Attempts have been made for some time to make the THz frequency range available for imaging applications, in particular in security technology for checking and inspecting people.
U.S. Pat. No. 5,859,609 discloses a device for holographic approximated real time imaging of concealed articles by means of THz radiation. A vertical linear antenna arrangement is moved over a circular path to achieve cylindrical scanning of 360° of a covered target such as for example a clothed person. The data are present in the form of a non-focused millimeter wave illumination which is capable of reaching a covering such as for example of a clothed person and which is capable of penetrating a covering such as for example clothing. The millimeter wave illumination has to be focused or reconstructed mathematically, that is to say by computation, into recognisable images.
Such a device suffers from the disadvantage that for producing imaging of a three-dimensional article by means of a synthetic aperture in two dimensions on the one hand a large number of sources and detectors are required in a first direction and in addition the arrangement of sources and detectors has to be moved completely around the object in order also to be able to generate an image with a synthetic aperture in a second direction perpendicular to the row of sources and detectors. That is linked on the one hand to high costs by virtue of the large number of sources and detectors required, but on the other hand it also involves a comparatively long measurement time as the entire arrangement must be rotated once though 360° in a circle, for example for recording a complete person.