Design Of Pseudoelliptic Filters With Controllable Transmission Zeros Using High-Q Double-Layer Suspended Stripline Resonators

This article presents a novel synthesis-based design procedure for pseudoelliptic filters using high-Q double-layer suspended stripline (DSSL) resonators. The DSSL resonator consists of an air-filled cavity and a suspended thin substrate with metallic top and bottom strips connected using metallic via hole. The resonator achieves a much higher unloaded quality factor than the single-layer SSL resonator. Resonant characteristics and coupling properties of the innovative DSSL resonator are analyzed in detail. In addition, a systematic design procedure of the pseudoelliptic DSSL filter is presented using two examples of sixth-order DSSL filters with two TZs at upper or lower stopband. The procedure is completed by establishing a relationship between the coupling coefficients and the physical structure dimensions based on an efficient full-wave simulation. The established relationship allows accurately obtaining the physical dimensions of the filter from the electrical parameters calculated by the synthesis method. Furthermore, for demonstration of the proposed design procedure, two filter prototypes are synthesized, designed, fabricated, and measured. The synthesized, simulated, and measured results show an excellent agreement.