Design of dielectric-filled cavity filters with ultrawide stopband Characteristics

A methodology is presented for the design of small cavity filters, relying entirely on the use of commercial general-purpose design software. Pertinent filter structures comprise resonated segments of ridge waveguide with evanescent-mode inter-resonator coupling sections, supplemented by impedance-transforming port networks. The ridge and evanescent-mode waveguide segments combine to form a metal-clad dielectric core made of either a single dielectric or a composite material. A parameterized equivalent-circuit model is used to describe each segment based on numerical three-dimensional electromagnetic field analyses. For a bandpass filter, the technique yields low passband insertion loss, an ultrawide upper stopband region, and excellent power handling. The approach provides the option to fabricate structures at low per-unit cost with the help of newly available moldable dielectric materials. The efficacy of the technique is demonstrated with an experimental 1-1.45-GHz bandpass filter.