<i>Ka</i>-Band Single-Layered, Wideband Circularly Polarized Array With Multilevel <i>E</i>-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 sub-array 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% (25.9-37.9 GHz) and a 3dB AR bandwidth of 43.75% (25-39 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.