yarvin-norman@CS.YALE.EDU (Norman Yarvin) (02/28/91)
From: yarvin-norman@CS.YALE.EDU (Norman Yarvin) I have a few questions about radar. First, in a radar searching for airplanes, to get a three-dimensional picture the beam must be scanned over all combinations of two angles. This seems like it would take unduly long, to give any precision. A lower bound on resolution is given by the wavelength, but how precise are radars in practice? Do many of them simply not determine height? Do they determine height in some other manner than scanning the beam TV-style? Second, radars on fighters seem to be located in the nose cone, and to point forward. The AWACS planes seem to have a large radar, in the shape of a disc attached to the top of the plane. What is the mechanism these radars use to scan their beams? I know of two classes of mechanisms: phased-array grids, and the rotation of an antenna. These don't need to be visible; they might be concealed/protected behind radar-transparent material. Is the AWACS's disk shielding a rotating antenna? And what sort of mechanism can fit in a fighter's nose? Second, the limit on a radar's range is due to a combination of antenna geometry and output power. Is it the AWACS's superior antenna or its higher power that gives it range advantages over fighter radars? Norman Yarvin yarvin-norman@cs.yale.edu "...those skilled at attack maneuver in the highest heights of the sky. Thus they can preserve themselves and gain complete victory." -- Sun Tzu, _The Art of War_
rats@ihlpm.att.com (David Woo) (03/01/91)
From: rats@ihlpm.att.com (David Woo) |From: yarvin-norman@CS.YALE.EDU (Norman Yarvin) |Second, radars on fighters seem to be located in the nose cone, and to point |forward. The AWACS planes seem to have a large radar, in the shape of a |disc attached to the top of the plane. What is the mechanism these radars |use to scan their beams? I know of two classes of mechanisms: phased-array |grids, and the rotation of an antenna. These don't need to be visible; they |might be concealed/protected behind radar-transparent material. Is the |AWACS's disk shielding a rotating antenna? And what sort of mechanism can |fit in a fighter's nose? AWACS uses a rotating antenna underneath the rotating radome. Fighter aircraft can use a mechanical fully-scanned radar. Other possibilities include a mechanically scanned phased-array radar. Why, per chance, do you want a mechanically scanned phased-array radar? Because a phased-array radar may be limited in it's angle of scan via electronic means. Some versions of American cruise missiles use a mechanically scanned phased-array radar for precisely this reason. Previously, many American military aircraft utilised hydraulics to scan the radar antennas. Advances in brushless DC motordrive technology have allowed these troublesome beasts to be replaced with electric actuators. It allows for new possibilities, for example, Wright-Patterson was working on replacing the old actuators on the C-130 radar with superior actuators to allow the C-130 to become terrain following, like the F-111. However, the project was killed to to lack of funds.
nak%archie@att.att.com (Neil A Kirby) (03/01/91)
From: nak%archie@att.att.com (Neil A Kirby) In article <1991Feb28.052606.10693@cbnews.att.com> yarvin-norman@CS.YALE.EDU (Norman Yarvin) writes: [radar stuff deleted] >Second, radars on fighters seem to be located in the nose cone, and to point >forward. The AWACS planes seem to have a large radar, in the shape of a >disc attached to the top of the plane. What is the mechanism these radars >use to scan their beams? Video footage shows that the entire disk on the E-3 AWACS rotates. I'm not sure about the hawkeye. Most modern fighters used phased array grids in the nose. >Second, the limit on a radar's range is due to a combination of antenna >geometry and output power. Is it the AWACS's superior antenna or its higher >power that gives it range advantages over fighter radars? Both. Most tactical fighters can't possibly house a big antenna or the high power gear to really light one up. Neil Kirby
brian@uunet.UU.NET (brian douglass personal account) (03/01/91)
From: edat!brian@uunet.UU.NET (brian douglass personal account) In article <1991Feb28.052606.10693@cbnews.att.com> yarvin-norman@CS.YALE.EDU (Norman Yarvin) writes: >Is the >AWACS's disk shielding a rotating antenna? And what sort of mechanism can >fit in a fighter's nose? The AWACS radome rotates itself, as the whole thing is an antenna. The radar in a fighter sweeps back and forth while pointed forward. > >Second, the limit on a radar's range is due to a combination of antenna >geometry and output power. Is it the AWACS's superior antenna or its higher >power that gives it range advantages over fighter radars? > I think both, but others know better than I. The real advantage is in tactics. AWACS could spot an aircraft across the the whole of Iraq, and direct fighters to intercept. This while the figthers hav their radars off and give no signature. This allowed Coalition forces to crawl right into an Iraqis tail, and then "burn em down" when he turns on his fire control radar. Poor dumb Iraqi has every buzzer and alarm go off in his cockpit just as an AIM-9J slides up his tail pipe. Rumor is that the radar on an F-15C is so good, it can actually count the number of blades on an oncoming jet's engines, and then determine what kind of plane it is based on this and profile. This at 20 miles out! Anyway, that is the rumor, but it comes from someone (not I) who should know. Could anyone else elaborate? -- Brian Douglass brian@edat.uucp "Do you know what Saddam Hussein and his father have in common?" "Neither one knows when to pull out!"
