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

Bob Camp lists at rtty.us
Thu Dec 15 20:53:57 EST 2011


Hi

Looking at the gizmo they have on display, I'd bet you get a pretty good return off the bottom of the beast. Not quite as good a return off of the top. Indeed the issue does date to F-117 days, they had to calculate mission parameters to keep the "sides" from facing the wrong way...

Bob


On Dec 15, 2011, at 8:29 PM, Jim Lux wrote:

> 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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