind the antenna elements,

Both of the proposed monopole antennas have a compact size compared to conventional printed monopole antennas, which need to have a length of approximately a quarter of

electrical length of the Hilbert Curve antenna cannot benefit much from using such space filling geometry.

It is important to point out that although fractal geometries are self-filling structures that can be scaled without increasing the overall size, not all the geometries can contribute to the compact antenna design. Previous research found that some fractal geometries such as Hilbert and Peano curves, which exhibit a high degree of space filling, cannot effectively reduce the resonant frequency of the antenna due to the cancelling of the current between closely

Low Cost Compact Multiband Printed Monopole Antennas and Arrays for Wireless Communications

It is known that to reach the resonant condition, the dimension of the antenna must be a fraction of the wavelength at its resonant frequency. This means that the lower resonant frequency is, the larger the size of the antenna will be. From the limitations of the electrically small antennas defined by Chu [1], it is clear that antennas of smaller size always exhibit a higher quality factor whereas the bandwidth of an antenna is inversely proportional to the quality factor. As such the size reduction of an antenna will lead to the deterioration of its radiation performance. Therefore, compact multiband antenna design with promising radiation performance has attracted much research interests.

To be a low cost solution, it is desirable to fabricate the monopoles in PCB technology using only a single layer of substrate and a planar structure. Being a planar structure, the radiating element must have a geometry that can excite higher modes within a limited volume, to have a multiband operation. One approach that can be employed is to use fractal geometries to design compact multiband printed monopole antennas. Fractal geometry is a family of geometries that have the characteristics of inherent self-similar or self-affinity, which were used to describe and model complex shapes found in nature such as mountain ranges, waves and trees [2]. Recently, fractal techniques have been brought to the field of electromagnetic theory, a research field which has been called fractal electrodynamics; it has also been implemented in antenna design and named "fractal antenna engineering". This topic has been attracting much research interest. There are several advantages of using fractal geometries. First of all, it can reduce the size of the antenna, which makes it a good candidate for antenna miniaturization. Fractal geometries are self-filling structures that can be scaled without increasing the overall size. This characteristic provides opportunities for antenna designers to explore new geometries suitable for small antenna design. Secondly, fractal is a geometry that is self-repeated at different scales, which means that the fractal technique can be explored for designing antenna with multiple band operation and similar radiation patterns.

It is important to point out that although fractal geometries are self-filling structures that can be scaled without increasing the overall size, not all the geometries can contribute to the compact antenna design. Previous research found that some fractal geometries such as Hilbert and Peano curves, which exhibit a high degree of space filling, cannot effectively reduce the resonant frequency of the antenna due to the cancelling of the current between closely spaced lines [3].

#### **2.1. Dual band fractal monopole** spaced lines [3].

**2. Compact and electrically small printed multiband monopoles**

wide operation bandwidth.

58 Progress in Compact Antennas

attracted much research interests.

lines [3].

The currently available and future commercial wireless systems require antennas having wide bandwidth to support higher data rate and be able to operate at multiple frequency bands defined by various protocols. Compact size printed monopole antennas are important for the wireless applications due to its advantages of easy fabrication, omnidirectional radiation and

It is known that to reach the resonant condition, the dimension of the antenna must be a fraction of the wavelength at its resonant frequency. This means that the lower resonant frequency is, the larger the size of the antenna will be. From the limitations of the electrically small antennas defined by Chu [1], it is clear that antennas of smaller size always exhibit a higher quality factor whereas the bandwidth of an antenna is inversely proportional to the quality factor. As such the size reduction of an antenna will lead to the deterioration of its radiation performance. Therefore, compact multiband antenna design with promising radiation performance has

To be a low cost solution, it is desirable to fabricate the monopoles in PCB technology using only a single layer of substrate and a planar structure. Being a planar structure, the radiating element must have a geometry that can excite higher modes within a limited volume, to have a multiband operation. One approach that can be employed is to use fractal geometries to design compact multiband printed monopole antennas. Fractal geometry is a family of geometries that have the characteristics of inherent self-similar or self-affinity, which were used to describe and model complex shapes found in nature such as mountain ranges, waves and trees [2]. Recently, fractal techniques have been brought to the field of electromagnetic theory, a research field which has been called fractal electrodynamics; it has also been implemented in antenna design and named "fractal antenna engineering". This topic has been attracting much research interest. There are several advantages of using fractal geometries. First of all, it can reduce the size of the antenna, which makes it a good candidate for antenna miniaturization. Fractal geometries are self-filling structures that can be scaled without increasing the overall size. This characteristic provides opportunities for antenna designers to explore new geometries suitable for small antenna design. Secondly, fractal is a geometry that is self-repeated at different scales, which means that the fractal technique can be explored for

designing antenna with multiple band operation and similar radiation patterns.

It is important to point out that although fractal geometries are self-filling structures that can be scaled without increasing the overall size, not all the geometries can contribute to the compact antenna design. Previous research found that some fractal geometries such as Hilbert and Peano curves, which exhibit a high degree of space filling, cannot effectively reduce the resonant frequency of the antenna due to the cancelling of the current between closely spaced

Studies show that Minkowski Island geometry is a good candidate for the design of multiband printed monopole antennas. Compared to other fractal geometries such as Hilbert curves, Minkowski Island geometry can work more efficiently with respect to the frequency reduction, due to its meandered-like configuration [3]. As demonstrated in Figure 1, when a Hilbert curve is employed to design a printed monopole antenna, the closely spaced lines can cause a large amount of current cancellation compared to the Minkowski Island geometry, which means that the effective electrical length of the Hilbert Curve antenna cannot benefit much from using such space filling geometry. **1.2.1 Dual band fractal monopole** Studies show that Minkowski Island geometry is a good candidate for the design of multiband printed monopole antennas. Compared to other fractal geometries such as Hilbert curves, Minkowski Island geometry can work more efficiently with respect to the frequency reduction, due to its meandered-like configuration [3]. As demonstrated in Figure **1**, when a Hilbert curve is employed to design a printed monopole antenna, the closely spaced lines can cause a large amount of current cancellation compared to the Minkowski Island geometry, which means that the effective electrical length of the Hilbert Curve antenna cannot benefit much from using such space filling geometry.

It is important to point out that although fractal geometries are self-filling structures that can be scaled without

cannot effectively reduce the resonant frequency of the antenna due to the cancelling of the current between closely

 Figure 1: (a) The 2nd iteration of Minkowski Island geometry ; (b) current cancellation of a Hilbert Curve (b) [3]. **Figure 1.** (a) The 2nd iteration of Minkowski Island geometry; (b) current cancellation of a Hilbert Curve (b) [3].

In [4], two compact dual-band printed fractal monopoles for WLAN applications were presented. These two monopoles are designed using the 1st and 2nd iteration of the Minkowski Island, as presented in **Figure 2**. **Figure 2**(a) shows the printed monopole based on the 1st iteration Minkowski Island. Its size is 28 mm ×18 mm with a partial ground plane having a width of 35 mm and length of 10 mm on the back side of the substrate. The width of the microstrip line is 0.5 mm. **Figure 2**(b) shows another proposed fractal monopole using the 2nd iteration Minkowski Island. Its size is 21.5 mm ×18 mm and the size of the ground plane is 30 mm ×10 mm. The depth *t*, shown in Figure 1, is 1/4 of the side length (*s*/4) at each iteration for both antennas. The line widths of both antennas were set based on two factors: the antenna input impedance and the fact that the microstrip line needs to be narrow enough to avoid the intersection between adjacent lines. This issue is more significant for fractal of higher iterations. As a result of using a higher iteration fractal, narrower microstrip line needs to be used and the width of the microstrip line is reduced to 0.25 mm. Both of the proposed antennas are printed on the top side of the substrate, 0.813 mm thick Roger 4003 with relative permittivity εr=3.38, while the ground plane is printed at the bottom side. Behind the antenna elements, there is no ground plane. In [4], two compact dual-band printed fractal monopoles for WLAN applications were presented. These two monopoles are designed using the 1st and 2nd iteration of the Minkowski Island, as presented in Figure 2. Figure 2(a) shows the printed monopole based on the 1st iteration Minkowski Island. Its size is 28 mm ×18 mm with a partial ground plane having a width of 35 mm and length of 10 mm on the back side of the substrate. The width of the microstrip line is 0.5 mm. Figure 2(b) shows another proposed fractal monopole using the 2nd iteration Minkowski Island. Its size is 21.5 mm ×18 mm and the size of the ground plane is 30 mm ×10 mm. The depth *t*, shown in Figure 1, is 1/4 of the side length (*s*/4) at each iteration for both antennas. The line widths of both antennas were set based on two factors: the antenna input impedance and the fact that the microstrip line needs to be narrow enough to avoid the intersection between adjacent lines. This issue is more significant for fractal of higher iterations. As a result of using a higher iteration fractal, narrower microstrip line needs to be used and the width of the microstrip line is reduced to 0.25 mm. Both of the proposed antennas are printed on the top side of the substrate, 0.813 mm thick Roger 4003 with relative permittivity εr=3.38, while the ground plane is printed at the bottom side. Behind the antenna elements, there is no ground plane.

> Both of the proposed monopole antennas have a compact size compared to conventional printed monopole antennas, which need to have a length of approximately a quarter of

802.11b/g standards.

