Fast Electronic Beam Steering By Parasitic Antenna Arrays

Millimeter-wave communications and multiple-antenna systems can solve the problems which are lacking of spectrum resources and system capacity shortage in the next generation communications systems,and also face many challenges.The high-frequency short-wavelength of millimeter wave makes it possible to apply multiple-antenna systems to mobile terminals,but the path loss of millimeter wave is large.Besides,multiple-antenna systems are not suitable for portable mobile terminals with limited battery capacity and small size.In order to solve this problem,it is proposed to apply a special antenna array named parasitic antenna array.These antenna array's structure is very simple,and only have one RF chain,so power consumption is low.Besides it is convenient to achieving beam steering.In order to solve the limitation of multiple-antenna system with the frequency of millimeter wave,the parasitic antenna arrays are used as a model.The aim of the passage is to study the fast beam steering of the parasitic antenna arrays.The parasitic antenna arrays have the characteristics of simple structure,small size of the antenna arrays,low power consumption,low hardware complexity,and strong directivity.According to the load condition of the parasitic elements,the beam steering of the parasitic antenna arrays can be divided into two categories: adaptive beamforming and codebook beam steering.For adaptive beamforming of the parasitic antenna arrays,two algorithms are examined,one is the algorithm named impedance matching and convex optimization,the other is the algorithm named improved minimum variance distortionless response(MVDR).By adaptively changing the load impedance of the parasitic elements,the weights of the antenna array are changed.The value of the vector strengthens the constraint condition so that the algorithm converges and quickly approaches the optimal solution.The beam pattern is directed to the desired direction and places nulls at the interfering directions within a small number of iterations,which improves the signal-to-noise ratio and beam gain.Although the algorithm of adaptive beamforming can achieve fast beamforming,the two algorithms have higher complexity,whereas the other method named codebook beam steering is simple to some extent.In this thesis,the combination of parasitic element states is employed to implement fixed codebook beam steering.The research process is divided into three steps,that is,the most basic axis points to the codebook,the codebook of the five antenna arrays,and the seven antenna array codebooks.The codebook state realizes 5,16,and 64 changes,and realizes the purpose of refining the angle of beam steering progressively.The fixed codebook beam steering antenna has a simple structure and the codebook is easy to i mplement.Through presetting the codebook,accurate and fast beam steering of the antenna array can be realized.Finally,the two beam steering methods of the parasitic antenna arrays are compared to draw conclusions.