A modern bandpass microstrip filter with spurious response suppression and size reduction

In this paper, a modern bandpass filter using a capacitively stepped impedance resonator (CSIR) is examined using analytical formulations to design a filter in the S-band for spurious frequency relocation and size reduction. A prototype filter is designed at 3.35 GHz with significant spurious suppression up to 31 and 23-dB at frequencies 6.70 and 10.05 GHz respectively. A circuit size reduction of about 40% is achieved when compared to a hair-pin filter and more than 86% when compared to an edge-coupled bandpass filter configuration with comparable passband performance and superior out-of-band suppression.