**2. UWB-MIMO antenna with single band-notched characteristic**

Compact ultra-wideband MIMO antenna exhibiting band-notch characteristics at WLAN band (5 to 5.9 GHz) for portable wireless devices is presented in this section [31]. The following sub sections discusses the detailed description of the proposed design.

#### **2.1 Antenna design**

*LNotch* <sup>¼</sup> *<sup>c</sup>*

*LNotch* <sup>¼</sup> *<sup>c</sup>*

<sup>λ</sup> <sup>¼</sup> *<sup>c</sup> f Notch*

*<sup>ε</sup>eff* <sup>¼</sup> ð Þ <sup>1</sup> <sup>þ</sup> *<sup>ε</sup><sup>r</sup>*

where *c* denotes light speed, *fNotch* represents notch center frequency, *LNotch* is the total length of slot or strip, *εeff* indicates effective dielectric constant and *ε<sup>r</sup>*

Several investigations were reported earlier to create band notch function at WLAN band for ultra-wideband systems in [19–30]. Methods include inserting λ/4 and λ/2 slot resonators on the ground plane [19], using a pair of ground stubs locating along the edge of the ground plane [20], inserting open stub in the printed folded monopole [21], etching folded U-shaped slots in the feed line of the antenna [22, 23], incorporating SRR slots on radiating element [24], quarter-wave stub connected to the ground [25], adding protruding two rectangular stubs on the ground plane [26], with a slot of length 1.0 λ in the radiator [27], open-ended quarter-wavelength L-shaped slots were etched on the rectangular radiating patches [28], using C-shaped and Z-shaped slot resonators on the ground [29], employing

The antenna designs presented in the above literature exhibiting acceptable isolation and notching characteristics, but some designs were not compact enough and few are a bit complex. So, the design of simple and compact band-notched

or

**52**

**Figure 3.**

denotes dielectric constant.

elliptical SRR on the radiating element [30].

*Possible locations of resonant structure on UWB antenna.*

*Innovations in Ultra-WideBand Technologies*

2 *f Notch*

4 *f Notch*

ffiffiffiffiffiffi *εeff*

ffiffiffiffiffiffi *εeff*

ffiffiffiffiffiffi *εeff*

<sup>p</sup> , (1)

<sup>p</sup> , (2)

<sup>p</sup> , (3)

<sup>2</sup> , (4)

The geometry of the proposed single band-notch UWB-MIMO antenna and photograph of the fabricated antenna are shown in **Figure 4(a)** and **(b)**. The design is printed on an FR4 substrate having dielectric constant (*εr*) of 4.4, a thickness of 0.8 mm, and a loss tangent of 0.02. The overall size of the proposed antenna is L <sup>W</sup> h mm<sup>3</sup> = 26 <sup>40</sup> 0.8 mm<sup>3</sup> . The antenna comprises two identical rectangular planar monopole radiating elements, denoted as PM1 and PM2 having sizes LR WR as shown in **Figure 4(a)**. Both PM1 and PM2 are fed by the 50-ohm coplanar waveguide having dimensions FL1 WF. And, the common ground is formed by joining LG WG and LG L reduced ground planes and is also printed on the same side of the substrate. The planar monopoles PM1 and PM2 are positioned perpendicularly to each other to reduce the mutual coupling between the elements and to improve the isolation between the antenna ports. A long rectangular strip of size SL SW is extended from the common ground plane between the monopoles to further enhance isolation and improve the impedance bandwidth of the antenna. The ground strip extends the current path which shifts the first resonance frequency to lower band and blocks the surface currents to minimizes the mutual coupling. An inverted U-slot resonator is placed on the feed line to create a bandnotch function at 5–5.9 GHz. The antenna optimized dimensions are given as follows: (unit: mm): D1 = 5.1, D2 = 6.1, D3 = 11.2, FL1 = 9.5, FL2 = 1.5, FL3 = 0.4, L = 26, LG = 8, LR = 10, SL = 18, SW = 1, W = 40, WF = 1.8, WG = 3.2, WR = 11, U1 = 7.8, U2 = 0.4, and UW = 0.3. **Figure 5(a)** and **(b)** shows the simulated *S*-parameters such as *S*<sup>11</sup> and *S*<sup>21</sup> of the Antenna 1 (UWB-MIMO antenna without ground strip), Antenna 2 (UWB-MIMO with a ground strip), and the proposed antenna. It can be observed that the proposed ultra-wideband MIMO antenna is operating from 2.2 to 11.4 GHz with good impedance bandwidth except at notch band from 5 to 5.9 GHz. Also, the mutual coupling of less than 20 dB is obtained over the entire UWB band.

