From: owner-skunk-works-digest@netwrx1.com (skunk-works-digest) To: skunk-works-digest@netwrx1.com Subject: skunk-works-digest V9 #41 Reply-To: skunk-works@netwrx1.com Sender: owner-skunk-works-digest@netwrx1.com Errors-To: owner-skunk-works-digest@netwrx1.com Precedence: bulk skunk-works-digest Tuesday, June 13 2000 Volume 09 : Number 041 Index of this digest by subject: *************************************************** FWD (EXT) Re: National Missile Defense [was - eeyore and tigger] Re: FWD (EXT) Re: National Missile Defense [was - eeyore and tigger] XF-19 Boeing E-3 Sentry Grumman E-2 Hawkeye Lockheed P-3 Orion Re: FWD (EXT) Re: National Missile Defense RCS reduction of radar antennas Re: RCS reduction of radar antennas *************************************************** ---------------------------------------------------------------------- Date: Sun, 11 Jun 2000 14:42:44 -0700 From: "Terry W. Colvin" Subject: FWD (EXT) Re: National Missile Defense [was - eeyore and tigger] You may have heard by now about how the national missile defense is all a big reaganesque fantasy, etc. I was just wondering if anyone here has any strong opinions in this regard. The local paper, the San Jose Mercury News, decided to cash in its credibility thus: they ran an article with a column on the front page and the entiiiiirrrre baaack paaaage, going on and on about how the concept is flawed, would neeeeever work, how it was all a big boon- doggle, how 4 out of 5 defense scientists surveyed agreed it would never work, etc. That was in Wednesday's paper. The entire back page. In all that verbiage, there was not one word in there, not a single word, about the last two THAAD missile firings, both successful. I suppose there was some bizarre line of reasoning that lead to the decision that the fact that a feat has already been accomplished is irrelevant to the arguement of whether or not it is possible. The saaaammme daaaaay that the huge negative article was running, the defense scientists at Sandia used a ground base laser to destroy an incoming missile. Think about that for a minute. That story was reported in the Merc, on page 10A, twoooo seeennnntences, one of which was totally irrelevant to the event, having to do with Israelis vs Lebanese or something. So. One sentence. Vs the back page. I would have let it drop, but today they ran ANOTHER eeyore article. you remember Eeyore, the donkey? Dismal, droopy character, not extropian at all: "It'll never wooork, oh deeear, woooe is meeee...", whereas Tigger is more my style, bouncing around on his tail, always having fun and enjoying life: Woo hoo! Wooo hooo! So I fired off a letter to the editor, scolding him, asking if they had anyone there at that paper who was responsible for *balance*. In the Eeyore article, there was no actual news. All of it was merely political commentary. When an actual news item happened, they gave it two sentences. Was this the Mercury *News*, or was it the San Jose Mercury Propaganda Sheet? Could they manage to mix a little Tigger with the Eeyore? I know some say the National Missile Defense could be made to work but shouldnt. I guess we need to wait until a city is actually nuked off the face of the earth to start developing such a thing? What say ye, extropians? spike - --------------- >the last two THAAD missile firings, both successful. I'd be very skeptical of the military's claim of success. The main problem has always been distinguishing the warhead from the cloud of decoys that would certainly be there. A few years ago they claimed to have solved the problem and had a successful test, but much later it turned out that they'd installed a electric heater on the mock warhead so it gave off a much stronger infrared signal. The latest round of testing is no more honest a inside informant told the New York Times on Friday. With realistic decoys the system had absolutely no luck finding the warhead so they just dumbed down the testing. First they reduced the number of decoys, it didn't help, then they tried to make sure the radar signal of the decoys was either much greater or much less than the decoys and that did help, but not enough. Finely they made sure all