Acoustic resonator surface wave filter with improved barrier damping in the upper barrier area and low damping loss

摘要

In a resonator-type SAW filter, at least one series-arm SAW resonator has an interdigital transducer with reflectors on both sides, and the reflectors are separated from the interdigital transducer by a distance of from (N/2 + 0.55) lambda 1 to (N/2 + 0.81) lambda 1, where N is an arbitrary non-negative integer and lambda 1 is the wavelength of the surface acoustic waves excited by the SAW resonator. Alternatively, from 30% to 80% of the electrode fingers constituting the interdigital transducer in at least one series-arm SAW resonator are apodized, dividing the interdigital transducer into an excitation region and a dummy region, and the electrode fingers in the dummy region are offset from the electrode fingers in the excitation region by a distance of 0.05 lambda 1 to 0.31 lambda 1.