Displacement errors in antenna near-field measurements and their effect on the far field

The effects of probe displacement errors in the near-field measurement procedure on the far-field spectrum are studied. Expressions are derived for the displacement error functions that maximize the fractional error in the spectrum for both the on-axis and off-axis directions. The x- y- and z-displacement error in planar scanning are studied and the results are generalized to errors in spherical scanning. Some simple near-field models are used to obtain order-of-magnitude estimates for the fractional error as a function of relevant scale lengths of the near-field, defined as the lengths over which significant variations occur