Patent ID: 7489210

Claim:
A surface acoustic wave filter, comprising: a longitudinal mode resonator type first surface acoustic wave filter unit provided with a central IDT electrode and respective outer IDT electrodes on both sides of the central IDT electrode, and respective reflectors further on the outsides of said outer IDT electrodes; and a longitudinal mode resonator type second surface acoustic wave filter unit provided with a central IDT electrode and respective outer IDT electrodes on both sides of the central IDT electrode, and respective reflectors further on the outsides of said outer IDT electrodes, wherein the central IDT electrode of said first surface acoustic wave filter unit and the central IDT electrode of said second surface acoustic wave filter unit are structured to have the same electrode finger arrangement; each one terminal of said central IDT electrodes is grounded, and each of the other terminals of said central IDT electrodes is connected in parallel to each other to form an unbalanced input port or an unbalanced output port; electrode fingers of a set of the outer IDT electrodes of said first surface acoustic wave filter unit and electrode fingers of a set of the outer IDT electrodes of said second surface acoustic wave filter unit are arranged in an opposite direction to each other; and a pair of ports formed by connecting four terminals in parallel, of which input-output phases are the same phase out of eight terminals of said outer IDT electrodes are made into balanced output ports or balanced input ports.