decoys were highly polished and perfectly spherical so their radar signature wouldn't change, the mock warhead was cone shaped and as it tumbled the radar signal flashed and made it very easy to spot. > You may have heard by now about how the national missile defense > is all a big reaganesque fantasy, etc. I was just wondering if anyone > here has any strong opinions in this regard. I think it's a screwy idea. It would never work against a massive attack because defense will always be more expensive than offence, if it takes 10 dollars to shoot down 10 cents of hardware the other side will just overwhelm you. As for a small attack, well if I were an insane dictator of some little jerkwater country I wouldn't use ICBM's to deliver my bombs, they're harder to make than nukes and much more expensive; I'd use FedEx or UPS to deliver my H Bomb, the transportation would only cost a few dollars not a few billion. It has other advantages too, a rocket can be tracked so everyone would know who was responsible for having Manhattan vaporized, America might be irritated at me. Better if things just go boom and nobody knows why. I could even send a letter of condolence afterwards. John K Clark - -- Terry W. Colvin, Sierra Vista, Arizona (USA) < fortean1@frontiernet.net > Home Page: < http://www.geocities.com/Area51/Stargate/8958/index.html > Sites: Fortean Times * Northwest Mysteries * Mystic's Cyberpage * TLCB * U.S. Message Text Formatting (USMTF) Program - ------------ Member: Thailand-Laos-Cambodia Brotherhood (TLCB) Mailing List TLCB Web Site: < http://www.tlc-brotherhood.org >[Allies, CIA/NSA, and Vietnam veterans welcome] Southeast Asia (SEA) service: Vietnam - Theater Telecommunications Center/HHC, 1st Aviation Brigade (Jan 71 - Aug 72) Thailand/Laos - Telecommunications Center/U.S. Army Support Thailand (USARSUPTHAI), Camp Samae San (Jan 73 - Aug 73) - Special Security/Strategic Communications - Thailand (STRATCOM - Thailand), Phu Mu (Pig Mountain) Signal Site (Aug 73 - Jan 74) ------------------------------ Date: Mon, 12 Jun 2000 01:44:20 -0700 From: JAZ Subject: Re: FWD (EXT) Re: National Missile Defense [was - eeyore and tigger] >You may have heard by now about how the national missile defense >is all a big reaganesque fantasy, etc. I was just wondering if anyone >here has any strong opinions in this regard. I really don't trust the government on the validity of their testing. I remember when the Sgt. York gun was being tested and they said it passed a test. The target even though it was rated as "killed" kept flying and had to be shot down after it left the gunnery range. On the other hand, if China or N. Korea nukes Los Angeles, I don't think there will be a city left standing in the agressor country, and the people of the United States will demand a defense system, and we will end up with one that works or heads will roll. James Zuchelli ------------------------------ Date: Mon, 12 Jun 2000 08:51:18 -0700 From: David Lednicer Subject: XF-19 Andreas, here's how you can find the document: go to: http://techreports.larc.nasa.gov/cgi-bin/NTRS only put a check in the box next to: CASITRS (RECONselect) type: "XF" in the search box and hit "Begin Search" the document I found will be second on the list. BTW - I see you have moved from Michigan to New Mexico. How do you like the change in weather? (I grew up in Michigan and know how awful it can get!) ------------------------------ Date: Mon, 12 Jun 2000 13:19:20 -0700 From: "Terry W. Colvin" Subject: Boeing E-3 Sentry Based on a civil airframe The E-3 is a costly machine, yet as an airborne warning and control system it is a very cost effective "force multiplier". First flown in the EC-137D prototype, the Westinghouse APY-1 surveillance radar is mounted with its antenna in the large rotodome above the rear fuselage to search to a radius of 250 miles (402 km). The airframe is based on that of the Model 707-320B civil transport, and the first of 24 Core E-3A Sentries entered service in March 1977. Steady improvement The next 10 aircraft were completed as Standard E-3A Sentries, as were NATO's 18 aircraft. Older aircraft have been upgraded, and the operators can monitor all air