# A Wideband Circularly Polarized Antenna with a Multiple-Circular-Sector Dielectric Resonator
## 2 Antenna Design
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Parameter** & **Value** & **Parameter** & **Value** \\ \hline \(r_{1}\) & 22.21 mm & \(r_{11}\) & 12.41 mm \\ \(r_{2}\) & 32.04 mm & \(r_{12}\) & 16.51 mm \\ \(r_{3}\) & 40.25 mm & \(g_{w}\) & 110 mm \\ \(r_{4}\) & 12.70 mm & \(w_{s}\) & 7.50 mm \\ \(r_{5}\) & 16.26 mm & \(l_{s}\) & 38.00 mm \\ \(r_{6}\) & 19.39 mm & \(w_{f}\) & 35.0 mm \\ \(r_{7}\) & 12.60 mm & \(l_{f}\) & 76.50 mm \\ \(r_{8}\) & 34.90 mm & \(h_{data}\) & 51.50 mm \\ \(r_{9}\) & 38.28 mm & \(h_{sub}\) & 1.52 mm \\ \(r_{10}\) & 22.10 mm & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The optimized design parameters of the proposed antenna. Figure 2: The geometry of the proposed antenna: (**a**) 3D view; (**b**) Feeding configuration. SMA: SubMinature version A.  
bandwidth. In addition, the reflection coefficient in the middle frequency range is improved, while the overall \(-10\) dB reflection bandwidth is only slightly affected when increasing the value of \(g_{w}\). However, the overall 3 dB AR bandwidth of the proposed antenna is reduced when \(g_{w}\) is increased further. The value of \(g_{w}\) is finally set to 110 mm, as this value provides the widest 3 dB AR bandwidth. Figure 4: Effect of the ground plane size \(g_{w}\) on: (**a**) Reflection coefficient; (**b**) Axial ratio. Figure 3: Simulated H-field distributions on the top surface of the proposed multiple-circular-sector dielectric resonator (DR) with time period \(T\) at: (**a**) 2.3 GHz; (**b**) 2.5 GHz. The effects of the DR height \(h_{dra}\) on the reflection coefficient and AR performance were studied, and the simulated results are illustrated in Figure 5. It was found that the operating frequency band moves to a lower frequency region, and that the AR levels are increased close to 3 dB when \(h_{dra}\) is increased. When \(h_{dra}\) equals 56.5 mm, the reflection coefficient levels around 2.18 GHz are increased to more than \(-10\) dB, resulting in two separate \(-10\) dB reflection bandwidths (see Figure 5a). Meanwhile, as shown in Figure 5b, the 3 dB AR bandwidth becomes narrower when \(h_{dra}\) is reduced to less than 46.5 mm. Finally, the optimal value of \(h_{dra}\) was found to be 51.5 mm. Finally, we conducted a simulation to investigate the effect of a slight air gap between the DR layer and the ground plane. The simulated results are shown in Figure 6. It is evident that the air gap affects the antenna gain. Owing to the existence of a slight air gap between the DR layer and  
Figure 5: Effect of the DR height \(h_{dra}\) on: **(a)** Reflection coefficient; **(b)** Axial ratio. Figure 6: Effect of an air gap on antenna gain. the ground plane during the gluing process, as well as the fabrication tolerances, a maximum gain tolerance of 1.4 dB is observed when air gap varies from 0 to 0.2 mm. The design guideline for the proposed CP DRA with a multiple-circular-sector DR is as follows. First, choose initial design parameters for the coupling slot width \(w_{s}\), the length \(l_{s}\), and the microstrip stub length (\(l_{f}-g_{w}/2\)) based on earlier work [21]. In this work, the initial values of slot length \(l_{s}\), slot width \(w_{s}\), and microstrip stub length (\(l_{f}-g_{w}/2\)) are set at \(0.25\lambda_{0}\), \(0.2l_{s}\), and \(0.25\lambda_{g}\), respectively, where \(\lambda_{0}\) is the free-space wavelength and \(\lambda_{g}\) is the guided wavelength in the dielectric substrate corresponding to the designed frequency of 2.3 GHz. The ground plane size \(g_{w}\) is initially set at \(\lambda_{0}\). Next, obtain a wide bandwidth of \(-10\) dB reflection and a bandwidth of 3 dB AR by optimizing the radii of the twelve circular-sector DRs. Finally, adjust the parameters \(w_{s}\), \(l_{s}\), \(g_{w}\), \(h_{dra}\), and \(l_{f}\) to improve the reflection coefficient and AR performance further.