A Hybrid Transmission-Line/SAW-Resonator Analog Signal-Interference Dual-Band Bandpass Filter

An analog signal-interference dual-narrowband bandpass filter (BPF) by combining transmission lines and surface-acoustic-wave (SAW) resonators is proposed. The filter is based on three-path transversal filtering sections (TFSs) with two embedded one-port SAW resonators. By cascading the TFSs inseries through transmission lines, passbands with enhanced fractional bandwidths (FBWs) (i.e., larger than the electromechanical coupling coefficient k
_t
²
of the employed acoustic-wave resonator) can be realized. For the purpose of validation, a two-stage microstrip dual-narrowband BPF with two passbands located at 868.95 and 916.5 MHz has been designed, fabricated, and characterized. It demonstrated an insertion loss (IL) of 0.89 dB at 868.95 MHz, 1.57 dB at 916.5 MHz and a bandwidth (BW) of 3.2 MHz (FBW = 3.21 k
_t
²
) at 868.95 MHz, and 2.3 MHz (FBW = 1.92 k
_t
²
) at 916.5 MHz.