Diplexer Synthesis Technology Research

Basic theory concerns diplexer synthesis and the efficient techniques involved are investigated. A procedure for synthesizing microwave diplexers is discussed as well. It is based on the evaluation of the characteristic polynomials of the diplexer having taken into consideration the mutual loading effect caused by the three-port junction connecting the TX and RX filters. Four typical types of three-port junctions are considered, suitable for rectangular waveguide, microstrip and coaxial diplexers modeling, which are well representative of a class of practical diplexers implementations.The novel method is particularly suited for small separation between the two diplexer channels:as known, this is the most difficult case in the diplexers design, due to the strong interaction between the TX and RX filters. The proposed synthesis approach offers noticeable design flexibility, as it allows the synthesis of the two composing filters independently of their connections to the diplexer, taking into account at the same time the interaction produced in the diplexer junction. Moreover the choice of the filters topology is absolutely arbitrary (the number of poles and the transmission zeros of the two filters have to be specified). The presented approach is validated by the design and fabrication of a diplexer for global system for mobile communications base stations.In this thesis, after making sense of the synthesis procedure presented by Macchiarella, some aspects concerning the synthesis technique have been explored and investigate.The main results obtained are as follows:1.The linear frequency transformation which is employed to obtain the initial characteristic polynomials of the two composing filters using the well-established filters synthesis techniques available in the literature, Cameron, for instance.2.The group delay characteristics based on the polynomials and matrix of a diplexer are also discussed in detail. Besides the isolation of the diplexer is proposed.3.The normalized coupling matrices for diplexers of some specific types are given, from which we can obtain the response.4.The detailed process for deriving the characteristic polynomials of diplexers of some typical types are included in the index. A software for synthesizing microwave diplexers has been programmed.