With over 40 years of continuous development, radar has become the preferred technology for level measurement in many of today's industrial applications.For non-contacting radars, the microwave frequency transmitted by the radar is one area in which there have been recent developments.Traditionally, three different frequency bands have been used for level measurement: the C-band (~6 GHz), the X-band (~10 GHz), and the K-band (~26 GHz). These frequency bands combine many attractive properties for accurate and reliable millimeter-precision measurement. Recently, radars using 75–85 GHz frequencies (the lower part of the W-band) have been introduced as a further option. The use of 75-85 GHz radars is mainly driven by the development of automotive radar applications such as parking sensors. Frequency is a fundamental property of any radar as it has direct effects on measurement performance. It is important to remember that different frequencies are not equally suitable for all applications. Indeed, radars using different frequencies are required to solve different problems.
This paper will first describe the fundamental physical properties of different frequencies and thereafter explain what practical effects these properties have in some common, real-life level measurement applications. To this end, this paper differentiates between non-contacting radar transmitters using low microwave frequency (C and X-band, 6–11 GHz), mid frequency (K-band, 24–29 GHz) and high frequency (W-band, 75–85 GHz).