activities within radar range and control the efforts of friendly air units. Inflight refueling capability boosts endurance most usefully. Principal versions Core E-3A (initial model with nine display consoles), Standard E-3A (10 US and 18 NATO aircraft with greater computing power, improved communications, and overwater capability), E-3A/Saudi (five Saudi Arabian aircraft with CFM56 turbofans but inferior communications), E-3B (Core E-3As upgraded to Standard E-3A configuration), E-3C (updated Standard E-3As with five more consoles and improved communications), E-3D (seven British aircraft with CFM56 engines and improved electronic support measures due to enter service from 1991 as Sentry AEW.Mk 1s), and E-3F (four French aircraft similar to the E-3D). Principal users France, Great Britain, NATO, Saudi Arabia, and USA. Technical Data Type: Boeing E-3A Sentry 20-seat airborne warning and control system plane. Engines: four 21,000-lb (9,526-kg) thrust Pratt & Whitney TF33-P-100/100A turbofans. Performance: maximum speed 530 mph (853 km/h) at 29,000 ft (8,840 m); initial climb rate not revealed; operating ceiling 29,000 ft (8,840 m); range 1,000 miles (1,609 km) for a 6-hour patrol. Weights: empty not revealed; maximum take-off 325,000 lb (147,418 kg). Dimensions: span 145 ft 9 in (44.42 m); length 152 ft 11 in (46.61 m); height 41 ft 9 in (12.73 m); wing area 3,050.0 sq ft (283.35 m^2). Armament: none. - -- Terry W. Colvin, Sierra Vista, Arizona (USA) < fortean1@frontiernet.net > Home Page: < http://www.geocities.com/Area51/Stargate/8958/index.html > Sites: Fortean Times * Northwest Mysteries * Mystic's Cyberpage * TLCB * U.S. Message Text Formatting (USMTF) Program - ------------ Member: Thailand-Laos-Cambodia Brotherhood (TLCB) Mailing List TLCB Web Site: < http://www.tlc-brotherhood.org >[Allies, CIA/NSA, and Vietnam veterans welcome] Southeast Asia (SEA) service: Vietnam - Theater Telecommunications Center/HHC, 1st Aviation Brigade (Jan 71 - Aug 72) Thailand/Laos - Telecommunications Center/U.S. Army Support Thailand (USARSUPTHAI), Camp Samae San (Jan 73 - Aug 73) - Special Security/Strategic Communications - Thailand (STRATCOM - Thailand), Phu Mu (Pig Mountain) Signal Site (Aug 73 - Jan 74) ------------------------------ Date: Mon, 12 Jun 2000 13:58:49 -0700 From: "Terry W. Colvin" Subject: Grumman E-2 Hawkeye Early warning comes of age After the Second World War airborne surveillance radar made rapid progress, making it possible to detect increasingly smaller objects at ever lengthening ranges. This led to the concept of airborne early warning planes, including the Grumman E-1 Tracer for the US Navy. To succeed this plane, Grumman produced the E-2. The prototype flew in October 1960, and the E-2A entered service in January 1964. Advanced electronics The late 1960s and the 1970s saw a revolution in electronic miniaturization, allowing the creation of more capable radars and advanced computers to aid in the assessment of radar and other data. This turned the Hawkeye from an AEW platform into a true warning and command system able to watch airspace to a radius of 300 miles (483 km), tracking more than 2,000 surface and air targets, and directing 40 friendly fighters. More than 215 aircraft have been ordered. Principal versions E-2A (initial model with APS-96 radar capable of overwater operation), E-2B (conversion with APS-120 radar and a more capable computer system adding overland capability), E-2C (definitive model delivered from 1973 with APS-125 radar and ALR-59 electronic support measures, being replaced by APS-138/139 radar and ALR-73ESM, to be replaced by APS-145 radar), and TE-2C (trainer). Principal users Egypt, Israel, Japan, Singapore, and USA. Technical Data Type: Grumman E-2C Hawkeye five-seat carrier-borne and land based airborne early warning and command system plane. Engines: two 4,910-ehp (3,663-kW) Allison T56-A-425 turboprops. Performance: maximum speed 374 mph (602 km/h) at optimum altitude; initial climb rate not revealed; service ceiling 30,800 ft (9,390 m); radius 200 miles (322 km) for a 4-hour patrol. Weights: empty 38,063 lb (17,265 kg); maximum take-off 51,933 lb (23,556 kg). Dimensions: