A Double-Layer Filtering Antenna Based on Composite Resonator with Multiple Radiation Nulls

A double-layer filtering antenna based on composite resonator (CR) with multiple radiation nulls is proposed in this paper. The composite resonator integrated in a 50 Ω feeding line can provide a resonant mode together with a pair of radiation nulls at both sides of the working band. A slot in the ground plane is designed for coupling between patch antenna mode and CR mode. Based on this structure, a filtering antenna centering at 3.5 GHz for 5G communication band is designed. Maximum realized gain of 6.09 dBi is achieved. Three radiation nulls observed in the gain response significantly improve the stopband performance of the filtering antenna.