Inline Box-Like Dielectric Filters With Asymmetric and Symmetric Responses

In this article, a new class of inline filters with box-like properties and pseudoelliptic responses are presented. The proposed filters employ dual-ridge dual-mode resonators (DRDMRs). Each DRDMR can be used in modular filter design as a basic building block, which provides two poles and a transmission zero (TZ). Asymmetric and symmetric filtering responses can be obtained by simply changing the resonant frequencies of the DRDMRs while all coupling coefficients remain unchanged in both values and signs. By properly arranging the position of the coaxial feeding probe, the input–output coupling of the two resonant modes can be controlled flexibly and thus control the TZ position. Intracavity coupling is realized by the all-iris structure of the dual-mode form. To validate the feasibility, an inline fourth-order filter with a pair of symmetric TZs has been designed and manufactured. The experimental result agrees well with the simulated result.