span 80 ft 7 in (24.56 m); length 57 ft 6.75 in (17.54 m); height 18 ft 3.75 in (5.58 m); wing area 700.0 sq ft (65.03 m^2). Armament: none. - -- Terry W. Colvin, Sierra Vista, Arizona (USA) < fortean1@frontiernet.net > Home Page: < http://www.geocities.com/Area51/Stargate/8958/index.html > Sites: Fortean Times * Northwest Mysteries * Mystic's Cyberpage * TLCB * U.S. Message Text Formatting (USMTF) Program - ------------ Member: Thailand-Laos-Cambodia Brotherhood (TLCB) Mailing List TLCB Web Site: < http://www.tlc-brotherhood.org >[Allies, CIA/NSA, and Vietnam veterans welcome] Southeast Asia (SEA) service: Vietnam - Theater Telecommunications Center/HHC, 1st Aviation Brigade (Jan 71 - Aug 72) Thailand/Laos - Telecommunications Center/U.S. Army Support Thailand (USARSUPTHAI), Camp Samae San (Jan 73 - Aug 73) - Special Security/Strategic Communications - Thailand (STRATCOM - Thailand), Phu Mu (Pig Mountain) Signal Site (Aug 73 - Jan 74) ------------------------------ Date: Mon, 12 Jun 2000 14:11:59 -0700 From: "Terry W. Colvin" Subject: Lockheed P-3 Orion Submarine hunter At the end of the 1950s the US Navy needed a replacement for its Lockheed P2V Neptune anti-submarine plane, and Lockheed won the contract with a derivative of its L-188 Electra airliner. The Orion prototype flew in November 1959 with a fuselage revised for advanced electronics and a long weapon bay. New systems and job satisfaction During a long production life due to end only in the early 1990s, the P-3 went through three major versions totalling more than 750 aircraft, and is to be supplemented by the P-7, which is in essence a completely updated P-3 with new engines. Principal versions P-3A (165 of the initial version with water/alcohol-injected T56-A-10W turboprops each delivering 4,500 shp/3,356 kW), P-3B (152 of an improved version with T56-A-14 engines and the Deltic tactical processing system), P-3C (definitive model with the A-NEW electronic system, later aircraft being delivered in steadily improved Update I, Update II, and Update III forms), CP-140 Aurora (aircraft for Canada with the electronic suite of the Lockheed S-3 Viking). Principal users Australia, Canada, Iran, Japan, The Netherlands, New Zealand, Norway, Pakistan, Portugal, Spain, and USA. Technical Data Type: Lockheed P-3C Orion 10-seat maritime patrol and anti-submarine plane. Engines: four 4,910-shp (3,661-kW) Allison T56-A-14 turboprops. Performance: maximum speed 473 mph (761 km/h) at 15,000 ft (4,570 m); initial climb rate 1,950 ft (594 m) per minute; service ceiling 28,300 ft (8,625 m); radius 1,550 miles (2,494 km) for a 3-hour patrol. Weights: empty 61,490 lb (27,892 kg); maximum take-off 142,000 lb (64,410 kg). Dimensions: span 99 ft 8 in (30.37 m); length 116 ft 10 in (35.61 m); height 33 ft 8.5 in (10.29 m); wing area 1,300.0 sq ft (120.77 m^2). Armament: up to 20,000 lb (9,072 kg) of disposable stores. Note: Some P-3 Orions carry depth charges and rockets. [TWC] - -- Terry W. Colvin, Sierra Vista, Arizona (USA) < fortean1@frontiernet.net > Home Page: < http://www.geocities.com/Area51/Stargate/8958/index.html > Sites: Fortean Times * Northwest Mysteries * Mystic's Cyberpage * TLCB * U.S. Message Text Formatting (USMTF) Program - ------------ Member: Thailand-Laos-Cambodia Brotherhood (TLCB) Mailing List TLCB Web Site: < http://www.tlc-brotherhood.org >[Allies, CIA/NSA, and Vietnam veterans welcome] Southeast Asia (SEA) service: Vietnam - Theater Telecommunications Center/HHC, 1st Aviation Brigade (Jan 71 - Aug 72) Thailand/Laos - Telecommunications Center/U.S. Army Support Thailand (USARSUPTHAI), Camp Samae San (Jan 73 - Aug 73) - Special Security/Strategic Communications - Thailand (STRATCOM - Thailand), Phu Mu (Pig Mountain) Signal Site (Aug 73 - Jan 74) ------------------------------ Date: Mon, 12 Jun 2000 17:25:19 -0700 From: Timothy Toth Subject: Re: FWD (EXT) Re: National Missile Defense >You may have heard by now about how the national missile defense >is all a big reaganesque fantasy, etc. I was just wondering if anyone >here has any strong opinions in this regard. I don't think the problem is the validity of their testing but rather the validity of their claims. I