Abstract: This invention relates to a method and apparatus by which a coarse estimate of radar signal polarisation can be obtained. An array comprises at least three differently directed detectors. The polarisation is estimated by measuring an amplitude relationship, such as a ratio of amplitudes, for two adjacent detectors and for two non-adjacent detectors. This provides sufficient information to obtain a coarse estimate of the polarisation state, obtainable by using the value of the amplitude relationship for the two adjacent detectors together with a look-up table to estimate values of the amplitude relationship for the two non-adjacent detectors for different polarisation states, and then comparing the measured and estimated values for this amplitude relationship.

Abstract: A method and apparatus estimate the detection range R.sub.1 of a radar in the presence of noise and clutter. The radar return signals from a range cell under test and from a plurality of surrounding range cells on either side of the range cell under test are measured. From the values of the return signals from the surrounding cells, a factor .alpha. is determined. The mean value of those signals is then multiplied to form a threshold value for determining the presence or absence of a target. A desired false alarm rate is maintained, however. A number of radar return signals sufficient substantially to average out local variations in clutter are used to determine a mean clutter value m.sub.c. A value which is a function of .alpha. and m.sub.c is output as the estimate of detection range R.sub.1.