#### **2.2 Study of MIMO antenna**

Since the ground and radiating elements are having smaller dimensions, the flow of surface currents on the ground plane and near-field radiation leads to poor impedance matching and high mutual coupling, which restricts the performance of MIMO antenna. The ultra-wideband MIMO antenna without and with ground strip

**Figure 4.** *(a) Geometry of the proposed antenna and (b) fabricated antenna.*

is shown in **Figure 6(a)** and **(b)**, respectively. The effects of the ground strip on impedance bandwidth and mutual coupling between the MIMO antenna elements are plotted in **Figure 7(a)** and **(b)**. With ground strip between the PM1 and PM2 (Antenna 2), the first resonance is generated at 2.5 GHz with a lower cutoff frequency of 2.3 GHz and provides good impedance bandwidth from 2.3 to 11.4 GHz as depicted in **Figure 7(a)**. And, from **Figure 7(b)**, the mutual coupling of lower than 20 dB between the antenna elements is observed throughout the UWB band which is less than 17 dB. In addition, the flow of surface currents is effectively

suppressed by the ground strip and thus less amount of current is leaked into the port 2 when port 1 is excited as displayed in **Figure 7(c)**. The ground strip can work as a reflecting surface so that the direction of surface currents is diverted and thus the distance between the ports is increased. Hence, the isolation between the MIMO antenna ports is significantly enhanced. Also, the ground strip between the MIMO antenna elements will improve impedance matching characteristics and minimizes the mutual coupling of the MIMO antenna. The MIMO antenna is also studied by varying the ground strip length SL and width SW and are plotted in **Figure 8(a)–(d)** and the same tabulated in **Table 1**. It can be observed from that the total length and width of the ground strip has more effect on the impedance bandwidth (|*S*11| <10 dB) than the isolation or mutual coupling. In this work, the ground strip length SL =

*(a) UWB-MIMO antenna without a ground strip (Antenna 1), (b) UWB-MIMO antenna with a ground*

*Simulated* S*-parameters. (a) Simulated* S*11 parameter. (b) Simulated* S*21 parameter.*

*UWB-MIMO Antenna with Band-Notched Characteristics for Portable Wireless Systems*

*DOI: http://dx.doi.org/10.5772/intechopen.93809*

To create band-notch filtering function for ultra-wideband systems, slots of various shapes or split-ring resonators or strips can be used on or next to the feed line or the radiating element or the ground plane as reported earlier. The slot or SRR or strip can act as a band-notch resonator. The notch band center frequency is controlled by the length of the resonator and notch band bandwidth is controlled by the width of the resonator. In this design, an inverted U-shaped slot is used as a band-notch resonator and is etched on the feed line of Antenna 2 which forms the

18 mm and width SW = 1 mm is adopted.

**Figure 5.**

**Figure 6.**

**55**

*strip (Antenna 2).*

*UWB-MIMO Antenna with Band-Notched Characteristics for Portable Wireless Systems DOI: http://dx.doi.org/10.5772/intechopen.93809*

**Figure 5.** *Simulated* S*-parameters. (a) Simulated* S*11 parameter. (b) Simulated* S*21 parameter.*

**Figure 6.**

*(a) UWB-MIMO antenna without a ground strip (Antenna 1), (b) UWB-MIMO antenna with a ground strip (Antenna 2).*

suppressed by the ground strip and thus less amount of current is leaked into the port 2 when port 1 is excited as displayed in **Figure 7(c)**. The ground strip can work as a reflecting surface so that the direction of surface currents is diverted and thus the distance between the ports is increased. Hence, the isolation between the MIMO antenna ports is significantly enhanced. Also, the ground strip between the MIMO antenna elements will improve impedance matching characteristics and minimizes the mutual coupling of the MIMO antenna. The MIMO antenna is also studied by varying the ground strip length SL and width SW and are plotted in **Figure 8(a)–(d)** and the same tabulated in **Table 1**. It can be observed from that the total length and width of the ground strip has more effect on the impedance bandwidth (|*S*11| <10 dB) than the isolation or mutual coupling. In this work, the ground strip length SL = 18 mm and width SW = 1 mm is adopted.

