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 TE201 and TE103 modes. TE102, TE202, and TE104 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.