Bandpass Filter Prototype Inspired Filtering Patch Antenna/Array

Planar filtering patch antenna and its related array inspired by a novel bandpass filter (BPF) prototype are proposed in this article. It is reasonable to replace the LC tank of a BPF prototype with a half-mode (HM) patch resonator with reference to their lumped circuits. That is, the HM patch would serve as a part of the BPF, as well as a radiator. This design method of implementing the filtering antenna is verified by a newly developed prototype. The physical model is realized in a simple form of a patch antenna fed by differential coupled lines. A microstrip-to-slotline transition is implemented to excite the coupled lines. Two radiation nulls beside the passband are obtained, thereby leading to a sharp band skirt. Based on this filtering antenna, a two-element patch array is designed. A CPW-to-slotline transition is designed to excite the united coupling lines, which serves as both a balun and a power divider. A high out-of-band rejection level within a wide stopband is achieved. For demonstration, the proposed filtering antenna and array are fabricated and measured. Reasonable agreement between the measured and simulated results is observed. Besides, the measured in-band gain of the filtering antenna array is over 10 dBi and flat, whereas the out-of-band rejection level is almost 30 dB.