mmitchel@msd.gatech.edu (Mark A. Mitchell) (03/05/91)
From: mmitchel@msd.gatech.edu (Mark A. Mitchell) yarvin-norman@CS.YALE.EDU (Norman Yarvin) wrote: } } First, in a radar searching for }airplanes, to get a three-dimensional picture the beam must be scanned over }all combinations of two angles. Precise radars are rarely used for hemispherical searches. Most systems or implacements or ships (etc.) have multiple systems: search radars, target acquisition radars, and target track radars. (The first two functions and even all three are sometimes combined.) The typical search radar rotates in azimuth and has a "fan" beam of some sort in elevation to cover most of a hemisphere (generally speaking, angles close to the zenith are ignored.) } Do many of them simply }not determine height? Do they determine height in some other manner than }scanning the beam TV-style? Yes, some simple search radars do not determine height or elevation angle. Many do, however, and there are a number of ways to acheive this. One method is a set of stacked elevation beams. Phased arrays and frequency- scanned arrays used this method. A number of other methods are described in [1]. }Second, radars on fighters seem to be located in the nose cone, and to point }forward. The AWACS planes seem to have a large radar, in the shape of a }disc attached to the top of the plane. What is the mechanism these radars }use to scan their beams? I know of two classes of mechanisms: phased-array }grids, and the rotation of an antenna. Those are probably the predominant methods. There are others, such as frequency-scanning, frequency-selective scanning lenses, feed scanning, etc. [1] provides more detail than most anyone could need. } Is the }AWACS's disk shielding a rotating antenna? And what sort of mechanism can }fit in a fighter's nose? Yes, the AWACS disk is a rotating radome and search antenna. Phased-arrays, mechanically scanned reflectors, and mechanically scanned (non-phased-) arrays are used in the nosecones of fighter aircraft. }Second, the limit on a radar's range is due to a combination of antenna }geometry and output power. Is it the AWACS's superior antenna or its higher }power that gives it range advantages over fighter radars? Both, but especially the antenna size and unlimited azimuth scan. [1] _Microwave_Scanning_Antennas_,_Vol._I_, ed. R.C. Hansen, Peninsula Publishing, Los Altos, CA, 1985, pp. 163-165. -- "If all else fails, immortality can always | Mark A. Mitchell Georgia Tech be assured by a spectacular error." | mmitchel@msd.gatech.edu
mmitchel@msd.gatech.edu (Mark A. Mitchell) (03/05/91)
From: mmitchel@msd.gatech.edu (Mark A. Mitchell) nak%archie@att.att.com (Neil A Kirby) wrote: } }Most modern fighters used phased array grids in the nose. Umm ... No. There may be some confusion here about what a phased-array is. A phased-array is an electronically scanned device with active phase shifters at each radiating element. There are non-phased arrays, usually called something like "slotted waveguide array" or "planar array". This is what you will find in the nose of an F-14,-15,-16, or -18. These arrays are mechanically steered. Slightly older vintage fighters use mechanically scanned reflector antennas, e.g. F-4 and F-111. The U.S. does have one phased-array equipped combat aircraft: the B-1B. It has a phased-array with mechanical augmentation. (Details of all these aircrafts' radars can be found in _Jane's_Weapon_Systems_.) -- "If all else fails, immortality can always | Mark A. Mitchell Georgia Tech be assured by a spectacular error." | mmitchel@msd.gatech.edu
henry@zoo.toronto.edu (Henry Spencer) (03/05/91)
From: henry@zoo.toronto.edu (Henry Spencer) >From: edat!brian@uunet.UU.NET (brian douglass personal account) >Rumor is that the radar on an F-15C is so good, it can actually >count the number of blades on an oncoming jet's engines, and then >determine what kind of plane it is based on this and profile. This >at 20 miles out! Anyway, that is the rumor, but it comes from >someone (not I) who should know. Could anyone else elaborate? I doubt that anyone can elaborate in an unclassified way. Techniques like this, which come under the general heading of "non-cooperative target identification", are the deepest and darkest secrets in radar technology today. Even radars exported to supposedly-trusted allies often omit any n-c-t-i provisions present in the original. -- "But this *is* the simplified version | Henry Spencer @ U of Toronto Zoology for the general public." -S. Harris | henry@zoo.toronto.edu utzoo!henry
henry@zoo.toronto.edu (Henry Spencer) (03/05/91)
From: henry@zoo.toronto.edu (Henry Spencer) >From: nak%archie@att.att.com (Neil A Kirby) >Video footage shows that the entire disk on the E-3 AWACS rotates. I'm not >sure about the hawkeye. Likewise. At least one of the earlier Navy radar aircraft had a fixed radome with a rotating antenna inside, but that approach was discarded as inferior. >Most modern fighters used phased array grids in the nose. Actually, most modern fighters use mechanically-scanned flat-plate antennas. True phased-array antennas, with all or most of the scanning done by phase shifting, are just starting to be practical for fighters. The problem with phased arrays is all the electronics needed to make them work; modern semiconductors are just now getting to the point of making them viable for combat aircraft. It's easy to be confused by the flat-plate antennas. These can be considered as phased arrays that point in one fixed direction, at right