An air-filled cavity-backed 2×2 slot sub-array fed by inverted microstrip gap waveguide

A wideband 2×2-slot element for a 60 GHz antenna array is designed by making use of air filled cavity fed by inverted microstrip gap waveguide. The designed element is a triple layer structure in which the upper layer contains four radiating slots backed by an air-filled cavity. The cavity is excited by a coupling slot fed by an inverted microstrip gap waveguide formed in the air-gap between the middle and lower layers. The designed 2×2-slot element is considered in an infinite array environment. A sample 32×32 slot array aperture is simulated using infinite array approach. The results show that the mismatch is better than -15 dB and the directivity larger than 38 dBi over 56.3-67.9GHz frequency range, i.e. 20.7 % bandwidth.