Study Of Reconfigurable Antennas

In order to increase the capabilities of wireless integrated information systems and widen their bandwidths, the concept of reconfigurable antenna is presented. At present, the research of this realm is still at the beginnings throughout the world, and there are many unknown domains need to be explored. Thus the research on reconfigurable antennas is a challenging task. In this dissertation, thorough researches on reconfigurable antennas have been accomplished, and several design schemes of reconfigurable antennas are presented. This work demonstrates great potential application prospects of reconfigurable antennas. The author's major contributions are as follows:1. In the design of frequency reconfigurable monopole antenna, a part of radiation structure is used to provide dc-bias for switches. This method could avoid harmful effects of metallic biasing lines on the impedance and radiating pattern of antennas, therefore could settle difficult problems caused by the dc-bias lines of reconfigurable antennas.2. A printed dipole antenna with wideband frequency agility is designed and fabricated. The frequency-tunable characteristic of the antenna can be obtained by adding two PIN diode switches to the two dipole arms. A frequency shift of 101.3% is achieved from both switches on to both switches off, and the two radiation patterns are close to each other.3. A novel miniaturized microstrip slot antenna with tunable frequency is proposed. Due to adopting a plane spiral structure, the antenna configuration is more compact, and the size is reduced by approximately 40% compared to one of the conventional straight slot antennas. By loading PIN diode switches on spiral slot, the antenna achieves good frequency tuning characteristic. Because these switches are directly located on non-radiation slot, the influence of switches on frequency tuning property of the antenna is weakened obviously, thus the frequency tuning characteristic can be realized more easily.4. A novel microstrip patch antenna with switchable polarization is proposed. The four parasitic truncating corners of the radiating patch of the proposed antenna are connected to ground through four PIN diodes. By controlling the states of the four diodes, the antenna can produce the linear, left-hand circular, or right-hand circular polarization radiation. Due to its own construction, DC-blocking capacitors are not necessary in this design.5. A novel corner-truncated square microstrip patch antenna which can switch between two circular polarizations is proposed. It consists of a square radiating patch and a 3 dB hybrid coupler. By using only a SPDT switch, the polarization switching can be achieved. This design of the dc-bias network is extremely simple. From experimental results, the proposed antenna avoids the frequency offset phenomena which often happened to antennas with switchable circular polarization.6. A novel microstrip patch antenna with switchable polarization is proposed. A dual-feed technique is used to exciting two orthogonal linear modes with equal amplitude. By controlling the states of the four SPDT switches in the feeding network, the phase difference of the two modes can be switched between 0°, 180°and±90°. When the phase difference is equal to 0°or 180°, the antenna generates linear polarization (LP) radiation. And when the phase difference is equal to±90°, the antenna can achieve left-handed or right-handed circular polarization (LHCP/RHCP). For the four different states, the operating frequencies of the antenna are almost uniform.7. By combining genetic algorithm (GA) with the method of moment (MoM), the reconfigurability of a planar frequency reconfigurable wire antenna is investigated. In the process of optimizing the switch configuration on reconfigurable antennas, GA needs to use an analyzing procedure of MoM hundreds of thousands of times. In this dissertation, we regard the switches in reconfigurable antennas as loads, and then utilize fast MoM to accelerate the speed of analysis of antennas. Furthermore, a planar reconfigurable wire antenna is investigated by combination GA with the fast MoM. The results show that the planar antenna has an outstanding reconfigurability from 40 MHz to 400 MHz. Due to employing the fast MoM, the speed of the optimization of reconfigurable antenna is improved greatly.8. A scheme of reconfigurable microstrip patch antenna with pattern agility is presented, and the capabilities of reconfiguration of the antenna are explored by using the method GA conjunction with the finite difference time domain (FDTD) method. The design results indicate that this antenna has good reconfigurabilities of radiation patterns at 5.0 GHz. The reconfiguration range of bothθandφpolarized gain patterns of the antenna from (50°,0°) to (130°,0°) in the x-z plane, and from (50°,0°) to (130°,0°) in the x-y plane has good pattern reconfigurabilities and high polarized gain.9. A scheme of cage antenna with both frequency and pattern agility is presented, and the reconfigurabilities of this antenna are investigated by combining GA with the fast MoM. The design results demonstrate that the frequency reconfigurability of this antenna is from 60 MHz to 1170 MHz when VSWR is below 2.0, and from 110 MHz to 1100 MHz when below 1.1. In the frequency scanning range of 110 MHz-1100 MHz, the antenna can provide beam steering capability with full range by adjusting the switch states.