**4. Frequency reconfigurable antenna design**

In this section analyzed the reconfiguration of UWB mode of proposed design to another narrowband and dual band modes. This reconfiguration is done by implementation of filter structures on the ground plane by placing of five switching elements p-i-n diodes inside it, as indicated in **Figure 8**. The switches D1–D5 are positioned in such a way to obtain the required structures I–IV for desired frequency bands. If diode D1 is on and remaining are off, we will get a filter structure like structure-I for dual band.

For biasing of p-i-n diodes, apply the dc voltage across the p-i-n diodes with the help of metal strips dimension of 2 × 0.6 mm<sup>2</sup> , as indicated in **Figure 8**. As shown in **Figure 8**, blocking capacitor of 100 pF is also connected with diode, to provide the isolation between the dc and the RF signal. A beam lead p-i-n diodes (ALPHA-6355) are placed inside the ground slot, where 0.7 V dc is required for biasing of diode. During ON state (forward bias) of diode, it exhibit resistance of 2.6 ohm while in case of OFF state (reverse bias) it represents 0.081 pF [28].

**Figure 9** shows the electrical equivalent circuit of the diode for both states (ON/ OFF state). For On state, it represents a series combination of fixed inductor (*Ls*) and a current-controlled resistor (*Rs*), whereas for OFF state, it indicates a shunt combination of intrinsic-layer capacitance (*Cp*) and the resistance (*Rs*) in series with fixed inductance (*Ls*). The intrinsic-layer capacitance (*Cp*) is a combination of the stray capacitance *Cs* and the junction's capacitance *Cj*.

As per **Table 1**, narrow bands, dual bands and UWB band are obtained by changing the states of diodes and compare the frequency bands and 10-dB bandwidth in simulation and measurement mode. The proposed antenna is initially simulated with the help of simulation software CST Microwave Studio (MWS) [27] and thereafter, fabricated on FR4 substrate with optimized values. **Figure 10** shows the fabricated prototype of the proposed antenna.

A setup is used for frequency band reconfigurable structure to observe the measured reflection coefficient (S11) with the help of vector network analyzer (VNA) and radiation characteristics by using anechoic chamber, shown in **Figure 11**.

**7**

**Figure 9.**

**Figure 8.**

*Frequency Reconfigurable UWB Antenna Design for Wireless Applications*

The simulated and measured reflection coefficients S11 for all five states are shown in **Figure 12**. Comparison of simulated S11 with measured ones is indicated as a good agreement between them. From **Table 1**, for narrowband states I achieve the bandwidth of 16% (5.05–5.89 GHz) and 14% (5.01–5.79 GHz) in simulation and measurement mode respectively. For state II (narrowband), obtained bandwidth of 11% (8.76–9.80 GHz) and 10% (8.68–9.69 GHz) in simulation and measurement

*Equivalent circuit for p-i-n diode: (a) ON-state (forward bias) and (b) OFF-state (reverse bias).*

*DOI: http://dx.doi.org/10.5772/intechopen.86035*

*Switchable filter structure on the ground plane (unit: millimeters).*

*Frequency Reconfigurable UWB Antenna Design for Wireless Applications DOI: http://dx.doi.org/10.5772/intechopen.86035*

#### **Figure 8.**

*UWB Technology - Circuits and Systems*

**4. Frequency reconfigurable antenna design**

help of metal strips dimension of 2 × 0.6 mm<sup>2</sup>

case of OFF state (reverse bias) it represents 0.081 pF [28].

the stray capacitance *Cs* and the junction's capacitance *Cj*.

the fabricated prototype of the proposed antenna.

like structure-I for dual band.

**Figure 7.**

In this section analyzed the reconfiguration of UWB mode of proposed design to another narrowband and dual band modes. This reconfiguration is done by implementation of filter structures on the ground plane by placing of five switching elements p-i-n diodes inside it, as indicated in **Figure 8**. The switches D1–D5 are positioned in such a way to obtain the required structures I–IV for desired frequency bands. If diode D1 is on and remaining are off, we will get a filter structure

*Simulated reflection coefficient S11 of the antenna for different values of l2 and W2 in structure-III.*

For biasing of p-i-n diodes, apply the dc voltage across the p-i-n diodes with the

**Figure 9** shows the electrical equivalent circuit of the diode for both states (ON/ OFF state). For On state, it represents a series combination of fixed inductor (*Ls*) and a current-controlled resistor (*Rs*), whereas for OFF state, it indicates a shunt combination of intrinsic-layer capacitance (*Cp*) and the resistance (*Rs*) in series with fixed inductance (*Ls*). The intrinsic-layer capacitance (*Cp*) is a combination of

As per **Table 1**, narrow bands, dual bands and UWB band are obtained by changing the states of diodes and compare the frequency bands and 10-dB bandwidth in simulation and measurement mode. The proposed antenna is initially simulated with the help of simulation software CST Microwave Studio (MWS) [27] and thereafter, fabricated on FR4 substrate with optimized values. **Figure 10** shows

A setup is used for frequency band reconfigurable structure to observe the measured reflection coefficient (S11) with the help of vector network analyzer (VNA) and radiation characteristics by using anechoic chamber, shown in **Figure 11**.