can't imagine them being crazy enough to do tests that have no validity at all, just for the sake of it. After all they do prefer to fight with things that work, which may happen to be the reason why they have to make false claims (to keep the money flowing in, for further devellopement) You also have to keep in mind that such a system could never work with just one type of weapon. One has to imagine several systems (For example what about laser weapons...) , probably each having some flaws, or weak points, each taking down a certain number of weapons, ending up with a result as close to 100% as possible (just like carrier defence or air defence). Each system just like all other major weapon systems would continuously be improved once in service, and newer improved weapons would be built with the knowledge gained from the older weapons. Officialy the 100 interceptors proposed would only be capable of defeating a maximum of 25 to 30 warheads (and that probably includes some decoys). But then other systems are being developped and more interceptors have been proposed. What is amusing is how all this is being politically used by other states (especially Russia and China) to create tensions, between NATO allies. One has to remember several things. Even the Russians recognize that even with 1000-1500 warheads such a system would have no effect (the start treaty just signed by the Russians sets the limit at 3500 but the Russians still have about 20.000 warheads stockpiled, which America is paying to destroy, with not much result it seems). The Russians and Chinese are both advanced in Laser defence systems, and are cooperating on a Chinese system that has just been tested. The Russians already have an ABM system (currently ABM-3), as it so detabilised the world, as they claim an american system would? It is supposed to be only capable of defending Moscow, but if the Americans can defend a country with a limited system why can't the Russians? The Russians admit then deny that several countries are threats but at the same time they fully recognize that they provide most of these states with nuclear technology. All the research in these fields have yielded significant results that can be used for other applications. In addition to all this you have to remember that for a lot of people a nuclear weapon is still just a weapon and a nuclear 'war' just a war, which you have to make as 'winnable' as possible. Which is why hardened centers are built, and which is why the Russians have invested so much in the last few years in mobile launchers and hardened centers (more than 200 according to some estimates). The system currently officialy proposed is a limited capability system designed more to avoid blackmail by certain unstable people rather than a system capable of defeating a major attack. In the same trend you will notice that there has been a lot of things going on (major exercices for example) related to reactions/avoidance of act of terrorim using WMD against the US. What we are seeing is just a little show, and I hope you all appreciate it a such (For example I hope you all had as good a laugh as I did when it was revealed that Puttin's great proposition for cooperation implied that the system be deployed in Russia and not in the US, supposedly because they are closer to the 'rogue countries'.) All this talk about possible ABM systems is just like the fabulous revelation made a few years back that the US had 'invisible' aircraft (when in fact stealth aircraft had already existed for quite some years). I am not saying that the US has a capable ABM system already fielded, but neither do I say that the US has 'invisible' aircraft. Timothy ------------------------------ Date: Mon, 12 Jun 2000 22:04:27 -0700 From: Timothy Toth Subject: RCS reduction of radar antennas On the difficulties of integrating radar antennas in stealth platforms... Reflections from antennas can amount to an important part of the RCS of an aircraft, and of course simply covering the radome with RAM is impossible as it would preclude all return signals from reaching the radar antenna. Finding info on the subject is not easy, but this is what I have. Does anyone