To create band-notch filtering function for ultra-wideband systems, slots of various shapes or split-ring resonators or strips can be used on or next to the feed line or the radiating element or the ground plane as reported earlier. The slot or SRR or strip can act as a band-notch resonator. The notch band center frequency is controlled by the length of the resonator and notch band bandwidth is controlled by the width of the resonator. In this design, an inverted U-shaped slot is used as a band-notch resonator and is etched on the feed line of Antenna 2 which forms the

is shown in **Figure 6(a)** and **(b)**, respectively. The effects of the ground strip on impedance bandwidth and mutual coupling between the MIMO antenna elements are plotted in **Figure 7(a)** and **(b)**. With ground strip between the PM1 and PM2 (Antenna 2), the first resonance is generated at 2.5 GHz with a lower cutoff frequency of 2.3 GHz and provides good impedance bandwidth from 2.3 to 11.4 GHz as depicted in **Figure 7(a)**. And, from **Figure 7(b)**, the mutual coupling of lower than 20 dB between the antenna elements is observed throughout the UWB band which is less than 17 dB. In addition, the flow of surface currents is effectively

*(a) Geometry of the proposed antenna and (b) fabricated antenna.*

*Innovations in Ultra-WideBand Technologies*

**Figure 4.**

**54**

**Figure 7.**

*(a)* S*11 without and with a ground strip, (b)* S*21 without and with a ground strip (c) surface current distribution at 3.8 GHz when port 1 excited without and with a ground strip.*

proposed band-notch UWB-MIMO antenna as shown in **Figure 9(a)–(c)**. The

*(a) An inverted U-slot resonator, (b) UWB-MIMO antenna with ground strip (Antenna 2), (c) proposed*

**Parameter Value (mm) Bandwidth (***S***11<** �**10 dB) Mutual coupling (***S2***<sup>1</sup> <** �**20 dB)**

 2.6–8.6 3.2–11.4 2.4–11.0 2.9–11.4 2.4–11.3 2.8–11.4 18 (proposed) 2.2–11.4 2.6–11.4

 2.0–11.1 2.8–11.4 2.1–11.2 2.8–11.4 2.2–11.2 2.7–11.4 1 (proposed) 2.2–11.4 2.6–11.4

Strip length SL 10 2.6–6.4 3.3–11.4

*UWB-MIMO Antenna with Band-Notched Characteristics for Portable Wireless Systems*

*DOI: http://dx.doi.org/10.5772/intechopen.93809*

Strip width SW 5 2.0–11.1 2.8–11.4

*The* S*<sup>11</sup> and* S*<sup>21</sup> for various strip lengths and widths except at notch band.*

**Table 1.**

**Figure 9.**

**57**

*band-notched UWB-MIMO antenna.*

ffiffiffiffiffiffi *<sup>ε</sup>eff* <sup>p</sup> <sup>≈</sup> <sup>λ</sup> 2

where *LN* denotes the total length of U-slot and *fN* is notch center frequency. When *fN* = 5.7 GHz and *ε<sup>r</sup>* = 4.4, the calculated length of the U-slot resonator using equation (5) is 16.01 mm. The simulated or designed total length of the inverted U-

*LU*�*Slot* <sup>¼</sup> <sup>2</sup> *<sup>U</sup>*<sup>1</sup> <sup>þ</sup> *<sup>U</sup>*<sup>2</sup> <sup>≈</sup> <sup>λ</sup>

Good agreement between the calculated (theoretical) length and simulated (practical) length is observed. **Figure 10(a)–(c)** shows the *S*11, *S*<sup>21</sup> and surface currents without and with inverted U-slot resonator. As seen in **Figure 10(a)**, the proposed antenna is working from 2.2 to 11.4 GHz with good impedance bandwidth and generates band-notch characteristics from 5 to 5.9 GHz with *S*<sup>11</sup> of �5 dB at 5.7 GHz. And the mutual coupling of below �20 dB over the entire working band is observed as from the **Figure 10(b)**. It is evident from **Figure 10(c)** that at 5.7 GHz,

2

, (5)

*:* (6)

*LN* <sup>¼</sup> *<sup>c</sup>* 2 *f <sup>N</sup>*

length of the U-shaped resonator is calculated using Eq. (5) [19]:

slot resonator is 16 mm and is determined by using equation (6).

