SPUDT/in-line coupled resonator filters

This paper presents results obtained for 71 MHz filters designed and implemented using a combination of single phase unidirectional transducers (SPUDT) and in-line coupled resonators (RFI). For simplicity the device will be referred to as a SPUDT-RFI. This approach is ideally suited for cases in which low price and small size are important considerations. A typical example is the application of these filters in GSM cellular telephones. The design and implementation of these filters is very challenging, since they require very thick layers of aluminum to provide the required reflectivity and bandwidth in a small space. A technique that involves the use of multi-level metallization to optimize both the SPUDT and the resonator will also be presented