A compact SIW bandpass filter based on modified CRLH

A compact substrate integrated waveguide bandpass filter based on composite right/left hand CRLH is designed, fabricated and tested. The CRLH characteristics can be generated by incorporating series interdigital slots on the top surface and ground plane. The slot acts as series capacitor and shunt inductor. To make it compact, the lengths of these interdigital fingers are modified by applying the Kaiser distribution. This results in the resonance being shifted to a lower frequency. When the interdigital slots are applied only on the top surface, the measurement results show an insertion loss of 1.8dB at 5.8GHz, which is 6% of frequency shift. Moreover, when the modified interdigital slots are applied on both sides, the resonance is shifted further to a lower frequency of 5GHz with multiple resonances. The insertion loss is 2.7dB and 3dB bandwidth of 700MHz. The total frequency shift is more than 18% and thus makes it a compact filter design.