A Class of Box-Like Bandpass Filters With Wide Stopband Based on New Dual-Mode Rectangular SIW Cavities

This article proposes a new class of box-like substrate integrated waveguide (SIW) filters with wide stopband. First, a two-pole doublet bandpass filter with one finite-transmission zero (FTZ) is proposed using a new planar dual-mode rectangular SIW cavity, which is realized by TE
₂₀₁
and TE
₁₀₃
modes. TE
₁₀₂
, TE
₂₀₂
, and TE
₁₀₄
modes are suppressed intrinsically by arranging feeding lines at the horizontal centerline of the dual-mode SIW cavity. Then, a four-pole box-section filter with one FTZ is proposed using one dual-mode and two single-mode rectangular SIW cavities, and the two single-mode cavities have different width-length ratios to further improve the stopband performance. To further improve the cutoff skirt, a new design method for five-pole quasi-elliptic SIW filter is proposed, which is achieved by the four-pole filter loaded by one single-mode SIW cavity. Some design examples with the center frequency of 10 GHz are presented to verify the performance of the proposed dual-mode SIW filters and the design method.