Research And Design On Freqeuency Reconfigurable Antennas

Compact, low cost and broadband electrically small antennas is an efficient way to satisfy the requirement of highly integrated miniaturized systems to support multiple applications in modern electronics and wireless communications. Observing the relationship between bandwidth and size of the antennas, traditional bandwidth enhanced technologies fail to miniaturize antenna and wide band antennas have some disadvantages. Frequency reconfigurable antennas with a relatively narrow impedance bandwidth of the operating frequency provide an alternative solution for the before mentioned problems. At present, the research of this realm is still at the beginning and there are many unknown domains need to explored. The research and analysis on frequency reconfigurable antennas have been accomplished and some antennas have been designed in this work.Firstly, the background and the domestic and international status of the frequency reconfigurable antennas are briefly analyzed and summarized; then briefly introduce the basic parameters evaluating antenna performance and the processes of genetic algorithms in antenna design.Secondly, according to the classic transmission line theory, the applications of the antennas using metamaterials are analyzed as well in this work; then explore the special quality and the design method of the epsilon negative transmission line, given the realization of the program and design process of the frequency reconfigurable antennas. Based on those technologies, a compact reconfigurable internal antenna for mobile handset applications is proposed. The feature of the antenna was simulated for different values of capacitor controlled by a DC voltage source. Simulation results show that the required frequency can be tuned nearly from1.8GHz to2.6GHz with the return loss below-10dB. Overall size of the antenna is35mm*8mm*0.8mm. The overall shape of the radiation patterns and electrical performance are suitable for mobile handset applications. Simulated results verify the feasibility of the proposed antenna.In the last part, the radiation mechanisms of the planar monopole antenna are analyzed, and then discuss the property of several feeding methods. A resonant antenna based on inductively coupled is designed. By explore its equivalent circuit model; a compact frequency tunable antenna with impedance matching is proposed using one varactor. The simulated and measured results show that the proposed antenna can achieve a frequency ranging about from1.8to2.19GHz with the maximum return loss of-20dB. Antenna maintains good antenna impedance matching. After improve the antenna structure, a wide frequency tunable planar antenna with two varactor diodes is proposed. Adjusting one of the varactor diodes can control the resonant frequency sensitively, and adjusting the other one can solve the impedance mismatching problem while the resonant frequency varied. Therefore, the winder the range of the working frequencies and the size of the antenna is smaller. The simulated and measured results show that the measured tunable frequency varies from1.39GHz to2.59GHz when return loss is lower than-20dB. Apparently, the tuning range is about1.2GHz and the ratio of the frequency is about1.87:1.