Design of DCS duplexer using SAW ladder filter

The frequency responses of SAW ladder filters, which consist of a one-port resonator in a parallel arm and one in a series arm, are investigated and their applications in designing a duplexer are also illustrated. The one-port resonators with apodized interdigital transducers and width-controlled reflection gratings are employed to increase the operating bandwidth as well as to suppress the effects of spurious modes. The transmission matrix method along with the image parameter method is applied to design the duplexer, which consists of two SAW ladder filters connected in parallel. Simulation results indicate that with a proper design of transmission line for impedance matching, a switchless duplexer with very low loss can be tailored using SAW devices.