Radar-Based High-Accuracy Angle Measurement Sensor Operating in the K-Band

The growing need for high-precision measurement instruments in modern industrial facilities leads to new measurement principles to reduce sensor costs while maintaining accuracy. A novel measurement principle suited for these applications is based on radar, which originally is associated with measurements in free space. For high precision, guided waves can be used to prevent disturbing reflections from the environment. Another advantage of a waveguide-based measurement is that the electromagnetic wave can be guided in a circle to measure rotational motions, which are in particular relevant in machine tools. This paper describes an FMCW radar sensor in the K-band for angle measurements. The sensor principle is described in detail, including its high-frequency components and the mechanical constraints to achieve a full angle range of 360°. The propagation characteristics of the radar signal in a curved waveguide with an adapted feeding structure using a Riblet coupler are presented. In addition to simulations, measurements with a prototype setup are presented to verify the radar-based angle measurement principle. The achieved accuracy is ±0.05° which corresponds to an accuracy in distance of ±125 μm.