Miniaturized filter with harmonic suppression characteristics by embedding microstrip resonators in half-mode substrate-integrated waveguide resonant cavities

A novel filter design is proposed that employs harmonic rejection characteristics based on half-mode substrate-integrated waveguide resonance cavities and microstrip resonators. The objective is to expand the filter's blocking bandwidth and reduce the filter's size. The filter employs two half-mode substrate-integrated waveguide resonant cavities, which serve to effectively reduce the size of the filter. Moreover, the higher-order modes TE₂₀₁ and TE₂₀₂ are unable to propagate within the resonant cavities. The suppression of the TE₁₀₂ mode is achieved by setting the coupling window between the resonant cavities at the weakest field strength of this mode. Concurrently, two microstrip resonators are integrated into the coupling window, thereby enabling the realization of a fourth-order filter response with only two resonant cavities. The filter was processed and measured, and the results were found to be in good agreement with the simulation. It is proved that the design method proposed in this paper is feasible.