Wideband Dual-Polarized Differential-Fed Filtering Microstrip Patch Antenna with High Suppression and Wide Stopband

This paper presents a wideband dual-polarized filtering antenna with high suppression level and wide stopband. In the proposed antenna, the driven patch operates in a TM10 mode with an inherent radiation null caused by a higher mode TM12. Four dual-strip structures connected with the feeding probes are placed below the driven patch to achieve the capacitive coupling, thus resulting in a low-frequency radiation null with a sharp roll-off rate. The introduction of the parasitic patch and strips generates an in-band resonance and two high-frequency radiation nulls, which widens the upper stopband. Four slots are etched on the driven patch to excite the third resonance, thus achieving the wide operation band. The prototype of the proposed antenna is fabricated. With four controllable radiation nulls, the out-of-band suppression levels are above 29 dB in low-frequency band greater than 1 GHz and above 21 dB in high-frequency band up to 7 GHz, respectively. Due to the three in-band resonances, a wide impedance bandwidth of 2.93-3.96 GHz with a fractional band of 30% is obtained. With the rotational symmetry structure driven by differential probes, the proposed dual-polarized antenna has a cross-polarization ratio better than 28 dB, a high polarization isolation above 43 dB, and a good peak gain about 9.9 dBi.