Distortion of Radiation Patterns Close to an Array

Author: Edmund A. Laport

All radiation patterns are computed for distances that are very large with respect to the largest dimension of the array. It is assumed that the rays from each radiator at the point of field measurement are virtually parallel. The pattern is not fully "formed" at distances less than some ten times the largest dimension of the array or greater.

FIG. 2.51. Examination of pattern stability by vector diagram of fields in null region.

The region in which the pattern shape is a function of distance is called the "Fresnel region." Beyond this it is called the "Fraunhofer region." One can be greatly deceived in the adjustment and proof of performance of an array if patterns are measured in the Fresnel region. Distance is measured from the geometric center of the array plan.