802.11b/g standards.

to the simulation results, the radiation efficiency is 94% and 88% at 2.45 GHz, 97% and 93% at 5.26 GHz for the printed monopole of 1st and 2nd iteration of Minkowski Island, respectively. From these results, it is found that although higher size reduction can be achieved using higher iteration of the fractal geometry, the bandwidth as well as the radiation efficiency also decreases. This should be considered as a trade-off between size reduction and antenna performance. Figure 4 shows the measured E-and H-plane radiation pattern of the printed monopole with 2nd iteration of Minkowski Island at its dual resonant frequencies. Measure‐ ments showed that both antennas have similar radiation patterns so the measurement results for the other prototypes (the printed monopole of 1st iteration of Minkowski Island) are not

Low Cost Compact Multiband Printed Monopole Antennas and Arrays for Wireless Communications

0° 15° 30° 45° 60°

0° 15° 30° 45° 60°

<sup>75</sup>° <sup>90</sup>° <sup>105</sup>°

−105° −90° −75°

(a)

<sup>75</sup>° <sup>90</sup>° <sup>105</sup>°

−105° −90° −75°

(b)

−60° −45° −30° −15°

120° 135° 150° 165° ±180° −165° −150° −135° −120°

−30 −20 −10 <sup>0</sup>

−60° −45° −30° −15°

120° 135° 150° 165° ±180° −165° −150° −135° −120°

−12 −8 −4 <sup>0</sup>

 Figure 4: : Measured radiation patterns of the proposed antenna with the 2nd iteration of Minkowski Island: (a) at 2.45 GHz, E-plane; and (b) at 2.45 GHz, H-plane; (c) at 5.3 GHz, E-plane and (d) at 5.3 GHz, H-plane [4].

(c) (d)

**Figure 4.** Measured radiation patterns of the proposed antenna with the 2nd iteration of Minkowski Island: (a) at

2.45°GHz, E-plane; and (b) at 2.45°GHz, H-plane; (c) at 5.3°GHz, E-plane and (d) at 5.3°GHz, H-plane [4].

0° 15° 30° 45° 60°

http://dx.doi.org/10.5772/58815

61

0° 15° 30° 45° 60°

<sup>75</sup>° <sup>90</sup>° <sup>105</sup>°

−105° −90° −75°

<sup>75</sup>° <sup>90</sup>° <sup>105</sup>°

−105° −90° −75°

(b)

−60° −45° −30° −15°

120° 135° 150° 165° ±180° −165° −150° −135° −120°

(a) (b)

−30 −20 −10 <sup>0</sup>

(a)

−60° −45° −30° −15°

120° 135° 150° 165° ±180° −165° −150° −135° −120°

−12 −8 −4 <sup>0</sup>

The frequency ratio of the multiband fractal antenna is investigated in [4]. It is shown that as a multiband antenna, the frequency ratio of the fractal antenna using the Minkowski geometry is nearly fixed. This indicates that in order to extend the fractal technique to other multiband antennas design, there is a need to explore an effective solution to overcome this limit. One technique that can be employed to extend the frequency ratio of the fractal-based multiband antenna design is to combine the fractal geometry with the meander line. One compact antenna suitable for a commercial wireless USB device is proposed by using such technique [5]. Since the objective is to design a printed fractal monopole antenna for WLAN USB dongle applications, based on the industrial requirement, the overall size of this antenna including the ground plane is chosen to be 20 mm×60 mm and the available space for antenna design

A variation of the Koch fractal, which also can be referred as Cohen dipole fractal geometry, was used in this design. The Cohen dipole geometry, which is a variation of Koch fractal, was first proposed by Nathan Cohen [6] to design a dipole antenna with the feeding at the center position. Different from a conventional printed monopole antenna, the antenna radiating element is printed on the same layer of the ground plane. This type of antenna is named Inverted-L Antenna (ILA). As a typical printed monopole antenna, the antenna element with the feeding line and the ground plane are printed at the top and bottom side of the substrate, respectively. Meanwhile, the feeding port is located at the end of the substrate as shown in Figure5. This might be a problem in a practical industry design as other components, such as RF module, also need to be mounted on the same ground plane. Such problem can be solved by

given to avoid repetition.

**1.2.2 Fractal ILA antenna** 

using ILA antenna.

is limited to no more than 20 mm × 10 mm.

(a) (b) Figure 2: Exploded view of the fractal monopole antenna with geometry of: (a) 1st iteration Minkowski Island; (b) 2nd iteration of Minkowski Island proposed in [4]. **Figure 2.** Exploded view of the fractal monopole antenna with geometry of: (a) 1st iteration Minkowski Island; (b) 2nd iteration of Minkowski Island proposed in [4].

Figure 2: Exploded view of the fractal monopole antenna with geometry of: (a) 1st iteration Minkowski Island; (b)

wavelength. Moreover, it is found that without using any additional impedance matching techniques, both of these two proposed antennas exhibit good impedance match at multiple frequency bands, which is confirmed by the measurement results shown in Figure 3. These results show that the printed monopole of 1st iteration of Minkowski Island exhibits 10-dB return loss from 2.30-2.48 GHz, 3.3-3.7 GHz and 4.9-6.0 GHz, which covers the entire required frequency bands for 802.11a/b/g and WiMAX communications. For the 2nd iteration of Minkowski Island fractal monopole, the 10-dB return loss bands are 2.31-2.47 GHz and 5.0-5.5 GHz, which covers the two desired frequency bands for WLAN 802.11b/g standards. 2nd iteration of Minkowski Island proposed in [4]. Both of the proposed monopole antennas have a compact size compared to conventional printed monopole antennas, which need to have a length of approximately a quarter of wavelength. Moreover, it is found that without using any additional impedance matching techniques, both of these two proposed antennas exhibit good impedance match at multiple frequency bands, which is confirmed by the measurement results shown in Figure 3. These results show that the printed monopole of 1st iteration of Minkowski Island exhibits 10-dB return loss from 2.30 - 2.48 GHz, 3.3 - 3.7 GHz and 4.9 - 6.0 GHz, which covers the entire required frequency bands for 802.11a/b/g and WiMAX communications. For the 2nd iteration of Minkowski Island fractal monopole, the 10-dB Both of the proposed monopole antennas have a compact size compared to conventional printed monopole antennas, which need to have a length of approximately a quarter of wavelength. Moreover, it is found that without using any additional impedance matching techniques, both of these two proposed antennas exhibit good impedance match at multiple frequency bands, which is confirmed by the measurement results shown in Figure 3. These results show that the printed monopole of 1st iteration of Minkowski Island exhibits 10-dB return loss from 2.30 - 2.48 GHz, 3.3 - 3.7 GHz and 4.9 - 6.0 GHz, which covers the entire required frequency bands for 802.11a/b/g and WiMAX communications. For the 2nd iteration of Minkowski Island fractal monopole, the 10-dB return loss bands are 2.31 - 2.47 GHz and 5.0 - 5.5 GHz, which covers the two desired frequency bands for WLAN

return loss bands are 2.31 - 2.47 GHz and 5.0 - 5.5 GHz, which covers the two desired frequency bands for WLAN

Figure 3: Measured reflection coefficient of the proposed antenna with the: (a) 1st iteration and (b) 2nd iteration of Minkowski Island geometry [4]. **Figure 3.** Measured reflection coefficient of the proposed antenna with the: (a) 1st iteration and (b) 2nd iteration of Minkowski Island geometry [4]. Figure 3: Measured reflection coefficient of the proposed antenna with the: (a) 1st iteration and (b) 2nd iteration of Minkowski Island geometry [4].

The measured results also show that the radiation patterns at the H-plane are almost isotropic and in the E-plane they exhibit broadside radiation patterns, as expected. The measured maximum gain is around 1.5 dB at 2.45 GHz and 2.3 dB at 5.2 GHz for both antennas. According to the simulation results, the radiation efficiency is 94% and 88% at 2.45 The measured results also show that the radiation patterns at the H-plane are almost isotropic and in the E-plane they exhibit broadside radiation patterns, as expected. The measured maximum gain is around 1.5 dB at 2.45 GHz and 2.3 dB at 5.2 GHz for both antennas. According The measured results also show that the radiation patterns at the H-plane are almost isotropic and in the E-plane they exhibit broadside radiation patterns, as expected. The measured maximum gain is around 1.5 dB at 2.45 GHz and 2.3

monopole of 1st iteration of Minkowski Island) are not given to avoid repetition.

monopole of 1st iteration of Minkowski Island) are not given to avoid repetition.

GHz, 97% and 93% at 5.26 GHz for the printed monopole of 1st and 2nd iteration of Minkowski Island, respectively. From these results, it is found that although higher size reduction can be achieved using higher iteration of the fractal geometry, the bandwidth as well as the radiation efficiency also decreases. This should be considered as a trade-off between size reduction and antenna performance. Figure 4 shows the measured E- and H-plane radiation pattern of the printed monopole with 2nd iteration of Minkowski Island at its dual resonant frequencies. Measurements showed that both antennas have similar radiation patterns so the measurement results for the other prototypes (the printed

dB at 5.2 GHz for both antennas. According to the simulation results, the radiation efficiency is 94% and 88% at 2.45 GHz, 97% and 93% at 5.26 GHz for the printed monopole of 1st and 2nd iteration of Minkowski Island, respectively. From these results, it is found that although higher size reduction can be achieved using higher iteration of the fractal geometry, the bandwidth as well as the radiation efficiency also decreases. This should be considered as a trade-off between size reduction and antenna performance. Figure 4 shows the measured E- and H-plane radiation pattern of the printed monopole with 2nd iteration of Minkowski Island at its dual resonant frequencies. Measurements showed that both antennas have similar radiation patterns so the measurement results for the other prototypes (the printed to the simulation results, the radiation efficiency is 94% and 88% at 2.45 GHz, 97% and 93% at 5.26 GHz for the printed monopole of 1st and 2nd iteration of Minkowski Island, respectively. From these results, it is found that although higher size reduction can be achieved using higher iteration of the fractal geometry, the bandwidth as well as the radiation efficiency also decreases. This should be considered as a trade-off between size reduction and antenna performance. Figure 4 shows the measured E-and H-plane radiation pattern of the printed monopole with 2nd iteration of Minkowski Island at its dual resonant frequencies. Measure‐ ments showed that both antennas have similar radiation patterns so the measurement results for the other prototypes (the printed monopole of 1st iteration of Minkowski Island) are not given to avoid repetition.

wavelength. Moreover, it is found that without using any additional impedance matching techniques, both of these two proposed antennas exhibit good impedance match at multiple frequency bands, which is confirmed by the measurement results shown in Figure 3. These results show that the printed monopole of 1st iteration of Minkowski Island exhibits 10-dB return loss from 2.30-2.48 GHz, 3.3-3.7 GHz and 4.9-6.0 GHz, which covers the entire required frequency bands for 802.11a/b/g and WiMAX communications. For the 2nd iteration of Minkowski Island fractal monopole, the 10-dB return loss bands are 2.31-2.47 GHz and 5.0-5.5

**Figure 2.** Exploded view of the fractal monopole antenna with geometry of: (a) 1st iteration Minkowski Island; (b) 2nd

(a) (b)

 Figure 2: Exploded view of the fractal monopole antenna with geometry of: (a) 1st iteration Minkowski Island; (b) 2nd iteration of Minkowski Island proposed in [4].