**Figure 8.**

*(a)* S*11 for different strip lengths SL, (b)* S*21 different strip lengths SL, (c)* S*11 for different strip widths SW, (d)* S*21 for different strip widths SW.*


*UWB-MIMO Antenna with Band-Notched Characteristics for Portable Wireless Systems DOI: http://dx.doi.org/10.5772/intechopen.93809*

#### **Table 1.**

**Figure 7.**

**Figure 8.**

**56**

*(d)* S*21 for different strip widths SW.*

*(a)* S*11 without and with a ground strip, (b)* S*21 without and with a ground strip (c) surface current*

*(a)* S*11 for different strip lengths SL, (b)* S*21 different strip lengths SL, (c)* S*11 for different strip widths SW,*

*distribution at 3.8 GHz when port 1 excited without and with a ground strip.*

*Innovations in Ultra-WideBand Technologies*

*The* S*<sup>11</sup> and* S*<sup>21</sup> for various strip lengths and widths except at notch band.*

**Figure 9.**

*(a) An inverted U-slot resonator, (b) UWB-MIMO antenna with ground strip (Antenna 2), (c) proposed band-notched UWB-MIMO antenna.*

proposed band-notch UWB-MIMO antenna as shown in **Figure 9(a)–(c)**. The length of the U-shaped resonator is calculated using Eq. (5) [19]:

$$L\_N = \frac{c}{2f\_N\sqrt{\varepsilon\_{\text{eff}}}} \approx \frac{\lambda}{2},\tag{5}$$

where *LN* denotes the total length of U-slot and *fN* is notch center frequency. When *fN* = 5.7 GHz and *ε<sup>r</sup>* = 4.4, the calculated length of the U-slot resonator using equation (5) is 16.01 mm. The simulated or designed total length of the inverted Uslot resonator is 16 mm and is determined by using equation (6).

$$L\_{U-\text{Slot}} = 2\,\text{U}\_1 + \text{U}\_2 \approx \frac{\lambda}{2}.\tag{6}$$

Good agreement between the calculated (theoretical) length and simulated (practical) length is observed. **Figure 10(a)–(c)** shows the *S*11, *S*<sup>21</sup> and surface currents without and with inverted U-slot resonator. As seen in **Figure 10(a)**, the proposed antenna is working from 2.2 to 11.4 GHz with good impedance bandwidth and generates band-notch characteristics from 5 to 5.9 GHz with *S*<sup>11</sup> of �5 dB at 5.7 GHz. And the mutual coupling of below �20 dB over the entire working band is observed as from the **Figure 10(b)**. It is evident from **Figure 10(c)** that at 5.7 GHz,

#### **Figure 10.**

*(a)* S*11 without and with inverted U-slot, (b)* S*21 without and with inverted U-slot (c) current distribution at 5.7 GHz when port 1 and port 2 excited.*

mm to 0.4 mm, the notch bandwidth is increasing from (5.2–5.7) GHz to (4.94–6.1) GHz with notch center frequency *fN* at 5.7 GHz. The slot width UW of 0.3 mm is chosen in this proposed design to get the desired band notch from 5 to 5.9 GHz. **Figure 11(c)** and **(d)** shows the effects of inverted U-slot resonator on the *S*<sup>21</sup> of the MIMO antenna for various slot lengths and widths. Also, it is observed that variation in the slot length U1 and width UW has a negligible effect on the mutual

S*11-parameter for (a) various slot lengths, (b) various slot widths; and* S*21 for (c) various slot lengths,*

*UWB-MIMO Antenna with Band-Notched Characteristics for Portable Wireless Systems*

