Design of high isolation diplexer with novel matching network

This paper reports a new kind of matching network for microstrip diplexer. By properly adjusting the input admittance of the matching network, each channel of the diplexer can be designed independently. The diplexer can be easily realized by the connection of different bandpass filters without further tuning. The matching network is comprised by some open- and short-circuited transmission lines, and source-load coupling can also be conveniently introduced. Moreover, the proposed matching network occupies little place, and thus the size of the diplexer is mostly determined by the filters. To illustrate the concept, a diplexer has been designed, fabricated and measured. Simulated and measured results are found to be in good agreement with each other.