Research On Optimal Array Layout Of Small Heterogeneous OTH Radar

The main transmission medium of sky wave Over-The-Horizon(OTH)radar is the ionosphere.It is a kind of radar that uses the refraction of ionosphere to high-frequency electromagnetic wave to detect targets outside the line of sight.It has the advantages of long detection distance,wide detection range and low cost in long-range early warning.It has an important strategic position in the fields of air defense,early warning and monitoring.In the research of OTH radar,jamming suppression,waveform design and optimized array layout have always been regarded as important research directions.Therefore,how to suppress jamming at low cost,how to automatically generate high-performance pattern and how to arrange arrays to optimize array performance have become urgent problems to be solved.As two very important branches of array signal processing which are widely used in communication,radar and other fields,beamforming and sparse array can be used to solve the above problems.The main research contents of this paper are as follows:(1)Traditional OTH radars generally use complex weighting to suppress interference,that is,to control the phase and amplitude at the same time.However,this traditional interference suppression method will bring high cost.In order to reduce the cost of interference suppression,a phase only technology is proposed,that is,the ideal beam can be generated only by controlling the phase.Combined with the principle of Kronecker decomposition,an interference zeroing algorithm based on the arrangement of phase shifter is obtained.Based on the arrangement of phase shifter,the concept of Kronecker array and the control idea of sidelobe level are proposed.(2)For OTH radar pattern,the narrower the mainlobe width is,the stronger the radiation capacity in the mainlobe direction is.In the shape optimization,once the mainlobe width is not set well,it may not be able to generate a good pattern directly.In order to solve this problem,using the idea of relaxation optimization,a shaped pattern algorithm which can automatically generate the minimum mainlobe width is proposed in this thesis.(3)In the pattern of sparse OTH array with uniform layout,the phenomena of grating lobe and coupling often appear.In order to solve this problem,this thesis proposes a novel method based on the sparse direction independent Hankel matrix,which does not need to be based on the principle of sparse array.(4)For the traditional oth array with uniform layout,a classical optimization method is based on l1 reweighted sparse array layout algorithm.By introducing and reproducing the algorithm,the concept of“array element selection" for optimizing the excitation of each array element is introduced.However,the simple array structure of the traditional one-dimensional OTH array will restrict the performance of the radar and can not take into account the effects of pitch angle and azimuth angle at the same time.Therefore,the two-dimensional OTH array came into being.The two-dimensional array can carry out omni-directional scanning and expand the scope of the radar.At the same time,the two-dimensional beam performs better in space anti-jamming and ionospheric propagation pattern recognition.For the optimal layout of two-dimensional OTH arrays,this thesis proposes an optimal array layout algorithm based on 0/1 constrained array element selection,and realizes the sparse array layout in L-array and Y-array.Taking an OTH subarray as a whole as an array element and constraining the overall excitation of each subarray by 0/1 variable,the subarray selection method expanded by array element selection is obtained.The layout selection in one-dimensional direction and rotation angle selection in fixed position are carried out for the same type of subarray.(5)For the optimal layout of two-dimensional heterogeneous OTH arrays with more flexible layout and higher degree of freedom,this thesis still adopts the previous subarray selection method,considering a heterogeneous array composed of L-shaped subarray and Y-shaped subarray at the same time.Firstly,the layout position of each subarray is optimized,and then the rotation angle is introduced to realize the joint optimization of the placement position and angle of the subarray,Finally,expand the selected dimension to the two-dimensional plane for selection.