A radar receiver for a Doppler radar system, the receiver being a pulse-Doppler radar receiver, a monopulse radar receiver, and/or a radar receiver using phase-coded pulse compression, the receiver comprising: (a) an analogue receiver unit for receiving a radar echo signal and arranged to convert the radar echo signal into an intermediate frequency, IF, analogue signal; (b) a digital receiver including an analogue-to-digital converter (300A-D) arranged to receive the IF analogue signal from the analogue receiver and to sample the IF analogue signal, wherein the sampling by the analogue-to-digital converter (300A-D) is undersampling according to the Nyquist criterion, so that a plurality of IF digital signals are produced, in different Nyquist zones, including one or more aliased IF digital signals, the digital receiver being arranged to select an IF digital signal from the one or more aliased digital signals; and (c) a digital demodulator arranged to convert the selected IF digital signal to a baseband digital signal having in-phase, I, and quadrature, Q, components, the I and Q components being produced by multiplying the selected IF digital signal by a cosine signal and by a sine signal, respectively, characterised in that: each cosine signal and each sine signal is represented by a sample stream consisting only of three levels, the carrier frequency of the selected IF digital signal being chosen to be 1⁄4 of the sampling rate of the analogue-to-digital converter (300A-D) in sampling the IF analogue signal so that the three levels correspond to maxima, minima, and zeros of the cosine and sine signals, and the radar receiver further comprises: (d) a digital beam-forming network arranged to receive a plurality of the baseband digital signals, from each of the plurality of receiver channels (A-D), and to convert them into a plurality of comparison signals each on one of a plurality of comparison channels, each comparison channel including a digital correlator arranged to form a cross-correlation function between the comparison signal and a code applied to pulses transmitted by the radar. (a) an analogue receiver unit for receiving a radar echo signal and arranged to convert the radar echo signal into an intermediate frequency, IF, analogue signal; (b) a digital receiver including an analogue-to-digital converter (300A-D) arranged to receive the IF analogue signal from the analogue receiver and to sample the IF analogue signal, wherein the sampling by the analogue-to-digital converter (300A-D) is undersampling according to the Nyquist criterion, so that a plurality of IF digital signals are produced, in different Nyquist zones, including one or more aliased IF digital signals, the digital receiver being arranged to select an IF digital signal from the one or more aliased digital signals; and (c) a digital demodulator arranged to convert the selected IF digital signal to a baseband digital signal having in-phase, I, and quadrature, Q, components, the I and Q components being produced by multiplying the selected IF digital signal by a cosine signal and by a sine signal, respectively, characterised in that: each cosine signal and each sine signal is represented by a sample stream consisting only of three levels, the carrier frequency of the selected IF digital signal being chosen to be 1⁄4 of the sampling rate of the analogue-to-digital converter (300A-D) in sampling the IF analogue signal so that the three levels correspond to maxima, minima, and zeros of the cosine and sine signals, each cosine signal and each sine signal is represented by a sample stream consisting only of three levels, the carrier frequency of the selected IF digital signal being chosen to be 1⁄4 of the sampling rate of the analogue-to-digital converter (300A-D) in sampling the IF analogue signal so that the three levels correspond to maxima, minima, and zeros of the cosine and sine signals, (d) a digital beam-forming network arranged to receive a plurality of the baseband digital signals, from each of the plurality of receiver channels (A-D), and to convert them into a plurality of comparison signals each on one of a plurality of comparison channels, each comparison channel including a digital correlator arranged to form a cross-correlation function between the comparison signal and a code applied to pulses transmitted by the radar.