| 摘要 |
PROBLEM TO BE SOLVED: To make impedance outside a passing band of each filter sufficiently large without necessitating impedance matching or with simple structure by constituting two surface acoustic wave band pass filters by connecting resonators in the shape of plural stage ladders. SOLUTION: The surface acoustic wave filters F1, F2 are constituted of a serial resonator Rso and a parallel resonator Rp as the resonators in the shape of one pair of terminals with a comb-line electrode and a reflector. The serial resonators Rso is inserted on the side of common connection points (a), (b) with the surface acoustic wave filter F2 in parallel with the surface acoustic wave filter F1. This circuit structure is similar for the surface acoustic wave filter F2 and each of the surface acoustic wave filters F1, F2 is constituted by connecting the required number of combinations of each of the serial resonator Rso and the parallel resonator Rp with a series. Relation of f1<f2 is satisfied by mutually different band center frequencies f1, f2 of the surface acoustic wave filters F1, F2 here. |
