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 the reflection properties of small targets in near zones of focused and unfocused apertures are described. It is shown that the “minimal distance” can be substantially lowered using the suitable microwave lens when measuring the reflection properties of medium and large-sized targets.