Cascaded trisection substrate-integrated waveguide filter with high selectivity

A cascaded trisection substrate-integrated waveguide bandpass filter with better frequency selectivity is presented. The proposed coupling scheme can be divided into two trisection topologies. By changing the signs of coupling coefficients between cascaded resonators, two transmission zeros can be simultaneously placed at the higher or lower stopband, or one can be located below and the other above the passband. A filter sample is designed and fabricated with standard single-layer printed circuit board technology. The measured S-parameters agree well with the simulated counterparts, and good performance of the filter is predicted.