The article expresses the conditions that must be met when measuring the radio-locating cross-section of a target in terms of amplitude and incident field phase variation. A number of minimal distance criteria are examined. The analysis of minimal distance for the cases when the antenna has a uniformly lighted square aperture is given, and the relation that binds the minimal distance to the sensitivity of measurements. The measurements of ...

... uniformly illuminated rectangular aperture is derived which is valid in the Optical Fresnel Zone. This equation is formulated in terms of the ordinary radiation field gain multiplied by a correction factor which depends upon the aperture dimensions and the distance, R, from the aperture at which the gain is measured. IRE Transactions Antennas and Propagation