Design Of Microstrip Duplexers For Mobile Communications Using Single-Sided Filters

This paper describes a novel approach to the design of high selectivity duplexers in microstrip technology for applications in mobile communications systems. The configuration proposed makes use of two single-sided filters (devices characterized by requirements in one passband and one stopband, both of finite extension). Using this class of filters it is possible to obtain high selectivity and small insertion losses at the same time (even with low unloaded Q microstrip resonators); in fact the number of resonators required for a given attenuation mask is much smaller with respect to that required for classical bandpass filter configurations. Suitable filter topologies are introduced, which allow having the filter stopband either above or below the filter passband (this is a requirement in the duplexer configuration). A design procedure for the duplexer class considered is presented; a test device, designed with this procedure, has been used for verifying the actual behavior of the novel duplexer configuration; the results obtained are discussed in the paper.