A High Out-of-Band Suppression and Selective Filtering Patch Antenna

This letter presents a high-performance filtering antenna with enhanced out-of-band suppression, high selectivity, and a simple structure. The antenna is composed of a radiating patch on the top surface of the dielectric substrate and parasitic stubs on the underside of the substrate. By utilizing a triple-resonance mode, bandwidth is significantly enhanced. The low-frequency resonance mode is excited by etching a pair of symmetric L-shaped slots in the radiating patch. The mid-frequency resonance mode corresponds to the fundamental mode of the main radiating patch. The high-frequency resonance mode is generated by introducing a quarter-wavelength open-circuit rectangular stub beneath the dielectric substrate. Additionally, these two structures introduce radiation nulls at the edges of the low- and high-frequency bands, respectively. Additional T-shaped and U-shaped stubs improve band selectivity with radiation nulls at specific edges. The proposed filtering antenna has been constructed and tested. Testing reveals a −10 dB impedance bandwidth of 17.7% [(2.26 to 2.7) GHz], 8.14 dBi peak gain, the frequency selectivity exceeds 252 dB/GHz and an out-of-band gain below −10.5 dB.