Compact Substrate-Integrated Bandstop Filters Using Double-Resonant Coaxial Resonators

This letter reports on the RF design and practical development of miniaturized substrate-integrated-(SI)-coaxial-resonator-based bandstop filters (BSFs). Size compactness is achieved through the use of double-resonant coaxial resonators that are shaped by two coupled capacitively loaded posts within the volume of a circular cavity. The operating principles of the double-resonant SI-coaxial-resonator-based BSF concept are demonstrated by means of coupled-resonator diagrams and synthesized examples of both single-stage and multi-stage higher order BSF configurations. For proof-of-concept validation, various single- A nd two-stage coaxial-resonator-based BSF prototypes were designed, manufactured, and measured at $S$-band.