Research On Near Field Beam Pattern Control Technology Based On Thinned Array

Near field beam pattern control technology is capable of adjusting the emitted energy of the antenna array to the specified focal point,and it has been extensively applied in microwave biomedical hyperthermia,wireless power transmission,RFIDs,remote sensing etc.When the antenna array is working in radiation near field,the far field hypothesis is not appropriate in the research process.It is necessary to build the near field model and conduct the research and simulation for the near field antenna array.In order to improve the performance of near field antenna array and synthesis the focal beam pattern and shaped beam pattern in near field region,the design of freedom is normally raised by increase the number of elements,then the radiation energy can be adjusted.As the number of array elements increase,it will increase system overhead and the difficulty of array designing vastly.Thus,there are rich prospects in research of near field beam control.In this paper,the near field beam response control and thinned array design are studied as follows:1.Two different mathematical models of the near field antenna array based on array signal processing theory and antenna array theory are studied in this paper.The diversity of these two models is explained through theoretical analysis and simulation,and the model based on the antenna array is selected as the basis of the research on near field beamforming because it gives the correct feedback on the focus shift phenomenon in the distance dimension.2.A near field array response control algorithm based on the adaptive beamforming is presented in this paper.The proposed algorithm is inspired by the compose of the optimal weight vector in adaptive beamforming.The designed weights are constructed as an iterative form to achieve flexible response control at an arbitrary near field position,and the global beam pattern control can be achieved in this way.For better beam performance,the maximum white noise gain criterion is established to design weights,then the low sidelobe and shaped beam pattern can be gained.The good focal performance of the proposed algorithm is demonstrated through multiple sets of simulation experiments and the comparison against traditional beam pattern control methods.3.The genetic algorithms and the greedy search algorithm and their modified versions are applied in the design of thinned array.A probability learning method is introduced to improve the convergence performance of genetic algorithm,and the pattern search algorithm is adopted to improve the search efficiency.The uniform array is thinned under the premise of constant thinning rate to minimize the side-lobe performance loss,some simulation experiments are carried out in this paper.4.The beam pattern control algorithm and array thinning method proposed in this paper are applied on 2.4GHz 5 by 5 and 80 MHz 41 by 41 plane antennas.The design of the low side-lobe focal beam pattern is realized under the premise of qualified thinning rate of 70%,and simulation experiments are carried out to show the performance on the low side-lobe of the joint design method at the cost of partial performance loss of the main-lobe.