Research On Array Scanning And Target Positioning Method Based On Beamforming Technology

Antenna array technology is a technical means to achieve beam energy focusing and spatial scanning,and has been widely used in radar and communication systems.Beamforming steering vectors based on traditional phased array(PA)are angle-dependent functions.An array with a linear frequency offset between transmitted signals is called as Frequency Diverse Array(FDA).The linear frequency offset is set to be much smaller than the carrier frequency.Although the beams of FDA can scan specific space automatically and contain range information that is not in phased array beams,there are limits such as range-angle coupled beam pattern and the periodicity of beams,which affect the performance of FDA beams to obtain range and angle information.Based on the discussion of array transmit-receive principle and array beamforming technology,this thesis studies methods to improve the array beam scanning performance.An array system that can perform beam scanning and multi-targets positioning without requiring prior information about target position is proposed in this thesis.The system uses a nonlinear frequency offset to form a non-periodic scanning beam.In the system,weighted array element amplitudes make the radiated energy more focused on the main lobe.By receive beamforming,the positioning imaging of single target or multi-targets is obtained.The contents of this thesis are listed as follows:Firstly,range and angle scanning performance of transmitted beams is analyzed.The array signal model is discussed and the beam pattern function is derived.Digital Beamforming(DBF)technology and beam pattern synthesis technology are mentioned.Beam patterns of PA and FDA are introduced by array factors.The single-frequency and full-frequency signal receiving methods of FDA are discussed.The transmitted beam pattern is simulated,and parameters affecting range and angle scanning performance are discussed.In addition,suggestions of expanding scanning area and schemes of improving resolution are introduced in this thesis.Secondly,the Frequency Separated Beam pattern Synthesis(FSBS)system in which angle scanning beam and range scanning beam are separated in frequency domain is proposed.The system can design the transmitted signals of array elements by beam pattern synthesis and form scanning beams.The transmitted signal model and receive beamforming method of FSBS system are introduced.Target positioning simulation results are performed to verify the feasibility of FSBS system.The method for improving the scanning efficiency of FSBS system based on multi-beam forming is proposed.Finally,a bistatic system based on Amplitude Weighted Log-Frequency Offset(AWLFO)array is also proposed for far-field target positioning.An AWLFO array is proposed as the transmit array,while a phased array is used as the receive array.The proposed system scans large space and it requires no prior information for the range or angle of targets.Target positioning imaging is obtained through receive beamforming.Simulation results verify the feasibility of the system for single-target and multi-targets positioning.