Plane-wave synthesis by an antenna-array and RCS determination: theoretical approach and numerical simulations

Radar cross-section (RCS) measurements of a target performed in an anechoic chamber with the conventional one antenna calibration technique may yield erroneous results at frequencies lower than those for which the chamber has been initially designed, essentially because the absorbers become ineffective and the field emitted by the antenna no longer satisfies the plane-wave (PW) condition on the target. A possible way to circumvent these difficulties is to use a phased antenna-array that synthesizes a PW in a bounded domain, usually called the quiet zone (QZ). In this paper, we propose a calibration technique that allows an accurate reconstruction of the RCS of a target located in the near-field of the array, even when electrically conducting walls are present. A theoretical study of the problem at hand is presented that allows one to specify clearly the hypotheses that are being made and to identify the parameters that govern the accuracy of the RCS reconstruction. When the target-array, antenna-antenna, and target-walls-target interactions are neglected, it is demonstrated that this calibration technique synthesizes a PW in QZ if the calibration object is a line source (two-dimensional) or an infinitesimal dipole (three-dimensional). Three-dimensional full-wave numerical simulations, that take all the previously mentioned interactions into account, illustrate the efficiency of this technique when the array and conducting walls are a few wavelengths apart from the target.