High‐Gain Filtering Antenna Array With Enhanced Out‐of‐Band Suppression and Gain Boosted by Hollowed‐Out Ring‐Shaped Substrate

ABSTRACT This letter proposes a compact high‐gain filtering antenna array with enhanced out‐of‐band suppression. The design integrates a rectangular radiation patch with two groups of parasitic patches, fed by a bifurcated feed line through dual slots in the ground plane. Substrate 2 is changed into a hollowed‐out ring‐shaped substrate, so as to realize the structure of the built‐in air layer and improve the impedance matching and gain of the antenna. The feeding structure creates a radiation null at the lower band edge, achieving low‐frequency selectivity. These elements generated three resonance points, expanding the impedance bandwidth. Dual radiation nulls are generated at the high‐band edge through slotting on the radiation patch and the coupling between the radiation patch and the parasitic patch, enhancing out‐of‐band suppression in the high‐frequency band. A fabricated 2 × 2 filtering antenna array prototype demonstrates a 15.81% impedance bandwidth (22.31–26.14 GHz), peak realized gain of 14.32 dBi, and average total efficiency exceeding 88%. The configuration offers enhanced out‐of‐band suppression while maintaining structural simplicity.