Research On The Synthesis Technology Of Microwave Duplexers

With the continuous development of information technology over the last years, frequency spectrum is increasingly tense. The performance requirements of communication systems have become higher and higher, which have greatly stimulated the need for high performance microwave filters and duplexers. Therefore it is necessary to intensively study the relevant theory of microwave filters and duplexers. This thesis mainly involves the synthesis theory and design method of microwave filters and duplexers.As the theoretical foundation, this thesis first introduces the coupling matrix synthesis theory for general Chebyshev filtering function. Then the synthesis approach for general Chebyshev filters terminated complex loads is studied. Subsequently, a synthesis approach for duplexers is studied, which models the specific T-junction by lumped parameters network (rectangular waveguide E-plane and H-plane T-junctions are considered). It is based on the evaluation of the characteristic polynomials of the duplexer including the three-port junction connecting the TX and RX filters. An iterative procedure is used to obtain the polynomials of the duplexers which satisfy the constraints. The coupling matrix of TX and RX are finally evaluated from the duplexer polynomials.However, the specific T-junction was modeled by a simple series admittance or a shunt admittance, which has a significant difference from actual physical structure, and it could only analyze specific T-junctions which has significant limitations. To overcome these shortcomings, a method which models the T-junction by scattering parameters to synthesize duplexers is proposed in this thesis. It is based on the network synthesis technology to get the numerator and denominator polynomials of the duplexer’s scattering parameters. Compared with the method of which the T-junction is modeled by lumped parameters, this approach has more accurate results and broader applicability. Finally, several filters and duplexers which adopt the methods described in this thesis are designed. The correctness and practicability of the theories are validated by the simulated results.