Microstrip bandpass filters with dissimilar resonators for suppression of spurious responses

Microstrip bandpass filters with an extended rejection bandwidth are proposed, using dissimilar resonators for spurious suppression. The combination of dissimilar resonator structures with same fundamental frequency but with different spurious frequencies may improve the stopband rejection of a bandpass filter by the partially mutual cancellation of spurious responses. Specifically, a 4th-order coupled-resonator microstrip bandpass filter, centered at f₀=1.97GHz, with better than 21.48 dB stopband rejection up to 9.72 GHz (4.93f₀) is implemented and investigated.