Electromagnetic Field Transformation from a Surface Closed Around the Antenna to its Aperture.

The article proposes a direct algorithm for reconstructing the electromagnetic field at the antenna aperture, which can be used to solve problems of diagnostics and spatial filtering. The algorithm is based on the solution of Maxwell's equations in the form of advanced potentials of the electromagnetic field. It is shown that advanced electromagnetic waves, which are a solution to Maxwell's equations, are equivalent to retarded electromagnetic waves when the parameters of the medium are stationary and linear. The direct algorithm is formulated as the multiplication of the transformation operator matrix by the known vector of the electromagnetic field on a closed surface. In this case, the transformation outward (to the far field) or inward (to the aperture) of the surface is described by the same operator and differs only in the signs of the input quantities. Unlike the known algorithms, the direct one does not require scanning the electromagnetic field on canonical surfaces or solving a large system of integral equations. It makes the new algorithm optimal for use in new near-field antenna measurement systems based on industrial robots, unmanned aerial vehicles, etc. Verification of the developed algorithm using experimental data has shown the possibility of reconstructing the normalized distribution of the electric field strength at the antenna aperture with an error less than 2 dB. [ABSTRACT FROM AUTHOR]