Quasi-Elliptic Multi-band BPFs using Multi-Resonant Acoustic-Wave Lumped-Element Resonators

Compact surface acoustic wave (SAW) resonator based multi-band bandpass filters (BPFs) with quasi-elliptic transfer functions are reported. They are based on multi-resonant acoustic wave lumped resonator (AWLR) stages that are shaped by multiple one-port type acoustic wave resonators (AWRs) and one lumped-element inductor. The concept can be scaled to transfer functions with: i) a high number of passbands by readily increasing the number of the AWRs in the multi-resonant stage and ii) a higher order by cascading AWLRs using impedance inverters. As such, for N in-series cascaded multi-resonant stages, each comprising K AWRs, K passbands with enhanced fractional bandwidth (FBW) can be created, and the overall transfer function will have K\bullet(N)-poles and N\bullet(K+1)-transmission zeros (TZs). The operating principles of the multi-band AWLR concept are provided through detailed design examples. For proof-of-concept demonstration purposes, two-stage dual-band (i.e. N=K=2) and triple-band ((i.e. N=2 and K=3) BPF prototypes were designed, manufactured and characterized. They exhibit i) two passbands with f_cen1,2=1033.4 and 1039.9MHz, FBWs >0.78k_t2 and Q_effS>6200 ii) three passbands with f_cen1,2,3=1029.8,1033.4 and 1039.9MHz,FBWs>0.48k_t2 and Q_effS>5400.