A Dual-Band Dual-Polarized Filtering Antenna

This letter presents and analyzes a dual-band, dual-polarized filtering antenna design. By inserting two pairs of vertical metal walls with different heights into a slot-coupled magneto-electric dipole (ME dipole) antenna, four radiation nulls are generated to ensure a high dual-band frequency selectivity. To analyze its working principle, a stub-loaded transmission line circuit is employed as the equivalent circuit to approximate the antenna structure. The ME dipole radiator, extended feedline and the two pairs of vertical metal walls can be regarded as four open-circuited stubs loaded on a transmission line. Based on the transmission line theory, when the length of each open-circuited stub equals a quarter wavelength of a specific frequency, a transmission zero is generated. Using this method, the antenna realizes a dual-band bandpass-type radiation response without adding intricate components. For demonstration, a dual-polarized prototype operating at 3.4 and 4.9 GHz is simulated, fabricated and measured. The measured in-band gains are about 6.5 dBi, and a better than 16 dB out-of-band radiation rejection level is achieved.