# A Wideband Circularly Polarized Antenna with a Multiple-Circular-Sector Dielectric Resonator
## 2 Antenna Design  
Figure 1 illustrates the concept of the multiple-circular-sector structure. The multiple-circular-sector structure was previously introduced in earlier works [19; 20]. It was initially proposed by [PERSON] et al. for the design of an ultra-wideband patch antenna [19]. In a subsequent work [20], [PERSON] et al. successfully implemented a wideband circularly polarized multiple-circular-sector slot antenna. As shown in Figure 1a, the multiple-circular-sector shape includes twelve small circular sectors, all with identical central angles of \(\alpha=30^{\circ}\). Thus, these circular sectors create a complete circular shape of 360\({}^{\circ}\). Each circular sector has a different radius \(r_{i}\) (\(i=1\) to 12). The relationship between the radius and angle \(\phi\) is given in Figure 1b. In this study, the DR is designed using the concept of a multiple-circular-sector shape. It is termed the multiple-circular-sector DR. Figure 2a shows the geometry of the proposed antenna. The feeding structure is illustrated in Figure 2b. The proposed antenna includes a multiple-circular-sector DR, a ground plane, a 50-\(\Omega\) microstrip feed line, and a Taconic RF-35 dielectric substrate (with a dielectric constant of 3.5, a thickness of \(h_{sub}=1.52\) mm, and a loss tangent of 0.0018). The 50-\(\Omega\) microstrip feed line with a length of \(l_{f}\) and a width of \(w_{f}\) is printed on the bottom layer of the dielectric substrate. Figure 1: Multiple-circular-sector structure: (**a**) Shape of the multiple-circular-sector; (**b**) Radii at different angles. The ground plane, which is mounted on the upper layer of the dielectric substrate, has dimensions of \(g_{w}\times g_{w}\). A narrow rectangular slot with dimensions of \(w_{s}\times l_{s}\) is etched onto the ground plane. The energy from the microstrip feed line is coupled through this narrow slot to excite the proposed DR. The multiple-circular-sector DR with a dielectric constant of 9.8 is composed of twelve circular-sector DRs, each with an identical central angle of \(30^{\circ}\) and different radii. The GA is applied to optimize the radii of the twelve circular-sector DRs to achieve wideband CP operation. In the implementation of the GA, an iteration number of 1000, a population of 20, a mutation rate of 0.1, and single-point crossover scheme are used. The optimal design parameters of the proposed antenna are summarized in Table 1 for the generation of left-handed circular polarization (LHCP). In order to verify the generation of LHCP, the H-field distribution on the top surface of the proposed multiple-circular-sector DR is investigated. Figure 2(a) presents the simulated H-field distribution observed in the positive \(z\)-direction at a frequency of 2.3 GHz. When \(t=0\), the vector of the major H-field distributions points from the upper right corner to the lower left corner. In contrast, the vector of the major H-field distributions at \(t=T/4\) points from the lower right corner to the upper left corner. This vector is orthogonal to that at \(t=0\), and rotates clockwise as the time \(t\) elapses, thereby generating LHCP in the positive \(z\)-direction. The H-field distribution observed in the positive \(z\)-direction at 2.5 GHz is illustrated in Figure 2(b). Similar to the case at 2.3 GHz, the vector of the major H-field distributions at \(t=0\) is orthogonal to that at \(t=T/4\), and rotates clockwise as the time \(t\) increases. Therefore, LHCP is also produced in the positive \(z\)-direction. The effects of the ground plane size \(g_{w}\) on the reflection coefficient and AR performance are also investigated. The simulated results are illustrated in Figure 4, in which the AR values are observed in the broadside direction (\(\theta=0^{\circ}\)). As shown in the figure, dual-band CP operation is achieved with \(g_{w}=80\) mm. When \(g_{w}\) increases, two CP bands are merged to form a wide 3 dB AR