Researches on Circularly-Polarized SIW Cavity-Backed Filtennas

Abstract

Substrate integrated waveguide (SIW) cavity-backed structure, as a multi-mode resonator featuring low loss and low profile, is suitable for the implementation of circularly polarized (CP) antennas. By embedding CP patches into SIW cavities, radiation nulls can be generated by the modes of SIW cavity and the mixed electric and magnetic coupling between the patch and the SIW cavity, simultaneously, to form filtering responses. By adopting these filtering mechanisms, three examples of SIW cavity-backed filtennas are proposed and studied. A wideband single-layer dual-CP SIW cavity-backed patch filtenna with an out-of-band rejection level over 13 dB is achieved. The radiation nulls are realized by the TE110 mode of the SIW cavity and the mixed coupling between the patch and the cavity. Then modified perturbations are used in our second work to reduce the frequency of TE220 mode of the SIW cavity to improve the high-band side roll-off characteristics. What’s more, four filtering slots are asymmetrically introduced to introduce extra radiation null to achieve a high rejection level of 21 dB extend to 1.5f0. As no additional filtering circuits are used in the filtenna element, a novel 2 × 2 SR filtenna array with wide AR bandwidth of 18% and rejection level up to 33 dB is achieved. At last, a millimeter-wave 4 × 4 SR filtenna array based on higher-order SIW cavity modes is developed. The modified TE410 mode and TE330 mode cooperating with four embedded patches are used to form a 2 × 2 subarray. Four 2 × 2 subarrays combined with a filtering 2 × 2 SR feeding network are used to realize a 4 × 4 SR filtenna array with compact feeding network and good filtering performance.