SIW bandpass filter based on negative order resonance

A substrate integrated waveguide (SIW) bandpass filter based on negative order resonance is designed, fabricated and tested. Composite right/left hand (CRLH) functionality is generated by incorporating series interdigital slots on the surface of the SIW. The slot acts as series capacitor and shunt inductor, and the resonance generated is below the waveguide cut-off frequency. The bandpass filter presented in this paper is designed by applying the Kaiser distribution on the interdigital fingers. This resulted in shifting the resonance frequency to a higher frequency. The simulations are performed by Agilent ADS Momentum and EMPro FEM. The measurement results show a low insertion loss of 0.8 dB at 7.19 GHz. The 3-dB bandwidth is 645 MHz with a return loss is greater than 15 dB.