Water temperature measurement by microwave six-port interferometry at 24 GHz

Microwave interferometry enables the possibility of highly accurate distance measurements by evaluating phase differences. The reflected power is a function of the effective radar cross-section, the measurement distance, and the attenuation in air. An irradiated plain water surface shows a temperature-dependent behavior by means of the reflected power. This is due to the fact that the complex permittivity of water, as well as the refractive index, strongly depends on the water temperature within the 24 GHz Industrial, Scientific and Medical (ISM) band. Consequently, the effective radar cross-section depends on the temperature as well. This paper describes a method of monitoring the water temperature as a new application of an interferometric radar in Six-Port technology for water level measurements.