Millimeter-Wave Filtering Antenna and Array With Multiple Flexible Radiation Nulls Based on Hybrid Coupling of SIW Cavities and Split-Ring Slots

A millimeter-wave (MMW) filtering antenna with multiple radiation nulls is proposed. The antenna element consists of second-order eighth-mode substrate integrated waveguide (EMSIW) cavities, two rectangular coupling slots, two stacked patches etched with diverse slots. There are five radiation nulls to provide sharp band-edge selectivity, which are respectively introduced by the EMSIW cavities, split-ring slots with different sizes and square slots on the patches independently. Hence, a miniaturized filtering antenna with multiple flexible radiation nulls and wide stopbands is achieved based on multilayer structures. The prototype of the proposed filtering antenna was fabricated and measured. At the measured operating band covering from 24.03 GHz to 28.58 GHz, the maximum gain is 6.2 dBi. The suppression level of the upper band achieves more than 20 dB till 1.68f₀. Furthermore, several 1×4 subarrays are fabricated and assembled. Good performance of beam scanning can be observed.