In-Line Wideband Waveguide Bandpass Filters Using Hybrid Irises and Non-Uniform Resonators with Over-Octave Spurious Suppression

This paper reports on a geometrical-shaping-based resonator design approach for in-line wideband rectangular waveguide bandpass filters (BPFs) aiming to improve the spurious suppression. The rectangular resonator is shaped with capacitive and inductive irises and the shaped resonator features irregular boundaries with the first spurious mode spectrally over an octave away from the fundamental mode. X-band 13%-fractional-bandwidth five-pole BPFs composed of uniform capacitive-iris-loaded resonators (filter I) and non-uniform hybrid-iris-loaded resonators (filter II) are developed. The shaping and non-uniform configuration of the resonators contribute to significantly improved stopband performance of the filter. The filter prototypes are manufactured additively and monolithically by incorporating Polyjet 3-D printing and electroless copper plating processes. The 3-D printed filters demonstrate excellent passband performance with the measured return loss and insertion loss of over 20 dB and lower than 0.3 dB, respectively. The first spurious passband appears at over 1.1× and 1.5× octaves away from the fundamental-mode passband for the filter I and filter II, respectively.