Quad-band filtering antenna based on slotted half-mode substrate-integrated waveguide cavity

A quad-band filtering antenna based on a slotted half-mode substrate-integrated waveguide cavity is proposed. Three cavity edges are shorted by metallic posts and one edge is opened. Then three rectangular slots are etched to obtain multi-band operations and coaxial feeding is employed. Four radiation frequencies with similar field distributions but different resonating size can effectively radiate cavity energy through the opened edge and etched slots, resulting in good in-band antenna features. On the other hand, three radiation nulls whose dominant field is concentrated around the feeding port can generate little energy leakage, leading to good out-of-band filtering characteristics. The proposed design has been fabricated with an overall size of 0.40λ0 × 0.20λ0. Measured radiation frequencies are at 3.35, 3.88, 4.54, and 5.18 GHz with high gain of about 5.0 dBi and efficiency of 70.0%, whereas measured radiation nulls are at 3.54, 4.24, and 4.91 GHz with very low gain of −16.75, −13.46, and −12.06 dBi and efficiencies of 0.59, 0.88, and 1.42%. Moreover, unidirectional patterns with stable radiation are experimentally confirmed.