*Time Domain Performance Evaluation of UWB Antennas DOI: http://dx.doi.org/10.5772/intechopen.94546*

#### **Figure 10.**

and 2000–3300. Impulse response in the x-z plane of the SQMA is shown in

plane is fairly constant throughout the entire UWB. Even though computed transfer function in the x-z plane shown in **Figure 8(b)** has variations, it remains within the acceptable limits. The nulls observed in the transfer function in

of the RMA in the x-z plane has more resemblance to a Dirac-delta, when

**Figure 8(a)** indicates that the antenna transfer function of the RMA in the x-y

**Figure 8(b)** can be attributed to the monopole pattern of RMA. Impulse responses computed in the x-y and x-z planes for the RMA is shown in **Figure 8(c)** and **8(d)**. In the x-y plane, the impulse response preserves the expected Dirac-delta shape, unlike that in the SQMA. Even though not in the perfect shape, impulse response

*Measured antenna transfer functions: (a) SQMA, x-y plane (b) SQMA, x-z plane (c) RMA, x-y plane (d)*

**Figure 7(d)**.

*Innovations in Ultra-WideBand Technologies*

compared to SQMA.

**Figure 9.**

**120**

*RMA, x-z plane.*

*Measured impulse responses: (a) SQMA, x-y plane (b) SQMA, x-z plane (c) RMA, x-y plane (d) RMA, x-z plane.*

#### *3.3.2 Experimental results*

For the measurements, the transmitting and receiving antennas were positioned in their far field, at a distance of 25 cm. Source power level in the VNA was set at 10 dB to improve signal to noise ratio in the measured data.

**Figure 9(a)** and **(b)** indicate the measured antenna transfer functions in the x-y and x-z planes for the SQMA. The measurements seem to follow simulations indicated in Section 3.3.1. **Figure 9(c)** and **(d)** indicate the transfer functions in the x-y and x-z planes for the RMA. While the transfer functions in the x-y planes remain constant with variation within 10 dB, the measured values for the x-z plane shows large variations at particular frequencies.

The **Figure 10(a)–(d)** shows the corresponding impulse responses, obtained by performing an IFFT on the measured transfer functions and they resemble delta functions across all the angles in the x-y plane.

**Figures 11** and **12** shows the time domain performance indicators of the antennas for x-y and y-z planes. For the RMA, as the **Figure 11(a)** shows, the FWHM is constant and ringing is minimum at all angles in the x-y plane. The SQMA however shows variations, though within acceptable limits, which could be attributed to its relatively larger size. Computations also futher confirms that fidelity of the received

**Figure 11.** *Computed (a) FWHM (b) ringing and (c) Fidelity measured in the x-y plane.*

pulses in the case of RMA is constant and better compared to the SQMA. The performance indicators show variations in the x-z plane in tune with the corresponding radiation patterns. Impulse responses are convoluted with the pulse form given in Eq. (13) to study the effect of the antenna geometry on a transmitted the baseband pulse. Computed fidelity of the received pulses of the RMA is constant and better compared to the SQMA. Variation in Fidelity in the *<sup>θ</sup>* <sup>¼</sup> 00, *<sup>ϕ</sup>* <sup>¼</sup> <sup>0</sup><sup>0</sup> and *<sup>θ</sup>* <sup>¼</sup> 1800, *<sup>ϕ</sup>* <sup>¼</sup> <sup>0</sup><sup>0</sup> directions could be attributed to the nulls in the radiation patterns at those angles.

variation in antenna phase center can be quantified in terms of group delay or antenna transfer function, a curb on the former being 1nS over the entire band and

