Wide-Stopband SIW Filters Using Modified Multi-Spurious Modes Suppression Technique

A modified multi-spurious modes suppression technique is proposed to realize wide-stopband substrate-integrated waveguide (SIW) bandpass filters (BPFs), which is to set the external ports and internal coupling windows to the positions of weakest electric fields of specific spurious modes. To extend the stopband as wide as possible with the limited design degrees of freedom, different feeding and coupling positions are fully exploited to reject unwanted modes in specific cavities. By suppressing the out-of-band spurious peaks as much as possible and removing the first unsuppressed spurious resonance to the farthest position, the widest stopband can be achieved intrinsically. A second- and a third-order SIW BPFs are synthesized, designed, fabricated, and tested as demonstrations, realizing the stopbands of 2.51f0and 3.85f0with the rejection level better than 25 dB and 20 dB, respectively.