Accessing to UMTS filtering specifications using new microstrip miniaturized loop-filters

A new topology for the design of microstrip loop-filters is proposed in this paper. This new geometry is used in a coupled-loop-resonator filter in order to improve the out of band rejection (by introducing an additional transmission zero), as well as insertion loss (thanks to a significant circuit size reduction). The design methodology of these filters is first described and then experimental performances are discussed. Finally, a high performance duplexer, specified for UMTS frequencies and requirements (i.e. in the 1.9-2.17 GHz frequency band), is presented. Measured insertion loss is lower than 2.5 dB and an isolation level greater than 40 dB is achieved between Tx/Rx channels, thanks to the multiple out of band transmission zeros introduced in the filter synthesis.