Reflectionless Filtering Antenna Array With Self-Decoupling Response

In this paper, a ${1} \times {2}$ reflectionless filtering antenna array with self-decoupling response is proposed. The antenna array element consists of a reflectionless microstrip bandpass filter (BPF) with complementary-duplexer structure and a cascaded U slot patch antenna. By feeding the U-slot antenna with the output port of the reflectionless BPF, a reflectionless filtering antenna can be obtained. In complementary-duplexer-based reflectionless BPFs, an absorptive auxiliary (bandstop) channel loaded by a resistor is used to absorb the out-of-band RF power not transmitted by the main BPF channel. By using this concept in antenna arrays, and according to the reciprocity principle, the RF coupled energy, or induced currents in each antenna element due to the surrounding antennas can be absorbed, thereby achieving decoupling of the antenna array. To verify, a $1 \times 2$ antenna array prototype with or without the reflectionless filtering structure is designed and simulated. The simulation results show that the $10-\mathrm{dB}$ reflectionless bandwidth of a single antenna is from 2.5 to 5.0 GHz, and the maximum coupling between antenna elements is reduced from 25.6 dB to -29.1 dB.