angles to the plate. Building this kind of antenna is not that big a deal; it's making the phase relationships, and hence the beam direction, variable that costs heavily in electronics. The flat-plate antennas have various advantages over the old dish antennas, but they share the property that they have to be mechanically scanned. I think the only combat aircraft in active service that has a phased-array antenna is the B-1B, which got a significant reduction in head-on radar cross-section out of replacing the B-1A's dish with a phased-array antenna tilted somewhat downward. Several of the next-generation fighter radars are planned to be phased arrays, but I don't believe any of them is flying yet. -- "But this *is* the simplified version | Henry Spencer @ U of Toronto Zoology for the general public." -S. Harris | henry@zoo.toronto.edu utzoo!henry
scott@swindle.Berkeley.EDU (Scott Silvey) (03/05/91)
From: scott@swindle.Berkeley.EDU (Scott Silvey) nak%archie@att.att.com (Neil A Kirby) writes: |> Both. Most tactical fighters can't possibly house a big antenna or the |> high power gear to really light one up. I've heard that if there are nearby aircraft, the AWACS shuts off it's radar ... otherwise the pilots get cooked from the massive radiation output. Also, it's apparently dangerous to walk in front of a fighter operating it's radar on the ground for the same reasons. /-----------------------------------------------------------------------------\ | Scott Silvey | Message actually given by rn: | | scott@xcf.berkeley.edu | | | | "****** 33993 unread articles in comp.windows.x... | | Flames to /dev/null | ...read now? [ynq]" | \-----------------------------------------------------------------------------/
scott@swindle.Berkeley.EDU (Scott Silvey) (03/05/91)
From: scott@swindle.Berkeley.EDU (Scott Silvey) edat!brian@uunet.UU.NET (brian douglass personal account) writes: |> Rumor is that the radar on an F-15C is so good, it can actually |> count the number of blades on an oncoming jet's engines, and then |> determine what kind of plane it is based on this and profile. This |> at 20 miles out! Anyway, that is the rumor, but it comes from |> someone (not I) who should know. Could anyone else elaborate? I have also heard of the "target ID" feature on some US fighters, but I have no idea how it works. I would doubt that the radar could actually resolve the individual whirling blades and then count them ... perhaps it might use something tricky like doppler-shift?. It would have to go right down the tail pipe or intakes anyway. I would guess a computer tries to measure the radar signature and perhaps the RWR measures radar output of an oncomming aircraft, comparing such numbers with some prepared catalog of known parameters? /-----------------------------------------------------------------------------\ | Scott Silvey | Message actually given by rn: | | scott@xcf.berkeley.edu | | | | " ****** 33993 unread articles in comp.windows.x, | | Flames to /dev/null | read now? [ynq] " | \-----------------------------------------------------------------------------/
urbanf@tuura.UUCP (Urban Fredriksson) (03/06/91)
From: urbanf@tuura.UUCP (Urban Fredriksson) edat!brian@uunet.UU.NET (brian douglass personal account) writes: >From: edat!brian@uunet.UU.NET (brian douglass personal account) >In article <1991Feb28.052606.10693@cbnews.att.com> yarvin-norman@CS.YALE.EDU (Norman Yarvin) writes: >>Is the >Rumor is that the radar on an F-15C is so good, it can actually >count the number of blades on an oncoming jet's engines, and then >determine what kind of plane it is based on this and profile. This >at 20 miles out! Anyway, that is the rumor, but it comes from >someone (not I) who should know. Could anyone else elaborate? There was a US project in the 1970's ('Musketeer'?) which supposedly studied ways to distinguish between different aircraft types using radar. One thing it was looking for was different engine characteristics. Counting the blades I don't really believe, but doppler effect and vibrations maybe? There definitely is some work beeing done in this field, because it has been officially stated that the aircraft recognition libraries will not be shared between the four nations in the EFA programme. | Urban Fredriksson |"The enemy of your enemy is not | I do NOT speak | | Stockholm, Sweden | always your friend." | for my employer! | | I will be off the Net during April and June |
major@uunet.UU.NET (Mike Schmitt) (03/06/91)
From: bcstec!shuksan!major@uunet.UU.NET (Mike Schmitt) > I've heard that if there are nearby aircraft, the AWACS shuts off it's > radar ... otherwise the pilots get cooked from the massive radiation output. The radar acts just like a big microwave oven. Static electricity build up is the big concern. The fear is that if the fighter gets too close to the AWACS - it will jetison ordnance and/or trigger the ejection seat. (Now THAT will ruin your day!). However, that has never happened. According to old AWACS operators around here - if fighters get too close they are told to stay away - that AWACS isn't going to move - so you'd better stand off. During refuel of AWACS - at around 1/4 mile - the radar is turned "off" (or goes to 'dummy load'). During refueling - the boom operator is in direct line of the radar dome. During AWACS operations in Korea - Korean fighter pilots liked to fly real close to AWACS - guess they were cooking their kim chi (sp?). No need to worry on the ground - the AWACS radar is not operated below 18,000 feet. mike schmitt