Generalized Parallel Coprime Array for Two-Dimensional DOA Estimation:A Perspective from Maximizing Degree of Freedom

Parallel arrays with coprime subarrays have shown its potential advantages for two dimensional direction of arrival(DOA)estimation.In this paper,by introducing two flexible coprime factors to enlarge the inter-element spacing of parallel uniform subarrays,we propose a generalized parallel coprime array(GPCA)geometry.The proposed geometry enjoys flexible array layouts by the coprime factors and enables to extend the array aperture to achieve great improvement of estimation performance.Meanwhile,we verify that GPCA always can obtain M2 degrees of freedom(DOFs)in co-array domain via 2M sensors after optimization,which outperforms sparse parallel array geometries,such as parallel coprime array(PCA)and parallel augmented coprime array(PACA),and is the same as parallel nested array(PNA)with extended aperture.The superiority of GPCA geometry has been proved by numerical simulations with sparse representation methods.

Array-error estimation method for multi-channel SAR systems in azimuth

For multi-channel synthetic aperture radar（SAR） systems, since the minimum antenna area constraint is eliminated,wide swath and high resolution SAR image can be achieved.However, the unavoidable array errors, consisting of channel gainphase mismatch and position uncertainty, significantly degrade the performance of such systems. An iteration-free method is proposed to simultaneously estimate position and gain-phase errors.In our research, the steering vectors corresponding to a pair of Doppler bins within the same range bin are studied in terms of their rotational relationships. The method is based on the fact that the rotational matrix only depends on the position errors and the frequency spacing between the paired Doppler bins but is independent of gain-phase error. Upon combining the projection matrices corresponding to the paired Doppler bins, the position errors are directly obtained in terms of extracting the rotational matrix in a least squares framework. The proposed method, when used in conjunction with the self-calibration algorithm, performs stably as well as has less computational load, compared with the conventional methods. Simulations reveal that the proposed method behaves better than the conventional methods even when the signal-to-noise ratio（SNR） is low.

DOA Estimation Based on Subspace Compensation for Unfolded Coprime Array

Direction of arrival(DOA)estimation for unfolded coprime array(UFCA)is discussed,and a method based on subspace compensation is proposed.Conventional DOA estimation meth-ods partition the UFCA into two subarrays for separate estimations,which are then combined for unique DOA determination.However,the DOA estimation performance loss is caused as only the partial array aperture is exploited.We use the estimations from one subarray as initial estimations,and then enhance the estimation results via a compensation based on the whole array,which is im-plemented via a simple least squares(LS)operation constructed from the initial estimation and first-order Taylor expansion.Compared to conventional methods,the DOA estimation performance is improved while the computational complexity is in the same level.Multiple simulations are con-ducted to verify the efficiency of the proposed approach.

Sparse three-dimensional imaging for forward-looking array SAR using spatial continuity

For forward-looking array synthetic aperture radar(FASAR),the scattering intensity of ground scatterers fluctuates greatly since there are kinds of vegetations and topography on the surface of the ground,and thus the signal-to-noise ratio(SNR)of its echo signals corresponding to different vegetations and topography also varies obviously.Owing to the reason known to all,the performance of the sparse reconstruction of compressed sensing(CS)becomes worse in the case of lower SNR,and the quality of the sparse three-dimensional imaging for FASAR would be affected significantly in the practical application.In this paper,the spatial continuity of the ground scatterers is introduced to the sparse recovery algorithm of CS in the threedimensional imaging for FASAR,in which the weighted least square method of the cubic interpolation is used to filter out the bad and isolated scatterer.The simulation results show that the proposed method can realize the sparse three-dimensional imaging of FASAR more effectively in the case of low SNR.

BEAM BROADENING SYNTHESIS FOR SAR ANTENNA ARRAY BASED ON PROJECTION MATRIX ALGORITHM

A new beam broadening synthesis technique for Synthetic Aperture Radar(SAR) antenna array, namely Projection Matrix Algorithm(PMA) is presented. The theory of PMA is introduced firstly, and then the iterative renewed manner is improved to resolve the unbalance problem under amplitude and phase control. In order to validate the algorithm correct and effective, an actual engineering application example is investigated. The beam synthesis results of 1.0~4.5 times broadening under the phase only control and the amplitude and phase control using improved PMA are given. The results show that the beam directivity, the beam broadening, and the side-lobe level requirements were met. It is demonstrated that the improved PMA was effective and feasible for SAR application.

Zigzag emitting array synthesis aperture acoustical holography

Zigzag Emitting Array Synthesis Aperture ( ZEASA ), a new model of the acoustical imaging is presented and discussed in the paper. The imaging system of this model has not only enough emitting energy for underwater acoustical imaging but also a large field of view. Its scanning speed is high and its cost is relatively low. The form of the point spread function of the system is given. It is found that if the system parameters are controlled properly, the major lobe of the point spread function is similar to that of the system with a square receiving array, and the side lobes along the axis direction of the linear receiving array are lowered. An imaging system with a 64-element. linear receiving array and a 64-element zigzag emitting array is simulated and the analysis of ZEASA is proved to be correct by the results of the simulation.