«

Adam Chapman wrote:
> The main reason I suggested the mirror periscope idea is because ny
> aircraft needs to have a very low radar cross-section.
> A spherical gimbal would have the same radar cross section when the
> radar is looking at the aircraft from all directions, where as a simple
> flat plate mirror pokking out of the bottom would only have a
> significant radar signature over a very short range of directions.
>
> Any new ideas would be appreciated

Depends on the size of the mirror and the wavelength of the radar. If
the size of the mirror is anywhere near the wavelength of the radar,
you will not get a specular reflection, you will get a diffractive one
(physical optics, not geometrical optics, and the return will be over
much wider range of angles.

For mininum radar return from the mirror it could have a glass
substrate and a multi-layer interference coating (reflective at desired
wavelength). Coating materials selected to minimize response at radar
frequency. Unfortunately, such a mirror will take a fairly
sophisticated effort to design. For that matter, the radar return from
a rectangular metal mirror at a given wavelength is not trivial to
compute either, especially when combined with a complex structure. One
way out is to use a gimballed structure shaped not spherically, but
some other low cross-section shape, with a window coated with metallic
or at least conductive coating that is transparent to IR. Such windows
have been developed for some time for use in stealthy aircraft.