A Novel Compact Wide-Stopband Filter With Hybrid Structure by Combining SIW and Microstrip Technologies

Based on the hybrid microstrip and substrate-integrated waveguide (SIW) technologies, a compact filter with wide-stopband characteristics is presented in this letter. Two microstrip-based uniform impedance resonators (UIRs) are etched between two SIW cavities, which not only resonate to generate transmission poles, but also constitute coupling-null structures to prevent the propagation of TE102 mode. In addition, the staggered higher mode frequencies of the UIRs and SIW cavities also contribute to harmonics rejection of the two resonant structures. The suppression method of higher order modes is carefully illustrated. For validation, a prototype operated at 10 GHz is designed, fabricated, and measured. The experimental results show good agreement with simulation. Besides suppressing the TE102 and TE201 modes, the proposed filter also has the capability to suppress other harmonics, presenting an ultrawide stopband compared with the conventional SIW filters.