(a) (b)

 Figure 2: Exploded view of the fractal monopole antenna with geometry of: (a) 1st iteration Minkowski Island; (b) 2nd iteration of Minkowski Island proposed in [4].

Both of the proposed monopole antennas have a compact size compared to conventional printed monopole antennas, which need to have a length of approximately a quarter of wavelength. Moreover, it is found that without using any additional impedance matching techniques, both of these two proposed antennas exhibit good impedance match at multiple frequency bands, which is confirmed by the measurement results shown in Figure 3. These results show that the printed monopole of 1st iteration of Minkowski Island exhibits 10-dB return loss from 2.30 - 2.48 GHz, 3.3 - 3.7 GHz and 4.9 - 6.0 GHz, which covers the entire required frequency bands for 802.11a/b/g and WiMAX communications. For the 2nd iteration of Minkowski Island fractal monopole, the 10-dB return loss bands are 2.31 - 2.47 GHz and 5.0 - 5.5 GHz, which covers the two desired frequency bands for WLAN

Both of the proposed monopole antennas have a compact size compared to conventional printed monopole antennas, which need to have a length of approximately a quarter of wavelength. Moreover, it is found that without using any additional impedance matching techniques, both of these two proposed antennas exhibit good impedance match at multiple frequency bands, which is confirmed by the measurement results shown in Figure 3. These results show that the printed monopole of 1st iteration of Minkowski Island exhibits 10-dB return loss from 2.30 - 2.48 GHz, 3.3 - 3.7 GHz and 4.9 - 6.0 GHz, which covers the entire required frequency bands for 802.11a/b/g and WiMAX communications. For the 2nd iteration of Minkowski Island fractal monopole, the 10-dB return loss bands are 2.31 - 2.47 GHz and 5.0 - 5.5 GHz, which covers the two desired frequency bands for WLAN

Figure 3: Measured reflection coefficient of the proposed antenna with the: (a) 1st iteration and (b) 2nd iteration of Minkowski Island geometry [4].

Figure 3: Measured reflection coefficient of the proposed antenna with the: (a) 1st iteration and (b) 2nd iteration of Minkowski Island geometry [4].

(a) (b)

The measured results also show that the radiation patterns at the H-plane are almost isotropic and in the E-plane they exhibit broadside radiation patterns, as expected. The measured maximum gain is around 1.5 dB at 2.45 GHz and 2.3 dB at 5.2 GHz for both antennas. According to the simulation results, the radiation efficiency is 94% and 88% at 2.45 GHz, 97% and 93% at 5.26 GHz for the printed monopole of 1st and 2nd iteration of Minkowski Island, respectively. From these results, it is found that although higher size reduction can be achieved using higher iteration of the fractal geometry, the bandwidth as well as the radiation efficiency also decreases. This should be considered as a trade-off between size reduction and antenna performance. Figure 4 shows the measured E- and H-plane radiation pattern of the printed monopole with 2nd iteration of Minkowski Island at its dual resonant frequencies. Measurements showed that both antennas have similar radiation patterns so the measurement results for the other prototypes (the printed

**Figure 3.** Measured reflection coefficient of the proposed antenna with the: (a) 1st iteration and (b) 2nd iteration of

The measured results also show that the radiation patterns at the H-plane are almost isotropic and in the E-plane they exhibit broadside radiation patterns, as expected. The measured maximum gain is around 1.5 dB at 2.45 GHz and 2.3 dB at 5.2 GHz for both antennas. According

(a) (b)

The measured results also show that the radiation patterns at the H-plane are almost isotropic and in the E-plane they exhibit broadside radiation patterns, as expected. The measured maximum gain is around 1.5 dB at 2.45 GHz and 2.3 dB at 5.2 GHz for both antennas. According to the simulation results, the radiation efficiency is 94% and 88% at 2.45 GHz, 97% and 93% at 5.26 GHz for the printed monopole of 1st and 2nd iteration of Minkowski Island, respectively. From these results, it is found that although higher size reduction can be achieved using higher iteration of the fractal geometry, the bandwidth as well as the radiation efficiency also decreases. This should be considered as a trade-off between size reduction and antenna performance. Figure 4 shows the measured E- and H-plane radiation pattern of the printed monopole with 2nd iteration of Minkowski Island at its dual resonant frequencies. Measurements showed that both antennas have similar radiation patterns so the measurement results for the other prototypes (the printed

monopole of 1st iteration of Minkowski Island) are not given to avoid repetition.

monopole of 1st iteration of Minkowski Island) are not given to avoid repetition.

GHz, which covers the two desired frequency bands for WLAN 802.11b/g standards.

802.11b/g standards.

802.11b/g standards.

60 Progress in Compact Antennas

iteration of Minkowski Island proposed in [4].

Minkowski Island geometry [4].

 Figure 4: : Measured radiation patterns of the proposed antenna with the 2nd iteration of Minkowski Island: (a) at 2.45 GHz, E-plane; and (b) at 2.45 GHz, H-plane; (c) at 5.3 GHz, E-plane and (d) at 5.3 GHz, H-plane [4]. **Figure 4.** Measured radiation patterns of the proposed antenna with the 2nd iteration of Minkowski Island: (a) at 2.45°GHz, E-plane; and (b) at 2.45°GHz, H-plane; (c) at 5.3°GHz, E-plane and (d) at 5.3°GHz, H-plane [4].

The frequency ratio of the multiband fractal antenna is investigated in [4]. It is shown that as a multiband antenna, the frequency ratio of the fractal antenna using the Minkowski geometry is nearly fixed. This indicates that in order to extend the fractal technique to other multiband antennas design, there is a need to explore an effective solution to overcome this limit. One technique that can be employed to extend the frequency ratio of the fractal-based multiband antenna design is to combine the fractal geometry with the meander line. One compact antenna suitable for a commercial wireless USB device is proposed by using such technique [5]. Since the objective is to design a printed fractal monopole antenna for WLAN USB dongle applications, based on the industrial requirement, the overall size of this antenna including the ground plane is chosen to be 20 mm×60 mm and the available space for antenna design

A variation of the Koch fractal, which also can be referred as Cohen dipole fractal geometry, was used in this design. The Cohen dipole geometry, which is a variation of Koch fractal, was first proposed by Nathan Cohen [6] to design a dipole antenna with the feeding at the center position. Different from a conventional printed monopole antenna, the antenna radiating element is printed on the same layer of the ground plane. This type of antenna is named Inverted-L Antenna (ILA). As a typical printed monopole antenna, the antenna element with the feeding line and the ground plane are printed at the top and bottom side of the substrate, respectively. Meanwhile, the feeding port is located at the end of the substrate as shown in Figure5. This might be a problem in a practical industry design as other components, such as RF module, also need to be mounted on the same ground plane. Such problem can be solved by

**1.2.2 Fractal ILA antenna** 

using ILA antenna.

is limited to no more than 20 mm × 10 mm.

#### **2.2. Fractal ILA antenna**

The frequency ratio of the multiband fractal antenna is investigated in [4]. It is shown that as a multiband antenna, the frequency ratio of the fractal antenna using the Minkowski geometry is nearly fixed. This indicates that in order to extend the fractal technique to other multiband antennas design, there is a need to explore an effective solution to overcome this limit. One technique that can be employed to extend the frequency ratio of the fractal-based multiband antenna design is to combine the fractal geometry with the meander line. One compact antenna suitable for a commercial wireless USB device is proposed by using such technique [5]. Since the objective is to design a printed fractal monopole antenna for WLAN USB dongle applica‐ tions, based on the industrial requirement, the overall size of this antenna including the ground plane is chosen to be 20 mm×60 mm and the available space for antenna design is limited to no more than 20 mm × 10 mm.

