Propagating Waveguide Filters Using Dielectric Resonators

In this paper a new class of propagating waveguide in-line pseudoelliptic filters exploiting dielectric resonators is presented. The basic structure is a singlet, which is implemented by a mode dielectric resonator placed into a rectangular waveguide above cutoff. Couplings are controlled by a proper positioning of the puck. The fundamental propagating mode of the waveguide is exploited to both excite and bypass the resonator so as to obtain bypass coupling capability, allowing the generation of transmission zeros. Higher order filters are obtained by cascading singlets through quarter-wave or half-wave waveguide sections. The quarter-wave section behaves as an admittance inverter, while the half-wave section behaves as a resonator, the latter resulting in filters which combine dielectric and cavity resonators. Thanks to this combination, unique performances such as wide bandwidth and sharp transition bands can be obtained. To validate the proposed method a third-order filter with 2.3% fractional bandwidth (FBW) and a fifth-order filter with 8.15% FBW have been designed and manufactured, thus demonstrating the approach feasibility.