Novel Dual-Mode Bandpass Filters Based on SIW Resonators under Different Boundaries

Two novel substrate integrated waveguide (SIW) resonators under different boundaries are proposed and analyzed. The closed-form solutions of the guided-mode field and the formulas for calculating the resonant frequencies of the SIW resonators under different boundaries are given. The coexistence mechanism of quasi-TEM (TE
₀₀
) and TE mode was illustrated by the proposed equivalent principle. Two modes of each filter, TE100 (TEM mode) and TE
₁₀₂
, TE
₀₀₁
(TEM mode) and TE
₂₀₁
, can be tuned independently by the perturbation slotlines. Finally, two dual-mode SIW bandpass filters utilizing the two SIW resonators are fabricated to demonstrate the proposed method. The measured results are in agreement with the simulated results.