**Figure 8**, blocking capacitor of 100 pF is also connected with diode, to provide the isolation between the dc and the RF signal. A beam lead p-i-n diodes (ALPHA-6355) are placed inside the ground slot, where 0.7 V dc is required for biasing of diode. During ON state (forward bias) of diode, it exhibit resistance of 2.6 ohm while in

, as indicated in **Figure 8**. As shown in

**6**

*Switchable filter structure on the ground plane (unit: millimeters).*

#### **Figure 9.**

*Equivalent circuit for p-i-n diode: (a) ON-state (forward bias) and (b) OFF-state (reverse bias).*

The simulated and measured reflection coefficients S11 for all five states are shown in **Figure 12**. Comparison of simulated S11 with measured ones is indicated as a good agreement between them. From **Table 1**, for narrowband states I achieve the bandwidth of 16% (5.05–5.89 GHz) and 14% (5.01–5.79 GHz) in simulation and measurement mode respectively. For state II (narrowband), obtained bandwidth of 11% (8.76–9.80 GHz) and 10% (8.68–9.69 GHz) in simulation and measurement


**Table 1.**

*Details of combinations of p-i-n diodes with simulated and measured frequency band and bandwidth in each states.*

**Figure 10.** *Images of the fabricated antenna: (a) top view and (b) bottom view.*

mode respectively. For next state III, antenna resonant in dual band mode and achieve impedance bandwidth of 13% (2.21–2.52 GHz) and 15% (5.07–5.89 GHz) under simulation and 12% (2.20–2.50 GHz) and 15% (5.05–5.90 GHz) during measurement. For State IV, antenna identifies the operating bandwidth of 14% (2.18–2.52 GHz) and 10% (8.78–9.71 GHz) and 13% (2.19–2.50 GHz) and 9% (8.70– 9.60 GHz) during simulation and measurement mode respectively. For V state of UWB mode, antenna indicates the operating bandwidth of 141% (2.87–16.87 GHz) and 140% (2.97–16.80 GHz) under simulation and measurement mode respectively.

The resonant bands are achieved by switching states of diodes can serve several wireless applications such as WLAN, WiMAX, WiFi and UWB. As per IEEE standards the WLAN is identify for 802.11b/g/n (2.4–2.48 GHz), 802.11a/h/j/n (5.2 GHz) and ISM band (2.4–2.5 GHz). Wireless standards WiMAX, WiFi and UWB are identify for frequency bands of 2.3–2.4 and 5.15–5.85 GHz, 2.40–2.48

**9**

**Figure 12.**

*Simulated and measured reflection coefficient S11 of the proposed antenna for states I-V (from (a)-(e) as per* **Table 1***).*

**Figure 11.**

*Frequency Reconfigurable UWB Antenna Design for Wireless Applications*

*DOI: http://dx.doi.org/10.5772/intechopen.86035*

*Images of measurement setup for proposed antenna.*

*Frequency Reconfigurable UWB Antenna Design for Wireless Applications DOI: http://dx.doi.org/10.5772/intechopen.86035*

**Figure 11.** *Images of measurement setup for proposed antenna.*

*UWB Technology - Circuits and Systems*

**Diode D1 D2 D3 D4 D5 Frequency bands (in** 

III ON OFF OFF OFF OFF 2.21–2.52

IV OFF ON OFF OFF OFF 2.18–2.52

**GHz)**

2.20–2.50 and 5.05–5.90

2.19–2.50 and 8.70–9.60

I ON OFF OFF ON OFF 5.05–5.91 5.01–5.79 16 14 Narrow band II OFF ON OFF OFF ON 8.76–9.80 8.68–9.69 11 10 Narrow band

> and 5.07–5.89

and 8.78–9.71

V ON ON ON ON ON 2.87–16.56 2.85–15.85 141 140 UWB

*Details of combinations of p-i-n diodes with simulated and measured frequency band and bandwidth in each states.*

