A Wideband Filtering Patch Antenna With Enhanced Selectivity and Wide Stopband

A filtering metal patch antenna utilizing a pair of folded metal resonators and double‐layer 2 × 2 patches is proposed for expanding bandwidth, enhancing frequency selectivity, and widening the stopband based on characteristic mode analysis (CMA). The folded metal resonator with an L‐shaped stub provides two reflection zeros when the currents on the upper and lower parts are the same. Meanwhile, an extra reflection zero can be obtained by the 2 × 2 patches excited by the folded metal resonator. Therefore, the three reflection zeros can provide a wide bandwidth. In addition, a radiation null can be generated by the opposite currents on the main strip and L‐shaped stub parts of the folded metal resonator. Moreover, benefitting from the out‐of‐phase electric field on the stacked 2 × 2 patches, an extra radiation null is introduced, thus enhancing the frequency selectivity. Compared with the existing filtering patch antenna, it has the widest bandwidth, enhanced frequency selectivity, and a wider stopband. A prototype was measured at 3.5 GHz with a fractional bandwidth (FBW) of 41.8%. The ratio of 3‐dB gain bandwidth to 15‐dB gain bandwidth is 0.81, and the 15‐dB stopband rejection can achieve to 2.2 f 0 .