A method for the analysis of ramp-inherent linearity distortions in automotive radar applications

Through the use of sensors to provide information about the vehicles surroundings, driver assistance systems increase traffic safety. These sensors must not deliver wrong data due to noise or external distortion. In FMCW Radar systems additionally a highly linear ramp is essential. Hence nonlinear ramps have direct impact on the baseband spectrum. Weak targets could be covered and therefore not detected. This paper describes a method for evaluating the RF ramp linearity, based on analysis of the baseband signal. Therefore the analysis is easier, as the baseband frequency is only a few MHz depending on chirp modulation parameters and target distance. The instantaneous frequency is measured, so that deviations from the ideal slope can be detected immediately. Results are compared with simulations and high frequency measurements with a commercial availably spectrum analyzer which calculates the mean frequency deviation over a high number of ramps.