Extended Doublet Bandpass Filters Implemented with Microstrip Resonator and Full-/Half-Mode Substrate Integrated Cavities

Two extended doublet bandpass filters with compact size and good spurious suppression characteristic are proposed. One is built up by a dual-mode microstrip resonator with a full-mode substrate integrated cavity, while the other is composed of a microstrip resonator and a half-mode cavity. The relationship between the location of their transmission zeros and the impedance ratio of the microstrip resonator is analyzed theoretically. Our proposed filters only occupy the areas of 0.69λ/ and 0.51λ/, and they also have wide upper stopband. The predicted performances are demonstrated by the reasonable agreement obtained between their simulated and measured S-parameters.