Rays

In the basic version, only the direct ray from the antenna (single point) to the examined point on the spherical surface is considered. All transmissions of this ray are evaluated.

A consideration of reflections and diffractions makes no sense because of the assumption of a single point radiation source. The reflection conditions (angle of incident ray = angle of reflected ray) are seldom true (in contrast to a real antenna which is not concentrated in a single point) and therefore nearly no reflected rays are found.

If the antenna is reduced to a single point, many diffracted rays are neglected (especially if the distance between antenna and objects is small). A real antenna (not reduced to a single point) would have reflections on the object.

Figure 1. Example of a wall configuration.

Since the reflection loss reduces the power of this ray, the error in the superposition of the reflected and direct rays can be neglected (if 10 dB or more reflection loss is applied, the sum of both rays in logarithmic scale is nearly identical to the direct ray alone).

The only exception is the reflection at the mast itself. As the mast is often built with metal, the reflection loss is very low. So, reflections at the mast are not attenuated significantly, and therefore they have a strong influence on the superposed signal power (they can destruct the radiated signal in one direction). The same applies to the wall if the antenna is mounted in front of the wall. Therefore, reflections at walls are also considered.