*DOI: http://dx.doi.org/10.5772/intechopen.93809*

The proposed antenna offers good impedance bandwidth (|*S*11|<10 dB) from 2.2 to 11.4 GHz with band notch at 5–5.9 GHz as demonstrated in **Figure 12(a)**. Hence, the frequency interference from WLAN band can be effectively suppressed by the proposed UWB MIMO antenna. And, from **Figure 12(b)**, it is found that the simulated and measured mutual coupling (*S*21) value is about 20 dB in the operating band except at few frequencies around 6.2 and 7.2 GHz (18 dB) demonstrating good isolation between the ports. At 6.2 and 7.2 GHz the *S*<sup>21</sup> is 16 dB. From **Figure 12(c)**, the antenna has good 2:1 VSWR from 2.2 to 11.4 GHz excluding at notch-band, i.e. from 5.0 to 5.9 GHz. It is observed that the VSWR of about 3.5 at 5.7 GHz. The summary of simulated and mesured results presented in **Figure 12** are provided in **Table 3**. The simulated and measured radiation patterns of the proposed antenna on the *E*-plane and *H*-plane at 3.8, 6.5, and 10 GHz when port 1 is excited and port 2 is terminated with 50-ohm load, and vice-versa are shown in **Figure 13(a)** and **(b)**. Good agreement between the simulated and measure 2-D radiation patterns is observed. At 3.8 and 6.5 GHz frequencies, PM1 and PM2 have quite omnidirectional radiation patterns in H-planes, i.e. the *XZ* plane and the *YZ* plane, respectively. However, at 10 GHz because of the higher-order resonances,

coupling of MIMO antenna.

**Figure 11.**

**59**

*(d) various slot widths.*

**2.3 Results and discussion**


#### **Table 2.**

*The notch bands and notch center frequencies for different slot lengths and widths.*

heavy current is concentrated around the inverted U-slot resonator which acts a band-notch filter, so the current flow on the radiating elements is blocked and hence no radiation from the antenna. Therefore, notch band from 5 to 5.9 GHz WLAN band is created.

The parametric analysis on the slot length U1 and slot width UW is performed to describe the effects of inverted U-slot. **Table 2** shows the notch bands and notch center frequencies for different slot lengths and widths. **Figure 11(a)** and **(b)** illustrates the *S*<sup>11</sup> of the MIMO antenna for different slot lengths U1 and slot widths UW, respectively. It is evident that as the slot length U1 increasing from 6.8 mm to 8.1 mm, the center frequency of notch *fN* is decreasing from 6.5 GHz to 5.4 GHz and notch band is shifting from (6.26–6.7) GHz to (4.8–5.7) GHz. The required band notch from 5 to 5.9 GHz is generated for U1 of 7.8 mm which is used in this design. Form **Figure 11(b)**, it can be observed that increasing the slot width UW from 0.25

*UWB-MIMO Antenna with Band-Notched Characteristics for Portable Wireless Systems DOI: http://dx.doi.org/10.5772/intechopen.93809*

**Figure 11.** S*11-parameter for (a) various slot lengths, (b) various slot widths; and* S*21 for (c) various slot lengths, (d) various slot widths.*

mm to 0.4 mm, the notch bandwidth is increasing from (5.2–5.7) GHz to (4.94–6.1) GHz with notch center frequency *fN* at 5.7 GHz. The slot width UW of 0.3 mm is chosen in this proposed design to get the desired band notch from 5 to 5.9 GHz. **Figure 11(c)** and **(d)** shows the effects of inverted U-slot resonator on the *S*<sup>21</sup> of the MIMO antenna for various slot lengths and widths. Also, it is observed that variation in the slot length U1 and width UW has a negligible effect on the mutual coupling of MIMO antenna.

## **2.3 Results and discussion**

The proposed antenna offers good impedance bandwidth (|*S*11|<10 dB) from 2.2 to 11.4 GHz with band notch at 5–5.9 GHz as demonstrated in **Figure 12(a)**. Hence, the frequency interference from WLAN band can be effectively suppressed by the proposed UWB MIMO antenna. And, from **Figure 12(b)**, it is found that the simulated and measured mutual coupling (*S*21) value is about 20 dB in the operating band except at few frequencies around 6.2 and 7.2 GHz (18 dB) demonstrating good isolation between the ports. At 6.2 and 7.2 GHz the *S*<sup>21</sup> is 16 dB. From **Figure 12(c)**, the antenna has good 2:1 VSWR from 2.2 to 11.4 GHz excluding at notch-band, i.e. from 5.0 to 5.9 GHz. It is observed that the VSWR of about 3.5 at 5.7 GHz. The summary of simulated and mesured results presented in **Figure 12** are provided in **Table 3**. The simulated and measured radiation patterns of the proposed antenna on the *E*-plane and *H*-plane at 3.8, 6.5, and 10 GHz when port 1 is excited and port 2 is terminated with 50-ohm load, and vice-versa are shown in **Figure 13(a)** and **(b)**. Good agreement between the simulated and measure 2-D radiation patterns is observed. At 3.8 and 6.5 GHz frequencies, PM1 and PM2 have quite omnidirectional radiation patterns in H-planes, i.e. the *XZ* plane and the *YZ* plane, respectively. However, at 10 GHz because of the higher-order resonances,

heavy current is concentrated around the inverted U-slot resonator which acts a band-notch filter, so the current flow on the radiating elements is blocked and hence no radiation from the antenna. Therefore, notch band from 5 to 5.9 GHz

