Beampattern Synthesis Technology Based On Frequency Diverse Array

Compared with phased array radar,frequency diverse array(FDA)radar is a new type of radar system with a high degree of freedom which has more flexible beam scanning characteristics and requires more advanced array signal processing technology.Due to the small frequency offset attached to antenna,the beampattern of frequency diverse array is related to distance,angle and time.Therefore,it has great potential in applications such as interference suppression and radio frequency stealth.There is a coupling between distance and angle in the frequency diverse array under the condition of linear frequency offset.Then the problem of periodic grating lobe radiation is generated,resulting in the inability to concentrate the emitted energy.The proposed nonlinear frequency offset has been able to achieve decoupling,however,due to the needs of functions such as precise positioning,the design about the beampattern of frequency diverse array has a higher standard.In order to form a beampattern with concentrated mainlobe energy and low sidelobe level,under the condition of far-field target,a comprehensive design is carried out for single-carrier frequency diverse array and multi-carrier frequency diverse array respectively in this dissertation.The main research work and innovation points are summarized as follows:(1)The beampattern of pulsed radar is studied in this dissertation,which is based on singlecarrier frequency diverse array.And the influence of functional frequency offset on the beampattern of frequency diverse array is systematically analyzed.In order to minimize sidelobe level and achieve the purpose of focusing mainlobe energy,the observation area is divided and the problem is reduced to an energy distribution problem.Aiming at this problem,an optimization algorithm based on the differential evolution algorithm is proposed to obtain the frequency offset by means of iterative evolution.Taking pulse wave as an example,the optimization algorithm is compared with the genetic algorithm,the interior point method and other algorithms.Simulation results verify that the proposed method can obtain the frequency offset with better performance.In addition,considering that environmental factors may cause frequency offset errors,the influence of small disturbances on the beam pattern is analyzed,and the robustness of the algorithm proposed in this paper is verified.(2)Based on the symmetrical multi-carrier frequency diverse array,the beampattern of frequency diverse array with conventional frequency offset is studied in this dissertation.In view of the problem that the mainlobe width is too large and the peak sidelobe level is high,a frequency offset weight optimization scheme suitable for conventional frequency offset is proposed.The problem is transformed into a nonlinear programming model for solving.By weighting frequency offset function,the mainlobe energy focusing performance and the sidelobe suppression performance are improved.(3)Aiming at the problem about optimizing the beampattern of multi-carrier frequency diverse array,a beampattern synthesis method which is jointly optimized from frequency offset function and array structure is proposed in this dissertation.Firstly,an improved frequency offset function which strengthens the correlation of frequency offset between corresponding antenna and carrier is proposed.Secondly,a method to optimize array structure is proposed.This method achieves the purpose of increasing array elements spacing without generating grating lobes by adding antennas at both ends of the symmetrical frequency diverse array and removing equal amounts of antennas from the entire array.Antennas to be removed are selected by the adjusted greedy algorithm.The simulation results verify that the proposed method can effectively optimize the beampattern of the multi-carrier frequency diverse array.In addition,the change of the beampattern is also analyzed after the system parameters are adjusted.