Ladder Type Saw Filter and its Application to High Power Saw Devices

SAW filters with one-port SAW resonators being connected in a ladder structure, which is called ladder type SAW filter, have many features such as low insertion-loss, wide pass-band and simple filter design and so on. The design methodology, features of characteristics, and developments of higher frequency filter are described for an application in cellular phones. Furthermore, in order to apply to high power SAW devices such as the antenna duplexer of cellular phones, the material of inter-digital transducers (IDT) was improved to have high power durability. The optimum design in a ladder type SAW filter, the improvement in materials for IDT, and the optimum design of the package, all contributed the success of realizing a small SAW antenna duplexer.