Diplexer using a circulator and interchangeable filters

A microwave diplexer is proposed that uses a passive or active three-port clockwise circulator device. The use of a circulator in place of a manifold structure in the diplexer means that the filters can be tuned or even exchanged without the need to modify the manifold. In the experimental realization of this diplexer, two edge-coupled microstrip filters were used and the two passbands were at 2.85 GHz and 3.15 GHz. An analytic analysis of the isolation between the output ports of the diplexer is presented that agrees well with measurements.