WLAN dual-band applications. However, adding the horizontal microstrip line with the appropriate length, the frequency ratio of the fractal antenna can be more controlled. After further optimization of the reflection coefficient over the desired frequency band, the width of the vertical microstrip line was chosen to be 1 mm and the width of the horizontal microstrip

Low Cost Compact Multiband Printed Monopole Antennas and Arrays for Wireless Communications

http://dx.doi.org/10.5772/58815

63

Figure 7 compares the reflection coefficient between simulation and measurement results. It can be seen that there is a good agreement between the simulated and measured reflection coefficient. The experimental result indicates that the proposed antenna has a S11<-10 dB with

1.2.3 Compact Printed Monopole Antenna with Chip Inductor

Figure 7: Comparison of the simulated and measured S11 of the fractal ILA in [5]

Besides using fractal techniques to design printed monopoles of reduced size, another technique which can be employed is to introduce a lumped element, more specifically a chip inductor, into the antenna radiating element. In this way, the effective electrical length of the printed monopole is increased by an actual chip inductor instead of

Figure 8 shows the layout of the printed monopole antenna proposed in [7]. This antenna has a two-armed structure and for such monopole antenna the resonant frequency can be created by letting the overall length of each arm to be approximately a quarter of its effective wavelength on the substrate. The chip inductor is embedded in the middle of the left arm and generally speaking, the higher the value of the inductance, the lower the resonant frequency that can be achieved. However, increasing the inductance will also reduce the bandwidth and radiation efficiency of the

This antenna was printed on a Roger 4003 substrate with relative permittivity of 3.38 and thickness of 0.813 mm. The antenna and ground plane were printed on different sides of the substrate and there is no copper below the antenna section. The area of this antenna is only 10 mm ×10.5 mm, which is only 0.08λ2.4GHz×0.084λ2.4GHz, whereλ2.4GHz represents the free space wavelength at 2.4 GHz. The higher band of the antenna is determined by the overall length L4 + L5, which is approximately a quarter of a wavelength at 5.3 GHz. With the chip inductor, the overall length L1 +L2 +L3, which determines the lower band resonant frequency, is only 12.5 mm. This value is smaller than the length required for conventional monopole antennas. After adding the chip inductor, the resonant frequencies of the lower and higher band can be tuned by respectively changing the length of the arm L3 and L5, as demonstrated in the next section. By optimizing the length and width of each arm, this antenna is tuned to resonate at the desired frequencies. For more details about how to choose the value of the chip inductor and model it in the EM simulation

Figure 8: The configuration of the electrically small printed monopole antenna proposed in [7]

employing the fractal geometries that can bend a microstrip line of large length in a finite area.

antenna, which is the reason why a chip inductor with a higher inductance is not chosen in this study.

line was 0.5 mm. For the fractal, the width of the microstrip line was set to 0.35 mm.

**Figure 6.** The exploded view of the printed fractal ILA antenna proposed in [5]

a bandwidth from 2.25 to 2.60 GHz and 5.06 to 5.62 GHz.


S11| (dB)

**Figure 7.** Comparison of the simulated and measured S11 of the fractal ILA in [5]

software, readers can refer to [7].

A variation of the Koch fractal, which also can be referred as Cohen dipole fractal geometry, was used in this design. The Cohen dipole geometry, which is a variation of Koch fractal, was first proposed by Nathan Cohen [6] to design a dipole antenna with the feeding at the center position. Different from a conventional printed monopole antenna, the antenna radiating element is printed on the same layer of the ground plane. This type of antenna is named Inverted-L Antenna (ILA). As a typical printed monopole antenna, the antenna element with the feeding line and the ground plane are printed at the top and bottom side of the substrate, respectively. Meanwhile, the feeding port is located at the end of the substrate as shown in Figure 5. This might be a problem in a practical industrial design as other components, such as RF module, also need to be mounted on the same ground plane. Such problem can be solved by using ILA antenna.

**Figure 5.** A typical configuration of the conventional printed monopole antenna

Figure 6 shows the exploded view of the proposed printed fractal ILA antenna in [5]. This antenna is designed on the Roger 4003 substrate with dielectric constant of 3.38 and thickness of 0.813 mm. The space occupied by the monopole antenna on the substrate is 10 mm ×20 mm and the size of the ground plane is 50 mm×20 mm, which is a typical size for a USB dongle. This structure was further optimized by doing numerical simulations in Ansoft HFSS to achieve a better impedance match at the required frequency bands. It is found that the size of the fractal geometry is critical in defining both the resonant frequencies while the existence of the horizontal microstrip line plays the role of adjusting the resonant frequencies to the desired region. Without the horizontal microstrip line, it is found that the proposed antenna can only exhibit resonances at around 2 and 6 GHz, which fails to cover the desired frequencies for WLAN dual-band applications. However, adding the horizontal microstrip line with the appropriate length, the frequency ratio of the fractal antenna can be more controlled. After further optimization of the reflection coefficient over the desired frequency band, the width of the vertical microstrip line was chosen to be 1 mm and the width of the horizontal microstrip line was 0.5 mm. For the fractal, the width of the microstrip line was set to 0.35 mm.

**Figure 6.** The exploded view of the printed fractal ILA antenna proposed in [5]

**2.2. Fractal ILA antenna**

62 Progress in Compact Antennas

no more than 20 mm × 10 mm.

by using ILA antenna.

Printed monopole

**Figure 5.** A typical configuration of the conventional printed monopole antenna

The frequency ratio of the multiband fractal antenna is investigated in [4]. It is shown that as a multiband antenna, the frequency ratio of the fractal antenna using the Minkowski geometry is nearly fixed. This indicates that in order to extend the fractal technique to other multiband antennas design, there is a need to explore an effective solution to overcome this limit. One technique that can be employed to extend the frequency ratio of the fractal-based multiband antenna design is to combine the fractal geometry with the meander line. One compact antenna suitable for a commercial wireless USB device is proposed by using such technique [5]. Since the objective is to design a printed fractal monopole antenna for WLAN USB dongle applica‐ tions, based on the industrial requirement, the overall size of this antenna including the ground plane is chosen to be 20 mm×60 mm and the available space for antenna design is limited to

A variation of the Koch fractal, which also can be referred as Cohen dipole fractal geometry, was used in this design. The Cohen dipole geometry, which is a variation of Koch fractal, was first proposed by Nathan Cohen [6] to design a dipole antenna with the feeding at the center position. Different from a conventional printed monopole antenna, the antenna radiating element is printed on the same layer of the ground plane. This type of antenna is named Inverted-L Antenna (ILA). As a typical printed monopole antenna, the antenna element with the feeding line and the ground plane are printed at the top and bottom side of the substrate, respectively. Meanwhile, the feeding port is located at the end of the substrate as shown in Figure 5. This might be a problem in a practical industrial design as other components, such as RF module, also need to be mounted on the same ground plane. Such problem can be solved

Substrate

Ground plane

Figure 6 shows the exploded view of the proposed printed fractal ILA antenna in [5]. This antenna is designed on the Roger 4003 substrate with dielectric constant of 3.38 and thickness of 0.813 mm. The space occupied by the monopole antenna on the substrate is 10 mm ×20 mm and the size of the ground plane is 50 mm×20 mm, which is a typical size for a USB dongle. This structure was further optimized by doing numerical simulations in Ansoft HFSS to achieve a better impedance match at the required frequency bands. It is found that the size of the fractal geometry is critical in defining both the resonant frequencies while the existence of the horizontal microstrip line plays the role of adjusting the resonant frequencies to the desired region. Without the horizontal microstrip line, it is found that the proposed antenna can only exhibit resonances at around 2 and 6 GHz, which fails to cover the desired frequencies for

Antenna feeding point

Figure 7 compares the reflection coefficient between simulation and measurement results. It can be seen that there is a good agreement between the simulated and measured reflection coefficient. The experimental result indicates that the proposed antenna has a S11<-10 dB with a bandwidth from 2.25 to 2.60 GHz and 5.06 to 5.62 GHz.

1.2.3 Compact Printed Monopole Antenna with Chip Inductor

Besides using fractal techniques to design printed monopoles of reduced size, another technique which can be employed is to introduce a lumped element, more specifically a chip inductor, into the antenna radiating element. In this way, the effective electrical length of the printed monopole is increased by an actual chip inductor instead of

Figure 8 shows the layout of the printed monopole antenna proposed in [7]. This antenna has a two-armed structure and for such monopole antenna the resonant frequency can be created by letting the overall length of each arm to be approximately a quarter of its effective wavelength on the substrate. The chip inductor is embedded in the middle of the left arm and generally speaking, the higher the value of the inductance, the lower the resonant frequency that can be achieved. However, increasing the inductance will also reduce the bandwidth and radiation efficiency of the

This antenna was printed on a Roger 4003 substrate with relative permittivity of 3.38 and thickness of 0.813 mm. The antenna and ground plane were printed on different sides of the substrate and there is no copper below the antenna section. The area of this antenna is only 10 mm ×10.5 mm, which is only 0.08λ2.4GHz×0.084λ2.4GHz, whereλ2.4GHz represents the free space wavelength at 2.4 GHz. The higher band of the antenna is determined by the overall length L4 + L5, which is approximately a quarter of a wavelength at 5.3 GHz. With the chip inductor, the overall length L1 +L2 +L3, which determines the lower band resonant frequency, is only 12.5 mm. This value is smaller than the length required for conventional monopole antennas. After adding the chip inductor, the resonant frequencies of the lower and higher band can be tuned by respectively changing the length of the arm L3 and L5, as demonstrated in the next section. By optimizing the length and width of each arm, this antenna is tuned to resonate at the desired frequencies. For more details about how to choose the value of the chip inductor and model it in the EM simulation

Figure 8: The configuration of the electrically small printed monopole antenna proposed in [7]

employing the fractal geometries that can bend a microstrip line of large length in a finite area.

antenna, which is the reason why a chip inductor with a higher inductance is not chosen in this study.

 Figure 7: Comparison of the simulated and measured S11 of the fractal ILA in [5] **Figure 7.** Comparison of the simulated and measured S11 of the fractal ILA in [5]

software, readers can refer to [7].

