Research On Frequency Diverse Array Transmit Beam Control Technology

Phased arrays have been widely used in modern radar systems.Compared with phased arrays,the Frequency Diverse Array(FDA)differs in that each array element uses a different transmit signal carrier frequency.On the basis of the original carrier frequency,each element of the FDA is added with a small frequency offset,which makes the FDA beampattern correlate with the angle as well as the transmission distance.In view of the new distance-related characteristics of the FDA,the transmit beam control technology is deeply studied.At the same time,considering the frequency offset error of the FDA,the influence of the error on the beam is evaluated and the robustness design for FDA is carried out.The research focus of this thesis includes the following aspects: jamming application,focusing method,frequency offset error analysis and optimization.The main work and innovations are as follows:(1)Transmission control method for FDA Jamming beam: A S-shaped jamming beamforming method is proposed to jam multiple enemy targets in a specific region at a specific time.Arbitrary controllable beam width,steepness of beam edge and beam amplitude can be achieved in different directions.By using the beam to change with distance,the interference signal is radiated to the enemy target,thereby realizing effective interference and improving its concealment.For engineering verification,this thesis presents the concrete realization method of S-shaped interference beamforming and carries out simulation analysis.(2)Transmission control method for FDA focusing beam: A constrained nonlinear programming model is established for the distance-angle coupling problem in the conventional FDA beam.The distance-angle decoupling beampattern is generated by optimizing the frequency offset parameters,and the energy focusing effect of beampattern is improved.In addition,considering the time-varying of the FDA beam,the statistical analysis and numerical examples of the time-invariant beam scheme based on time modulation are used to prove the ineffectiveness of the invariant focus transmit beam control for FDA.(3)Robust transmit beam control method for FDA: Firstly,aiming at the influence of frequency offset parameter error on the transmitting beam,the interval model of the transmitting beam is established by interval mathematics method,and the upper and lower bounds of array steering factor and power pattern function are deduced.The performance degradation of the transmitting beam caused by frequency offset error is analyzed.Secondly,based on the semi-definite relaxation technique,the problem of robust beamforming for FDA is modeled as a quadratic programming problem with quadratic constraints.The expression of signal power is derived and the approximate rank-1 solution is calculated by iterative convergence.The optimized beamforming method has lower sidelobe level under the same frequency offset error.