**States Simulated Measured Simulated Measured**

**10-dB bandwidth (%) Characteristics**

13 and 15 12 and 15 Dual band

14 and 10 13 and 9 Dual band

mode respectively. For next state III, antenna resonant in dual band mode and achieve impedance bandwidth of 13% (2.21–2.52 GHz) and 15% (5.07–5.89 GHz) under simulation and 12% (2.20–2.50 GHz) and 15% (5.05–5.90 GHz) during measurement. For State IV, antenna identifies the operating bandwidth of 14% (2.18–2.52 GHz) and 10% (8.78–9.71 GHz) and 13% (2.19–2.50 GHz) and 9% (8.70– 9.60 GHz) during simulation and measurement mode respectively. For V state of UWB mode, antenna indicates the operating bandwidth of 141% (2.87–16.87 GHz) and 140% (2.97–16.80 GHz) under simulation and measurement mode respectively. The resonant bands are achieved by switching states of diodes can serve several wireless applications such as WLAN, WiMAX, WiFi and UWB. As per IEEE standards the WLAN is identify for 802.11b/g/n (2.4–2.48 GHz), 802.11a/h/j/n (5.2 GHz) and ISM band (2.4–2.5 GHz). Wireless standards WiMAX, WiFi and UWB are identify for frequency bands of 2.3–2.4 and 5.15–5.85 GHz, 2.40–2.48

*Images of the fabricated antenna: (a) top view and (b) bottom view.*

**8**

**Figure 10.**

**Table 1.**

**Figure 12.** *Simulated and measured reflection coefficient S11 of the proposed antenna for states I-V (from (a)-(e) as per* **Table 1***).*

**Figure 13.** *Surface current distribution of the proposed antenna for different frequencies.*

and 5.15–5.85 GHz and 3.1–10.6 GHz respectively. Proposed design also covers the airborne radar applications works at 9.2 GHz.

From **Figure 12(e)**, the resonance is identified at the frequency of 3.0, 5.0, 7.0 and 9.6 GHz. As per the observation of **Figure 13**, it is found that the first resonance is controlled by the inverted L shaped slot dimensions since the maximum surface current is present across it. Second resonance 5.0 GHz is obtained due to the octagonal shape of radiating element and the feedline attached to the patch. Third resonance at 7.0 GHz is obtained due to the rectangular slot created on the ground plane. The two rectangular slits dimensions of *l*2 and *W*2 are responsible to generate tank circuit causes the fourth resonance at 9.5 GHz. The surface current distribution is observed at theses resonance frequencies as shown in **Figure 13**.

From **Figure 14**, the 3D-gain of the antenna is observed at different resonant frequencies, where the maximum radiation is identify at the various values of angles (theta and phi). It is noticed that at higher frequency, the directivity is improved so that the gain is increased. **Figure 15** represents the measured antenna gain in single band, dual band and UWB modes for various switching states. It is analyzed that at lower frequency range gain is reduced whereas at higher frequencies (above 6 GHz) gain is improved as compared to reference gain level of 4 dB. It is also observed that antenna exhibit the acceptable gain in narrowband and dual-band modes. **Figure 15(b)** shows the average gain of 3.9 dB is achieved for UWB mode of the proposed antenna.

**Figure 16(a)** indicates the variation of the simulated radiation efficiency from 96.9 to 79.5% and from 97.2 to 70.3% for switching states I and II respectively, for the proposed antenna. The variation of the simulated radiation efficiency from 95.5 to 73.3% and from 94.0 to 78.1% is observed for state III and IV respectively. **Figure 16(b)** shows the simulated radiation efficiency variation from 98.9 to 85.8% for UWB

**11**

**Figure 15.**

*and (b) UWB.*

**Figure 14.**

*Frequency Reconfigurable UWB Antenna Design for Wireless Applications*

mode. It is noticed that the radiation efficiency is stay above the 70% in all the narrow band, dual band and UWB band. Another observation is that at higher

*Measured gain of the proposed antenna for different switching states: (a) single-band and dual-band modes* 

frequency range the simulated radiation efficiency is decreases.

