Design and analysis of interdigital coupled ultra wideband bandpass filter using multimode resonator

Abstract

In this paper, an interdigital coupled microstrip bandpass filter incorporated with shorted stub multi-mode resonator at ultra-wideband spectrum is presented. Proposed filter is characterized by its ultra compactness achieved through multi-mode resonator. The proposed filter is incorporated with interdigitated transmission line based on Lange Coupler topology. This structure enhances capacitive coupling between feed line and MMR which improves lower frequency selectivity of BPF. The parameters viz. fractional bandwidth of 105%, return loss above 20 dB and insertion loss below 1 dB at centre frequency of 4.875 GHz are recorded. The bandwidth of the filter is measured to be 5.15 GHz (2.3 to 7.45 GHz). The filter shows good linearity with its group delay recorded 0.2 ns with small variations of 0.1 ns at maximum in its passband. The compactness of proposed filter makes it suitable for various modern wireless applications.