Compact quasi-elliptic wideband bandpass filter using mixed coupling lumped-element dual-resonance resonators

This paper presents a quasi-elliptic wideband bandpass filter (QEWB-BPF) constituting a pair of lumped-element dual-resonance resonators (LE-DRRs) with mixed electric and magnetic coupling (MEMC). Two resonant modes of proposed LE-DRR can be controlled separately. Due to virtual ground in LE-DRR, the cancelling effect of two paths of MEMC, and inductive perturbation, four TZs are realized around the passband. As an example, a QEWB-BPF with measured central frequency (CF) at 1.82 GHz and 3 dB fractional bandwidth (FBW) of 24.4% is designed and fabricated. The measured minimal insertion loss (IL) is 0.95 dB, and a 30 dB rejection upper stopband from 2.11 to 4.79 GHz is also obtained. The fabricated QEWB-BPF has a compact circuit size of 0.133 lambda(g) x 0.215 lambda(g).