Miniaturized Microwave Filter Using Circular Spiral Resonators in a Single Metal Cavity

This paper proposes a novel miniaturized microwave filter based on circular spiral resonators (CSRs) embedded in a single metal cavity. The spiral structure is used to design filters in planar circuits with compact size, but not applied in cavity filters. The proposed CSR is firstly presented and analyzed, which has obvious size reduction compared to traditional cavity resonators, and still remain high filtering performance. Then, a second order filter using two CSRs sharing a metal cavity is designed, and it has two transmission zeroes (TZs) produced by the source-load coupling without additional coupling structure, which can improve the nearby stopband-rejection. The circuit size is 0.049λ0 *0.026λ0 *0.047λ0. Finally, the proposed second order filter is fabricated and measured, the measured results are in good agreement with the simulated results.