I. Introduction
With the development of wireless technologies, such as satellite navigation and communications [1], millimeter wave (mm-Wave) radars and imagers [2], as well as the fifth-generation (5G) mobile communications [3], the electrical properties of antennas have become increasingly important for ensuring well-rounded system performance. Compared with the linearly polarized (LP) antennas, the circularly polarized (CP) ones possess a variety of advantages, such as being less sensitive to alignment-induced polarization mismatch, more robust to multipath interference, and immune to the Faraday rotation effect that occurred in the ionosphere [4]. On the other hand, due to the growing demands for high-throughput and multifunctional wireless systems, polarization diversity has been widely utilized in the Tx/Rx modules [5]. Hence, high-performance antennas and arrays supporting dual-CP radiation have garnered a great amount of attention, particularly over the past decade [6].