# Implications of Metamaterial on Ultra-Wide Band Microstrip Antenna Performance
## 2 Antenna Design  
A UWB microstrip antenna of circular patch with elliptical slot rings was designed. This antenna consists of a printed circular patch modified with elliptical slot rings excited by a rectangular edge-fed microstrip line. The circular patch design is selected for outer dimensions of antenna design due to its excellent radiation efficiencies, impedance bandwidth and omni-directional far-field beam pattern [26]. In this antenna, Rogers 5880-LZ substrate of a length 45 mm and a width of 31 mm is used with a dielectric constant of \(\varepsilon_{\mathrm{r}}\) = 1.96, substrate thickness h = 1.27 mm and a loss tangent of 0.0009. Moreover, a partial conducting ground plane with a length of 11 mm and a width of 31 mm is implemented; the ground plane length of 11 mm was selected after performing several parametric simulations to produce the best wideband results. Fundamentally, three lunar slots are employed on the patch's circular shape to reduce the antenna reflection loss (S\({}_{11}\)) and enhance the VSWR. Antenna's detailed geometry is demonstrated in Figure 1, Tables 1 and 2.  
The parametric simulation was conducted on a ground length ranges between 8 mm-13 mm to achieve optimal design performance. Figure 2 shows the return loss with the ground plane variations, which in return affects the resonant frequency. As a consequence of the return loss value and UWB requirements, 11-mm length of the ground plane is noticeable to be the most appropriate value with  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Part** & **Length (mm)** & **Part** & **Length (mm)** \\ \hline L1 & 45.00 & L9 & 4.900 \\ L2 & 11.00 & L10 & 2.650 \\ L3 & 2.651 & L11 & 7.680 \\ L4 & 4.130 & W1 & 31.00 \\ L5 & 2.900 & W2 & 9.000 \\ L6 & 2.000 & W3 & 8.480 \\ L7 & 2.650 & W4 & 1.030 \\ L8 & 2.900 & W5 & 3.920 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Antenna dimensions.  
Figure 1: Circular antenna structure.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Ellipse** & **Major Radius (mm)** & **Ration** \\ \hline A & 15.0 & 1 \\ B & 7.42 & 1.5 \\ C & 6.89 & 1.5 \\ D & 5.30 & 1.5 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Ring specifications.  
a frequency range between 3.5 GHz and 9 GHz; the best return loss obtained is \(-40\) dB at 4.6 GHz, as illustrated in Figure 3. The VSWR of this design is less than two for the impedance bandwidth between 3.5 GHz and 9 GHz. The maximum gain obtained is almost 5 dB in the UWB band, as shown in Figure 4.  
Moreover, the radiation pattern is another essential antenna parameter; The proposed antenna's radiation pattern at different frequencies of 4 GHz, 6 GHz, 8 GHz and 10 GHz in both E- and H-planes are presented in Figure 5 at Phi = 0\({}^{\circ}\) and Phi = 90\({}^{\circ}\). Obviously, the radiation pattern is almost omni-directional at Phi = 0\({}^{\circ}\) plane. The proposed antenna with 11 mm partial ground was fabricated and displayed in Figure 6. The return loss measurement shows that the antenna has a frequency bandwidth between 3.5 GHz and 8.4 GHz and a return loss up to \(-38\) dB at 4.2 GHz, Figure 7. The simulated and measured results are in good agreement with a compression in the measured results between 5 GHz to 6 GHz. The small variation between the measured and simulated results can be attributed to the use of SMA-N adapter during the VNA calibration process. Overall, both results have acceptable performance over the design range.  
Figure 4: Simulated maximum gain.  
Figure 3: Simulated S\({}_{11}\) for the optimal value of ground length 11 mm.  
Figure 2: Simulated S\({}_{11}\) for ground length 8–13 mm.  
Figure 5: Radiation pattern at Phi = 0\({}^{\circ}\) & 90\({}^{\circ}\).  
Figure 6: Fabricated circular microstrip antenna with elliptical rings.  
Figure 7: S\({}_{11}\) for the fabricated microstrip antenna.