Broadband Filtering Patch Antenna Based on Quad-Mode Resonance With High Out-of-Band Rejection Level

This letter proposes a broadband filtering patch antenna based on quad-mode resonance, exhibiting high out-of-band rejection level and enhanced selectivity. The antenna employs a stacked structure of the driven patch and parasitic patch to achieve dual-mode resonance within the band. By loading C-shaped slots and flag-shaped strips on the driven patch, two additional modes are also generated within the band, achieving quad-mode resonance and obtaining a broadband response. Meanwhile, the two loaded structures introduce two near-band radiation nulls based on far-field radiation cancellation, achieving high out-of-band rejection level and enhanced selectivity. Additionally, I-shaped and L-shaped slots are etched to better control the position of nulls and enhance the filtering performance. The measured results show that the proposed antenna operates in the 2.45 GHz ISM band with a relative bandwidth of 21.6%. The out-of-band rejection levels on both sides are 30 and 29.8 dB, respectively, with selectivity of 183.3 and 200 dB/GHz, respectively. The antenna's wideband and strong anti-interference capabilities make it a promising candidate for the RF front-end system.