*3.3.1 Results of simulation in CST*

radiation. The coupling of the guided waves to the radiator is strongly dependent on parameter *d* and the resonances in the structure can be matched by suitably choosing *d*. For the RMA, the geometric parameters are: *s* = 2.3, *g* = 0.28, *d* = 4.25, *l*<sup>1</sup> = 9, *b*<sup>1</sup> = 10, *lg* = 17.75, *l*<sup>2</sup> = 6, *b*<sup>2</sup> = 7.3, *g*<sup>1</sup> = 0.45, *g*<sup>2</sup> = 1.35, *g*<sup>3</sup> = 2, *g*<sup>4</sup> = 2.7, *t* = 1, *sf* = 2, *l <sup>f</sup>* = 3, *L* = 30,

Measured and simulated return losses of the two antennas are shown in **Figure 5**. The prominent resonances in the SQMA are at 3.8 GHz, 8 GHz and

*W* = 12, *ε<sup>r</sup>* = 4.4, *tan* ð Þ*δ* = 0.02, *h* = 1.6. Unit of all lengths are in *mm*.

**3.2 Performance evaluation in the frequency domain**

*Measured and simulated S*11ð Þ *dB of the (a) SQMA and (b) RMA.*

*Design and parameters of (a) SQMA (b) RMA.*

*Innovations in Ultra-WideBand Technologies*

**Figure 4.**

**Figure 5.**

**116**

Magnitude of the transfer function *h* ! *Rx*ð Þ *ω*, *θ*, *φ* simulated in CST for the x-y plane of the antennas are shown in **Figure 7(a)** (Using Eq. (3)). It is seen that the intensity plots for *h* ! *Rx*ð Þ *ω*, *θ*, *φ* and *h* ! *Tx*ð Þ *ω*, *θ*, *φ* differ only in their relative

**Figure 6.** *Simulated radiation patterns at different frequencies for the the antennas (a) SQMA (b) RMA.*

amplitudes. Magnitude of the transfer function decay gradually as a function of frequency over most of the azimuth angles (x-y plane). The loss of omnidirectionality of the pattern of SQMA at frequencies above 8 GHz is reflected in its transfer function as relatively low intensities at at certain angles. Sharp nulls are seen between 300–500, 1300–1500, 2100–230<sup>0</sup> and 3200–3300. Transfer function in the x-z plane of the SQMA is shown in **Figure 7(b)**. The nulls in the radiation

pattern at 1800 can be seen in the transfer functions which show intensity

*Time Domain Performance Evaluation of UWB Antennas*

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

Impulse response in the x-y plane is well formed with good peak value over almost all the angular regions as shown in **Figure 7(c)**. Amplitude degradation beyond 8 GHz in the SQMA impulse response is reflected between 300–120<sup>0</sup>

*Computed transfer functions of the RMA in the (a) x-y (b) x-z planes; computed impulse responses the RMA in*

variations.

**Figure 8.**

**119**

*the (c) x-y (d) x-z planes.*

#### **Figure 7.**

*Computed transfer functions of the SQMA in the (a) x-y (b) x-z planes; computed impulse responses the SQMA in the (c) x-y (d) x-z planes.*

amplitudes. Magnitude of the transfer function decay gradually as a function of frequency over most of the azimuth angles (x-y plane). The loss of omni-

*Innovations in Ultra-WideBand Technologies*

*Computed transfer functions of the SQMA in the (a) x-y (b) x-z planes; computed impulse responses the*

**Figure 7.**

**118**

*SQMA in the (c) x-y (d) x-z planes.*

directionality of the pattern of SQMA at frequencies above 8 GHz is reflected in its transfer function as relatively low intensities at at certain angles. Sharp nulls are seen between 300–500, 1300–1500, 2100–230<sup>0</sup> and 3200–3300. Transfer function in the x-z plane of the SQMA is shown in **Figure 7(b)**. The nulls in the radiation

pattern at 1800 can be seen in the transfer functions which show intensity variations.

Impulse response in the x-y plane is well formed with good peak value over almost all the angular regions as shown in **Figure 7(c)**. Amplitude degradation beyond 8 GHz in the SQMA impulse response is reflected between 300–120<sup>0</sup>

#### **Figure 8.**

*Computed transfer functions of the RMA in the (a) x-y (b) x-z planes; computed impulse responses the RMA in the (c) x-y (d) x-z planes.*

and 2000–3300. Impulse response in the x-z plane of the SQMA is shown in **Figure 7(d)**.

**Figure 8(a)** indicates that the antenna transfer function of the RMA in the x-y 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 **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 of the RMA in the x-z plane has more resemblance to a Dirac-delta, when compared to SQMA.

*3.3.2 Experimental results*

**Figure 10.**

*plane.*

**121**

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

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

**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

The **Figure 10(a)–(d)** shows the corresponding impulse responses, obtained by performing an IFFT on the measured transfer functions and they resemble delta

**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

10 dB to improve signal to noise ratio in the measured data.

*Time Domain Performance Evaluation of UWB Antennas*

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

large variations at particular frequencies.

functions across all the angles in the x-y plane.

**Figure 9.**

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