A Wideband Filtering Patch Antenna with Multiple Radiation Nulls For Good Stopband Suppression

This paper presents a novel wideband filtering patch antenna with multiple radiation nulls for good stopband suppression. A series of filtering structures are integrated within the antenna configuration without adding any extra circuits. Firstly, a U-shaped strip is connected with the feeding probe of the patch antenna to generate an upper-band-edge null. Meanwhile, a pair of square rings coupled to the U-strip are introduced to insert another null to perform the upper stopband. Similarly, the lower stopband is also suppressed by two nulls, which are inserted by two split-ring-slots on the patch and on the ground plane respectively. As results, a good filtering patch antenna is readily constructed, then a wide working band of 19.2% and a high out-of-band suppression level over 20dB are achieved. In addition, the filtering antenna is additionally adapted to be differentially fed to improve the cross-polarization of the H-plane radiation pattern. Besides filtering functions, above filtering structures also broadens the impedance bandwidth and increases the broadside gain from 8.2 to 9.23dBi compared to the original patch antenna.