口径近场的特征谱

 提出口径近场特征谱的概念，以描述口径设计近场特征。特征谱包括角域谱和时域谱，分别定义为口径近场区空域场和频域场在角域和时域的变换。理论分析和计算结果表明，特征谱可以在角域和时域上分离有限大口径的直达波和绕射波，因而可以用来描述口面尺寸、形状和场分布等条件改变时绕射场的相对变化，这对紧缩场设计具有参考价值。基于口面场卷积法，计算、比较了限度为5 m×5 m圆口径和方口径近场在X波段特征谱分布。并导出：口径近场角谱为口径场角谱和网络响应函数角谱的乘积，网络响应函数等效于一个空间角谱滤波器。

Diagnostic Spectrum of Aperture Near Field

The concept of diagnostic spectrum of aperture near field is presented to describe the near field characteristics of an aperture. The diagnostic spectrums include angular spectrum and time spectrum, which are defined as transformation of spatial and frequency near field in angle and time domains respectively. Theoretical analysis and numerical computation show that the direct and diffractive waves of an aperture can be distinguished by the diagnostic spectrum. Therefore, they can be used to describe the relative diffractive field changes of an aperture while its size,shape and field distribution changed. This is useful for compact range (CR) design. Near field of a 5 m×5 m circular and quadrangular aperture is computed and compared based on aperture field convolution method. It can be deduced that the aperture near field angular spectrum is a product of the aperture field angular spectrum and the spatial network response function angular spectrum. Therefore, the spatial network function acts as a spatial angular spectrum filter.