传统的高分辨波达方向（DOA）估计算法中，一般都假设信号位于远场，此时入射到阵列的信源波前为平面波前，空间信号的定位参数可由DOA来确定。然而，当信源处于阵列的Fresnel区域时，信号波前需用球面波来描述，每个信源的定位信息要用DOA和距离联合描述。因此，远场情况下的一些线性理论推导已不再成立，传统的远场算法的估计不再适用(In traditional high resolution direction of arrival (DOA) estimation algorithms, it is generally assumed that the signal is located in the far field, where the source wavefront incident to the array is plane wavefront, and the location parameters of the spatial signal can be determined by DOA. However, when the source is in the Fresnel region of the array, the wavefront of the signal needs to be described by spherical wave, and the location information of each source needs to be described by DOA and distance. Therefore, some linear theoretical deductions are no longer valid in the far-field case, and the estimation of the traditional far-field algorithm is no longer applicable.)