## 3 A Pair of Rectangular Slots and Parasitic Patch for the 3 dB ARBW and the Gain Enhancement
### A Rectangular Parasitic Patch (Model 2)  
CP performance improvement of the CSA model 1 was necessary as its 3 dB ARBW was much narrower than its impedance bandwidth. Many methods have been investigated to enhance the 3 dB ARBW using a parasitic center patch [20] and a coplanar parasitic patch [21]. In this design, a parasitic patch on the circular slot was introduced to model 1 to generate another resonant frequency to broaden the 3 dB ARBW. The performance of the parasitic patch is influenced by a current path that depends on the parasitic length \(W_{p}\), the parasitic width \(L_{p}\), and its parasitic center on the \(x\)- and \(y\)-axes. In this step, the effect of the parasitic width, patch length, and its center on the \(x\)- and \(y\)-axes are simulated. Figure 4a-d depict the simulation results. Figure 4a shows the effect of the parasitic  
Figure 3: Effect of the symmetrical slot length of 0, 30, and 40.79 mm on (**a**) \(S_{11}\), (**b**) axial ratio, and (c) gain. widths \(W_{p}\) of 0, 20, and 31 mm with a fixed parasitic length \(L_{p}\) of 12 mm, \(X_{p}\) of 8 mm, and \(Y_{p}\) of 5 mm on the 3 dB axial ratio bandwidth. The parasitic widths of 0 and 20 mm produced 3 dB axial ratio bandwidths of 270 and 210 MHz, respectively. The antenna gain was lower, with a value of 3.47 dBic at 2.2 GHz. The parasitic width \(W_{p}\) of 31 mm generated a CP in the center frequencies of 2.35 and 3.44 GHz, producing 3 dB axial ratios of 360 and 160 MHz. This antenna design produced an antenna gain of 3.64 dBic at the frequency of 2.2 GHz. This simulation result shows that when the parasitic patch width is 31 mm, a better axial ratio bandwidth is created. Figure 4b shows the effect of the parasitic lengths \(L_{p}\) of 2, 6, and 12 mm with a fixed parasitic width \(W_{p}\) of 31 mm, \(X_{p}\) of 8 mm, and \(Y_{p}\) of 5 mm on the 3 dB axial ratio bandwidth. The parasitic length \(L_{p}\) of 2 mm generated dual CP frequencies of 2.35 GHz and 2.58 GHz, with 3 dB ARBWs of 229 MHz and 180 MHz, respectively. When the patch length \(L_{p}\) was 6 mm, the 3 dB axial ratios were 300 and 220 MHz at frequencies of 2.37 and 3.55 GHz, respectively. When the patch length \(L_{p}\) was 12 mm, the 3 dB axial ratios were 310 and 250 MHz in the center frequencies of 2.38 and 3.49 GHz, respectively. The center frequency of the CP shifted closer to each other and the gain increased by 4.1 dBic. Figure 4c shows the effect of the parasitic center \(Y_{p}\) of \(-5\), 0, and 5 mm with a fixed parasitic width \(W_{p}\) of 31 mm, and \(L_{p}\) of 12 mm on the 3 dB axial ratio bandwidth. When the parasitic center \(Y_{p}\) was \(-5\) mm, the 3 dB center frequencies (CF) were 2.63 and 3.7 GHz. When the parasitic center \(Y_{p}\) was 0 mm, the 3 dB CF were 2.56 and 3.56 GHz. When \(Y_{p}\) was 5 mm, the 3 dB CF occurred at 2.39 and 3.45 GHz. The simulation result showed that the parasitic center \(Y_{p}\) controls the 3 dB CF. Figure 4d shows the effect of the parasitic center \(X_{p}\) of \(-9\), 0, and 8 mm with the fixed parasitic width \(W_{p}\) of 31 mm and \(L_{p}\) of 12 mm on the 3 dB axial ratio bandwidth. When the parasitic center \(X_{p}\) was \(-9\), 0, and 8  
Figure 4: Variation in the axial ratio in relation to: (**a**) parasitic length \(L_{p}\), (**b**) parasitic width \(W_{p}\), (**c**) parasitic center on the \(y\)-axis \(Y_{p}\), and (**d**) parasitic center on the \(x\)-axis \(X_{p}\). mm, the 3 dB center frequency generated 3 dB ARBWs of 190 MHz, 290 and 190 MHz, and 340 and 250 MHz, respectively. The simulation result showed that the parasitic center \(X_{p}\) generates a higher frequency when its position is on the positive \(x\)-axis. However, a combination of the symmetrical slot length and a rectangular parasitic patch failed to enhance the 3 dB ARBW. The next step was to extend the slot lengths \(L_{s1}\) to 48.79 mm and \(L_{s2}\) to 40.79 mm. This modification successfully enhanced the 3 dB axial ratio up to 51.52% in the frequency range of 2.12-3.35 GHz.