Abstract: Radar imaging apparatus comprises a single transmit antenna (4) and at least one receive antenna (5), scanning means (e.g. a pantograph) for mechanically scanning the antennas over a surface of interest (16), position providing means (e.g. a computer driving the pantograph via an X-Y drive and a stepper motor) providing a position signal indicative of the instantaneous position of the transceiver, control means for operating the transmit antenna in a stepped frequency continuous wave mode, signal analysing means for analysing amplitude and phase components (27, 28) of the receive antenna signal, and signal combining means for combining the output of said signal analysing means with said position signal as in a synthetic aperture array to provide a radar image signal of the surface and underlying features.

Abstract: A method of demodulating a high frequency carrier signal having at least one parameter modulated by a low frequency modulating signal comprises translating the signal to a low intermediate frequency, digitizing the translated intermediate frequency signal at a correspondingly low sampling rate and applying terms from the resulting digital time series to a non-linear processor to produce an output representative of the instantaneous value of the modulated parameter. Deriving an instantaneous value of the modulated parameter removes the need to use a high intermediate frequency for the carrier and enables the signal to be sampled at a low sampling rate.