Sparse Array Synthesis With Controllable Minimum Spacing

Unequally spaced arrays are widely used in sonar detection,satellite communications,radar tracking and other fields,because the nonuniform layout can reduce the number of elements compared with the traditional uniform layout,and effectively suppress the grating sidelobe levels when synthesizing the patterns.However,when considering the structure of the real array antenna,the distance between adjacent elements must be taken into account,otherwise a too small distance will cause a strong mutual coupling effect or be unable to be processed in practice.A few years ago,there was an alternating convex optimization(ACO)method,which was used to synthesize the focused or shaped pattern of a single beam.This method affected the selected element position distribution by controlling the weighting coefficient,thereby realizing the control of the minimum element spacing.However,the situation considered is too simple,just a synthesis of a linear array of isotropic ideal point sources.The work of this paper is based on this method,under the condition of considering the minimum element spacing constraints,a comprehensive and more practical research has been carried out,mainly as follows:1)Under the feed structure of two-segment beamforming networks(BFN),an alternating linear programming optimization(ALPO)method is proposed to synthesize sum and difference pattern.Under the complex constraints of multi-region sidelobes,the sum and difference beam array with minimum element spacing and excitation dynamic range ratio(DRR)control is more efficiently synthesized.Besides,the full wave simulation and scanning function are verified.2)By introducing the weight vector "box" and shifting it to affect the element position distribution,and then constrain the spacing between the elements,thus a planar array with a controllable minimum spacing is synthesized.In addition,the solution of the sparse array element is obtained through the iterative optimization of the grid subdivision,which provides a larger space for the position solution,so that the calculation time in the optimization process will not increase much.After each iteration,the pattern performance can be satisfied,and the number of array elements can be further reduced.3)A refined extended alternating convex optimization(REACO)method is proposed to synthesize a multibeam sparse circular-arc antenna arrays with controllable minimum spacing.In this method,a collective excitation coefficient vector(CECV)and its energy upper bound are introduced for each element.By constraining the upper bound of the energy,the positions of the common element that generate the multi-beam pattern can be found.The CECV vector and the weight vector are used as optimization variables to effectively control the minimum distance of the selected element.In addition,the active element patterns(AEPs)of the array are obtained to approximate nearby element patterns,so that the element position and excitation are updated iteratively,thereby incorporating the mutual coupling effect into the synthesis process.