Quasi-Lumped Design of UMTS Diplexer Using Combined CPW and Microstrip

[[abstract]]In this letter, we propose a novel design of a universal mobile telecommunications system diplexer using a combined coplanar waveguide (CPW) and microstrip structure. The diplexer is composed of two bandpass filters (BPFs), which are termed the transmitting (Tx) and receiving (Rx) filters. The filter’s characteristics analyzed by a circuit model of the LC lumped elements are implemented using the CPW and microstrip. A transmission zero is implanted for each filter to reject the signal of the other filter’s band. The two filters are in a parallel-cascade layout and a microstrip is used to couple the I/O signals from/to the filters