A filtering patch antenna with reflectionless in a wide frequency range

A filtering antenna consists of a reflective filtering antenna (RFA) and a bandstop filter (BSF) is presented. Due to the L-shaped feeding structure, slots etching on the radiator and the ground plane, the RFA obtains good impendence matching, stable in-band gain, as well as four reflective radiation nulls, and that contribute an operating band of 19% and good frequency selectivity to the proposed filtering antenna. The RFA and BSF are cascaded directly, and the compact BSF is terminated by a resistor to absorb the stopband energy of the RFA, bringing good reflectionless characteristics in a wide frequency range to the proposed filtering antenna. The proposed filtering antenna has a 2-dB gain bandwidth of 22% (1.78-2.22 GHz), in-band gain of about 6.81 dBi, radiation suppression levels of higher than 23.4 and 21.4 dB for the lower and upper stopbands, respectively. Within 1.0-3.0 GHz, |S11| <= -12 dB, implying slight effect of reflected wave on the devices connected to the proposed filtering antenna.