Radar Sensors (24 and 80 GHz Range) for Level Measurement in Industrial Processes

The measurement of the filling level of liquid and solid goods in storage, process, and other tanks and silos is an important task in many industries. Examples of liquids are oil, gasoline, various chemicals and pharmaceuticals, water, and beverages. Also, a large variety of bulk solids can be given, for example fine granulated solids like flour, sugar, sand, grains, and various powders. Examples of more rough solids are pellets, coal, grit, stones, and others. Resulting from the different electrical properties (permittivity and conductivity) and the different sizes and structures, the reflection, scattering, and attenuation properties are strongly different. Radar sensors operating at frequencies up to 24 GHz are already well-established for level measurement applications. Radio regulations and the latest state- of-the-art technology have now also made radar level meters at high frequencies in the 80 GHz range commercially available. In this contribution, first the measurement scenarios and conditions given with liquids and bulk solids are both discussed and compared to each other. Secondly, criteria and technical backgrounds for a suitable choice between 24 GHz and 80 GHz radar systems dependent on the specific level measurement application are motivated and given. Thereafter, the realization of components for according radar sensors is presented and discussed, with a focus on the radio-frequency (RF) front-end electronics using monolithic microwave integrated circuits (MMIC) and different radar antenna concepts. For the latter, the given harsh conditions in the application are a challenge, as will be discussed. Finally, some exemplary results obtained from practical measurements with the discussed radar systems are presented and analyzed.