SIW Cavity Mode Analysis and Control Techniques for Compact Wide-Stopband Filters Design

In this brief, a compact novel type of wide-stopband bandpass filter (BPF) is presented based on perturbed dual-mode substrate integrated waveguide (SIW) cavity. The perturbed metallic vias are introduced at the center of SIW cavity to achieve a dual-mode SIW cavity by shifting the resonant frequency of TE101 mode toward TE201 mode. Moreover, by setting the external ports to the positions at electric field nulls of the high order spurious modes, the wide-stopband BPF can be realized. Through suppressing the unwanted modes, which includes at least seven modes, the widest stopband up to
$2f_{0}$
can be obtained in a single SIW cavity. To verify the proposed wide-stopband filter, two prototypes are designed, fabricated and measured, following the stopbands of
$2f_{0}$
with the rejection level better than 20dB and 30dB, respectively.