Larry asked:
> Exactly what is the composition of radar
absorbent material and how is it applied to the metal surfaces? How does rf
absorbent material react to different ranges of wavelengths?<
RAM (Radar Absorbent Material) varies, depending on the application. For
anechoic chambers, it's usually in the form of pyramids of some foamed plastic,
heavily loaded with graphite, and is pretty filthy stuff to be touching as
you're setting up in the chamber. This works reasonably well dow to around
400MHz, depending on the size of the pyramids. For lower frequencies, powdered
ferrite is added to the mix, and even ferrite slabs are used, placed under the
pyramids. It has been known for enough energy to be absorbed from a microwave
transmitter/antenna in an anechoic chamber for the pyramids to be heated to the
point where they catch fire! Very nasty, with lots of toxic gases and fumes,
and carbon dirt EVERYWHERE!
Stealth aircraft rely heavily on the reflection back to a monostatic radar
being low, because the signal goes off in another direction - this caused by
the geometry of the various surfaces: I suspect the RAM used there is a
resistive material, possibly with ferrite loading again.
73
Peter G3RZP
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