The basic principal of operation is the same for both technologies. High-frequency electromagnetic energy is transmitted into a vessel. A reflection occurs at the point where there is an impedance change between the vapor space and liquid level. This impedance change is caused by the two media having different dielectric constants. The higher the dielectric constant of the product, the larger the amplitude of the reflected signal.
The difference between the two technologies lies in the fact that through-air radar sends its energy out into the open air. In this way it can be attenuated by the vapor space in which it is traveling, and reflections from objects other than the level signal (false targets) can cause performance issues.
GWR transmits energy down a probe (i.e. waveguide) where it is focused. Very little energy is lost down the probe, therefore very low dielectric media can be measured. Using a probe, GWR virtually eliminates the variables that can influence through-air radar.
Author - Bob Botwinski