Integrated Dual-Band Filtering/Duplexing Antennas

In this paper, the state-of-the-art integrated filtering antennas with dual-band operation are first reviewed. Then, two designs of dual-band microstrip filtering antennas with a low-frequency ratio are presented. The 1^st design is a dual-band dual-polarization (DBDP) antenna with a frequency ratio of 1.2 on a single patch, by employing the coupled resonator technique. Two bands at each polarization are achieved by vertically coupling a hairpin resonator with a patch through a slot in the ground plane and then coupled to a dual-mode stub loaded resonator. Each band exhibits a 2^nd-order filtering performance with improved bandwidth and out-of-band rejection. Such an integration technique could significantly reduce the dimension and the complexity of the traditional DBDP antennas/arrays. In the 2^nd design, a novel dual-port dual-band antenna (with a frequency ratio of 1.38) with the integrated filtering and duplexing functions is proposed. The frequency duplexing function is implemented by coupling a single patch with two sets of resonator-based filtering channels via a U-slot resonator inserted in the ground. This device seamlessly integrates the functions of duplexers, filters, and antennas in a very compact structure.