Design and synthesis of microwave coupled resonator diplexers

A diplexer is a familiar device that separates a composite signal into its constituent parts to permit each part to be transmitted separately. The design of a diplexer is one of the basic problems in communications. Because of the mutual interaction effect of the two filters composing the diplexer, the characteristics of a diplexer are different from the responses of the individual two filters. The complexity of the interaction effect makes the design of a diplexer very complicated. This work provides a general design strategy for coupled coaxial resonator diplexers. These diplexers offer advantages in terms of low cost and good performance, and are therefore currently used in mobile base stations and GSM. The first step in designing any diplexer is the design of each of its two filter arms.