Near-field measurements and the determination of aerial patterns

Measurements carried out in the near-field region of aerial systems can be used to predict radiation patterns. While near-field methods are unlikely to be used where conventional aerial measurements are satisfactory they become of increasing interest under those situations where normal procedures are either inadequate or impossible to apply. Near-field techniques can be broadly divided into two classes, namely those in which the radiation pattern is simulated directly within the near-field region and those in which the radiation pattern is computed directly from the near-field measurements. Several methods representative of each of these two classes are discussed (e.g. those due to Cheng, Bickmore and Jull) and the range of validity and likely applicability of each is indicated.