Wavefront quality in antenna pattern measurement: the use of residuals

The concept of the far-field residual source distribution is presented as a convenient and accurate means of assessing the quality of a wavefront employed in antenna measurements. The residual defines the errors in radiation pattern measurements in terms of the plane wavefront quality of the technique employed and can be used to examine the far-field range, the compact range and the near-field/far-field transformation. It is shown that the spherical wavefront of the farfield range can be analytically decomposed into a residual spectrum which can be used to explain the classical errors found in radiation patterns measured at a finite distance. The significance of different types of illumination is examined for the compact range. It is demonstrated that heavily tapered distributions can provide high accuracy at wide angles, whereas more uniform illumination results in better accuracy for near-in sidelobe measurements. Finally, the residual is used to quantify the accuracy offered by the near-field/far-field transformation and, as expected, demonstrates this to be the most accurate antenna measurement technique available