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George Huxtable wrote:
> In the case of a radar reflector, with wavelengths of a few cm., and the
> dimensions of any mirror being only a few wavelengths, then "diffraction",
> which some of you may recall from schooldays, plays a major part. The result
> is that even the best reflector, unless is dimensions are absolutely
> immense, reflects its energy in a spread-out, diffuse, maner, with a
> beam-width of many degrees.

I'm guessing that the beamwidth (radians) is on the order of 1 over the
width of the reflector expressed in wavelengths. So at X band (3 cm
wavelength), a reflector 30 cm aross will have a beamwidth of roughly
1/10 radian, or 6 degrees.

> But the benefit, the only benefit, that you will get from the situation of
> reflectors being small(ish) measured in wavelengths, is that because the
> reflection is so diffuse, there's no call, at all, to get any high precision
> in the relative angling of the corner faces. I would go so far as to say
> that if it looks, by eye, to be about 90 degrees between the faces, that's
> good enough.

In optics it is said that an image will not fall seriously short of
perfection if the peak to valley errors on the wavefront do not exceed
1/4 wave. Perhaps that applies to the geometry of corner cube reflectors
as well. That is, if all the surfaces coincide with a perfect corner
cube within some fraction of a wavelength, then the final reflection
will be "diffraction limited".


A companion report comparing the performance of several radar reflectors
  is now available at the MAIB:

http://www.maib.gov.uk/publications/investigation_reports/2007/ouzo.cfm

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