Semitransparent screen for cutoff of the far fields in the shadow domain

In many cases it is desirable to achieve a sharp decay (cutoff) of the far field in the shadow domain. For the purpose, electrically thin semitransparent screen with a smooth impedance profile has been considered. Within the geometrical optics approximation the profile is synthesized analytically. The approximation is valid for a distance from the source to the screen that is much larger than the wavelength; the respective impedance is pure resistive. For shorter distances the geometrical optics is not valid and a numerical optimization procedure is applied; the impedance occurs to be complex. It is shown that it is the distance from the source to the screen that defines the achievable cutoff: for the distances on the order of 10 ... 20 wavelengths, a 40 dB cutoff is achievable within an angular sector of +/- 10 degrees around a desirable light-shadow boundary, at 0.5 ... 1 wavelength distances the related figure is 20dB. The screen is realized in the form of a grid, with the characteristic period being much smaller than the wavelength. The approach is relevant to electromagnetic interference, radar and satellite positioning.