Limitations of Spherical Near-Field Back Projection for Phased Array Tuning Applications

Author: Daniël Janse van Rensburg
Publication: URSI 2007
Copyright Owner: URSI

The calibration of electronically steered arrays require the determination of the aperture distribution of the antenna for a given set of excitation coefficients. A common approach taken in this process is to measure the radiating near-field of the antenna and to then mathematically back project to the actual aperture surface of the array to form an estimate of the aperture distribution. It is well known that the result obtained in this way is of limited resolution and accuracy and these limitations may at times render the result of little use for adjusting the array feed distribution. In this paper theoretical results will be presented for a steered array antenna, which will demonstrate the limitations of this back projection technique. These results will also show the accuracy with which the original excitation vector can be recovered. Parametric studies showing the impact of spherical angular truncation and over-sampling in the nearfield will be presented. This paper will also investigate the impact of spherical near-field scanner alignment anomalies (i.e. axis non-intersection, axis orthogonality and axis zero reference) on the achieved back projected resolution. Comparison to equivalent results obtained from a planar near-field back projection technique will also be presented.

View the paper