Medium fading of radar targets at sea with special reference to operation at 3 cm and 10 cm

At sea and in fair weather, the choice of operating wavelength for search radars for the detection of surface targets is largely influenced by the required angular resolution and maximum aerial aperture allowed. However, in considering maximum detection ranges in excess of 15 n miles, attenuation through very heavy precipitation favours a lower wavelength of the order of 10 cm, although angular resolution requirements are more easily and cheaply met by going to a wavelength of 3 cm or less. When aerial height is limited to 5 or 10 m only, the resultant low transition range demands the use of the shorter wavelength for surface targets, but in the case of large vessels able to carry scanners 40 to 50 m above sea level, the choice is more open. The paper presents data, analysis and some conclusions on the use of two radars on wavelengths of 3 and 10 cm colocated some 45 m above sea level, under precipitation-free conditions and outside the sea clutter region for either set under the conditions prevailing for the period of the trial. Attention is drawn to the wide variation of differential performance experienced in the trials, believed to be due to anomolous propagation even over the relatively short ranges considered.