A vital sign detection system comprising: a radar device configured to output an output signal (S out); a nonreciprocal network coupled to the radar device; a first antenna coupled to the nonreciprocal network; and a second antenna coupled to the nonreciprocal network; characterized in that the radar device is configured to deliver the output signal (S out) to the first antenna via the nonreciprocal network for transmitting it to a first side of a biological subject via the first antenna, and the first antenna is configured to receive a first reflection signal from the first side of the biological subject for delivering the first reflection signal to the second antenna via the nonreciprocal network and the second antenna is configured to then transmit the first reflection signal to a second side of the biological subject, and the second antenna being configured to receive a second reflection signal from the second side of the biological subject for delivering the second reflection signal to the radar device via the nonreciprocal network, said first and second sides (S1, S2) being opposite sides of the biological subject; wherein the radar device includes an injection-locked oscillator, ILO,, a power splitter and a frequency demodulator, the ILO includes an output port configured to output the output signal (S out) and an injection port configured to receive the second reflection signal for operation in a self-injection-locked state, the power splitter is coupled to the ILO and configured to divide the output signal (S out) into two paths, the output signal (S out) of one path is configured to be delivered to the nonreciprocal network, and the output signal (S out) of the other path is configured to be delivered to the frequency demodulator for outputting a vital sign signal; and wherein the nonreciprocal network is configured to deliver the output signal (S out) from the radar device to the first antenna for transmission, and then deliver the first reflection signal received by the first antenna to the second antenna for retransmission, and then deliver the second reflection signal received by the second antenna to the radar device for vital sign detection with random body movement cancellation. a radar device configured to output an output signal (S out); a nonreciprocal network coupled to the radar device; a first antenna coupled to the nonreciprocal network; and a second antenna coupled to the nonreciprocal network; characterized in that the radar device is configured to deliver the output signal (S out) to the first antenna via the nonreciprocal network for transmitting it to a first side of a biological subject via the first antenna, and the first antenna is configured to receive a first reflection signal from the first side of the biological subject for delivering the first reflection signal to the second antenna via the nonreciprocal network and the second antenna is configured to then transmit the first reflection signal to a second side of the biological subject, and the second antenna being configured to receive a second reflection signal from the second side of the biological subject for delivering the second reflection signal to the radar device via the nonreciprocal network, said first and second sides (S1, S2) being opposite sides of the biological subject; wherein the radar device includes an injection-locked oscillator, ILO,, a power splitter and a frequency demodulator, the ILO includes an output port configured to output the output signal (S out) and an injection port configured to receive the second reflection signal for operation in a self-injection-locked state, the power splitter is coupled to the ILO and configured to divide the output signal (S out) into two paths, the output signal (S out) of one path is configured to be delivered to the nonreciprocal network, and the output signal (S out) of the other path is configured to be delivered to the frequency demodulator for outputting a vital sign signal; and wherein the nonreciprocal network is configured to deliver the output signal (S out) from the radar device to the first antenna for transmission, and then deliver the first reflection signal received by the first antenna to the second antenna for retransmission, and then deliver the second reflection signal received by the second antenna to the radar device for vital sign detection with random body movement cancellation.