Echo Modeling And Waveform Design Technology Of Airborne Distributed Array Radar

Nowadays,advanced science and technology are developing rapidly,and the electromagnetic environment is changing rapidly.The detection performance of airborne radar using the down-view working mode is seriously affected by ground clutter and jamming signals.How to effectively suppress clutter and jamming to improve the detection performance of airborne radar is an urgent problem to be solved.Distributed subarrays antennas radar is a radar system composed of multiple spatially dispersed small aperture subarrays.Combined with the characteristics of the airframe structure,the flexible use of distributed array layout can further improve the power aperture product,push forward the detection range and improve the target positioning accuracy.In the context of large-scale arrays,the use of distributed arrays is different from ordinary arrays.In addition,the clutter characteristics are complex.Therefore,it is necessary to establish a refined echo model for distributed arrays and analyze the clutter characteristics in depth.As the carrier of system energy and information,the transmission waveform design is an important means to improve the overall performance of airborne radar.In this thesis,around the airborne distributed array radar,the array-level and subarray-level echo signal models are established,and the waveform design algorithms in different scenarios are studied in depth.The specific work content is as follows:1.The model of airborne distributed array radar echo signal is established.Combined with the characteristics of the distributed array structure,clutter modeling is performed using the Integration of equidistant ring surface scattering elements,and the distributed array echo signal model is derived based on the uniform area array.In order to solve the problems of multiple array elements and large dimensionality of the echo data,a method of subarray partitioning of a distributed array by using pattern gain equivalent is proposed,which improves the modeling efficiency compared with the traditional subarray partitioning method.2.The clutter property is analyzed and the echo data is processed.For the distributed sub-array scenario of airborne radar,an estimation formula for clutter rank is derived based on space-time frequency coupling and virtual aperture relationship.The clutter properties were analyzed in terms of the minimum variance spectrum,Fourier spectrum and the factors affecting the clutter properties.The performance of clutter suppression of non-adaptive and space-time adaptive processing(STAP)algorithms is compared through simulation experiments.3.The joint design of transmitting waveform and receiving filter in clutter environment is studied.The target and clutter signal model of airborne distributed array radar in MIMO mode is presented.A nonconvex quadratic optimization problem with maximum STAP output signal-to-clutter-plus-noise ratio(SCNR)as the optimization objective under constant-envelope constraints is established.The technique of semidefinite relaxation(SDR)and randomization construction and the technique of fractional programming and power method-like iterations were used to solve the nonconvex quadratic optimization problem.Simulation results show that the joint design algorithm has the performance to improve SCNR.4.The design of cognitive waveform and receiving filter in interference environment is studied.The similarity constraint waveform design algorithm is applied to the cognitive waveform design.A more ideal integrated sidelobe level(ISL)signal obtained by the well-correlated waveform design algorithm is used as a model signal to indirectly regulate the sidelobe characteristics of the design signal,and further optimize the waveform design algorithm under similarity constraints.The design algorithm of the mismatch filter under similarity constraints is studied,and the simulation proves that the algorithm achieves the optimization goal.