# Chiral Dielectric Metasurfaces for Highly Integrated, Broadband Circularly Polarized Antenna
## 3 Results and Discussion  
The individual contributions from the building components in the antenna design can be studied by analyzing the results in Figure 3 for \(S_{11}\), AR and boresight gain for the patch without (W/O) metasurface (dashed lines) and with the metasurface of solid cylinders (solid lines) depicted in the inset of Figure 3a. Calculations in this figure were made using the commercial software CST Studio. Results for \(S_{11}\) are presented in Figure 3a, whereas the corresponding AR and boresight-gain are shown in Figure 3b. Poor values for the impedance-matching (\(S_{11}\gtrsim-10\)) and gain (\(<8\)) are observed for the patch W/O metasurface. The antenna with the metasurface containing the solid cylinders improves the impedance-matching, AR values and boresight gains, in addition to an improved bandwidth performance. Such improvements are due to the dielectric cylindrical resonators and their corresponding near-field interactions. However, the radiation and AR performance are still low in all of these results, and additional strategies are required to design useful CP antennas. Following the reasoning of chiral dielectric metasurfaces for enhanced chiroptical effects [18], we considered slanted slots etched at the center of each cylinder, as schematized in the inset of Figure 4a. This mechanism not only improved AR but also the whole operating performance of the antenna, as it can be seen from Figure 4a,b. Calculations from CST Studio and ANSYS HFSS are presented with solid and dashed lines, respectively. Negligible differences are observed due to different convergences of the software packages. The applicability of this CDM-based CP antenna is demonstrated in Figure 4c,d with AR and gain corresponding to the system surrounded by a metal cavity (considered to be made of Al). This cavity surrounding the four-element CDM enables integration into antenna arrays by suppressing the mutual coupling between adjacent elementary cells. Although a small decrease was induced by the cavity in the impedance \(\text{BW}=[25.5\text{ GHz},31.3\text{ GHz}]\) and 3-dB \(\text{ARBW}=[27.1\text{ GHz},30.3\text{ GHz}]\), in relation to the impedance \(\text{BW}=[25.3\text{ GHz},31.6\text{ GHz}]\) and 3-dB \(\text{ARBW}=[26.9\text{ GHz},30.2\text{ GHz}]\) for the system without cavity, the corresponding gain (\(\gtrsim 9\)) and AR (AR \(\ll 3\)) were considerably improved. Moreover, a gain notch from Figure 4b was shifted out of the bandwidth range of interest when using the cavity, which certainly improves the CP radiation performance. Figure 5 shows the **E**-field distribution for the two orthogonal modes of the patch coupled to the CDM. These fields were calculated for the frequencies at which AR achieves the best results, according to Figure 4d. For illustrative purposes, results are presented for **E**-field distribution at the patch and CDM planes, and with radiation of an LCP electromagnetic field. As it can be inferred, an RCP antenna can be developed using the mirror image of CDM and the patch antenna. The evanescent behavior of the electromagnetic field in the cavity is also shown. The numerical results from hereon were obtained with the commercial software CST Studio for the antenna without the cavity. Results of the LCP (co-polarized) and RCP (cross-polarized) radiation patterns for the CDM-based antenna are presented for 27.5 GHz and 30 GHz in Figure 6a-d, respectively. For the co-polarized radiation at the \(\phi=90^{\circ}\)-plane, a 3-dB power beamwidth of \(66.3^{\circ}\) (in the range from \(38.3^{\circ}\) to \(-28^{\circ}\)) is observed for 27.5 GHz (Figure 6a) while for 30 GHz it is \(58.7^{\circ}\) (from \(31^{\circ}\) to \(-27.7^{\circ}\)) (Figure 6c). The condition AR \(\leq 3\)-dB is met when the difference between the co-polarized and cross-polarized patterns is \(\geq 15\)-dB. Therefore, there is a high AR performance in the whole 3-dB power beamwidth for the 27.5 GHz mode, but not for 30 GHz which is limited to \(43^{\circ}\) (from \(23^{\circ}\) to \(-20^{\circ}\)).