#### **2.3. Compact Printed Monopole Antenna with Chip Inductor**

Besides using fractal techniques to design printed monopoles of reduced size, another technique which can be employed is to introduce a lumped element, more specifically a chip inductor, into the antenna radiating element. In this way, the effective electrical length of the printed monopole is increased by the actual chip inductor instead of employing the fractal geometries that can bend a microstrip line of large length in a finite area.

Figure 8 shows the layout of the printed monopole antenna proposed in [7]. This antenna has a two-armed structure and for such monopole antenna the resonant frequency can be created by letting the overall length of each arm to be approximately a quarter of its effective wave‐ length on the substrate. The chip inductor is embedded in the middle of the left arm and generally speaking, the higher the value of the inductance, the lower the resonant frequency that can be achieved. However, increasing the inductance will also reduce the bandwidth and radiation efficiency of the antenna, which is the reason why a chip inductor with a higher inductance is not chosen in this study.

This antenna was printed on a Roger 4003 substrate with relative permittivity of 3.38 and thickness of 0.813 mm. The antenna and ground plane were printed on different sides of the substrate and there is no copper below the antenna section. The area of this antenna is only 10 mm ×10.5 mm, which is only 0.08 λ2.4GHz ×0.084 λ2.4GHz, where λ2.4GHz represents the free space wavelength at 2.4 GHz. The higher band of the antenna is determined by the overall length L4+L5, which is approximately a quarter of a wavelength at 5.3 GHz. With the chip inductor, the overall length L1+L2+L3, which determines the lower band resonant frequency, is only 12.5 mm. This value is smaller than the length required for conventional monopole antennas. After adding the chip inductor, the resonant frequencies of the lower and higher band can be tuned by respectively changing the length of the arm L3 and L5, as demonstrated in the next section. By optimizing the length and width of each arm, this antenna is tuned to resonate at the desired frequencies. For more details about how to choose the value of the chip inductor and model it in the EM simulation software, readers can refer to [7].

The lower bound of the quality factor (Qlb) of the antenna was calculated by using the formula

Low Cost Compact Multiband Printed Monopole Antennas and Arrays for Wireless Communications

http://dx.doi.org/10.5772/58815

65

From Table 1, it can be seen that the antenna has *ka* smaller than 0.5 and has a quality factor very close to its theoretical lower bound, where *a* is the radius of sphere that can enclose the

**Properties Proposed Antenna**

Qlb 15.9

Frequency (GHz) 2.45 Size (Wmm ×Lmm) 10×10.5 a (mm) 7.25 ka 0.37

Simulated Radiation efficiency (%) 72

Measured 3:1 VSWR bandwidth (%) 5.10

**Table 1.** Summary of performance of the proposed printed monopole antenna in [7]

Calculated Antenna Q 22.6

*Qlb* <sup>=</sup> <sup>1</sup> (*ka*)3 + 1 *ka*

**Figure 8.** The configuration of the electrically small printed monopole antenna proposed in [7]

maximum dimension of the antenna and *k* is the wavenumber.

[8]:

The measured radiation patterns of the two-armed monopole antenna at 2.45 and 5.3 GHz show that the antenna has omnidirectional radiation patterns as a typical monopole antenna. Table 1 presents both measured and simulated results, as well as the calculated quality factor of the proposed monopole antenna. The quality factor was calculated based on the equations given below, taken from [8]:

$$\mathbf{Q}(\omega\_0) = \frac{2\sqrt{\beta}}{FBW\upsilon(\omega\_0)}$$

$$FBW\upsilon\left(\omega\_0\right) = \frac{\omega\_\* - \omega\_-}{\omega\_0}$$

$$\sqrt{\beta} = \frac{s - 1}{2\sqrt{s}}$$

where the parameter *s* is the criterion for the maximum VSWR and ω+, ω- , ω0 represent the higher frequency bound, lower frequency bound and central frequency of the antenna, respectively.

**Figure 8.** The configuration of the electrically small printed monopole antenna proposed in [7]

**2.3. Compact Printed Monopole Antenna with Chip Inductor**

inductance is not chosen in this study.

64 Progress in Compact Antennas

in the EM simulation software, readers can refer to [7].

given below, taken from [8]:

respectively.

geometries that can bend a microstrip line of large length in a finite area.

Besides using fractal techniques to design printed monopoles of reduced size, another technique which can be employed is to introduce a lumped element, more specifically a chip inductor, into the antenna radiating element. In this way, the effective electrical length of the printed monopole is increased by the actual chip inductor instead of employing the fractal

Figure 8 shows the layout of the printed monopole antenna proposed in [7]. This antenna has a two-armed structure and for such monopole antenna the resonant frequency can be created by letting the overall length of each arm to be approximately a quarter of its effective wave‐ length on the substrate. The chip inductor is embedded in the middle of the left arm and generally speaking, the higher the value of the inductance, the lower the resonant frequency that can be achieved. However, increasing the inductance will also reduce the bandwidth and radiation efficiency of the antenna, which is the reason why a chip inductor with a higher

This antenna was printed on a Roger 4003 substrate with relative permittivity of 3.38 and thickness of 0.813 mm. The antenna and ground plane were printed on different sides of the substrate and there is no copper below the antenna section. The area of this antenna is only 10 mm ×10.5 mm, which is only 0.08 λ2.4GHz ×0.084 λ2.4GHz, where λ2.4GHz represents the free space wavelength at 2.4 GHz. The higher band of the antenna is determined by the overall length L4+L5, which is approximately a quarter of a wavelength at 5.3 GHz. With the chip inductor, the overall length L1+L2+L3, which determines the lower band resonant frequency, is only 12.5 mm. This value is smaller than the length required for conventional monopole antennas. After adding the chip inductor, the resonant frequencies of the lower and higher band can be tuned by respectively changing the length of the arm L3 and L5, as demonstrated in the next section. By optimizing the length and width of each arm, this antenna is tuned to resonate at the desired frequencies. For more details about how to choose the value of the chip inductor and model it

The measured radiation patterns of the two-armed monopole antenna at 2.45 and 5.3 GHz show that the antenna has omnidirectional radiation patterns as a typical monopole antenna. Table 1 presents both measured and simulated results, as well as the calculated quality factor of the proposed monopole antenna. The quality factor was calculated based on the equations

Q(*ω*0) <sup>=</sup> <sup>2</sup> *<sup>β</sup>*

*<sup>β</sup>* <sup>=</sup> *<sup>s</sup>* - <sup>1</sup> 2 *s*

higher frequency bound, lower frequency bound and central frequency of the antenna,

*FBWv*(*ω*<sup>0</sup>

where the parameter *s* is the criterion for the maximum VSWR and ω+, ω-

*FBWv*(*ω*0)

) <sup>=</sup> *<sup>ω</sup>*<sup>+</sup> - *<sup>ω</sup>ω*0

, ω0 represent the

The lower bound of the quality factor (Qlb) of the antenna was calculated by using the formula [8]:

$$Q\_{lb} = \left[\frac{1}{(ka)^3} + \frac{1}{ka}\right]$$

From Table 1, it can be seen that the antenna has *ka* smaller than 0.5 and has a quality factor very close to its theoretical lower bound, where *a* is the radius of sphere that can enclose the maximum dimension of the antenna and *k* is the wavenumber.


**Table 1.** Summary of performance of the proposed printed monopole antenna in [7]

#### **3. Low cost printed planar monopole for mobile terminals**

determined by both the inductance of the chip inductor and the overall length of branch A and B. Although the chip inductor can also influence the resonant frequency at 1800 MHz to some extent, this resonance is mainly determined by the length of branch A. The overall length of branch D and the length of branch E determine the resonant frequencies at 2.4 and 5.2 GHz, respectively. The frequency band at 3.8 GHz is related to the length of branch C and the width

Low Cost Compact Multiband Printed Monopole Antennas and Arrays for Wireless Communications

http://dx.doi.org/10.5772/58815

67

**Figure 9.** Structure of the multiband printed monopole antenna for mobile terminals [3]

**Figure 10.** The main dimensions of the multiband printed monopole antenna [3]

This antenna is printed on the inexpensive substrate FR4 (relative permittivity of 4.4) with thickness of 0.8 mm and size 100mm ×60mm, which is a reasonable circuit board size for a PDA or smart phone device. To achieve a better impedance matching at each band, the length and

of branch A.

The rapid growth in mobile communications increases the needs of designing multiband internal antennas for mobile terminals. Meanwhile, it is also desirable to design such antennas as compact as possible. Planar Invert-F Antenna (PIFA) is one type of conventional antennas that has been widely employed in mobile phones. In [9, 10], two coupled-fed compact multiband PIFAs for wireless wide area networks (WWAN) were proposed for internal mobile phone antenna applications. The size reduction of these two antennas was achieved by shorting the antenna to the ground and bending the antenna structure. Printed monopole slot antennas and printed loop antennas have also been widely studied for multiband internal mobile phones. In [11, 12], two folded monopole slot antennas that can cover the penta-band WWAN operation were proposed for clam-shell mobile phones. These two antennas were designed by making several slots on the top of the ground plane. In [13-15], printed halfwavelength and meandered loop techniques were proposed for the design of multiband antennas for mobile handsets. However, all of these antennas have operating bands only covering GSM850/900 and DCS/PCS/UMTS bands, which are not enough for nowadays wireless communications. To make the antenna resonant at additional bands including Wireless LAN, one novel PIFA structure combining shorted parasitic patches, capacitive loads and slots was designed to support both quad-band mobile communication and dual-band wireless local area network (WLAN) operations [16]. Although this antenna can operate at several bands, it is extremely difficult to fabricate due to its complex structure. In [17], multiband operation including the WWAN and WLAN 2.4 GHz was achieved by cutting slots of different lengths at the edge of the system ground plane of the mobile phone. Operation in additional bands including GSM/DCS/PCS/UMTS/WLAN/WiMAX were achieved by cutting the loop-like slot on the top of the ground plane and shorting it to the ground plane [18]. However, shorting the antenna to the ground makes the resonant frequencies of the antenna vulnerable to the length of the ground plane. In fact the ground plane size used in [18] is smaller than the size of the system ground plane for a mobile phone. Other techniques have also been developed to design compact multiband antennas for wireless communications. In [19], a multiband antenna that can support WWAN and 2.4 GHz WLAN frequency bands was implemented by using a switchable feed and ground. In [20], a small size multiband antenna for wireless mobile system was designed based on double negative (DNG) zeroth order resonator (ZOR). However, it is noticed that these antennas have rather complex structures and they are quite difficult to fabricate. In [21], a chip inductor was embedded in the printed monopole antenna, which resulted in a compact antenna for mobile handset application.