have other ideas/info ? (not classified of course!). And What do you think they did for the B-2, F-22, JSF? - -limit the number of antennas: by the use of multi purpose/reconfigurable antennas such as Phased array antenna, or 'smart antennas' (for eg. the 1997 US navy MERS demonstration program where 1 antenna replaced 18 antennas for IFF, UHF com, JTDS etc...) - -minimum dicontinuities: Discontinuities in shape or material result in higher RCS. To reduce these discontinuities conformal antennas or antennas matching the contour of the platform can be used. The 'smart skin' concept goes even further, the aim being to make part of the skin of the aircraft act as antennas (it also has many other application). A lot of US companies (including Lockheed Martin) involved in defense programs are developping (producing?) smart skins. I don't know where the B-2 stands as far as smart skins are concerned, because (officialy at least) even the F-22 is 'too old' a design to incorporate such technologies. However for the JSF smart skins have resulted, in addition to a reduction of the RCS, to savings estimated at $3.3 million and a 1.000 lb. per aircraft. - -smart radome: fabricated from frequency selective surfaces (FSS). A simple type of "smart radome" is a standard radome covered by a metallic film in which an array of small openings is made, the 'pattern' being specifically taillored to the frequency used by the radar. Out-of-band signals are still confronted by the equivalent of a continuous metal surface, because the openings are too small to let a meaningfull amount of microwave energy penetrate the film. A more complex type would be a dielectric radome , some suggest that this is what the B-2 is using (this would then be in the form of several layers of dielecrtic material each covering a different part of the spectrum). The problem with such a system is that the antennas would not be stealthy at their own working wavelenghts, and if you add to that the wide part of the spectrum at which these antennas would work...* - -Cancellation: Passive cancellation deliberately adds reflections to an antenna in an attempt to cancel out naturally occurring antenna reflections. But there are hundreds of reflection sites that must be balanced, and a small change in the frequency of the interrogating radar could convert a cancellation to a reinforcement. Thus this approach does not generally suffice. With active cancellation (a.k.a. active loading), the target must be smart enough to sense the angle of arrival, strength, frequency and waveform of the interrogating signal, then be smart enough to know the characteristics of its own reflection at the incident interrogator’s parameters. Finally, it must be fast enough to generate a signal with the proper phase and amplitude to just cancel the natural reflections. *The APQ-181 operates in the Ku-band (12-18GHz) and uses two radar electronically-scanned antennas.Ku-band radars suffer more from atmospheric absorption than X-band (10 GHz usually used by airborne radars) , and normally require more time and more power to scan a given volume. But, they have higher resolution than X-band radars, and for a given antenna size, have smaller sidelobes which will dissipate more quickly. It is said to use LPI features both in 'signal performance and operational techniques'. It probably emits in short bursts, of long low power impulsion over a wide range of frequencies (this helps the emision blend into background noise). However this technique, because of the long impulsions, requires two antennas (which the B-2 just happens to have) , one to emit one to receive. (On 'normal' radars the same antenna is used to emit and receive). In addition to this and as noted above the trend now seems to be towards multi-purpose antennas, thus probably an even wider range of frequencies. Timothy ------------------------------ Date: Tue, 13 Jun 2000 07:35:47 -0500 From: UFO Subject: Re: RCS reduction of radar antennas Just an aside.... why would you want radar on a stealth? Switch it on and you turn a stealth into a plain old airplane. Emittingh powerful radar emmisions is a no-no when you're trying not to be detected.

