Surface acoustic wave filter and communication apparatus

摘要

A surface acoustic wave (SAW) filter includes a piezoelectric substrate (100). A resin pattern (2) having a permittivity less than that of the piezoelectric substrate (100) and first (1) and second (3) conductor patterns are disposed on the piezoelectric substrate (100). The first conductor pattern (1) defines two one-terminal-pair SAW resonators (11,12) and two longitudinally coupled resonator SAW filters (13,14). A portion of the second conductor pattern (3) defines wiring traces (21,22,56-61) having different potentials. Portions of the wiring traces facing each other in a plan view are disposed on the resin pattern (2). The resin pattern is an insulating pattern. The configuration has several advantages: It reduces the parasitic capacitance between the wiring traces or different parts of the conductor pattern. It also improves common mode suppression when used in a balun configuration. By layering wiring traces on opposite sides of the insulating pattern, the three-dimensionally crossing wiring traces reduce space for the wiring traces and thus miniaturizes the SAW filter.