*Computed (a) FWHM (b) ringing and (c) Fidelity measured in the x-z plane.*

*Time Domain Performance Evaluation of UWB Antennas*

*DOI: http://dx.doi.org/10.5772/intechopen.94546*

In this work, we have demonstrated this point by comparing the time-domain performance of two similar antenna geometries: the SQMA and the RMA. PCB area occupied by the SQMA is approximately 2.7 times that of the RMA and resonances in the geometry are inherent due to the square patch itself. Because of the different modes that are excited in the geometry, its peak radiation points are disoriented in the higher side of the UWB. Severe pattern degradation has also been observed at these frequencies. In RMA, the radiation patterns are found to be stable with minimum degradation at the higher frequencies. The design of RMA has achieved this virtue by manipulating the surface currents in the geometry. Abrupt discontinuities that can cause reflections in the geometry are avoided by the impedance

As frequency domain characterizations hardly throw light into the pulse handling capabilities UWB antennas, a method to characterize them in the time domain

that on the latter is to remain within 10 dB.

**Figure 12.**

**123**

transformer designed in the ground plane.

## **4. Conclusion**

Printed UWB antennas are multi-resonant structures that operate over a wide frequency range. Even if the radiators designed for UWB exhibit excellent bandwidth, efficiency, etc., traveling phase centers present in the geometry can impair their use in time-domain applications. Changes in the antenna phase centers are reflected in the time domain as a dispersion in the transmitted/received pulses. A

**Figure 12.** *Computed (a) FWHM (b) ringing and (c) Fidelity measured in the x-z plane.*

variation in antenna phase center can be quantified in terms of group delay or antenna transfer function, a curb on the former being 1nS over the entire band and that on the latter is to remain within 10 dB.

In this work, we have demonstrated this point by comparing the time-domain performance of two similar antenna geometries: the SQMA and the RMA. PCB area occupied by the SQMA is approximately 2.7 times that of the RMA and resonances in the geometry are inherent due to the square patch itself. Because of the different modes that are excited in the geometry, its peak radiation points are disoriented in the higher side of the UWB. Severe pattern degradation has also been observed at these frequencies. In RMA, the radiation patterns are found to be stable with minimum degradation at the higher frequencies. The design of RMA has achieved this virtue by manipulating the surface currents in the geometry. Abrupt discontinuities that can cause reflections in the geometry are avoided by the impedance transformer designed in the ground plane.

As frequency domain characterizations hardly throw light into the pulse handling capabilities UWB antennas, a method to characterize them in the time domain

pulses in the case of RMA is constant and better compared to the SQMA. The performance indicators show variations in the x-z plane in tune with the

*Computed (a) FWHM (b) ringing and (c) Fidelity measured in the x-y plane.*

*Innovations in Ultra-WideBand Technologies*

patterns at those angles.

**4. Conclusion**

**122**

**Figure 11.**

corresponding radiation patterns. Impulse responses are convoluted with the pulse form given in Eq. (13) to study the effect of the antenna geometry on a transmitted the baseband pulse. Computed fidelity of the received pulses of the RMA is constant and better compared to the SQMA. Variation in Fidelity in the *<sup>θ</sup>* <sup>¼</sup> 00, *<sup>ϕ</sup>* <sup>¼</sup> <sup>0</sup><sup>0</sup> and *<sup>θ</sup>* <sup>¼</sup> 1800, *<sup>ϕ</sup>* <sup>¼</sup> <sup>0</sup><sup>0</sup> directions could be attributed to the nulls in the radiation

Printed UWB antennas are multi-resonant structures that operate over a wide frequency range. Even if the radiators designed for UWB exhibit excellent bandwidth, efficiency, etc., traveling phase centers present in the geometry can impair their use in time-domain applications. Changes in the antenna phase centers are reflected in the time domain as a dispersion in the transmitted/received pulses. A

is presented in this work. Temporal characterizations of the two antennas performed by the method outlined here reveal a close correspondence between the geometry of the antenna with its performance in the time domain. From the study, it is concluded that for good time-domain performance, excitation of multiple modes within the operating band of the UWB antennas has to be taken care of during the designing of the antennas itself and its physical dimension has to remain to a minimum. The first condition minimizes internal reflections and the subsequent cancelations in the antenna geometry while the second one ensures that there are no changes in the phase center of the antenna.