Timothy Toth wrote:

On the difficulties of integrating radar antennas in stealth
platforms...
Reflections from  antennas can amount to an important part of the RCS of
an aircraft, and of course simply covering the radome with RAM is
impossible as it would preclude all return signals from reaching the
radar antenna. Finding info on the subject is not easy, but this is what
I have. Does anyone have other ideas/info ? (not classified of course!).
And What do you think they did for the B-2, F-22, JSF?

-limit the number of antennas: by the use of multi
purpose/reconfigurable antennas such as Phased array antenna, or 'smart
antennas' (for eg. the 1997 US navy MERS demonstration program where 1
antenna replaced 18 antennas for IFF, UHF com,
JTDS etc...)

-minimum dicontinuities: Discontinuities in shape or material result in
higher RCS. To reduce these discontinuities conformal antennas or
antennas matching the contour of the platform can be used.
The 'smart skin' concept goes even further, the aim being to make part
of the skin of the aircraft act as antennas (it also has many other
application). A lot of US companies (including Lockheed Martin) involved
in defense programs are developping (producing?) smart skins. I don't
know where the B-2 stands as far as smart skins are concerned, because
(officialy at least) even the F-22 is 'too old' a design  to incorporate
such technologies. However for the JSF smart skins have resulted, in
addition to a reduction of the RCS, to savings estimated at $3.3 million
and a 1.000 lb. per aircraft.

-smart radome: fabricated from frequency selective surfaces (FSS).
A simple type of "smart radome" is a standard radome covered by a
metallic film in which an array of small openings is made, the 'pattern'
being specifically taillored to the frequency used by the radar.
Out-of-band signals are still confronted by the equivalent of a
continuous metal surface, because the openings are too small to let a
meaningfull amount of microwave energy penetrate the film.
A more complex type would be a dielectric radome , some suggest that
this is what the B-2 is using (this would then be in the form of several
layers of dielecrtic material each covering a different part of the
spectrum). The problem with such a system is that the antennas would not
be stealthy at their own working wavelenghts, and if you add to that the
wide part of the spectrum at which these antennas would work...*

-Cancellation: Passive cancellation deliberately adds reflections to an
antenna in an attempt to cancel out naturally occurring
antenna reflections. But there are hundreds of reflection sites that
must be balanced, and a small change in the frequency of
the interrogating radar could convert a cancellation to a reinforcement.
Thus this approach does not generally suffice.
With active cancellation (a.k.a. active loading), the target must be
smart enough to sense the angle of arrival, strength,
frequency and waveform of the interrogating signal, then be smart enough
to know the characteristics of its own reflection at
the incident interrogator’s parameters. Finally, it must be fast enough
to generate a signal with the proper phase and
amplitude to just cancel the natural reflections.

*The APQ-181 operates in the Ku-band (12-18GHz) and uses two radar
electronically-scanned antennas.Ku-band radars suffer more from
atmospheric absorption than X-band (10 GHz usually used by airborne
radars) , and normally require more time and more power to scan a given
volume. But, they have higher resolution than X-band radars, and for a
given antenna size, have smaller sidelobes which will dissipate more
quickly. It is said to use LPI features both in 'signal performance and
operational techniques'. It probably emits in short bursts, of long low
power impulsion over a wide range of frequencies (this helps the emision
blend into background noise). However this technique, because of the
long impulsions, requires two antennas (which the B-2 just happens to
have) , one to emit one to receive. (On 'normal' radars the same antenna
is used to emit and receive).
In addition to this and as noted above the trend now seems to be towards
multi-purpose antennas, thus probably an even wider range of
frequencies.

Timothy

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