Miniaturized fifth-order lowpass filters based on structure of artificial transmission line unit

Abstract

ABSTRACTIn this article, several miniaturized microstrip fifth-order lowpass filters with structure of unit artificial transmission line are presented. Reactive elements including inductors and capacitors are constructed by microstrip structures directly by parameter extraction from electromagnetic simulation. A transmission zero in stopband can be achieved by inductors and capacitors (LC) series-resonant circuit composed by parallel-plated capacitors and connecting lines. Meanwhile, loading interdigital capacitors would bring in another transmission zero. In comparison, fifth-order Butterworth and Chebyshev lowpass filters with one and two transmission zeros are fabricated, respectively, to verify the extra transmission zero effect caused by LC shunt resonant-circuits with interdigital capacitors. The proposed lowpass filters are compact and their sizes occupies less than 40% of conventional microstrip lowpass filters. The simulated and measured results demonstrate good agreements between them, which verifies feasibility of the proposed designing method.