Frequency-modulated interrupted continuous wave radar using pulses derived from a frequency-modulated signal in which the rate of frequency change increases at the boundary of a pulse repetition interval

An apparatus for determining a distance to an object, the apparatus comprising:

• a signal generator operable to generate a primary, frequency-modulated signal having a frequency which changes monotonically over a frequency range ΔF throughout a frequency sweep period TSW;
• a signal processor operable to derive from the primary signal a reference signal and a transmission signal, the transmission signal comprising a plurality of successive pulses during the frequency sweep period, the plurality of successive pulses having different frequencies and each pulse being transmitted at the beginning of a respective pulse repetition interval, wherein the primary signal has a frequency which varies, during a beginning part of each pulse repetition interval, at a greater rate than the mean rate ΔF/TSW of frequency change for the frequency sweep period TSW;
• an antenna for transmitting the transmission signal and for obtaining a received signal comprising a reflection of the transmission signal from an object;
• and
• a signal combiner operable to combine the reference signal with the received signal to derive a beat frequency indicative of the distance to the object.