One compact multiband printed monopole for mobile application has been recently presented in [3]. This design overcomes some of these limitations discussed above. Figure 9 shows the structure of the proposed antenna and the main dimensions of the antenna elements are given in Figure 10. The antenna element is printed on the top side of the substrate while the ground plane is located at the bottom side. Behind the monopole antenna, there is no ground. The chip inductor, of series Coilcraft 0402HP with an inductance of 20 nH, is embedded between the branch A and B as shown in Figure 10. This antenna has a multi-branch structure, each of which determines different resonant frequencies. The lowest resonant frequency, 960 MHz, is determined by both the inductance of the chip inductor and the overall length of branch A and B. Although the chip inductor can also influence the resonant frequency at 1800 MHz to some extent, this resonance is mainly determined by the length of branch A. The overall length of branch D and the length of branch E determine the resonant frequencies at 2.4 and 5.2 GHz, respectively. The frequency band at 3.8 GHz is related to the length of branch C and the width of branch A.

**3. Low cost printed planar monopole for mobile terminals**

66 Progress in Compact Antennas

The rapid growth in mobile communications increases the needs of designing multiband internal antennas for mobile terminals. Meanwhile, it is also desirable to design such antennas as compact as possible. Planar Invert-F Antenna (PIFA) is one type of conventional antennas that has been widely employed in mobile phones. In [9, 10], two coupled-fed compact multiband PIFAs for wireless wide area networks (WWAN) were proposed for internal mobile phone antenna applications. The size reduction of these two antennas was achieved by shorting the antenna to the ground and bending the antenna structure. Printed monopole slot antennas and printed loop antennas have also been widely studied for multiband internal mobile phones. In [11, 12], two folded monopole slot antennas that can cover the penta-band WWAN operation were proposed for clam-shell mobile phones. These two antennas were designed by making several slots on the top of the ground plane. In [13-15], printed halfwavelength and meandered loop techniques were proposed for the design of multiband antennas for mobile handsets. However, all of these antennas have operating bands only covering GSM850/900 and DCS/PCS/UMTS bands, which are not enough for nowadays wireless communications. To make the antenna resonant at additional bands including Wireless LAN, one novel PIFA structure combining shorted parasitic patches, capacitive loads and slots was designed to support both quad-band mobile communication and dual-band wireless local area network (WLAN) operations [16]. Although this antenna can operate at several bands, it is extremely difficult to fabricate due to its complex structure. In [17], multiband operation including the WWAN and WLAN 2.4 GHz was achieved by cutting slots of different lengths at the edge of the system ground plane of the mobile phone. Operation in additional bands including GSM/DCS/PCS/UMTS/WLAN/WiMAX were achieved by cutting the loop-like slot on the top of the ground plane and shorting it to the ground plane [18]. However, shorting the antenna to the ground makes the resonant frequencies of the antenna vulnerable to the length of the ground plane. In fact the ground plane size used in [18] is smaller than the size of the system ground plane for a mobile phone. Other techniques have also been developed to design compact multiband antennas for wireless communications. In [19], a multiband antenna that can support WWAN and 2.4 GHz WLAN frequency bands was implemented by using a switchable feed and ground. In [20], a small size multiband antenna for wireless mobile system was designed based on double negative (DNG) zeroth order resonator (ZOR). However, it is noticed that these antennas have rather complex structures and they are quite difficult to fabricate. In [21], a chip inductor was embedded in the printed monopole antenna, which resulted in a compact antenna for mobile handset application.

One compact multiband printed monopole for mobile application has been recently presented in [3]. This design overcomes some of these limitations discussed above. Figure 9 shows the structure of the proposed antenna and the main dimensions of the antenna elements are given in Figure 10. The antenna element is printed on the top side of the substrate while the ground plane is located at the bottom side. Behind the monopole antenna, there is no ground. The chip inductor, of series Coilcraft 0402HP with an inductance of 20 nH, is embedded between the branch A and B as shown in Figure 10. This antenna has a multi-branch structure, each of which determines different resonant frequencies. The lowest resonant frequency, 960 MHz, is

**Figure 9.** Structure of the multiband printed monopole antenna for mobile terminals [3]

**Figure 10.** The main dimensions of the multiband printed monopole antenna [3]

This antenna is printed on the inexpensive substrate FR4 (relative permittivity of 4.4) with thickness of 0.8 mm and size 100mm ×60mm, which is a reasonable circuit board size for a PDA or smart phone device. To achieve a better impedance matching at each band, the length and width of each branch of the antenna were optimized through numerical simulations. In the simulation set-up, the model of the chip inductor is built based on the studies presented in [7]. As stated before, the chip inductor mainly influences the first two lower frequency bands. In these two lower frequency bands, the value of the chip inductor is more critical in determining the lowest resonant frequency; as a result, in the simulation set-up, the equivalent inductance and series resistance of the chip inductor model were calculated at 960 MHz using the formulas provided in [7], and they are 20.6 nH and 2Ω, respectively. optimized through numerical simulations. In the simulation set-up, the model of the chip inductor is built based on the studies presented in [7]. As stated before, the chip inductor mainly influences the first two lower frequency bands. In these two lower frequency bands, the value of the chip inductor is more critical in determining the lowest resonant frequency; as a result, in the simulation set-up, the equivalent inductance and series resistance of the chip inductor model were calculated at 960 MHz using the formulas provided in [7], and they are 20.6 nH and 2Ω, respectively.

Figure 10. The main dimensions of the multiband printed monopole antenna [3]

This antenna is printed on the inexpensive substrate FR4 (relative permittivity of 4.4) with thickness of 0.8

achieve better impedance matching at each band, the length and width of each branch of the antenna were

and B. At 1800 and 1900 MHz, the current is mainly distributed on branch B. It is also clear that branches D and E are responsible for the resonant frequency at 2.4 and 5.2 GHz, respec‐ tively. Regarding the resonance at 3.8 GHz, it is mainly determined by branch C and the

**Figure 12.** The comparison of the simulated reflection coefficient between the multiband printed monopole antenna

with and without the embedded the chip inductor [3]

Figure 12. The comparison of the simulated reflection coefficient between the multiband printed monopole antenna

Figure 13. The simulated surface current distribution of the multiband printed monopole antenna [3] : (a) 960 MHz; (b)1800 MHz; (c)1900 MHz; (d)2.4 GHz; (e)3.8 GHz and (f)5.25 GHz. The stronger current is represented by lighter

Besides being a completely planar structure, another advantage of the proposed antenna is that the size of the ground plane has little influence on its resonant characteristics compared to the designs that short the antenna structure to the ground plane. The proposed monopole antenna with different length of ground plane has also been investigated. Figure 14 shows the simulated reflection coefficient of the proposed antenna with ground planes of different lengths. It was found that when decreasing the length of the

Figure 13 shows the simulated surface current distribution of the proposed antenna at each operation frequency. It is observed that at 960 MHz, there is a strong current on branches A and B. At 1800 and 1900 MHz, the current is mainly distributed on branch B. It is also clear that branches D and E are responsible for the resonant frequency at 2.4 and 5.2 GHz, respectively. Regarding the resonance at 3.8 GHz, it is

http://dx.doi.org/10.5772/58815

69

Besides being a completely planar structure, another advantage of the proposed antenna is that the size of the ground plane has little influence on its resonant characteristics compared to the designs that short the antenna structure to the ground plane. The proposed monopole antenna with different lengths of the ground plane has also been investigated. Figure 14 shows the simulated reflection coefficient of the proposed antenna with ground planes of different lengths. It was found that when decreasing the length of the ground plane, at the desired frequency bands the proposed antenna only exhibits small frequency shifts and some changes

mainly determined by branch C and the coupling between branch C and D.

Low Cost Compact Multiband Printed Monopole Antennas and Arrays for Wireless Communications

The scenario in which the antenna is put into the center of a plastic housing box was also investigated in this work. In the simulation model, the wall of the plastic housing is 1 mm thick, 14 mm high and has a dielectric permittivity of 3.5. The simulation results (Figure 15) indicate that, compared to the case when the antenna is radiating in free space, there is almost no influence on the reflection coefficient of the proposed antenna except for a small frequency

The measured radiation patterns of the proposed antenna in free space are presented in Figure 16. It is found that at all the desired frequencies the proposed antenna has radiation patterns similar to a typical monopole antenna, which normally has omnidirectional radiation patterns. The simulation results also suggest that the antenna has moderate gain and efficiency at its operation frequency bands. Table 2 summarizes the peak gain and radiation efficiency at the

coupling between branch C and D.

with and without the embedded the chip inductor [3]


on the amplitude of the reflection coefficient.

colors

shift at the 3.8 GHz band, when within the plastic housing.

