Unidirectional slot subarray-antenna with high efficiency for x-band application

Slot antennas in metallic ground planes are very attractive radiation elements for conformal antenna application. For unidirectional radiation, a slot requires a back reflector close to the aperture. Unfortunately, the resulting parallel plate structure enables parasitic parallel plate mode propagation resulting in a low radiation efficiency. In this contribution we investigate unidirectional, low profile slot configurations with parallel plate mode suppression by shorting pins. Starting with a parametric study on the effects of shorting pin location and back reflector distance, we present a bow tie slot element with 85% efficiency. This element was further used in a linear, four element antenna subarray with 70% efficiency.