A High-Q Miniaturized Suspended Stripline Resonator for Pseudoelliptic Filter Design

A miniaturized suspended stripline (SSL) resonator with high unloaded quality factor is proposed in this paper. The novel resonator consists of a thin substrate with double-layer strips on both sides connected by a metallic via hole, which is suspended in the middle of an air-filled cavity and a pair of cuboid metal bricks located at the open end of the strips with a gap to realize capacitive loading. Based on a theoretical analysis of the equivalent circuit and the electric field distribution, the proposed resonator has been found possessing much higher unloaded quality factor and more compact size than the conventional SSL resonators. A compact pseudoelliptic filter centered at 670 MHz with a bandwidth of 160 MHz and a low insertion loss of approximately 0.38 dB is designed, fabricated, and measured. Two transmission zeros generated by cross coupling mechanism are located near the passband to enhance the frequency selectivity. The measured results show excellent agreement with the synthesized and simulated ones.