Figure 9. Structure of the multiband printed monopole antenna for mobile terminals [3]

Figure 11 shows the measured and simulated reflection coefficient of the proposed antenna. This antenna was measured using the network analyzer Agilent PNA E8363B. It can be observed that there is a good agreement between the measurement and simulation results. The experiment result shows that the proposed antenna has 3:1 VSWR bandwidth covering 860-1060 MHz, 1710-2067 MHz, 2360-2500 MHz, 3250-4625 MHz, 5080-5410 MHz, which includes almost all the required frequency bands for GSM900 (890-960MHz), DCS (1710-1880MHz), PCS (1850-1990MHz), UMTS (1920-2170MHz), WLAN dual band (2400-2484/5150-5350MHz) and WiMAX (3400-3600MHz) operations. Figure 11 shows the measured and simulated reflection coefficient of the proposed antenna. This antenna was measured using the network analyzer Agilent PNA E8363B. It can be observed that there is a good agreement between the measurement and simulation results. The experiment result shows that the proposed antenna has 3:1 VSWR bandwidth covering 860-1060 MHz, 1710-2067 MHz, 2360-2500 MHz, 3250- 4625 MHz, 5080-5410 MHz, which includes almost all the required frequency bands for GSM900 (890-960MHz), DCS (1710-1880MHz), PCS (1850-1990MHz), UMTS (1920-2170MHz), WLAN dual band (2400- 2484/5150-5350MHz) and WiMAX (3400-3600MHz) operations.

Figure 11. The measured and simulated reflection coefficient of the multiband printed monopole antenna [3] **Figure 11.** The measured and simulated reflection coefficient of the multiband printed monopole antenna [3]

Figure 12 presents the comparison of the simulated reflection coefficient between the proposed antenna with and without the embedded chip inductor. It is found that without the chip inductor, at the lowest frequency band the antenna can only resonate at around 1.1 GHz. After introducing the chip inductor, this resonant frequency reduces to 960 MHz and also brings down other higher modes to become resonant at 1.8 GHz. It is also observed that the chip inductor has little influence on the resonant frequencies at 2.4 and Figure 12 presents the comparison of the simulated reflection coefficient between the proposed antenna with and without the embedded chip inductor. It is found that without the chip inductor, at the lowest frequency band the antenna can only resonate at around 1.1 GHz. After introducing the chip inductor, this resonant frequency reduces to 960 MHz and also brings down other higher modes to become resonant at 1.8 GHz. It is also observed that the chip inductor has little influence on the resonant frequencies at 2.4 and 5.2 GHz.

5.2 GHz. Figure 13 shows the simulated surface current distribution of the proposed antenna at each operation frequency. It is observed that at 960 MHz, there is a strong current on branches A

Low Cost Compact Multiband Printed Monopole Antennas and Arrays for Wireless Communications http://dx.doi.org/10.5772/58815 69

width of each branch of the antenna were optimized through numerical simulations. In the simulation set-up, the model of the chip inductor is built based on the studies presented in [7]. As stated before, the chip inductor mainly influences the first two lower frequency bands. In these two lower frequency bands, the value of the chip inductor is more critical in determining the lowest resonant frequency; as a result, in the simulation set-up, the equivalent inductance and series resistance of the chip inductor model were calculated at 960 MHz using the formulas

Figure 10. The main dimensions of the multiband printed monopole antenna [3]

This antenna is printed on the inexpensive substrate FR4 (relative permittivity of 4.4) with thickness of 0.8 mm and size 100mm ×60mm, which is a reasonable circuit board size for a PDA or smart phone device. To achieve better impedance matching at each band, the length and width of each branch of the antenna were optimized through numerical simulations. In the simulation set-up, the model of the chip inductor is built

Figure 9. Structure of the multiband printed monopole antenna for mobile terminals [3]

Figure 11 shows the measured and simulated reflection coefficient of the proposed antenna. This antenna was measured using the network analyzer Agilent PNA E8363B. It can be observed that there is a good agreement between the measurement and simulation results. The experiment result shows that the proposed antenna has 3:1 VSWR bandwidth covering 860-1060 MHz, 1710-2067 MHz, 2360-2500 MHz, 3250-4625 MHz, 5080-5410 MHz, which includes almost all the required frequency bands for GSM900 (890-960MHz), DCS (1710-1880MHz), PCS (1850-1990MHz), UMTS (1920-2170MHz), WLAN dual band

(2400- 2484/5150-5350MHz) and WiMAX (3400-3600MHz) operations.

**Figure 11.** The measured and simulated reflection coefficient of the multiband printed monopole antenna [3]

inductor has little influence on the resonant frequencies at 2.4 and 5.2 GHz.

Figure 12 presents the comparison of the simulated reflection coefficient between the proposed antenna with and without the embedded chip inductor. It is found that without the chip inductor, at the lowest frequency band the antenna can only resonate at around 1.1 GHz. After introducing the chip inductor, this resonant frequency reduces to 960 MHz and also brings down other higher modes to become resonant at 1.8 GHz. It is also observed that the chip

Figure 13 shows the simulated surface current distribution of the proposed antenna at each operation frequency. It is observed that at 960 MHz, there is a strong current on branches A

Figure 11. The measured and simulated reflection coefficient of the multiband printed monopole antenna [3]

formulas provided in [7], and they are 20.6 nH and 2Ω, respectively.

provided in [7], and they are 20.6 nH and 2Ω, respectively.

(2400-2484/5150-5350MHz) and WiMAX (3400-3600MHz) operations.

5.2 GHz.


68 Progress in Compact Antennas

Figure 12. The comparison of the simulated reflection coefficient between the multiband printed monopole antenna with and without the embedded the chip inductor [3] **Figure 12.** The comparison of the simulated reflection coefficient between the multiband printed monopole antenna with and without the embedded the chip inductor [3]

and B. At 1800 and 1900 MHz, the current is mainly distributed on branch B. It is also clear that branches D and E are responsible for the resonant frequency at 2.4 and 5.2 GHz, respec‐ tively. Regarding the resonance at 3.8 GHz, it is mainly determined by branch C and the coupling between branch C and D. Figure 13 shows the simulated surface current distribution of the proposed antenna at each operation frequency. It is observed that at 960 MHz, there is a strong current on branches A and B. At 1800 and 1900 MHz, the current is mainly distributed on branch B. It is also clear that branches D and E are responsible

Besides being a completely planar structure, another advantage of the proposed antenna is that the size of the ground plane has little influence on its resonant characteristics compared to the designs that short the antenna structure to the ground plane. The proposed monopole antenna with different lengths of the ground plane has also been investigated. Figure 14 shows the simulated reflection coefficient of the proposed antenna with ground planes of different lengths. It was found that when decreasing the length of the ground plane, at the desired frequency bands the proposed antenna only exhibits small frequency shifts and some changes on the amplitude of the reflection coefficient. for the resonant frequency at 2.4 and 5.2 GHz, respectively. Regarding the resonance at 3.8 GHz, it is mainly determined by branch C and the coupling between branch C and D.

Figure 12 presents the comparison of the simulated reflection coefficient between the proposed antenna with and without the embedded chip inductor. It is found that without the chip inductor, at the lowest The scenario in which the antenna is put into the center of a plastic housing box was also investigated in this work. In the simulation model, the wall of the plastic housing is 1 mm thick, 14 mm high and has a dielectric permittivity of 3.5. The simulation results (Figure 15) indicate that, compared to the case when the antenna is radiating in free space, there is almost no influence on the reflection coefficient of the proposed antenna except for a small frequency shift at the 3.8 GHz band, when within the plastic housing.

frequency band the antenna can only resonate at around 1.1 GHz. After introducing the chip inductor, this resonant frequency reduces to 960 MHz and also brings down other higher modes to become resonant at 1.8 GHz. It is also observed that the chip inductor has little influence on the resonant frequencies at 2.4 and The measured radiation patterns of the proposed antenna in free space are presented in Figure 16. It is found that at all the desired frequencies the proposed antenna has radiation patterns similar to a typical monopole antenna, which normally has omnidirectional radiation patterns. The simulation results also suggest that the antenna has moderate gain and efficiency at its operation frequency bands. Table 2 summarizes the peak gain and radiation efficiency at the

colors

Figure 13. The simulated surface current distribution of the multiband printed monopole antenna [3] : (a) 960 MHz; (b)1800 MHz; (c)1900 MHz; (d)2.4 GHz; (e)3.8 GHz and (f)5.25 GHz. The stronger current is represented by lighter

Besides being a completely planar structure, another advantage of the proposed antenna is that the size of the ground plane has little influence on its resonant characteristics compared to the designs that short the antenna structure to the ground plane. The proposed monopole antenna with different length of ground plane has also been investigated. Figure 14 shows the simulated reflection coefficient of the proposed antenna with ground planes of different lengths. It was found that when decreasing the length of the

desired frequencies. It is observed that at 5.2 GHz, the radiation efficiency is rather low compared to other resonant frequencies. This can be explained by the fact that there is a strong coupling between the branch **B** and **E** (see Figure 12) while the branch **E** is also very closed to the ground plane, with a negative impact on the radiation efficiency.

