A Bandwidth-Enhanced Cavity-Backed Slot Array Antenna for mmWave Fixed-Beam Applications

Abstract

A bandwidth-enhanced $8\times 8$ cavity-backed slot array antenna for fixed beam applications is presented. The antenna consists of four $2\times 2$ subarrays fed by ridge gap waveguide and a modified bow-tie coupling slot in the cavity layer. The proposed bow-tie coupling slot provides additional $\text{10}\%$ impedance bandwidth as compared to the traditional rectangular coupling slot. The fabricated prototype demonstrates an $|S_{11}|\leq -10\,$ dB fractional impedance bandwidth and a $3\,$ dB gain-drop bandwidth of approximately $\text{28}\%$ and $\text{25}\%$ , respectively, with peak gain of $26.4\,$ dBi, aperture efficiency $>\text{60}\%$ and cross-polar discrimination $>40\,$ dB. Measurements show good agreement with simulations. Moreover, we show the impact of the dimensions and shape of the cavity coupling slot on the bandwidth enhancement. The bandwidth enhancement is explained by the double-ridge slot behavior of the bow-tie coupling slot, which shows a more wideband behavior than the traditional rectangular coupling slot behaving like a cross section of a waveguide.