Abstract: A frequency modulated continuous wave (FMCW) radar is described. The radar includes a first discriminator for receiving a portion of the swept frequency signal generated by a frequency sweep generator and for producing a reference difference-frequency signal of frequency equal to the difference between the frequency of the swept frequency signal and the frequency of a time displaced swept frequency signal derived from the swept frequency signal. An analogue-to-digital converter is provided for sampling the target difference-frequency signal at a rate derived from the frequency of the reference difference-frequency signal. A processor (88) for determining frequency components of the digitized target difference-frequency signal is arranged to determine for at least one frequency component of the digitized target difference-frequency signal any phase difference between frequency sweeps of said swept frequency signal. The radar may be used for detecting foreign object debris (FOD) on runway surfaces and the like.

Abstract: An object detecting apparatus uses a radar system 24 which employes a directional antenna 6. A transmission parameter of the system 24 is calibrated for each transmission direction such that, at a boundary 22 of a detection area 20, there is a maximum signal intensity and a minimum sensitivity. The calibration is effected using reflectors of known reflective response which are positioned around the boundary 22 during calibration.

Abstract: A Doppler radar speed sensor for a land vehicle comprises a radar transmitter/receiver circuit (1) coupled to an aerial system (2). R.F. energy from a source (3) is transmitted by the aerial system in forward (9) and backward (10) directions and energy reflected from these directions is mixed with a sample of the transmitted energy in a mixer arrangement (8) to yield a pair of Doppler frequency components representative of the vehicle speed. In order to ensure that these components always have mutually different frequencies, and thereby avoid the necessity of constructing the mixer arrangement as a pair of quadrature-related mixers, the forward and backward directions make different angles (.theta.+.DELTA..theta. and .theta.-.DELTA..theta. respectively) with the direction of travel (15).