Figure 13. The simulated surface current distribution of the multiband printed monopole antenna [3] : (a) 960 MHz; (b)1800 MHz; (c)1900 MHz; (d)2.4 GHz; (e)3.8 GHz and (f)5.25 GHz. The stronger current is represented by lighter

Figure 14. The simulated return loss of the multiband printed monopole antenna with ground planes of different

The scenario in which the antenna is put into the center of a plastic housing box was also investigated in this work. In the simulation model, the wall of the plastic housing is 1 mm thick, 14 mm high and has a dielectric permittivity of 3.5. The simulation results ( Figure 15) indicate that, compared to the case when the antenna is radiating in free space, there is almost no influence on the reflection coefficient of the proposed antenna except for small frequency shift at

The scenario in which the antenna is put into the center of a plastic housing box was also investigated in this work. In the simulation model, the wall of the plastic housing is 1 mm thick, 14 mm high and has a

 Figure 15: Comparison of the simulated S11 of the multiband antenna when placed in a plastic housing and in free space [3]

The measured radiation patterns of the proposed antenna in free space are presented in Figure 16. It is found that at all the desired frequencies the proposed antenna has radiation patterns similar to a typical monopole antenna, which normally has omnidirectional radiation patterns. The simulation results also suggest that the antenna has moderate gain and efficiency at its operation frequency bands.Table 2 summarizes the peak gain and radiation efficiency at the desired frequencies. It is observed that at 5.2 GHz, the radiation efficiency is rather low compared to other resonant frequencies. This can be explained by the fact that there is a strong coupling between the branch B and E (see Figure 12 ) while the branch E is also very closed to the ground plane, with a negative impact on the radiation efficiency.

Table 2: Simulated Peak gain and radiation efficiency of the proposed antenna at each frequency band [3]

0.96 1.5 (93.7%) 1.8 2.6 (91.9%) 1.9 2.5 (92.2%) 2.4 2.7 (77.3%) 3.5 2.8 (86.8%) 5.2 1.7 (67.9%)

Frequency(GHz) Simulated Peak Gain(dBi) / Radiation Efficiency

The Specific Absorption Ratio is also analyzed in this study. The simulation result indicates that the SAR value averaged over 1 gram of head tissue is 1.4 W/Kg, which meets the released SAR limitation of 1.6 W/Kg. It is expected that the SAR value in reality will be smaller than the simulated one due to the adding of the case for the

and some changes on the amplitude of the reflection coefficient.

Low Cost Compact Multiband Printed Monopole Antennas and Arrays for Wireless Communications

**Figure 14.** The simulated return loss of the multiband printed monopole antenna with ground planes of different

**Figure 15.** Comparison of the simulated S11 of the multiband antenna when placed in a plastic housing and in free

The Specific Absorption Ratio is also analyzed in this study. The simulation result indicates that the SAR value averaged over 1 gram of head tissue is 1.4 W/Kg, which meets the released SAR limitation of 1.6 W/Kg. It is expected that the SAR value in reality will be smaller than the

simulated one due to the adding of the case for the mobile phones.

the 3.8 GHz band, when within the plastic housing.

Besides being a completely planar structure, another advantage of the proposed antenna is that the size of the ground plane has little influence on its resonant characteristics compared to the designs that short the antenna structure to the ground plane. The proposed monopole antenna with different length of ground plane has also been investigated. Figure 14 shows the simulated reflection coefficient of the proposed antenna with ground planes of different lengths. It was found that when decreasing the length of the ground plane, at the desired frequency bands the proposed antenna only exhibits small frequency shifts

http://dx.doi.org/10.5772/58815

71

colors

lengths [3]


S11| (dB)

lengths [3]

space [3]

mobile phones.


S11| (dB)

**Figure 13.** The simulated surface current distribution of the multiband printed monopole antenna [3] : (a) 960 MHz; (b)1800 MHz; (c)1900 MHz; (d)2.4 GHz; (e)3.8 GHz and (f)5.25 GHz. The stronger current is represented by lighter col‐ ors

ground plane, at the desired frequency bands the proposed antenna only exhibits small frequency shifts and some changes on the amplitude of the reflection coefficient. Low Cost Compact Multiband Printed Monopole Antennas and Arrays for Wireless Communications http://dx.doi.org/10.5772/58815 71

Figure 13. The simulated surface current distribution of the multiband printed monopole antenna [3] : (a) 960 MHz; (b)1800 MHz; (c)1900 MHz; (d)2.4 GHz; (e)3.8 GHz and (f)5.25 GHz. The stronger current is represented by lighter

Besides being a completely planar structure, another advantage of the proposed antenna is that the size of the ground plane has little influence on its resonant characteristics compared to the designs that short the antenna structure to the ground plane. The proposed monopole antenna with different length of ground plane has also been investigated. Figure 14 shows the simulated reflection coefficient of the proposed antenna with ground planes of different lengths. It was found that when decreasing the length of the

The scenario in which the antenna is put into the center of a plastic housing box was also investigated in

desired frequencies. It is observed that at 5.2 GHz, the radiation efficiency is rather low compared to other resonant frequencies. This can be explained by the fact that there is a strong coupling between the branch B and E (see Figure 12 ) while the branch E is also very closed to the ground plane, with a negative impact on the radiation efficiency.

Table 2: Simulated Peak gain and radiation efficiency of the proposed antenna at each frequency band [3]

0.96 1.5 (93.7%) 1.8 2.6 (91.9%) 1.9 2.5 (92.2%) 2.4 2.7 (77.3%) 3.5 2.8 (86.8%) 5.2 1.7 (67.9%)

Frequency(GHz) Simulated Peak Gain(dBi) / Radiation Efficiency

The Specific Absorption Ratio is also analyzed in this study. The simulation result indicates that the SAR value averaged over 1 gram of head tissue is 1.4 W/Kg, which meets the released SAR limitation of 1.6 W/Kg. It is expected that the SAR value in reality will be smaller than the simulated one due to the adding of the case for the

The scenario in which the antenna is put into the center of a plastic housing box was also investigated in this work. In

colors

mobile phones.

desired frequencies. It is observed that at 5.2 GHz, the radiation efficiency is rather low compared to other resonant frequencies. This can be explained by the fact that there is a strong coupling between the branch **B** and **E** (see Figure 12) while the branch **E** is also very closed to

**Figure 13.** The simulated surface current distribution of the multiband printed monopole antenna [3] : (a) 960 MHz; (b)1800 MHz; (c)1900 MHz; (d)2.4 GHz; (e)3.8 GHz and (f)5.25 GHz. The stronger current is represented by lighter col‐

ors

the ground plane, with a negative impact on the radiation efficiency.

70 Progress in Compact Antennas

Figure 14. The simulated return loss of the multiband printed monopole antenna with ground planes of different lengths [3] **Figure 14.** The simulated return loss of the multiband printed monopole antenna with ground planes of different lengths [3] the simulation model, the wall of the plastic housing is 1 mm thick, 14 mm high and has a dielectric permittivity of 3.5. The simulation results ( Figure 15) indicate that, compared to the case when the antenna is radiating in free space, there is almost no influence on the reflection coefficient of the proposed antenna except for small frequency shift at

the 3.8 GHz band, when within the plastic housing.

 Figure 15: Comparison of the simulated S11 of the multiband antenna when placed in a plastic housing and in free space [3] **Figure 15.** Comparison of the simulated S11 of the multiband antenna when placed in a plastic housing and in free space [3]

The measured radiation patterns of the proposed antenna in free space are presented in Figure 16. It is found that at all the desired frequencies the proposed antenna has radiation patterns similar to a typical monopole antenna, which normally has omnidirectional radiation patterns. The simulation results also suggest that the antenna has moderate gain and efficiency at its operation frequency bands.Table 2 summarizes the peak gain and radiation efficiency at the The Specific Absorption Ratio is also analyzed in this study. The simulation result indicates that the SAR value averaged over 1 gram of head tissue is 1.4 W/Kg, which meets the released SAR limitation of 1.6 W/Kg. It is expected that the SAR value in reality will be smaller than the simulated one due to the adding of the case for the mobile phones.


**4. Small size printed monopole array**

To increase the directivity of an antenna system, the use of antenna arrays is an effective solution if an additional antenna element can be added in the wireless device. A single feed antenna array has the advantages of easy fabrication and does not need any extra RF compo‐ nents such has a phase shifter. It is desirable to design such antenna in a planar structure as it can simplify the fabrication process and reduce the fabrication cost. One compact single feed multiband printed monopole antenna array using the 2nd iteration of the Minkowski fractal

Low Cost Compact Multiband Printed Monopole Antennas and Arrays for Wireless Communications

http://dx.doi.org/10.5772/58815

73

The 2nd iteration of the Minkowski fractal geometry (see Figure 1) was chosen for this design due to its compact size. Figure 17 shows the geometry of the proposed fractal monopole array. This antenna was fabricated on a Roger 4003 substrate of thickness 0.813 mm and relative permittivity 3.38. The substrate is 112 mm long and 65 mm wide, which is the size for a typical PDA terminal. The antenna is constituted by two equal 2nd iteration Minkowski fractal monopoles fed by a single microstrip line of 1.89 mm wide. The line width of the fractal geometries is 0.25 mm and they are connected to the feed line by another horizontal microstrip line of width 1.2 mm. The partial ground plane is printed on the back side of the substrate and

> Single-feed fractal array

geometry designed for WLAN dual band application is presented in [22].

112mm

**Figure 17.** The single-feed fractal monopole array on a PDA size substrate proposed in [22]

Ground plane

65mm

**4.1. Fractal monopole antenna array**

the antenna is printed on the top side.

Stub for impedance matching

**Table 2.** Simulated Peak gain and radiation efficiency of the proposed antenna at each frequency band [3]

**Figure 16.** Measured E-plane (X-Z Plane) and H-plane (X-Y plane) radiation patterns of the proposed multiband an‐ tenna at: (a) 960MHz; (b) 1800MHz; (c) 1900MHz; (d) 2.4GHz; (e) 3.5GHz; (f) 5.2GHz [3]
