| Researches on reconfigurable antennas with planar structures have been done, and several schemes of reconfigurable antennas are presented in this dissertation. This work shows potential applications of reconfigurable antennas.In Chapter 1, advances in the study of reconfigurable antennas started at the end of 1990s are introduced systematically. In order to increase the capabilities of wireless integrated information systems and widen their bandwidths, the concept of reconfigurable antenna is presented. One of the key technologies in the researches on reconfigurable antenna is microelectro-mechanical system (MEMS) technology. At present, this work is still at the beginnings, and much unknown domains need to be explored, so it is a challenge to do researches on reconfigurable antennas.In Chapter 2, mechanism of rectangle microstrip reconfigurable antenna is analyzed thoroughly. From the analysis, we draw a key conclusion that rectangle microstrip reconfigurable antenna can have good reconfigurability when the side length is greater than or equal to one operating wavelength, that is to say that the antenna operates with the higher modes.In Chapter 3, size reduction techniques for microstrip antennas are summarized systematically. A frequency reconfigurable antenna with size reduction technique is presented and a reconfigurable feeding network is also used to conveniently obtain a good impedance match performance. The results demonstrate that the antenna is capable of shifting its operating frequency over a one-octave bandwidth from to with the radiation pattern essentially unaffected by the frequency tuning and the size of the antenna is only a half compared with the traditional antenna at the lowest operation frequency point. Based on a systematic analysis of bandwidth enhancement techniques for microstrip antennas, another frequency reconfigurable antenna with a shape of "E" is proposed. The antenna can operate in two states and shift the operation frequency band between and as the state is changed. Furthermore, for each state this antenna has good co-pol radiation characteristics. The impendence match bandwidths of the two operation states are 35% and 47%, respectively, the latter one is also the best result reported up till now.In Chapter 4, characteristics of electromagnetic fields in periodic structures are introduced. A CPW leaky-wave antenna is analyzed in detail, and based on this work a pattern reconfigurable antenna is presented. The CPW reconfigurable leaky-wave antenna can operate with a single mainbeam at . This antenna can scan over the whole upper space by reconfiguring the perturbation period and using two feeding ports. To fast and precisely determine the phase constant of the fundamental spatial harmonic wave, the finite-difference time-domain (FDTD) method combined with Floquet's theorem is used successfully. In order to overcome the disadvantage that uniform periodic structure can only obtain large scanning angle steps, mixed periodic structures are presented. A kind of modified scheme to eliminate the intrinsic transmission stopband of this periodic leaky-wave antenna is also presented. These techniques are the key ones to make the reconfigurable antenna scanning over the whole upper space with small angle steps.In Chapter 5, a scheme of microstrip reconfigurable antenna is presented, and then a frequency and pattern reconfigurable antenna is optimized by using the FDTD method in conjunction with genetic algorithm (GA). The design results indicate that this antenna can reconfigure the operating frequencies and radiating patterns over an ultra-wide band. These research results have important reference value for future research on "one does it all" antenna. At last, a pattern reconfigurable antenna is optimized and designed by using the FDTD method combined with GA. A capability of pattern scanning in single plane can be achieved by using three switchable states at the frequency of .In Chapter 6, potential development directions and some possible key techniqu...
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