###### Abstract
Gain enhancement approaches include: forming an array [9], using a ground cavity [10; 11; 12; 13], parasitic element loading [1; 2; 3; 4], and partially reflective surface loading [14; 15]. These studies investigate mostly gain enhancement techniques but have not addressed the aperture efficiency of the antennas, which result in a compact geometry and wide overlapping impedance, gain, and cross-polarization bandwidths. Among these techniques, only the use of a ground cavity can simultaneously provide gain enhancement and low cross-polarization. More importantly, a cavity-backed configuration is also known to support wideband operation [13]. Consequently, choosing such a configuration shows potential for simultaneous enhancement of multiple antenna performance parameters. Existing cross-polarization reduction techniques include feed designing [16; 17] and shaping [18; 16]. Differential feeding [16] and aperture-coupled feeding [17] are two of the most frequently used feed designs for suppressing cross-polarization. With differential feeding, there is zero cross-polarization in principal planes if the antenna is geometrically symmetric [19]. However, this method is less effective in diagonal planes where maximum cross-polarization occurs [20]. In aperture-coupled feeding, the radiation from feedlines is shielded by ground planes, and as a result, the cross-polarization due to the feedlines is suppressed [21]. The abrupt discontinuity at edges, especially sharp corners, induces non-uniform and asymmetric currents, which cause cross-polarized radiation [18; 16]. With appropriate shaping, surface currents can be redistributed in such a way that cross-polarized components are reduced and/or co-polarized components are increased. The majority of these techniques were developed for reducing cross-polarization in principal planes. Therefore, they either are not as effective in diagonal planes, or their effects in diagonal planes were not investigated. In this work, we aim to have low cross-polarization in all azimuth planes, including diagonal planes where cross-polarization is most challenging to suppress [22; 23]. As our metric for cross-polarization is high, careful coordination of multiple techniques is required to meet the requirement because our preliminary studies showed that using a single method does not meet the design goals. This paper proposes a novel high-performance dual-polarized antenna that can be used for many applications, such as remote sensing and satellite communication, where compact antennas with low cross-polarization are required. Alternatives are corrugated horns that are bulky, heavy, and very costly to fabricate. The key antenna parameters are determined to broaden the bandwidth of the antenna simultaneously for the impedance, high gain, high aperture efficiency, and low cross-polarization, which results in the most compact antenna size. Simultaneous improvement of multiple antenna performance parameters was achieved by carefully selecting and deriving a compatible set of performance enhancement techniques. The design considerations and the basic antenna configuration are presented in Section 2. Section 3 demonstrates several numerical studies on critical antenna elements/dimensions. To verify the simulation results, an antenna prototype was fabricated, and the test results are discussed in Section 4. Lastly, we present our conclusions and propose directions for future work in Section 5.