Pseudo-elliptic in-line filters with dielectric resonators in propagating waveguide

In this paper a new class of in-line filters with pseudoelliptic responses exploiting the TE_01δ dielectric mode is presented. The basic structure consists of a single resonant dielectric puck placed into a rectangular propagating waveguide. Couplings are controlled by a proper positioning of the puck, and no irises are required. The fundamental propagating mode of the waveguide is exploited to bypass the resonator so as to obtain couplings between non adjacent resonators, allowing responses with a number of zeros equal to the number of poles. Direct input-to-output coupling is incorporated, resulting in very selective responses. With respect to classical waveguide filters, the maximum number of transmission zeros is obtained in a more compact waveguide section while not sacrificing the quality factor. Furthermore, in contrast with conventional dielectric resonator filters, which are limited to very narrow band applications, filters having a FBW up to 2% (or more) can be designed with the proposed approach. Higher order filters are obtained by cascading singlets, resulting in designs with high modularity. The connection between singlets is accurately taken into account in the equivalent circuit and no further optimization is required after the cascade, also allowing an exact positioning of the transmission zeros. Design of three pole filters demonstrate the flexibility of the proposed approach, while the measurement of a manufactured filter with a FBW of 2,3% demonstrate its feasibility.