A Low Profile Dual-Band Dual-Polarized Filtering Antenna with No Extra Circuit

This research introduces an innovative, compact dual-band dual-polarized antenna equipped with filtering capabilities for $5\mathrm{G}$ sub-6GHz base stations. Using the concept of multipath coupling, two controllable radiation nulls are achieved independently. The antenna's impedance bandwidth is widened by skillfully exciting the anti-phase TM22 mode and shifting it to a lower frequency band while preserving other resonant modes. Additionally, incorporating four shorted strips around the radiator effectively increases the average half power beamwidth in the higher frequency band from $51^{\circ}$ to $61^{\circ}$ . Finally, the integration of two wide-band planar baluns, linked to the input terminals of the differentially fed antenna, results in the creation of this dual-polarized filtering antenna with dual operating frequency bands. Experimental prototypes of the antenna element and 1 × 4 array were fabricated and tested. The reflection coefficients demonstrate the antenna's functionality across the 3.24-3.90 GHz (18.5 ^% ) and 4.74-5.06 GHz (6.5 ^% ) frequency bands, maintaining $\vert \mathrm{S}_{11}\vert < -14\ \text{dB}$ . Additionally, a high isolation level of 31 dB was measured from the input ports.