The impedance of free space is 377 Ohms/square. Spacepaint is a radar
absorbing technology that attempts to match this value over a range of
RF frequencies of interest. If it worked, we would not have to build
funny shaped aircraft that reduce RCS by minimizing direct return echos
(all those funny angles on the 117 are there for RCS mitigation, not
aerodynamics).
Tomm
Peter Chadwick wrote:
>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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