A W-band Quasi-Optical Array Antenna Feeding Network with High Taper Efficiency Using Optimal Ridge Excitation of an H-Plane Sectoral Waveguide

A novel H-plane quasi-optical (QO) feeding network for linear (sub-)array gap waveguide (GWG) antennas intended for beam-steering applications at W-band is presented. The QO feed comprises an H-plane sectoral GWG excited by an input stepped ridge gap waveguide (RGW) and transitioned to an overmoded rectangular groove gap waveguide (GGW) section, the latter being terminated with an array of RGW output probes. This work's key challenge and novelty is engineering the desired modal content in the QO structure for uniform amplitude excitation of array elements to enhance antenna gain with a low insertion loss. This was addressed by (i) realizing an optimal multi-mode excitation of the sectoral GWG and (ii) a proper phasing of a rich modal spectrum of the output overmoded GGW. An eigenmode-based semi-analytic approach was developed to investigate the impact of an input ridge length on the excited modal content and was shown to predict optimal results close to full-wave simulations. The demonstrated QO feed concept, applied to a 20-element array design, significantly outperforms existing solutions by achieving a 97% amplitude taper efficiency and showing less than 0.4 dB insertion loss over a 21% relative bandwidth (85–105 GHz).