Compact Mixed-Mode Filter Based on TE₁₀₁ Cavity Mode and TE01δ Dielectric Mode

A new class of compact in-line filters with pseudoelliptic responses is presented in this paper. The proposed filters employ a new type of mixed-mode resonator. Such a resonator consists of a cavity loaded with a suspended high permittivity dielectric puck, so that both cavity TE101mode and dielectric TE01δmode are exploited within the same volume. This structure realizes the transverse doublet topology and it is therefore capable of generating a transmission zero (TZ) that can be either located above or below the passband. Multiple mixedmode resonators can be used as basic building blocks to obtain higher order filters by cascading them through nonresonating nodes. These filters are capable of implementing TZs that are very close to the passband edges, thus realizing an extreme closein rejection. As a result of the dielectric loading, the proposed solution leads to a very compact structure with improved temperature stability. To validate the proposed class of filters, a second-order filter with 2.0% fractional bandwidth (FBW) and a fourth-order filter with 2.5% FBW have been designed and manufactured.