A Circularly Polarized Filtering Patch Antenna Based on Parasitic Patches With Slots

A circularly polarized (CP) filtering patch antenna based on parasitic patches with slots is presented. The structure consists of one CP feeding network, one driven patch, and two parasitic patches. Two radiation nulls (RNs) are caused when the parasitic patches with slots are introduced, and the locations of RNs could be controlled by the slot length. Besides, the impedance bandwidth and axial ratio (AR) bandwidth are both improved compared to the antenna without parasitic patches. A prototype is fabricated and measured. The impedance bandwidth is 14.9% (3.42–3.97 GHz), and the 3-dB AR bandwidth is 8.9% (3.53–3.86 GHz). The realized gain at center frequency of 3.70 GHz is high up to 8.1 dBiC. Two radiation nulls at 2.95 and 4.55 GHz are generated. The proposed CP filtering antenna has the advantages of simple structure and easy fabrication, and can be a promising choice for wireless communications.