Study On Digital Beamforming Algorithm In Broadband Anti-jamming Antenna

With the advancement of science and technology,as well as the development of the times,array antenna technology has become one of the key technologies that determine the national defense industry,aerospace exploration,and the benefits of the people's livelihood.Anti-jamming antenna,as a main field in array antenna technology,has become a research focus.In addition,the digital beamforming(DBF)of broadband anti-jamming antenna is an important part of array signal processing.Its essence is to change the array power pattern by adjusting the weights of each array element signal in array antenna,so that the main lobe of the beam points in direction of the desired signal,and the null point is aligned with direction of the interference signal.This technology is widely used in radar and wireless communications,and has expanded from military applications to the civilian market,which has enormous research value and development potential.Radar and communication systems generally transmit and receive narrowband signals.However,with the advancement of technology,broadband signal systems have become one of the development targets of anti-jamming antennas with their unique advantages.Therefore,this thesis centres on studying the digital beamforming algorithm in broadband anti-jamming antenna.The research content mainly includes four parts as follows:(1)Compared to narrowband signals used in traditional radar and communication systems,the broadband system requires array antenna to transmit and receive broadband signals.The amplitude and phase changes of the array signal should be rigorously considered that cannot be ignored.Therefore,the array signal mathematical model constructed under the broadband system is not the same as the traditional narrowband signal mathematical model.In order to facilitate the analysis and description of the algorithm,the uniform linear array is taken as array antenna model,based on which the mathematical model of the broadband array signal is further established.(2)The common algorithm is first introduced and analyzed as a theoretical basis before expatiating the broadband anti-jamming antenna digital beamforming algorithm studied in this thesis.This mainly involves algorithms based on space-time structure and space-frequency structure.The broadband DBF based on the space-time structure adopts the tapped delay line structure to perform beamforming through space-time two-dimensional filtering algorithms adapted to it with different criteria.There are two types of broadband DBF based on space-frequency structure: ISM algorithm and CSM algorithm.This thesis focuses on the algorithm based on space-time two-dimensional structure.(3)The traditional broadband anti-jamming DBF algorithm based on space-time two-dimension structure has obvious deficiency in engineering implementation.Considering that,a broadband anti-jamming DBF algorithm based on digital delay filter architecture is proposed.In this new design scheme,delay filter is used to compensate the received broadband signal data at first,making it equivalent to the incident direction perpendicular to the array plane.Then,the space-time anti-jamming filtering algorithm based on LMS iteration(Frost algorithm)is used to complete beamforming that does not require matrix inversion operation.The simulation results have shown that the new algorithm can align the main lobe to the desired signal and null point to the interference signal under the broadband signal system.It can maintain high gain for the desired signal and effectively suppress the interference signal.At the same time,it reduces the computational complexity of algorithm.(4)For the DBF algorithm and architecture of the broadband anti-jamming antenna proposed above,the premise of implementation requires broadband array signals be delayed by digital delay filters.Therefore,the design method of digital delay filter has been studied in this thesis.Although the structure of the common digital delay filter is simple,its coefficient update is insufficient to meet the requirement of the delay change in actual environment.This thesis studies the digital delay filter based on Farrow structure,which can be more flexible and efficient to delay filtering,improve the delay accuracy,reduce the amount of calculation,and be easy to implement on the hardware platform.In addition,a weighted optimization method for solving the Farrow filter coefficients is proposed in the thesis to further improve filter performance.