A Hybrid SAW-Resonator/Lumped-Element Dual-Band Bandstop Filter with Continuously Tunable Bandwidths

In this paper, a hybrid SAW-resonator/lumped-element dual-band bandstop filter with continuously tunable bandwidths (BWs) is reported. It is based on hybrid-technology design approach in which N identical dual-resonance filter cells-shaped by two SAW resonators, one coupling capacitor, two inductors and two varactors-are cascaded in series by N-l transmission lines Z
₀
. In this manner, two stopband notches with enhanced fractional bandwidths (FBWs) which are larger than the electromechanical coupling coefficient (k
_t²
) can be achieved. The continuously variable BWs are realized by adjusting the bias voltages of varactor diodes. For practical validation, a prototype using commercially-available one-port SAW resonators and chip LE components is designed, built and tested. It exhibits two stop-bands centered at 868.7 and 916.7 MHz that respectively expose continuous BW tuning between 1.06-3.27 k
_t²
and 0.89-2.62 k
_t²
.