## 5 Conclusions  
In this paper, the design procedure of a high-performance octagonal cavity-backed antenna was presented. The proposed antenna exhibits multiple attractive qualities: dual-polarization, wide impedance bandwidth, low cross-polarization, high gain, and high aperture efficiency. It 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 cavity-backed configuration ensures that the antenna supports stable broadside radiation with relatively high gain and low cross-polarization. An octagonal ground cavity, instead of a more commonly seen square one, was used because it offers lower cross-polarization and higher aperture efficiency while being more compact. By merging the resonances from the open prism and the radiating feedlines, wide impedance bandwidth was realized. The bandwidth can reach over 60% by adjusting the air gap between the two radiators and the ground plane. Multiple design considerations were adopted to ensure low cross-polarization. Some basic ones include ensuring a symmetric antenna configuration, adopting a differential feed, and feeding the antenna from the ground sidewalls instead of the bottom ground plane. Further cross-polarization reduction can be realized by moderately increasing the cavity sidewall height. To verify the design and fabrication process, an antenna prototype was fabricated and tested with excellent agreement between the simulated and measured results.  
To demonstrate the superior performance of the proposed antenna, we compared it with three high-performance cavity-backed antennas with wide impedance bandwidth in Table 3. Unfortunately, the majority of the antennas in the literature only aim to suppress  
Figure 11: OCROP radiation patterns at 1.5 GHz: (**a**) Simulated results; (**b**) Measured results.  
cross-polarization in the principal planes (i.e., P-planes) and do not provide information on cross-polarization in the diagonal planes (i.e., D-planes) where it peaks, e.g., [13; 28]. As can be seen, compared to these antennas, our antenna is compact and has the widest impedance bandwidth, lowest peak (across the entire impedance bandwidth), diagonal-plane cross-polarization, and highest aperture efficiency.  
It has shown that there is a small section of the operating band (i.e., lower frequencies) that is not sensitive to the cross-polarization suppression techniques used here. We will propose an additional cross-polarization suppression technique to overcome this issue in the future. In addition, since some applications require higher gain than reported here, we will investigate different gain enhancement techniques that are compatible with our design.  
Conceptualization, Y.L., D.I. and L.S.; methodology, Y.L.; software, Y.L.; validation, Y.L., D.I. and L.S.; formal analysis, Y.L.; investigation, Y.L., D.I. and L.S.; resources, Y.L., D.I. and L.S.; data curation, Y.L., D.I. and L.S.; writing--original draft preparation, Y.L., D.I. and L.S.; writing--review and editing, Y.L., D.I. and L.S.; visualization, Y.L.; supervision, D.I. and L.S.; project administration, D.I. and L.S.; funding acquisition, D.I. and L.S. All authors have read and agreed to the published version of the manuscript.  
This work was supported in part by the Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grant program.  
Data available within the article. The authors would like to thank [PERSON] and [PERSON] for their assistance in antenna fabrication and testing. The authors acknowledge CMC Microsystems for the provision of CAD tools that facilitated this research. The authors declare no conflict of interest.