A novel waveguide resonator is proposed in the paper. The resonator is composed of three rectangular partial-height posts inserted along a rectangular waveguide cross-section. A pair of lateral posts is mounted symmetrically whereas the third antipodal post is centered. The resonator enables bandreject, singlet-type, and pseudoelliptic responses. The operating regimes are achieved by a manipulation with the pair of lateral posts, namely by changing their heights or their locations in a waveguide cross-section. A filtering function is realized as the third mode is exploited as the resonant one. Measurement data are presented for WR90 waveguide. An explanation of the resonant phenomena in post-based sections in terms of eigen regimes and interacting oscillations is proposed.