*Simulated gain (dB) of the proposed antenna for different frequencies.*

*DOI: http://dx.doi.org/10.5772/intechopen.86035*

*Frequency Reconfigurable UWB Antenna Design for Wireless Applications DOI: http://dx.doi.org/10.5772/intechopen.86035*

#### **Figure 14.**

*UWB Technology - Circuits and Systems*

**10**

**Figure 13.**

*Surface current distribution of the proposed antenna for different frequencies.*

is observed at theses resonance frequencies as shown in **Figure 13**.

airborne radar applications works at 9.2 GHz.

and 5.15–5.85 GHz and 3.1–10.6 GHz respectively. Proposed design also covers the

From **Figure 14**, the 3D-gain of the antenna is observed at different resonant frequencies, where the maximum radiation is identify at the various values of angles (theta and phi). It is noticed that at higher frequency, the directivity is improved so that the gain is increased. **Figure 15** represents the measured antenna gain in single band, dual band and UWB modes for various switching states. It is analyzed that at lower frequency range gain is reduced whereas at higher frequencies (above 6 GHz) gain is improved as compared to reference gain level of 4 dB. It is also observed that antenna exhibit the acceptable gain in narrowband and dual-band modes. **Figure 15(b)** shows the average gain of 3.9 dB is achieved for UWB mode of the proposed antenna.

**Figure 16(a)** indicates the variation of the simulated radiation efficiency from 96.9 to 79.5% and from 97.2 to 70.3% for switching states I and II respectively, for the proposed antenna. The variation of the simulated radiation efficiency from 95.5 to 73.3% and from 94.0 to 78.1% is observed for state III and IV respectively. **Figure 16(b)** shows the simulated radiation efficiency variation from 98.9 to 85.8% for UWB

From **Figure 12(e)**, the resonance is identified at the frequency of 3.0, 5.0, 7.0 and 9.6 GHz. As per the observation of **Figure 13**, it is found that the first resonance is controlled by the inverted L shaped slot dimensions since the maximum surface current is present across it. Second resonance 5.0 GHz is obtained due to the octagonal shape of radiating element and the feedline attached to the patch. Third resonance at 7.0 GHz is obtained due to the rectangular slot created on the ground plane. The two rectangular slits dimensions of *l*2 and *W*2 are responsible to generate tank circuit causes the fourth resonance at 9.5 GHz. The surface current distribution

*Simulated gain (dB) of the proposed antenna for different frequencies.*

**Figure 15.**

*Measured gain of the proposed antenna for different switching states: (a) single-band and dual-band modes and (b) UWB.*

mode. It is noticed that the radiation efficiency is stay above the 70% in all the narrow band, dual band and UWB band. Another observation is that at higher frequency range the simulated radiation efficiency is decreases.

**Figure 16.**

*Simulated radiation efficiency of the proposed antenna for different switching states: (a) single-band and dual-band modes and (b) UWB.*

**Figure 17.** *Simulated and measured AR (axial ratio) (along θ = 78° and Ф = −89°) of the proposed antenna.*

The axial ratio (AR) measurement of the proposed antenna is done inside an anechoic chamber by using antenna measurement system with VNA. To obtain maximum ARBW (axial ratio bandwidth), the antenna measurement system is aligned along the directions of *θ* = 78° and Ф = −89°, where AR is stay below the 3 dB reference level. The simulated ARBW of 38% is achieved for frequency range from 4.65 to 6.85 GHz as shown in **Figure 17**. The measured ARBW is slightly less than the simulated one at the center frequency 5.65 GHz.

**13**

**Figure 18.**

*Measured and simulated E and H plane radiation patterns.*

*Frequency Reconfigurable UWB Antenna Design for Wireless Applications*

Patterns are analyzed at operating frequencies 2.4, 5.4, 7.5, and 10 GHz for E and

H plane (principal plane). From **Figure 18**, there is dumb bell shape and quasiomnidirectional like radiation patterns in H-Plane and E-Plane respectively, which represents that the proposed design is a good candidate for wireless communication. There is a good agreement seen between the measured and simulated radiation patterns for E and H plane with the slight difference caused due to assembly

*DOI: http://dx.doi.org/10.5772/intechopen.86035*

*Frequency Reconfigurable UWB Antenna Design for Wireless Applications DOI: http://dx.doi.org/10.5772/intechopen.86035*

*UWB Technology - Circuits and Systems*

**12**

**Figure 17.**

**Figure 16.**

*dual-band modes and (b) UWB.*

The axial ratio (AR) measurement of the proposed antenna is done inside an anechoic chamber by using antenna measurement system with VNA. To obtain maximum ARBW (axial ratio bandwidth), the antenna measurement system is aligned along the directions of *θ* = 78° and Ф = −89°, where AR is stay below the 3 dB reference level. The simulated ARBW of 38% is achieved for frequency range from 4.65 to 6.85 GHz as shown in **Figure 17**. The measured ARBW is slightly less

*Simulated radiation efficiency of the proposed antenna for different switching states: (a) single-band and* 

*Simulated and measured AR (axial ratio) (along θ = 78° and Ф = −89°) of the proposed antenna.*

than the simulated one at the center frequency 5.65 GHz.

