Message posted by Hal on March 14, 2002 at 21:53:42 PST:
Well, it's not enough to be stealthy at certain radio frequencies where an enemy has his radars, one must plan ahead and try to be stealthy at all frequencies--note I said TRY! Radar cross section is generally stated as so many square meters at a certain frequency, so yes, the RCS does vary with radio frequency. This gets a bit more messy when one considers the monostatic vs the bi-static cases. In the monostatic case, stealth wants to minimize the amt of radar energy that returns to a radar--it may go off at another angle, you just don't want it to return to the radar. In the bi-static case, you want to limit the amt of radar energy that splays off at various angles--this would be the case where a radar illuminates the stealth and reflected energy is used to guide a missile that is coming from a different direction. In making a larger 117 for example, the RCS would be approximately the same--nothing's perfect in this universe--at the same frequency. One doesn't scale the frequency in this case. One problem with making something bigger is the larger wake--and this is detectable with J and K band radars. Possibly this is the reason for the renewed interest in laminar flow with respect to an airframe--reduced wake turbelence. Another problem with making something larger is the heat signatures of larger engines. Physics can be really unkind in this realm; can really make you work hard to achieve the desired results. Yes, (in theory) a radar that could operate over a wide spectrum could be a stealth detector, but it's not that easy. Antennas are analagous to tuned circuits (actually they're impedance transformers) and they generally aren't broadbanded (multi-octave) in the microwave region. One would have to have a multitude of antennas, and feedlines (waveguide is also frequency sensitive) and then tie all of this together so that all antennas are pointing in the same direction at the same time, etc. And to preclude mutual interference, the radars/antennas would have to be operational on fractional harmonics--a 5 GHz radar would get a response on a 10 GHz receiver. I think you get the picture! It could be done, but it would be very difficult. Multiple independent radars all tied together might work. A much less problematic type of radar would be the bi-static search system. This would use one transmitter (at a time) and multiple receivers over a wide area. All of these receiver sites would have to be tied to the transmitter so as to have a common time base, and a method of correlating the received signals from all of the receiving units.
In Reply to: Re: I thought RCS was like aero on scale models posted by Joerg (Webmaster) on March 14, 2002 at 20:51:34 PST:
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