Dual-Polarized Filtering Antenna Based on a Second-Order SIR Filter

This letter presents a simple structure wideband dual-polarized filtering magneto-electric dipole (ME-dipole) antenna. It consists of four horizontal patches, four pairs of vertical patches and two feeding metal lines. Each vertical patch has a stepped-impedance structure. To approximate the antenna structure, a second-order stepped-impedance-resonator (SIR) filter is used as the equivalent circuit. By investigating the transmission characteristic of this equivalent circuit, the radiation nulls of the antenna structure can be predicted. Based on this method, a simple structure filtering antenna with three intrinsic radiation nulls is developed. Without adding extra filtering circuits or parasitic elements, the proposed antenna exhibits a bandpass-type realized gain response. For demonstration, a single-polarized antenna is proposed, and its operating mechanism is studied by using an equivalent circuit analysis method. Then, a dual-polarized one is fabricated and measured. The measured results show that the proposed antenna has an impedance bandwidth of 45.0% and an average in-band realized gain of 8.5 dBi. In addition, better than 20 dB out-of-band suppression levels and three controllable radiation nulls are realized. Good agreement can be observed between the simulation and measurement results.