Study And Design On Dual-band Circularly Polarized Microstrip Antenna

With the development of the communication system, microstrip antenna is playing an increasingly important role in modern communication system. As the one of the vital components in communication system, the whole communication system has been influenced by the performance of the antenna. However, with the constant progress of science and technology, more stringent requirements of the microstrip antenna have been proposed due to the demand for more sophisticated and more high-end devices. Many researches have been done so that a various forms of microstrip antenna with different functions appeared. Multi-band technology in the terminal equipment has played a very important role. Owing to the merits of its ability to provide more flexibility in the orientation angle between the transmitter and receiver antennas than linearly polarized radiation from personal wireless communication to space-based applications, circularly polarized antenna is widely used. Thus, the dual-band circularly polarized microstrip antenna is the main topic in this thesis.Based on the research achievements at home and abroad, the basic concepts and work principles of circular polarization were briefly introduced. A circularly polarized microstrip antenna, a dual-band microstrip antenna and two dual-band circularly polarized microstrip antennas are presented in the paper.Based on the basic concepts and work principles of circular polarization, a circularly polarized broadband microstrip antenna loading rectangular slot with coaxial feeding is proposed. With rectangular slots inserted into the lower patch, the circularly polarized electromagnetic wave can be radiated. Simulation results show that the good wideband characteristics are presented with its-10 d B impedance bandwidth achieving 31.21% and the 3d B Axial Ratio(AR) bandwidth covering about 15.32 % of the bandwidth. With the wide bandwidth, a small size, a simple and flexible structure, it can be widely used for various wireless communication applications.A novel E-shaped microstrip antenna is realized by changing the patch surface current path. The simulation results show that the-10 d B relative bandwidths of the antenna are 6.26% in the lower band and 19.13% in the higher band, respectively. Compared with the conventional microstrip antennas, it shows a higher bandwidth, a good performance and a simple configuration.Two dual-band circularly polarized microstrip antennas are fed on the basis of aperture coupled feed. The dual-band circularly polarized annular slot antenna for wireless local area network(WLAN) application is proposed completely covering the WLAN 2.45/5.8GHz bands. The dual-band circularly polarized wave can be produced by the outer annular slot loading the rectangular slot in the four corners. The-10 d B impedance bandwidths and 3d B Axial Ratio bandwidths are 30.81% and 12.42% in the lower band and 14.96% and 1.99% in the higher band, respectively. The second dual-band circularly polarized microstrip antenna is proposed due to the first dual-band circularly polarized microstrip antenna without ideal pattern in the higher band. Left hand circular polarization(LHCP) in the lower band and right hand circular polarization(RHCP) in the higher band is proposed. The dual-band circular polarizations are achieved by adopting two rectangular patches with different rotation angles on the front and back of a substrate. The-10 d B impedance bandwidths and 3d B Axial Ratio bandwidths are 18.43% and 3.21% in the lower band and 12.45% and 1.79% in the higher band, respectively. The proposed antennas with their simple structure, compact size, low cost and excellent performance could provide the reference for communication system applications.