Study On Sparse Array Meterwave Radar Based On SIAR

The spacial energy is uniformly distributed as the transmitting signals are orthogonal to each other,which are emited simultaneously by MIMO radar.Its theory could be originated from SIAR when the radiated orthogonal signals are in the form of orthogonal phase-coded and frequency-coded to each other.As multiple frequency signals are used,the coherent echo could be resolved;as the array elements are sparsely located,to guarantee obtaining lower sidelobes in the process of synthesizing transmitting and receiving directions,the positions of the elements could be optimized to avoid the effection of the multipath propagation.As a kind of meter-wave radar,it has better performance in anti-and anti-arm,long effectom range,its attenuation is little compared with microwave radar.The meter-wave radar has more geat inspection ability on slow velocity target.But as it has wide beam, the angle resolution is worse than others,its sidelobe is usually high,which prevent the anti-disturb ability.Espacilly when the beam is irradiated on the ground,more than one path multipath echo come into the target echo which great effect the measurement of the target angle.To overcome the above problem,several methods are proposed in this paper,the concrete contents are as follows:1.For the constraints of the number of element,the limited array aperture and the minimum element spacing in both horizontal and vertical dimensions,the optimization of array pattern synthesis in MIMO radar is presented in this paper.To lower the sidelobe level,both the transmitting and receiving patterns should be considered in the MIMO radar where sparse arrays are used.Extending the sparse constraints of regular grid to the constraints of inter-element distances in a plane,an improved multiple genetic algorithm by coding twice is proposed,with which the problem of pattern synthesis in MIMO radar with lower maximum relative sidelobe level is solved effectively.The optimal algorithm used in practical design is presented.The simulated results confirm the validity of this method in this paper.2.A new direction synthetic method for sparse array meter wave radar is presented based on synthetic impulse and aperture radar(SIAR) system.Concerned with the kind radar which simultaneously emits orthogonal signals with multi-carrier-frequency and possesses sparsely distributed transmitting and receiving arrays with respective location,as well as the situation for the presence of multipath propagation in the low flying target's echo,the method form the digital beam-forming(DBF) in azimuth and elevation dimensions.And a study has been made of planar general MUSIC algorithm based on decorrelating the multipath signals of multi-carrier-frequency radar.Through compensating the phase delay of both the transmitting and the receiving arrays and synthesizing the transmitting beam in two dimensions at the receiver,the angular resolution and measurement accuracy are improved and the computational complexity is reduced after transforming the three-dimensional(3-D) parameter estimation problem into a two-dimensional(2-D) one.3.From an introduction of the four dimensional ambiguity function of the transmitted signals, the angle resolution in both transmitting array and receiving array are studied.After the study of the signal model of the meter-wave radar,the detailed deduction of the CRBs of DOA estimation for azimuth and elevation for one target and multiple targets have been obtained,the comparison of CRB have been discussed through simulation and which make a theory basis for the study of super-resolution algorithm.4.As the error in the measurement of the target distance could effect the measurement in azimuth and elevation,considering that there are quantification errors in distance-dimension during the echo sampling,the idea of super-resolution is introduced into distance measuring and elaborate the procedure of super resolution.While for this kind radar,as multi-carrier-frequency signals are transmitted simultaneously,if the spectrum of the target echo after channel separation could be combined to form the whole band spectrum echo,the corresponding range resolution will be improved several times than conventional method,and it will be more convenient for detection and tracking.Considering the difference between the frequency modulation band and the interval between the adjacent frequencies,the spectrum joint after channel separation will be overlap or space.Methods of spectrum moving of each echo and the spectrum extrapolation with Root-MUSIC algorithm are proposed in this paper,by using which high resolution range image of the target could be obtained.5.In the presence of multi-path propagation,it is quite difficult for VHF radar to measure the altitude of a low elevation target.In this paper,a new alternating projection algorithm is proposed to estimate the DOA of the target.By projecting the correlation matrix of the target echo into different signal subspaces,this method can be used to estimate accurately the directions of both the direct wave and the reflected wave,and hence the altitude of the target is known precisely;another mehtod which is based on the flat position refleciton mode is proposed,which by using the differential preprocessing,the phase of the multipath wave can be compensated,the echo from multi-path propagation can be subtracted form the signal that received.Then the general DBF can be used to estimate the direction of the direct wave.The real data from some VHF radar demonstrates the validity and feasibility of the both new algorithm.