Near-field technique for inferring aperture antenna radiation patterns

The method of Brown and Jull for inferring the far field from the near field has been extended to arbitrary antennas, with measurements made in one plane only. The primary concern has been with aperture antennas. The theory of the computational reduction of the measured data has been obtained. The results of a practical application of this near-field technique (n.f.t.) to a circular-waveguide-aperture antenna are described. The modal distribution in the waveguide aperture is estimated. This distribution has been substituted into a variational expression for the waveguide admittance. The result is close to the measured value, thereby confirming the accuracy of the n.f.t.