Range distance requirements for measuring low and ultralow sidelobe antenna patterns

This paper considers the effects of quadratic phase errors due to finite length pattern ranges on the measurement of low and ultralow sidelobe antennas. The well-known rule-of-thumb distance is shown to be adequate nnly for measuring patterns having moderately low sidelobes (i.e. down to about -30 dB). This distance is shown to be inadequate for measuring low (-30 to -40 dB) and ultralow (below -40 dB) sidelobe patterns if the near-in sidelobes are to be preserved within reasonable errors (e.g. less than 1 dB). A relationship between first sidelobe errors and range distances is derived from calculated patterns for a number of amplitude distributions with various quadratic phase errors. This relationship is plotted in terms of the change (error) in the highest sidelobe versus range distances in multiples of on log-log paper. The resulting plot clearly shows the range distances required for various low sidelobe patterns and measurement tolerances.