| In recent years, with rapid development of modern mobile communications, satellite communications, wireless local communications and a variety of military and civilian radar,the demand of the antennas which is one of the essential components of wireless communication systems increases. Due to more perfect functions of the wireless communication system, communication systems, they often require a system to set up variety of transmitter and receiver antennas. In addition, in order to meet the requirements of high-capacity, multi-function, ultra-wideband integrated information, we often need to consider with reducing the costs, weight and size. Therefore, MEMS (Micro-Electro-Mechanical Systems) reconfigurable antennas became one of the main antennas'studies.MEMS reconfigurable antennas, emerged in recent years, are a new field of antenna technology. This antenna can alert its key parameters, such as frequency, radiation pattern, polarization, radar cross section and the input impedance and so on, by non-mechanical means but controller manner, such as MEMS switches. In this way, it can adapt to different circumstances the electromagnetic environment by non-mechanical means. There commonly are frequency reconfigurable, pattern reconfigurable, frequency and pattern reconfigurable, and the polarization reconfigurable and so on. This antenna is compact structure, less interference, small multi-path propagation effects, multi-mode multi-band and small size. So this antenna is widely used in the wireless communication system.This paper designs reconfigurable antennas based on MEMS switches. The main thesis is as follows:Firstly, researching significance and background is summarized and work to be done in this paper is clarified. Micro-strip reconfigurable antennas are designed because of their advantages. Therefore, the theoretical foundation of micro-strip antennas is introduced in the second chapter, including the main structure, parameters, advantages, analytical methods and feed modes.Secondly, this paper studies on the structure and principles of MEMS switches, selects the appropriate model, and analyze the transmission characteristics parameters of MEMS switches. Through comparing MEMS switches with traditional switches, its advantages and disadvantages are listed.Then, a second antenna design suitable for polarization reconfigurable is presented. This paper elaborates polarization reconfigurable antenna's basic principle and the key technologies, then designs a annular-ring micro-strip working in 2.4 GHz. The antenna is an annular-ring micro-strip with simple structure with single probe feed. Results demonstrate that both sense left hand and right hand circular polarization (RHCP/LHCP) can be achieved using this technique by loading two long rectangular ear pieces on the mutual orthogonal directions of the annular-ring micro-strip through the MEMS switches. The polarization diversity antenna can work in left hand circular polarization (LHCP) or in right hand circular polarization (RHCP) mode by changing the switches'states.Finally, this paper also studies the frequency reconfigurable antenna. We research and analyze the antenna's equivalent model and radiation characteristics, then propose a novel frequency reconfigurable micro-strip slot antenna. The twists antenna loads MEMS switches to achieve a good frequency adjustable features, and can switch its operation band in GSM 900, DCS 1 800, PCS 1 900 and the GPS band. The antenna structure makes the antenna more compact, reduce the antenna size. Simulation results can basically meet the design specifications in all operation bands.At the end, the thesis is summarized. |
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