Investigation Of Reconfigurable Microstrip Antenna

Researches on reconfigurable antennas based on microstrip patch antenna have been done, and several schemes of frequency reconfigurable and frequency-polarization reconfigurable antennas are presented in this dissertation. Antennas are necessary and critical components of radar and communication systems. Its performance determinates the communication quality. Rapid development of the wireless communication technologies raises greater demand of antennas. The reconfigurable antennas attract more and more attentions for their multi-functionality and the ability of adapting with changing system requirements or environmental conditions. The major achievements are listed as follows:Firstly, the state-of-arts on reconfigurable antennas are described. Some primary reconfiguration mechanisms of reconfigurable antennas are discussed. Based on the theoretical analysis of antenna operation, the linkages between frequency response and radiation characteristics are revealed. Consequently, this linkage is critical challenge on reconfigurable antenna research as designers prefer the antenna operation characteristics to be separable.Secondly, the effect on the operation frequency of shorting pin loaded on the microstrip antenna is analyzed. Based on this analysis a novel shorting pin loading frequency reconfigurable antenna (SLFRA) whose operation frequency can shift between two bands with wide frequency ratio is presented. With a reconfigurable tuning stub and the microstrip coplanar feeding structure the shortcomings of the SLFRA can be overcome effectively and a 3.2 frequency ratio between the two operation frequencies is obtained. As a further improvement, a slot and a varactor diode are loaded on the SLFRA. The loading effects are discussed. As a result, the operation frequency of improved structure can be tuned in a small range around each swithing band.Thirdly, a novel reconfigurable antenna with both frequency and polarization diversities is proposed. Using four pin-diode switches on a square patch, the antenna can operate either in linear polarization (LP) state or in a pair of orthogonal circular polarization (CP) states at two distinct frequency bands. The frequency bandwidths are improved by using a capacitive gap. Experimental results show that good performance is achieved. This novel antenna can be a good candidate for future frequency and polarization diversity applications in wireless communication systems.At last, the characteristics of compact CP microstrip antenna with inner square slot loaded are analyzed. Based on the reconfigurable antenna element provided in chapter 3, a two-element reconfigurable array with a novel topology is presented. This compact array design operates as a dual-band antenna with an inner and an outer reconfigurable antenna element while occuping only one element space. Even and odd mode analysis method is used for analyzing the coupling effects between the two array elements. And the simulation results prove the analysis conclusion. This novel array design solves the problem caused by the linkage between frequency response and radiation characteristics. This scheme is a good choice for achieving compound renconfigurable antennas with separatable frequency and radiation characteristics.