A. Morini et T. Rozzi, CONSTRAINTS TO THE OPTIMUM PERFORMANCE AND BANDWIDTH LIMITATIONS OF DIPLEXERS EMPLOYING SYMMETRICAL 3-PORT JUNCTIONS, IEEE transactions on microwave theory and techniques, 44(2), 1996, pp. 242-248
This work addresses the problem of the fundamental limitations to the
optimum performance of diplexers employing three-port junctions and pr
eassigned branching filters. In this situation it is a common misconce
ption that optimum results are achieved by utilizing a good power divi
der closed by two good branching filters. From the properties of the S
-matrix of a three-port junction, we show this not to be the case and
derive a set of necessary conditions to be satisfied in order that the
junction be successfully employed in the realization of diplexers. We
derive explicit expressions for the positions at which the filters mu
st be placed in the junction arms for optimum diplexer performance, re
sulting in considerable simplification of the difficult diplexer synth
esis problem. A theorem on the maximum achievable bandwidth is proved
and validated by means of two practical examples.