Quasi-optically Sight
The Electromagnetic waves almost behave like light beams and well can be calculated in accordance with optical rules. This isn't surprising either since light also only is regarded as an electromagnetic wave. The difference only consists in the frequency which is much higher at the light than at electromagnetic waves in the radar frequency range.
The quasi-optically sight is a little further than the visual view because of this one at deeper frequencies more effective diffraction. Well, the radar horizon lies far away than the visual horizon. Obstacles on the way there affect also differently. A couple of trees affect the visual sight fatally while electromagnetic waves can possibly penetrate this obstacle.
An observer location in larger height is just as effectively as a higher one antenna location for the electromagnetic waves in the optics since by the bend of the earth's surface flat objects disappear very fast behind the horizon.
The following diagram with the approximation equation clarifies the visibility of lowlevel-flying aircrafts for radar antenna height of 25 m (without consideration of obstacles in the landscape).
Figure 1: Quasi- optically sight
Figure 1: Quasi- optically sight
Figure 1: Quasi- optically sight
