A radar unit (100, 300) comprises: a frequency generation circuit (103, 106, 303, 306) configured to generate a millimetre wave, mmW, frequency modulated continuous wave, FMCW, transmit signal comprising a plurality of chirps; a transmitter circuit (108, 102, 308, 302) configured to transmit the generated mmW FMCW transmit signal: a receiver circuit (104, 110, 304, 310) configured to receive an echo of the mmW FMCW transmit signal; and; a built-in self-test, BIST, circuit (140, 340) coupled to the receiver circuit (104, 110, 304, 310) and configured to process the echo of the mmW FMCW transmit signal; wherein the radar unit (100, 300) is characterised in that: the receiver circuit (104, 110, 304, 310) is configured to operate with at least two different paths in the receiver circuit (104, 110, 304, 310) for respective at least two successive chirps of the plurality of chirps of the mmW FMCWtransmit signal and create therefrom at least two respective received chirp signals each in the respective path by injecting a DC offset into one of the at least two received successive chirps in its respective path and by selectably introducing a filter into its respective receiver path carrying the other one of the at least two received successive chirps, and the BIST circuit (140, 340) is configured to process and compare the at least two respective received chirp signals and determine therefrom an operational state of at least one circuit or component within the receiver circuit (104, 110, 304, 310). a frequency generation circuit (103, 106, 303, 306) configured to generate a millimetre wave, mmW, frequency modulated continuous wave, FMCW, transmit signal comprising a plurality of chirps; a transmitter circuit (108, 102, 308, 302) configured to transmit the generated mmW FMCW transmit signal: a receiver circuit (104, 110, 304, 310) configured to receive an echo of the mmW FMCW transmit signal; and; a built-in self-test, BIST, circuit (140, 340) coupled to the receiver circuit (104, 110, 304, 310) and configured to process the echo of the mmW FMCW transmit signal; wherein the radar unit (100, 300) is characterised in that: a receiver circuit (104, 110, 304, 310) configured to receive an echo of the mmW FMCW transmit signal; and; a built-in self-test, BIST, circuit (140, 340) coupled to the receiver circuit (104, 110, 304, 310) and configured to process the echo of the mmW FMCW transmit signal; the receiver circuit (104, 110, 304, 310) is configured to operate with at least two different paths in the receiver circuit (104, 110, 304, 310) for respective at least two successive chirps of the plurality of chirps of the mmW FMCWtransmit signal and create therefrom at least two respective received chirp signals each in the respective path by injecting a DC offset into one of the at least two received successive chirps in its respective path and by selectably introducing a filter into its respective receiver path carrying the other one of the at least two received successive chirps, and the BIST circuit (140, 340) is configured to process and compare the at least two respective received chirp signals and determine therefrom an operational state of at least one circuit or component within the receiver circuit (104, 110, 304, 310).