To depict test objects using electromagnetic waves, particularly to check people for suspicious articles, an apparatus is provided having: an antenna which emits electromagnetic waves, particularly millimetric waves, means for concentrating the emitted waves in three dimensions, and means for manipulating the waves at the point of high concentration such that this point serves as a moving virtual antenna for SAR evaluation. Whereby the means for three-dimensional concentration contain a rotatably mounted, focusing or defocusing, quasi-optical element and the means for manipulating the waves at the point of high concentration contain a reflector. In accordance with the invention, the quasi-optical element and the reflector are rotatably mounted about a common rotary axis and at the same angular velocity.