Compact Filtering Microstrip Antenna With Enhanced Out-of-Band Suppression

A compact filtering microstrip antenna with high selectivity and enhanced out-of-band suppression is presented in this article. Significantly reduced dimension is realized by incorporating a capacitive blind-via fence on the radiating apertures of a square microstrip antenna. Then, two pairs of quarter-wavelength open-ended slots are etched onto the patch to generate two radiation nulls precisely positioned at the upper and lower band edges. Additionally, two U-shaped slots are strategically employed at the center of the patch to mitigate strong current distribution, thereby significantly improving out-of-band suppression. Finally, an out-of-band suppression of 12.9 dB is attained up to 2.1f₀ (f₀ is the center frequency). As a proof of concept, a prototype with a compact size of 0.19 λ₀ × 0.19 λ₀ is fabricated and tested, showing a −10 dB-impedance bandwidth of 1.85 ~ 1.98 GHz and an average gain of 6.4 dBi. With the advantages of compact size, high selectivity and wideband out-of-band suppression, the proposed filtering antenna exhibits potential usages in compact wireless communication system.