Tunable Diplexer Design With Redundant Coupling

This article studied the interference between two channels of a tunable diplexer and proposed a feasible solution to alleviate the effect. A novel approach to synthesize the channel filter with the first element replicating the other channel’s effect is first developed. It led a set of simple formulae for fixed frequency diplexer design. After that, a framework incorporating a redundant coupling path to generate cancellation effect is derived using the coupling matrix theory. The proposed theories are demonstrated and verified using a combline diplexer design. The simulated and measured results suggest that the interference of the two channels can be greatly mitigated.