A Wideband Circularly Polarized Filtering Patch Antenna With Strip Network

A circularly polarized (CP) filtering patch antenna with a strip network is proposed, which utilizes two substrates with a spacing of 6 mm. A slotted loop is placed around a slotted patch on the top side of the upper substrate to excite two CP modes. A strip network printed on the bottom side of the upper substrate produces the third CP mode and a high-frequency radiation null, while low-band-edge and a high-band-edge radiation nulls are excited by a shorted pin. The three CP modes form a wider axial ratio (AR) bandwidth than the impedance bandwidth. The impedance matching bandwidth and the out-of-band radiation suppression level are further improved by another slot etched on the slotted loop and on the radiation patch. The antenna prototype is fabricated, and the measured results show that the −10 dB impedance matching bandwidth is 21.6% from 3.26 to 4.05 GHz, the 3 dB AR bandwidth is 23.1% from 3.14 to 3.96 GHz, the in-band peak gain is up to 7.6 dBic, and the radiation suppression levels are higher than 23 and 14 dB for the low- and high-frequency stopbands, respectively. These features make the proposed antenna a promising candidate for 5G NR n78 band mobile communication systems.