## 2 Antenna Design and Analysis
\begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Dimension** \\ \hline H & 26.1 \\ \hline B & 25.4 \\ \hline C & 14.3 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Dimensions of the RDRA (UNIT: mm). \begin{table}
\begin{tabular}{c c c} \hline \hline
**h1** & **b1** & **10-B S11 Bandwidth (\%)** \\ \hline \hline \multirow{6}{*}{10.75} & \multirow{6}{*}{0.75} & 5.43 \\ \cline{3-3}  & & 5.18 \\ \cline{3-3}  & & 5.92 \\ \cline{3-3}  & & 4.65 \\ \cline{3-3}  & & 4.69 \\ \cline{3-3}  & & 4.92 \\ \cline{3-3}  & & 5.17 \\ \cline{3-3}  & & 5.42 \\ \cline{3-3}  & & 5.96 \\ \cline{3-3}  & & 6.23 \\ \cline{3-3}  & & 6.58 \\ \hline \hline \multirow{6}{*}{11.75} & \multirow{6}{*}{1} & 6.89 \\ \cline{3-3}  & & 6.89 \\ \cline{3-3}  & & 7.19 \\ \cline{3-3}  & & 7.01 \\ \cline{3-3}  & & 6.75 \\ \cline{3-3}  & & 6.51 \\ \cline{3-3}  & & 4.90 \\ \cline{3-3}  & & 4.42 \\ \cline{3-3}  & &  
So far the optimized feed parameters and feed location were finalized. Single feed conformal metal strip of the RDRA provides a simulated reflection coefficient (S11) bandwidth of \(\sim\) 7.19%, covering the frequency range from 3.61-3.91 GHz and gain of \(\sim\)5.2 dBi over the same frequency range as shown in Figure 4; moreover the single feed cannot excite the circularly polarized fields, therefore, the design is said to be linearly polarized and in order to energize the RDRA single feed, a discrete edge port was used. To generate and examine the circular polarization field, the geometric evolution process of the anticipated antenna is depicted in Figure 2. In Figure 2b, an RDRA is designed as the initial model, following the dielectric waveguide model design principle. Then, the new feed was applied to make the cross-shaped structure. In order to simplify  
Figure 4: Simulated S-parameter and Gain of the single unit of linearly polarized RDRA. Figure 3: Reflection coefficients of the RDRA feed at various distances. the antenna, a new feed is introduced which makes the design cross shape. The cross-shape feed is usually symmetrical, which means the length and width of both strips are identical. i.e., (height) b\({}_{1}\) = 11.75 mm and (width) w\({}_{2}\) = 1 mm. Applying asymmetrical cross shape feed can help to attain decent circular polarized waves. The possibility of the generation of circular polarization of linearly polarized DRA by employing a new change in the design is depicted in Figure 2c. Based on the cross-shaped feed, RDRA is excited in its fundamental quasi-TE\({}_{111}\) mode at 3.41 GHz and the higher-order mode (TE\({}_{113}\)) at 4.20 GHz which is visible in Figure 5.  
The new configuration has not so significant impact on return loss infect simulated center frequency may shift to the left side from 3.70 GHz to 3.45 GHz. Because of the reduction of dielectric due to the conformal metal strip of the cross-shape feed, the effective dielectric of the RDRA reduces, and because of this resonant frequency shifts downwards. [7]. Simulated reflection coefficients and ARs are plotted in Figure 6. The AR bands of cross slot RDRA are100% in accord with the Impedance matching bandwidth in a lower band while the overlapping ratio in the upper band is below 1%. As shown the cross-shape feeds operate at two frequency bands. the simulated impedance bandwidths of the lower and upper bands are 8.7% (3.30-3.60 GHz) and 7.14% (4.10-4.55 GHz), respectively. The light-yellow shaded part shows the Return Loss of the upper band and lower bands while the light blue shaded part demonstrates the overlapping part of the 3-dB axial ratio. Figure 5: E-field distributions of RDRA designs in fundamental modes single feed (**a**) TE\({}_{111}\) at 3.7 GHz. (**b**) cross shape TE\({}_{111}\) at 3.41 GHz. (**c**) cross shaped-higher-order mode (TE\({}_{113}\)) at 4.20 GHz.