Compact tunable wideband bandpass filter using mixed coupling lumped dual-mode resonator

Abstract

In this paper, a compact microstrip varactor-tuned wideband bandpass filter (BPF) is proposed by using mixed coupling lumped dual-mode resonator. The proposed tunable wideband BPF has a pair of transmission zeros around the passband, resulting in high passband selectivity. The measured results show that the passband can be tuned in a frequency range from 1.01 to 2.04 GHz with an almost 3 dB constant fractional bandwidth of 28 ± 1%. Within the tuning range, the insertion loss varies from 2.1 to 1.65 dB and the return loss is better than 10 dB. In addition, the tunability of 3 dB fractional bandwidth at 1.5 GHz is from 23 to 43%.