## 3 A Pair of Rectangular Slots and Parasitic Patch for the 3 dB ARBW and the Gain Enhancement
### A Rectangular Parasitic Patch (Model 2)
This design also increased the antenna gain up to 4.71 dBic at the frequency of 2.2 GHz, with a peak gain of 4.8 dBic at the frequency of 2.28 GHz. However, the impedance frequency shifted to a higher frequency of 2.27-3.32 GHz, with the deepest curve of \(-45\) dB at the center frequency of 2.69 GHz. This impedance frequency must have been shifted to a lower frequency; therefore, to overcome this problem, the feedline width was deformed with a \(W_{f2}\) of 10 mm, as depicted in Figure 2. Model 2 has an impedance bandwidth of 1.84-2.72 GHz, an antenna gain of up to 4.65 dBic, an ARBW of 2.21-3.26 GHz or 51.52%, and a deep curve of 0.28 dB at the frequency of 2.42 GHz. Therefore, proper tuning is critical to determine the best parameters that produce a wider impedance bandwidth, a wider ARBW, and a higher gain. The comparison of the simulation results of the conventional model, model 1, and model 2 is depicted in Figure 5, and the performance is compared in Table 2.  
Figure 5(a),b show the measured and the simulated axial ratios as a function of theta (\(\theta\)) at the frequencies of 2.2 GHz and 2.4 GHz. At 2.2 GHz, the measured and simulated AR in the E-plane and H-plane produced a good result, even though the measured result was a little higher than the simulated result in the E-plane. At 2.4 GHz in the E-plane and H-plane, the measured and simulated results were also good, even though the line pattern was not entirely similar. Figure 5: Comparison of the conventional model, model 1, and model 2: (**a**) \(S_{11}\), (**b**) axial ratio, and (**c**) antenna gains. Figure 7 shows the electric field distribution at a frequency of 2.2 GHz at 0, 45, 90, 135, and 180\({}^{\circ}\). The electric field was dominant on the end of the upper feedline. For the electric field phase of 0 and 180\({}^{\circ}\), the amplitude was dominant on the diagonal of the patch and the top right corner. When the electric field phase was 45\({}^{\circ}\), the amplitude was dominant in the middle of the patch aligned with feedline and on the bottom left corner. The electric fields showed the left-hand pattern. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Model** & \begin{tabular}{c} _f\({}_{c}\)ibw_ \\ (GHz) \\ \end{tabular} & \begin{tabular}{c} **Impedance Bandwidth** \\ **IBW (GHz), \%** \\ \end{tabular} & \begin{tabular}{c} _f\({}_{c}\)arbu_ \\ **(GHz)** \\ \end{tabular} & \
\begin{tabular}{c} **3 dB ARBW** \\ **(GHz), \%** \\ \end{tabular} &
\begin{tabular}{c} **Gain** \\ **(dBic)** \\ \end{tabular} \\ \hline Conventional & 2.17 & 1.98–2.58 (27.26\%) & - & - & 1.85 \\ Model 1 & 3.02 & 2.10–3.41 (43.43\%) & 2.36 & 2.16–2.52 (15.25\%) & 3.65 \\ Model 2 & 2.18 & 1.84–2.71 (39.62\%) & 2.42 & 2.13–3.26 (46.69\%) & 4.66 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Performance of the CSA conventional model, model 1, and model 2. Figure 6: The measured and the simulated axial ratio (AR) vs. theta (\(\theta\)) at frequencies of **(a)** 2.2 GHz and **(b)** 2.4 GHz. Figure 7: Electric field distribution at a frequency of 2.2 GHz at: **(a)** 0, **(b)** 45, **(c)** 90, **(d)** 135, and **(e)** 180 degrees.