Targeted Suppression of Spurious Responses in Microstrip Bandpass Filters

This paper demonstrates how spurious responses of planar microstrip-line bandpass filters can be effectively and selectively suppressed. This is achieved by exciting a lambda/2 microstrip-line resonator at appropriate points dictated by the standing wave nulls of the E-field established on the line corresponding to the relevant resonant mode to be eliminated. Excitation is achieved via distributed capacitance instead of chip capacitors, hence saving time and cost for practical realization. The work in this paper has been confirmed with practical results.