A Hybrid Filter With Extremely Wide Bandwidth and High Selectivity Using FBAR Network

An extremely wideband hybrid bandpass filter (BPF) with high selectivity and low insertion loss is proposed in this brief. The hybrid BPF is composed of three coupled lines (CLs), six matching transmission lines (TLs) and two film bulk acoustic resonator (FBAR) networks with ladder-type structure. These two FBAR networks can help greatly enhance the upper and lower sideband roll-off of the hybrid BPF. At the same time, the passband is compensated by CLs and TLs. The odd-even mode theory is used to analyze the hybrid BPF to obtain the analytical solutions. Through electromagnetic-acoustic co-simulation and optimization, a hybrid BPF with extremely wideband is fabricated and measured. A discussion on the deviation between the simulation and the measured results is presented. The measured hybrid BPF has a 3-dB fractional bandwidth of 56 %, a minimum insertion loss of 1.733 dB and a shape factor of 0.83 simultaneously.