Genetic Algorithm Theories And Applications In Electromagnetic Engineering

ABSTRACTThis thesis investigates the theories and applications in EM engineering of Genetic Algorithms (GAs) The distribution symmetry of the offspring individuals in the Continuous space is indicated by ana~yzing the characteristics of the one-point crossover operator which operates on the binary coded chromosomes The similar analysis also demonstrates that the Gray coded offspring individuals have the same distribution symmetry , and additionally show the behavior of shifting from the parent individuals paralletly . This car. explain the claims that the Gray code showed better characteristics than the binary code in some applications reported by some literature . Additionally , the possibility characteristics of the binary and Gray coded offspring is analyzed rigorously for the one-point crossover operation ,with the conclusion that the offspring individuals have the tendency to distribute in the area adjacent to the parents . To overcome the shortcomings of low computational effectiveness and weak local search abilities of the GAs ,a hybrid GA composed of the SGA and the simplex method is presented and applied to the optimal design of the broadband stepped impedance transformer with some satisfactions .A study also has been made of the real coded GAs and a novel real coded GA is proposed .The performance of the present real coded GA has been compared with that of the SGA in optimizing several test functions ,and outperforms that of the SGA with higher efficiency and robustness.The thesis applies the GAs to the design of the stepped impedance transformer. Firstly , a transformer with a complex impedance load is designed by the GAs , which has a performance far better than that achieved by the conventional synthesis design. Secondly, a fixed length transformer is designed with an excellent performance compared with that derived by the one-quarter wavelength Chebyshev synthesis. Thirdly, a complex transformer is designed by the GAs to match four complex impedance loads (varying with frequency) and a real impedance.A 2-D coded GA is proposed to design the matching network composed of lumped components . The topology and component parameters of the matching network are optimized simultaneously . The network optimized by employing the 2-D coded GA shows better frequency response compared with the network synthesis method and the real frequency methodThe thesis also employs the GAs to microwave measurement . Firstly , the GAs are applied to calibration of the six-port reflectometer . Though the measurement accuracy is a bit low only four reflection standards are required in the calibration procedure , which is suited for the engineering applications . Secondly, the GAs are used to measure the complex dielectric perrnittivity of the layered lossy mediums. In the case of less layers, the complex dielectric permittivity and the lengths of the mediums can be evaluated simultaneously...