Dual-mode bandpass filter using microstrip SIR at Ka band

A novel dual-mode bandpass filter using microstrip SIR is presented. It is composed of step impedance square ring and designed at the operating frequency of 36 GHz with a bandwidth of 1.8 GHz. The filter has a size reduction of approximately 30%, in comparison with the conventional square ring filters. It also has a good return loss. Within the passband, S11 is bellow -20dB. Because of the step impedance design, we can easily change the center frequency and the spurious response by changing the impedance ratio.