Ka-Band Single-Layered, Wideband Circularly Polarized Array With Multilevel E-Plane Waveguide Sequential Rotation Network

In this letter, a single-layered broadband circularly polarized (CP) slot array is presented for millimeter-wave wireless applications, which is realized by sequentially rotating linearly polarized E-plane waveguide-fed slot subarrays. The presented subarray consists of four open-ended radiating cavities with surface-etched grooves to suppress the unwanted parasitic current distributions. The introduced grooves can be equalized as secondary radiation sources, thus improving the gain of the subarray and the entire CP array while suppressing the sidelobes. To realize wideband CP radiation, wideband compact multilevel E-plane waveguide sequential rotation network (SRN) is implemented. Compared with conventional multi-layered full-metal CP arrays, compact E-plane waveguide is introduced to combine the multilevel SRN and multiple radiators in the same layer while realizing a much wider axial ratio (AR) bandwidth. For demonstration, an 8 × 8 CP array with a multilevel SRN was fabricated and measured, exhibiting an impedance bandwidth of 37.62% (25.9 GHz to 37.9 GHz) and a 3 dB AR bandwidth of 43.75% (25 GHz to 39 GHz). The proposed single-layered CP array own the advantages of wideband, compact size, and high efficiency, which is a promising candidate for Ka-band wireless applications.