A planar near-field to far-field transformation using an equivalent magnetic current approach

A method is presented for computing far-field antenna patterns from near-field measurements. The method utilizes near-field data to determine equivalent magnetic current sources over a fictitious planar surface which encompasses the antenna, and these currents are used to ascertain the farfields. An electric field integral equation is developed to relate the near fields to the equivalent magnetic currents. A method of moments procedure is used to transform the integral equation into a matrix one. The matrix equation is solved with the conjugate gradient method (CGM), and, in the case of a rectangular matrix, a least-squares solution for the currents is found without explicitly computing the normal form of the equation. Near-field to far-field transformation for planar scanning may be efficiently performed under certain conditions by exploiting the block Toeplitz structure of the matrix and using CGM and the fast Fourier-transform (CGFFT), thereby drastically reducing computation and storage requirements. Numerical results are presented by extrapolating the far fields using experimental near-field data.<>