*(a)* S*11 without and with inverted U-slot, (b)* S*21 without and with inverted U-slot (c) current distribution at*

**Parameter Value (mm) Notch-band (GHz) Notch-center frequency** *fN* **(GHz)**

7.3 5.73–6.4 6.2 7.8 (proposed) 5.0–5.9 5.7 8.1 4.8–5.7 5.4

0.3 (proposed) 5.0–5.9 5.7 0.35 4.95–6 5.7 0.4 4.94–6.1 5.7

Slot length U1 6.8 6.26–6.7 6.5

Slot width UW 0.25 5.2–5.7 5.6

*The notch bands and notch center frequencies for different slot lengths and widths.*

The parametric analysis on the slot length U1 and slot width UW is performed to describe the effects of inverted U-slot. **Table 2** shows the notch bands and notch center frequencies for different slot lengths and widths. **Figure 11(a)** and **(b)** illustrates the *S*<sup>11</sup> of the MIMO antenna for different slot lengths U1 and slot widths UW, respectively. It is evident that as the slot length U1 increasing from 6.8 mm to 8.1 mm, the center frequency of notch *fN* is decreasing from 6.5 GHz to 5.4 GHz and notch band is shifting from (6.26–6.7) GHz to (4.8–5.7) GHz. The required band notch from 5 to 5.9 GHz is generated for U1 of 7.8 mm which is used in this design. Form **Figure 11(b)**, it can be observed that increasing the slot width UW from 0.25

WLAN band is created.

**Figure 10.**

**Table 2.**

**58**

*5.7 GHz when port 1 and port 2 excited.*

*Innovations in Ultra-WideBand Technologies*

**Figure 12.** *The simulated and measured results: (a)* S*11-parameter, (b)* S*21-parameter and (c) VSWR*


#### **Table 3.**

*The summary of simulated and measured results presented in Figure 12.*

the radiation patterns in the *H*-planes are less omnidirectional. And, at 6.5 and 10 GHz, PM1 and PM2 have the dumbbell-shaped or bidirectional patterns in the *E*planes, i.e. the *YZ* plane and the *XZ* plane, respectively. However, at 3.8 GHz, PM1 and PM2 do not have the "dumb-bell" shaped patterns in the *E*-planes, because, the strip on the ground plane changes the current distributions. It can be seen from **Figure 13** that the proposed antenna provides omnidirectional radiations in *H*-plane which is essential for portable wireless devices to receive the signals from all directions. And, it is also found that *H*-plane patterns of port 1 and port 2 are nearly mirror images demonstrating the good pattern diversity. The simulated and measured peak gain of the proposed design is plotted in **Figure 14(a)**. The peak gain of 2.4 to 7.5 dBi in the operating band is observed excepting at the notch band. At the notch band, the measured peak gain falls to 2.2 dBi. **Figure 14(b)** shows the simulated and measured radiation efficiency plot of the proposed antenna. The radiation efficiency of above 90% is found across the UWB band excluding at 5–5.9 GHz notch band. At notch band, the efficiency drops to 12%. It is evident from **Figure 14(a)** and **(b)** that the proposed antenna can avoid the frequency interference from WLAN band more efficiently.

