Lossy Broadband Matching Research Based On Optimization Theory

With the development of communication technology, the application of ad-hoc and spread spectrum technique in communication system, modern mobile communication technology call for higher requirement on the broadband of antenna. The lossless broadband matching is an effective technology in the design of antenna matching circuits. However, the variance of antenna's impedance caused by external environment makes the performance of matching circuit weaken. The thesis mainly discusses how to employ the lossy element to keep the matching circuit from affecting by the impedance change of antenna.In the part of theory, principle of lossless broadband matching and realization of algorithms of multi-objective optimization are introduced. Genetic algorithm and NSGA-II are discussed on detail, which are basement of lossy matching which will be studied in the back.In part of implementing, first, the impact on the matching performance caused by the change of antenna's impedance is given in the form of the change of transform power gain and voltage standing wave ratio. A case study is made to show the reason that lossy elements is used in matching. Then, after the objectives of lossy matching being given in the form of the S parameter of two-port network, the problem caused by using lossy element is brought forward. Finally, element value optimization for prescribed circuit by using genetic algorithm validates the function of lossy element. The tradeoff between transform power gain and voltage standing wave ratio on the premise of giving resister and Pi attenuator using the NSGA-II, will provide more choice for designers.The application of lossy matching technology to antenna broadband matching is provided elementarily, where many problems still exist. However, it offers a new method for matching circuit to adapt to the change of antenna impedance, which holds guide not only for the matching circuit of antenna, but also other kinds of broadband matching.