caf@omen.UUCP (Chuck Forsberg) (04/03/91)
From: caf@omen.UUCP (Chuck Forsberg) > From: micquis!john@asuvax.eas.asu.edu (John Moore) > Regarding discussions of passively tracking via radar: > It is possible to use signals from an independent source to passively track > aircraft. There was an experiment done some years ago where aircraft in the > vicinity of LAX were tracked by a passive radar system. It used the signals > from a TV satellite as the emitter. It worked! TV Satellite? The most powerful TV satellites are about 50 watts. That 50 watts is thinly spread over a wide area. One might be able to paint a Visitors' Mother ship with such a signal, but even a C5 might be too stealthy. A UHF TV station, with peak ERP in the megawatt range, sounds more likely. The receiving antenna would require extremely low sidelobes to reject the much more powerful signal of the transmitter. (Unlike radar, the TV carrier never shuts up.) A BBC program on the early development of radar demonstrated airplane interference (flutter) on a nearby 6 mHz shortwave station. Which raises the question: how low a frequency can radar operate on? Not counting over the horizon types, the lowest I've heard of is 30 mHz. Would the British WWII early warning radar pick up stealth A/C? -- "Compared to tanks, journalists are cheap - and you get more for your money." - Saddam Hussein
rmack@desire.wright.edu (04/05/91)
From: rmack@desire.wright.edu micquis!john@asuvax.eas.asu.edu (John Moore) writes: > It is possible to use signals from an independent source to passively track > aircraft. There was an experiment done some years ago where aircraft in the > vicinity of LAX were tracked by a passive radar system. It used the signals > from a TV satellite as the emitter. It worked! That is a truly stealthy > bistatic radar. Having done quite a bit of research lately on the B-2 bomber and its probable (or improbable) effectiveness, I can tell you that the US Air Force is well aware of the threat of bi-static radar and of its possible uses. In fact, the current continental US defense radar (PAVE PAWS) system is essentially bi-static, as the signal generator and the sensors are in different locations. The PAVE PAWS system will eventually surround the US with OTH radar tracking stations, half of which (east and west coasts) are currently active. However, this is not necessarily the same as "passive" radar detecting, as the source puts out a signal that is easily detectable. The advantage is that you might place the source of the signal in a hard-to-hit location, like earth orbit, as in the above mentioned satellite example. The US, the Soviets and other nations are considering this possibility. Radar technology is being advanced in the US in particular but I still don't think we're quite ready to build radar emitting satellites. Other bi-static systems are currently being used or tested with particular emphasis on aircraft carrying the transmitters and flying behind the front lines while forward sensors pick up the reflections. BTW- The USAF dismisses bi-static radar as a serious threat to stealth bomber/fighter capabilities and I am presently inclined to agree with them. The biggest advances in radar will probably come in increased computer processing abilities that may signifigantly increase radar stealthiness and the ability to detect stealthy targets. Bob Mack, Wright State Univerity