[time-nuts] "The GPS navigation is the weakest point,"

Jim Lux jimlux at earthlink.net
Thu Dec 15 20:29:53 EST 2011


On 12/15/11 4:53 PM, Bob Camp wrote:
> Hi
>
> Radar bounces off the flat sides very nicely ….
>

You are right, it does, but it doesn't bounce BACK towards the observer, 
which is what you care about.  Consider a flat plate at a 45 degree 
angle from you.  All the radar energy bounces to the side.  Turns out 
that it's diffraction from the edges of those sides that's the limiting 
aspect.


The first stealth planes (e.g. F-117) were all flat surfaces because you 
could actually calculate the reflections and make sure you didn't 
inadvertently create a corner reflector.

This is one reason that bistatic radar (transmitter and receiver in 
different places) is interesting.  You can detect things that have very 
low monostatic radar cross section (RCS).  (also, radar transmitters are 
easy to shoot at, because they're like a big beacon saying "here I 
am"... so put out a bunch of transmitters and one receiver and have the 
expensive signal processing and operators at the receiver, which is 
entirely passive).

Even better, you can use something benign as an illuminator... Many of 
us have used a TV station as a passive illuminator for a bistatic radar, 
using your analog TV set as the detector.


Later, as computational horsepower increased, they could make nice 
swoopy surfaces with low RCS, and what's more to the point, low bistatic 
RCS.





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