Patterns are analyzed at operating frequencies 2.4, 5.4, 7.5, and 10 GHz for E and H plane (principal plane). From **Figure 18**, there is dumb bell shape and quasiomnidirectional like radiation patterns in H-Plane and E-Plane respectively, which represents that the proposed design is a good candidate for wireless communication. There is a good agreement seen between the measured and simulated radiation patterns for E and H plane with the slight difference caused due to assembly

**Figure 18.** *Measured and simulated E and H plane radiation patterns.*


*UWB Technology - Circuits and Systems*

**Table 2.**

**15**

applications.

**Conflict of interest**

publication of this paper.

*Frequency Reconfigurable UWB Antenna Design for Wireless Applications*

misalignments. A consistent omnidirectional radiation is observed in the E plane and a nearly bi-directional pattern is observed along the H plane for all the operat

pattern. The E-plane pattern shows the unidirectional nature at higher frequen

decreases. **Table 2** shows the comparison of the proposed antenna characteristics, like as antenna size, impedance bandwidth, gain, radiation efficiency and operating

A frequency band reconfigurable antenna suitable for WLAN (2.4/5.2 GHz). ISM band (2.4–2.5 GHz), WiMAX (2.3–2.4 and 5.15–5.85 GHz), WiFi (2.40–2.48 and 5.15–5.85 GHz) and UWB (3.1–10.6 GHz) wireless standards are presented in this chapter. Proposed design also covers the airborne radar applications works at 9.2 GHz. The radiating element of octagonal shape and switchable slotted ground is implemented to achieve the frequency band reconfigurability between wireless standards. The switching between the narrowband, dual band and UWB modes is obtain by using five p-i-n diodes placed inside the inverted L shaped ground slot. The proposed design is provides the facility of easily integration with cogni

tive radio and multi radio wireless terminal devices. Proposed design achieve the bandwidth of 16% (5.05–5.89 GHz) and 14% (5.01–5.79 GHz) in simulation and measurement mode respectively for narrowband states I. Next it obtained bandwidth of 11% (8.76–9.80 GHz) and 10% (8.68–9.69 GHz) in simulation and measurement mode respectively for narrowband states II. Antenna resonant in dual band mode and achieve impedance bandwidth of 13% (2.21–2.52 GHz) and 15% (5.07–5.89 GHz) under simulation and 12% (2.20–2.50 GHz) and 15% (5.05– 5.90 GHz) during measurement for next state III. For next state IV, antenna identi

fies the operating bandwidth of 14% (2.18–2.52 GHz) and 10% (8.78–9.71 GHz) and 13% (2.19–2.50 GHz) and 9% (8.70–9.60 GHz) during simulation and measurement mode respectively. For UWB mode of V state, antenna indicate the operating bandwidth of 141% (2.87–16.87 GHz) and 140% (2.97–16.80 GHz) under simula

tion and measurement mode respectively. The average gain of 3.9 dB is achieved for UWB mode of the proposed antenna. The radiation efficiency is stay above the 70% in all the narrow band, dual band and UWB band. Radiation characteristics of the proposed antenna are achieved with good impedance matching at these resonant frequencies. The radiation pattern, gain and efficiency are consistent over all the operating bands making the proposed antenna a good choice for wireless

The author(s) declare(s) that there is no conflict of interest regarding the

Both the measured and simulated E and H plane radiation patterns are appear reasonably stable with respect to resonant frequency. It is also observed that there is

*θ* = ±90°) at lower frequencies for H-plane

*θ* = 180°) are considerably






*DOI: http://dx.doi.org/10.5772/intechopen.86035*

pinch-off along the end fire directions (

cies because at these frequencies the back lobes (along

modes, with reported multiband antennas for wireless standard.

ing frequencies.

**5. Conclusion**

*Comparison of propose designed with those in the state-of-art literature.*

**14**

*Frequency Reconfigurable UWB Antenna Design for Wireless Applications DOI: http://dx.doi.org/10.5772/intechopen.86035*

misalignments. A consistent omnidirectional radiation is observed in the E plane and a nearly bi-directional pattern is observed along the H plane for all the operating frequencies.

Both the measured and simulated E and H plane radiation patterns are appear reasonably stable with respect to resonant frequency. It is also observed that there is pinch-off along the end fire directions (*θ* = ±90°) at lower frequencies for H-plane pattern. The E-plane pattern shows the unidirectional nature at higher frequencies because at these frequencies the back lobes (along *θ* = 180°) are considerably decreases. **Table 2** shows the comparison of the proposed antenna characteristics, like as antenna size, impedance bandwidth, gain, radiation efficiency and operating modes, with reported multiband antennas for wireless standard.
