A radar unit (100, 300) is described that 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. The receiver circuit (104, 110, 304, 310) is configured to operate with at least two different paths for at least two successive chirps of the mmW FMCW transmit signal and create therefrom at least two respective received chirp signals; 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).