Along with the radiation patterns, envelope correlation coefficient (ECC) is also

*Simulated (solid line) and measured (dashed line) radiation patterns. (a) simulated and measured when port*

*UWB-MIMO Antenna with Band-Notched Characteristics for Portable Wireless Systems*

*DOI: http://dx.doi.org/10.5772/intechopen.93809*

an important parameter to study the MIMO antenna diversity and is calculated using *S*-parameters with the equation (7) of a two-port MIMO antenna system reported by Blanch et al. [32]. The envelop correlation coefficient (ECC) measures the similarity between the antenna radiation patterns and is very useful to estimate the performance of MIMO antenna. The lower the ECC value means the lesser is the

**Figure 13.**

**Figure 14.**

**61**

*1 excited. (b) Simulated and measured when port 2 excited.*

*Simulated and measured (a) peak gain, (b) radiation efficiency.*

*UWB-MIMO Antenna with Band-Notched Characteristics for Portable Wireless Systems DOI: http://dx.doi.org/10.5772/intechopen.93809*

**Figure 13.**

the radiation patterns in the *H*-planes are less omnidirectional. And, at 6.5 and 10 GHz, PM1 and PM2 have the dumbbell-shaped or bidirectional patterns in the *E*planes, i.e. the *YZ* plane and the *XZ* plane, respectively. However, at 3.8 GHz, PM1 and PM2 do not have the "dumb-bell" shaped patterns in the *E*-planes, because, the strip on the ground plane changes the current distributions. It can be seen from **Figure 13** that the proposed antenna provides omnidirectional radiations in *H*-plane which is essential for portable wireless devices to receive the signals from all directions. And, it is also found that *H*-plane patterns of port 1 and port 2 are nearly mirror images demonstrating the good pattern diversity. The simulated and measured peak gain of the proposed design is plotted in **Figure 14(a)**. The peak gain of 2.4 to 7.5 dBi in the operating band is observed excepting at the notch band. At the notch band, the measured peak gain falls to 2.2 dBi. **Figure 14(b)** shows the simulated and measured radiation efficiency plot of the proposed antenna. The radiation efficiency of above 90% is found across the UWB band excluding at 5–5.9 GHz notch band. At notch band, the efficiency drops to 12%. It is evident from **Figure 14(a)** and **(b)** that the proposed antenna can avoid the frequency interfer-

**Mutual coupling (***S2***1)**

Simulated 2.2–11.4 GHz <20 dB 3.6 5–5.9 GHz Measured 2.3–11.7 GHz <18 dB 3.4 5–6 GHz

**VSWR at notch band**

**Notch band**

*The simulated and measured results: (a)* S*11-parameter, (b)* S*21-parameter and (c) VSWR*

ence from WLAN band more efficiently.

**Figure 12.**

**Table 3.**

**60**

**Result Bandwidth (***S***<sup>11</sup> < 10**

*Innovations in Ultra-WideBand Technologies*

**dB)**

*The summary of simulated and measured results presented in Figure 12.*

*Simulated (solid line) and measured (dashed line) radiation patterns. (a) simulated and measured when port 1 excited. (b) Simulated and measured when port 2 excited.*

**Figure 14.** *Simulated and measured (a) peak gain, (b) radiation efficiency.*

Along with the radiation patterns, envelope correlation coefficient (ECC) is also an important parameter to study the MIMO antenna diversity and is calculated using *S*-parameters with the equation (7) of a two-port MIMO antenna system reported by Blanch et al. [32]. The envelop correlation coefficient (ECC) measures the similarity between the antenna radiation patterns and is very useful to estimate the performance of MIMO antenna. The lower the ECC value means the lesser is the

complete working band except at stopband. At the notch band i.e. at 5.7 GHz, the group delay of 5.8 ns in the face to face orientation and 6 ns in the side by side orientation ensures that the proposed antenna can transmit the UWB signal with minimum distortion. It is observed from the above results that there is good agreement between the simulated and measured *S*-parameters except for some deviations due to fabrication and soldering imperfections, losses in dielectrics and

*UWB-MIMO Antenna with Band-Notched Characteristics for Portable Wireless Systems*

*DOI: http://dx.doi.org/10.5772/intechopen.93809*

To mitigate the frequency interference from narrowband system like WLAN, a compact planar UWB antenna with single band-notched characteristics for portable wireless devices applications is discussed in this chapter. In this design, the monopoles are arranged perpendicularly to reduce to mutual coupling. A rectangular strip is extended from the ground plane to improve the impedance matching characteristics and to reduce the mutual coupling further or enhance the isolation. An inverted U-shaped slot is used on the feed line to realize the band-notch filtering function for suppressing the frequency interference from 5 to 5.9 GHz WLAN band. For validating the simulation results, all the proposed antennas have been fabricated and tested using the Agilent N5224A PNA, Anritsu MS2037C vector network analyzer and an anechoic chamber. The measured results of all the proposed antenna are well agreed with simulated results. The measured and simulated results show that the proposed antenna offer good impedance bandwidth of *S*11≤ 10 dB in whole UWB band (3.1–10.6 GHz) except at the designed notch bands while giving less mutual coupling (*S*21) of lower than 20 dB in the entire UWB band. The low envelope correlation coefficient, nearly constant gain, stable radiation patterns, more directive gain, TARC and less group delay, demonstrate that the proposed MIMO antenna is an appropriate choice for portable wireless UWB systems.

