Design of compact Bandpass filters using sixteenth mode and thirty-second mode SIW cavities

Abstract

This paper presents two novel bandpass filters using sixteenth mode substrate integrated waveguide (SMSIW) and thirty-second mode SIW (TMSIW) cavities, respectively. The overall size of SMSIW and TMSIW cavities can be reduced by a factor of 15/16 and 31/32 in comparison to the filters designed in the conventional SIW resonator, while keeping almost the same resonant frequency. Based on SMSIW cavity, a first-order filter with the center frequency of 2.45 GHz and a transmission zero (TZ) located at the upper-stopband is proposed. The second-order TMSIW cavity filter exhibits one TZ at the lower-stopband and two TZs at the upper-stopband, and it has a better performance of the passband than the former with the same size and center frequency. It also has a wider upper-stopband with suppression of an unwanted harmonic at 7.6 GHz. Two intersecting rectangular slots are etched between the two cavities with a smaller angle between them of 30 degrees. The whole size of the filter is 24.2 mm × 29.1 mm × 0.508 mm. The filters are fabricated in SIW technology, and the frequency response shows good agreement between simulated and measured results.