| The progressing in wireless communications contributes to the developments in antenna design. With the sharply increasing requirements for the data service and the rapid development of integrated circuit technology, developments in antenna are proceeding towards broadband and miniaturization. In the meantime, the Ultra-Wideband (UWB) technologies have received universal attention due to their attractive features such as large information transmission capacity, good security, excellent anti-multipath ability and high data rate. The applications of UWB techniques present myriad exciting opportunities and challenges for antenna design.With the miniaturization and functional diversification of the antenna, the antenna structure becomes more and more complicated. Modern antenna design problems generally involve a large number of parameters. These parameters can be either continuous, discrete, or both, making the design process slow and complicated. The traditional antenna design techniques rely on the engineers'experience to a large extent and can not achieve optimal design. The automated antenna design based on genetic algorithms (GAs) is expected to solve this problem.This dissertation makes a research on improved genetic algorithms and their applications to automated antenna design along with the analysis and design of miniaturized wideband microstrip antennas.1. In this dissertation, based on the analysis of the reason for the premature convergence in genetic algorithm, an improved adaptive GA is proposed and discussed. Then an optimization scheme based on the improved adaptive GA is proposed to perform automated antenna design. A software package for automated antenna design is developed.2. Two novel compact wideband microstrip patch antennas are designed. The optimization software package aforementioned is used here to optimize the parameters of the antenna as a whole, getting the final design. Firstly, the genetic algorithm (GA) is used to design patch shapes for broadband applications. The optimized shape shows a fourfold improvement in bandwidth compared with a standard square microstrip antenna; then, a novel broadband microstrip patch antenna is proposed and reported in detail. To expand the antenna's bandwidth, a U-shaped slot and two shorting walls are incorporated into this patch and positioned symmetrically with respect to the feed point. In addition, capacitance compensation feed technique is introduced to compensate the probe's inductance. The capacitance compensated excitation is achieved by means of a small planar plate mounted on the top of the coaxial probe. The operating bandwidth spans the frequency band from 3 GHz to 5 GHz, determined from 10 dB return loss. The radiation patterns are generally omni-directional over the entire band.3. Two novel compact UWB monopole antenna are presented. The optimization software package aforementioned is used here to optimize the parameters of the antenna as a whole, getting the final design. Firstly, a planar serrated antenna is reported in detail. This antenna has an operating bandwidth ranging from 2.7GHz to 11.5GHz determined from 10 dB return loss. The radiation patterns are generally omni-directional over the entire band; then, a printed quasi-self-complementary antenna is presented. The proposed antenna, which is fed by a CPW, has been demonstrated to provide an ultrawide 10-dB impedance bandwidth with compact size.4. To avoid the interference between the UWB system and the Wireless Local Area Network (WLAN) system, a band-notched UWB antenna is proposed by incorporating a complementary split ring resonator (CSSR) into the radiating patch. The optimization software package aforementioned is used here to optimize the parameters of the antenna as a whole, getting the final design. The CSSR parameters are analyzed in detail based on current distribution. Experimental results demonstrate that the proposed antenna provides a stop band of 5.10 GHz to 5.85 GHz while its 10-dB impedance bandwidth ranging from 2 GHz to exceeding 12 GHz. |
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