The effect of undersampling and finite truncation of the antenna near-field data on the predicted far-field pattern

Fourier transform theories are used in investigating two aspects of pattern prediction from near-field measurements related to the plane wave spectrum of Joy and Paris (1972) and the cylindrical wave expansion methods of Leach and Paris (1973). The possibility of accurately predicting the antenna pattern or portions thereof with data sampled below the 'Nyquist' rate is demonstrated. It is also shown that the effect of the finite truncation of the near-field measurement surface introduces an error by way of the convolution of the true pattern with a sinc function. Numerical examples illustrating these effects are adduced.