The prediction of aerial radiation patterns from near-field measurements

A new method is described of predicting an aerial radiation pattern from near-field measurements. The essence of this method is the expansion of the radiated field in terms of a series of radially expanding modes. The amplitude and phase of each mode are calculated by a Fourier analysis of the measured near field, and the radiation pattern is obtained as a Fourier series containing these measured amplitudes and phases. The theory is described in detail for a cylindrical (2-dimensional) aerial, and experimental results are presented to confirm the validity of this theory. The way in which the method may be extended to 3-dimensional aerials is explained. The method has the advantage that it can be applied anywhere in the near field