Study On Mainlobe Interference Suppression With Coherent Frequency Diversity Array Radar

With the continuous development of modern intelligent electronic jamming technology,new electronic jamming technology continues to appear.The form of electronic jamming is becoming more and more complex,which poses a serious threat to the survival and efficiency of radar system.In particular,the deceptive electronic jamming from the mainlobe direction has high similarity between the jamming target and the real target,and the incoming wave direction is the same as the target direction,resulting in the serious deterioration of the performance of phased array radar.The frequency diversity array radar forms a space-time coupling transmission pattern by introducing the step of transmission frequency,which provides the characteristic information of distinguishing the real target from the forward jamming at the transmitting end,greatly increases the flexibility of radar signal processing,and has important application value in radar anti-jamming.Taking the coherent frequency diversity array radar as the research object,this paper studies the range delay forwarding deceptive mainlobe interference suppression and the design of two-dimensional matched filter,mainly including:1.The basic knowledge of coherent frequency diversity array radar is introduced.Firstly,the signal model of coherent frequency diversity array radar is introduced.Through simulation and analysis of the characteristics of the transmission pattern of the model,it is pointed out that the amplitude response and phase response of the transmission pattern are related to the distance / time and angle variables,that is,the transmission pattern contains the information of distance(time)dimension and angle dimension.Secondly,the common beamforming technology is adopted at the receiving end to obtain the transmit receive joint pattern.Because the transmit pattern has the characteristics of space-time coupling,fast time matched filtering and equivalent transmit beamforming cannot be carried out independently.Therefore,the angle time two-dimensional matched filtering function under the coherent frequency diversity array radar system is introduced.The transmitted signal of the baseband(frequency modulation)and the continuous wave(frequency modulation)is composed of both the transmitted signal of the baseband and and the filtered signal;Finally,the angle time two-dimensional fuzzy function is introduced.Through the fuzzy function,the performance of two-dimensional matched filter processing and the influence of array element spacing,array element number and frequency step on spatial defocus can be analyzed,which is convenient to guide the design of matched filter and reasonably select the value of each parameter.2.The separation method of real target and mainlobe interference in coherent frequency diversity array radar system is proposed.Firstly,the working principles of digital RF storage technology and range gate towing technology are summarized,and the technical means of jamming machine transmitting mainlobe range deception jamming signal to realize range towing are described in detail;Secondly,the principle of range deception of radar by jammer in the acquisition stage of towing is analyzed.It is concluded that even if the mainlobe jamming signal and the real target signal are in the same range gate,the real distance between them is still an integer multiple of the maximum unambiguous range.In view of the coherent frequency diversity array radar system,the equivalent transmission pattern after beamforming at the receiving end contains range dimension information.After analysis,it is concluded that the difference between the real target signal and the mainlobe interference signal after angle time two-dimensional matched filtering will be reflected in the distribution of the equivalent angle dimension,and the mapping angle has the phenomenon of diffusion.At the same time,it is pointed out that when the incident angle is known and the radar parameters are determined,the mapping angle of the real target and each mainlobe interference and the central angle of the diffusion region can be calculated,and it is pointed out that the rational design of the frequency step is the decisive factor to realize the separation of the two.3.In view of the predictability of the mainlobe interference in the equivalent angle dimension,a design method of angle time two-dimensional matched filter based on parameterization is proposed.Taking the real target and the central angle of the angle diffusion region of the mainlobe interference mapping angle as a priori information,an angle time two-dimensional matched filter for suppressing the mainlobe interference can be designed.In order to suppress the deceptive interference of mainlobe distance,four design methods of angle time two-dimensional matched filter are proposed in this paper: the design of angle time twodimensional matched filter based on Chebyshev weighting processing;Design of angle time two-dimensional matched filter based on linear constrained minimum variance(LCMV)algorithm;Design of angle time two-dimensional matched filter for angle time two dimensional weighting processing based on LCMV algorithm;At the same time,aiming at solving the problem of mapping angle diffusion after angle time two-dimensional matched filter more effectively,a design method of angle time two-dimensional matched filter based on second order cone programming(SOCP)technology is proposed.By constraining the expected direction as the maximum response,the level constraint is applied to the mainlobe interference mapping angle,so that the equivalent angle region corresponding to the expansion of mainlobe interference has a lower response.Through the transformation of objective function and constraint vector,the original problem can be expressed as a secondorder cone programming problem.