The Sdudy Of Synthesizing Nonuniformly Coupled Transmission Lines

communication systems, such as satellite broadcasting, mobile communication system and optic system. With the development of broadband Monolithic Microwave Integrated Circuits and especially the application of System-on-Chip, broadband couplers and filters should be designed.It's hard to satisfy the condition of tight coupling and super broadband for conventional couplers. In this paper, broadband 3dB coupler is realized with nonuniformly coupled microstrip lines. Because of the related bandwidth in the design process, coupler with arbitrary frequency domain can be designed according to the different choice of normalizing frequency. Considering the relationship between the characteristic impedances of odd- and even-mode, the port impedance of nonuniformly coupled microstrip lines should be adjusted and be matched to the system impedance with exponential microstrip lines. Cascaded ABCD matrixes are employed to calculate the S-parameters of the designed couplers and the simulation results show that coupled nonuniform transmission lines are suitable for designing broadband directional couplers. The contents are arranged as following:In chapter 2, nonuniform transmission line(NTL) are modeled and analyzed. From the circuit model, the telegrapher's equations of the NTL can be obtained, which are similar to but more complex than the ones of uniform transmission line. The classical Sturm-Liouville(SL) equations and Zakharov-Shabat(ZS) equations referred to the circuit model of the NTL are introduced in this chapter. Meanwhile the theories solving inverse SL problems are also discussed.In chapter 3, several synthesis methods for NTL are introduced including conventional ones and the ones based on solving classical inverse problems. Conventional synthesis techniques can be categorized in time-domain and frequency-domain methods. The synthesis methods based on solving classical inverse problems are the points in this chapter, which involving construction of potential function, solving of characteristic impedance function and calculating of the dimensions of NTL.In chapter 4, synthesis techniques realizing microwave devices including filters and couplers are introduced. Based on conventional synthesis technique designing uniform stripline coupler, nonuniform stripline coupler can be realized by the similar method to cascaded uniform transmission line unit model. Because stripline is difficult to integrate with microstrip circuit, the synthesis technique of nonuniform microstrip couplers is particularly discussed. Certainly, the application of NTL in designing broadband filters is also investigated in this chapter.