A narrow band and high selectivity half-mode substrate integrated waveguide bandpass filter with interdigital slots

A novel in-line half-mode substrate integrated waveguide (HMSIW) bandpass filter with interdigital slots has been proposed in this letter. Here, the interdigital slot shows attenuation resonance characteristics and generates a finite frequency transmission zero (TZ). The proposed filter generates two TZs without additional coupling or extra space and exhibits wide stopband characteristics. To validate this method, the in-line two-pole quasi-elliptic bandpass filter is synthesized and fabricated on RT/Duroid 5880 substrate using printed circuit board technology. The experimental results show that center frequency, 3-dB fractional bandwidth, insertion loss, and return loss are 3.6 GHz, 6.0%, 1.9 and 18 dB, respectively, and are very much similar to the simulated S-parameters.