Dual-Circularly Polarized Array Antenna Based on Gap Waveguide Utilizing Double-grooved Circular Waveguide Polarizer

This paper presents a dual-circularly polarized array antenna based on gap waveguide technology operating at E band. Double-grooved circular waveguide polarizers that utilize two annulus grooves placed at 45\ub0 and 135\ub0 offset from both excitation ports are used in this work. The operating principles of the polarizer are analyzed. Multi-layer design using gap waveguide is implemented on the basis of the polarizer. The antenna consists of six layers, including three layers for the feeding networks, one layer for the polarizer, one layer of back cavity and another layer of radiating grid. A 2 72 unit cell is proposed firstly and employed to realize a 8 78 planar array. Corporate feeding networks that use compact E-plane T-junctions and H-plane T-junctions are proposed. The antenna has been fabricated and verified by measurements. The measured results of S-parameters agree well with the simulation and show that reflection coefficients are better than -10 dB for both circular polarizations from 76 to 81 GHz. The measured isolation between the input ports is larger than 25 dB in the operating band. The far-field measurements show that the antenna has realized gain larger than 24 dBi and axial ratios less than 1.5 dB from 76 to 81 GHz at boresight direction