Authors would like to express their gratitude towards University College of Engineering & Technology, Acharya Nagarjuna University, Guntur and management of Koneru Lakshmaiah Education Foundation, Guntur for their continuous support and encouragement during this work. Further, Dr. J. Chandrasekhar Rao and Dr. N. Venkateswara Rao would like to acknowledge with thanks DST through FIST grant SR/FST/ETI-316/2012, ECR/2016/000569 and Dr. B.T.P. Madhav, Prof. of ECE, KLEF for providing measurement facility in LCRC lab. I would like to thank Mr. P. Ramakoti Reddy, Electro Circuit Systems, Hyderabad, Mr. K. Vijaya Saradhi Reddy, Excel Radio Frequency Technologies, Hyderabad and Mr. Krishna Prasad, Scientist-ECIL, Hyderabad for their help in the fabrication and measurements of

conductors, effects of SMA connector, and measurement tolerances.

**3. Conclusion**

**Acknowledgements**

**63**

the prototype developed in this work.

**Figure 15.** *(a) Simulated and measured ECC, (b) Simulated and measured diversity gain, (c) Simulated and measured TARC, (d) Group delay of the proposed antenna.*

overlapping between the two radiation patterns. For MIMO antenna system to ensure the diversity performance as good, the ECC with value below 0.5 is adopted in most the cases. **Figure 15(a)** shows the simulated and measured ECC of the proposed antenna. The simulated ECC is about 0.005 and measured ECC is below 0.008 from 2.2 to 11.4 GHz.

$$ECC = \frac{\left| \mathbf{S}\_{11}^{\*} \mathbf{S}\_{12} + \mathbf{S}\_{21}^{\*} \mathbf{S}\_{22} \right|^{2}}{\left( \mathbf{1} - \left( \left| \mathbf{S}\_{11} \right|^{2} + \left| \mathbf{S}\_{21} \right|^{2} \right) \right) \left( \mathbf{1} - \left( \left| \mathbf{S}\_{22} \right|^{2} + \left| \mathbf{S}\_{12} \right|^{2} \right) \right)},\tag{7}$$

The diversity gain (DG) and total active reflection coefficient (TARC) are also essential parameters to study the MIMO antenna diversity performance. The diversity gain and total active reflection coefficient of the proposed antennas can be estimated by using the equations (8) and (9) [33] as follows:

$$DG = \mathbf{1}0\sqrt{1 - ECC}^2\tag{8}$$

$$TARC = \sqrt{\frac{\left(\mathbf{S}\_{11} + \mathbf{S}\_{12}\right)^2 + \left(\mathbf{S}\_{21} + \mathbf{S}\_{22}\right)^2}{2}} \tag{9}$$

The simulated and measured diversity gain plots are given in **Figure 15(b)**. The diversity gain of >9.95 dB is found in the UWB band. And, **Figure 15(c)** shows the simulated and measured TARC. It is observed that the TARC of less than �28 dB is obtained in the whole UWB band. The group delay of the proposed antenna is measured in face to face and side by side situations with the space of 30 cm is shown in **Figure 15(d)**. The group delay is almost uniform and is below 1 ns in the

### *UWB-MIMO Antenna with Band-Notched Characteristics for Portable Wireless Systems DOI: http://dx.doi.org/10.5772/intechopen.93809*

complete working band except at stopband. At the notch band i.e. at 5.7 GHz, the group delay of 5.8 ns in the face to face orientation and 6 ns in the side by side orientation ensures that the proposed antenna can transmit the UWB signal with minimum distortion. It is observed from the above results that there is good agreement between the simulated and measured *S*-parameters except for some deviations due to fabrication and soldering imperfections, losses in dielectrics and conductors, effects of SMA connector, and measurement tolerances.
