A compact distributed low-pass filter with wide stopband

Abstract

A distributed parallel resonance circuit is used to design a very compact low-pass filter with cutoff frequency 0.5GHz. The circuit has a section of transmission line shunt with an interdigital capacitor connecting with two low-impedance lines at both of its terminals. A finite transmission zero can be generated near the passband edge so that the filter has a sharp transition response. In addition, the stopband can be extended to more than 6GHz by properly choosing the structural parameters of the circuit. The measured responses match with the simulation quite well.