A full wave analysis of a conductor post insert reentrant coaxial resonator in rectangular waveguide combline filters

Due to its wide tunability region in performance and compactness in size, conductor post insert reentrant coaxial resonators are widely used in combline filters for mobile communications. This paper, for the first time, presents a full wave electromagnetic model for the reentrant coaxial resonator in rectangular waveguide combline filters. The model is based on the orthogonal expansion method and provides a formally exact modal solution to the problem. The model has been extensively verified by experiments and can be used in calculating resonant frequency, coupling values, or in constructing a key building block in full electromagnetic design of waveguide combline filters.