Sweep time variation algorithm for high accuracy FMCW radar measurements

Free space radar systems for civilian applications are often limited in bandwidth by regulatory authorities. Consequently, the accuracy of such radar systems is severely restricted, which in turn reduces its usage in industrial applications. However, it is still possible to achieve high accuracy, using an FMCW radar system combined with a phase evaluation algorithm. In this paper, the accuracy requirements for the application of the phase evaluation algorithm are derived. Furthermore, it is shown that in certain cases an improvement of the SNR does not lead to a higher accuracy. To avoid this limitation, an algorithm based on sweep time variation is presented. The objective of this algorithm is to reduce accuracy degradations by unwanted reflections in FMCW radar systems. Therefore, it becomes possible to use the combined frequency and phase algorithm. To evaluate the proposed algorithm, measurements of a 61GHz ISM band FMCW radar are taken and processed. The basic algorithm achieves a measurement accuracy of only 1.8mm. Using the new algorithm, based on combined frequency and phase evaluation, an accuracy improvement by a factor of hundred can be achieved. The proposed algorithm achieves an accuracy of nearly 20μm in the same measurement.