Design of Open and Short-Circuit Stubs for Filter Applications

Abstract

A resonator is designed to operate as a filter resonating at 2.485 GHz using standard techniques. The design is initiated from the standard LC circuit. Using the insertion loss method, band pass or band stop second order Butterworth filters, with inductive and capacitive elements, are realized. On applying filter transformations to the \(\lambda /4\) low pass filter, the standard \(\lambda /4\) open and short circuit filter design is obtained. The open/short circuit realization of the filter using Kuroda’s identity was modified as closed loop resonators, with open and closed stubs, to achieve band stop and band pass operations. The optimization of the obtained circuit is carried out by adding stubs on to the section. A proof of concept of the operation of a resonator as a BPF for short circuit \(\lambda /2\) lines and as BSF for open circuit \(\lambda /2\) lines is carried out in this work. The miniaturization of the filter is done by adding open circuit stubs to BSF and short circuit stubs to BPF maintaining the electrical length of the design fixed. The further miniaturization of the design is carried out using standard techniques. The softwares used for designing and validation of the filters are ANSYS Designer and HFSS.