Research And Design Of Wideband Pattern Reconfigurable Antennas

With the rapid development of modern information technology,the wireless communication system needs to adapt to more and more complex and changeable application scenes,which requires the antenna to be miniaturized,multifunctional and easy to integrate.The reconfigurable antenna can integrate multiple functions on one single antenna,which puts forward an effective solution to improve the performance of communication systems.A pattern reconfigurable antenna is able to change the direction of its radiation pattern according to the external environment.By directing signal to the expected radiation direction,it can meet a variety of communication requirements,reduce the noise interference and improve the stability of the system,which have attracted more and more attention from domestic and abroad researchers in recent years.Based on the application requirements of pattern reconfigurable antennas,this thesis conducts in-depth research on pattern reconfigurable antennas with broadband performance.The specific contents are as follows:1.A wideband omnidirectional and directional pattern reconfigurable antenna based on the metasurface is designed.The antenna consists of the metasurface,metal ground and feeding network.Firstly,the characteristic mode theory is used for the analysis of the metasurface,which obtains two characteristic modes with directional and omnidirectional radiation patterns.However,the pattern performance will deteriorate at high frequencies.By analyzing the change of characteristic current with frequency,we can improve the matasurface,so that the pattern of the two characteristic modes can be stable over a wide band.Then,according to the analysis of the characteristic current distribution on the metasurface,the feeding network is designed to excite the above two modes selectively.An omnidirectional and directional pattern reconfigurable antenna is realized.The two working states of the antenna cover the frequency range from 5.08 to 6.29 GHz,with an operating bandwidth of 21.4%.In the operating band the isolation of two port is better than 18 d B.The peak gain of omnidirectional and directional working states is respectively 4 d Bi and 6.8 d Bi.The proposed antenna has a wide operating bandwidth,low profile height(0.07,is the free space wavelength at the center frequency),and simple structure.2.A wideband pattern reconfigurable antenna based on dipoles is designed.The antenna consists of a feeding network,radiation structures,parasitic structures and a reflecting plate.The main radiation structure of the antenna is four folded dipoles.Each dipole is excited by the corresponding wideband balun,and a PIN diode switch is loaded on each balun,which forms a reconfigurable feeding network.By controlling the states of PIN diode switches,different dipoles can be excited.Thus,the radiation pattern can be changed.Four parasitic structures are used to optimize the bandwidth and pattern performance,and a reflecting plate is added to improve the gain of the antenna.Finally,four kinds of maximum beam directions are achieved in three-dimensional space.Simulation results show that the antenna covers the frequency range from 3 to 5.2 GHz,with an impedance bandwidth of 54%.The average gain in the operating band is about4 d Bi.The proposed antenna has excellent bandwidth performance.