Stealth, Radars and Discussions on 5th Generation Technology

[Vladimir79]

RCS would only increase at specific angles, if you are on head on detection,then it reduces significantly,like the raptor ,frontal RCS is very less ,su 35BM can detect it at only 80km ,but if the belly f he aircraft is exposed then the stealt is not that effective, i do not see why more lifting surface increases RCS when it is about Radar cross section . plus the tail unit ,is a maximum angle which also reduces RCS

The most important criteria for an LO fighter is the front and side RCS. The canards, front facing flaps, and increased wing surfaces present too much of a return. These are all cardinal sins of LO application.

 

[gambit]

I would not place too much faith on this 'patch' created by the Russians.

Another less frequently discussed consideration is that L-band frequencies typically sit below the design operating frequencies of stealth shaping features in many fighter aircraft and UAV designs. Shaping features such as engine inlet edges, exhaust nozzles, and other details become ineffective at controlled scattering once their size is comparable to that of the impinging radar waves. This problem is exacerbated by the skin effect in resistive and magnetic materials, which at these wavelengths often results in penetration depths incompatible with thin coatings or shallow structures.

It was therefore not surprising that during the 2000/2001 Australian media debate over the Wedgetail AEW&C aircraft, US participants were quick to vocally argue the “counter-stealth” capability of the Wedgetail's L-band AESA radar design.

Recently performed Radar Cross Section modelling and simulations performed on key shaping features of the F-35 Joint Strike Fighter show a pronounced degradation of shaping effects below the design's optimal X-band operation.

The L-band is around 1ghz and in radar detection engineering, it is WELL KNOWN that nothing is really 'invisible' at 1ghz and below. Plus, we never claim our LO aircrafts are 'invisible' to start. Kopp writes good articles but sometimes I wonder if he actually writes them or one of his lackeys does. This article is one of those times.

True...That the L-band can increase the odds of detection, BUT target information such as altitude, speed and aspect angle are so coarse that the L-band is never used beyond volume search capability. When a missile is closing in on a maneuvering target that is deploying ECM techniques in trying to evade said missile, fine target information is required due to high Mach closing speed and rapidly decreasing distance. To have those fine target information, the X-band with its high freqs coupled with high pulse repetition rates are employed.

Radar Frequency Bands

The link above is an example of how different freqs are usually utilized.

Now let us take a brief look at Kopp's article...

Assessing the Tikhomirov NIIP L-Band Active Electronically Steered Array

Scroll nearly to the bottom of the article and look at the chart labelled: Detection range in nautical miles, RCS in square metres.

The F-35's RCS is somewhere on the far right of that chart, between .001 and .000 figures. Now take a look at the vertical scale -- distance. We can see that for the F-22 and F-35, this L-band AESA radar may be able to detect them only in less than 20nm, well within AIM-120 range. More likely the Su would be dead before detection. This chart's title is also revealing when we look at the word: Co-altitude. That mean same altitude. In other words, this L-band AESA radar assembly installed on the Su's wing leading edges is best when the target is at the same altitude as the Su. How absurd is that?

Then there is this hilarious attempt to find target altitude...

Figure 3: The cheapest solution to the provision of a heightfinding capability is to point the aircraft nose at the target, and then perform an aileron roll manoeuvre while tracking the target, with resulting height resolution similar to azimuth resolution (Author, Flanker diagram Marco Falkenberg).

The cheaper option, with inherent limitations, is for the aircraft to fly an aileron roll manoeuvre whenever a height measurement of the target is required. A full 360° roll sees the target position measured through a full 2π angular extent, per manoeuvre. Whilst cheaper, this approach is not suitable for continuous tracking, and could present issues with clutter handling. Refer Figure 3.

One does not need to be a pilot to see how impractical this is. So the alternative is to install more arrays...

Figure 4: The more expensive but also more capable solution to the provision of a heightfinding capability is to add additional antennas on the vertical tails. This solution permits continuous height measurement of targets within the coverage of these antennas (Author).

The more expensive approach, which is suitable for continuous tracking, is to add an additional high gain receive antenna suite, which is vertically displaced relative to the plane of the aircraft's wing, and thus the AESA. Such an antenna could be integrated into the leading edge of one or both of the vertical tails of the Flanker with no difficulty. Phase alignment of the monopulse sum and difference signals produced by the wing and tail arrays could be readily achieved by inserting a delay line between the wing array outputs and the sum/differencing network. Refer Figure 4.

So now we have a monopulse operation in the L-band to try to detect a very LO object that must be at the same altitude as we are and at less than 20nm.

I am not going to go into details on how to jam a monopulse radar, especially one operating at such a low freq. Missile monopulse operation is in the X-band or higher and that is why it is more difficult, not impossible, to jam an X-band monopulse.

Our 'stealth' pilots have little to worry from this. What India should worry about is how much money to shell out for this 'snake oil'.

 

[gambit]

RCS would only increase at specific angles, if you are on head on detection,then it reduces significantly,like the raptor ,frontal RCS is very less ,su 35BM can detect it at only 80km ,but if the belly f he aircraft is exposed then the stealt is not that effective, i do not see why more lifting surface increases RCS when it is about Radar cross section . plus the tail unit ,is a maximum angle which also reduces RCS

The most important criteria for an LO fighter is the front and side RCS. The canards, front facing flaps, and increased wing surfaces present too much of a return. These are all cardinal sins of LO application.

While it is true that the top and underside of an aircraft provides the greatest radar return, it is actually a very low probability that such a situation could occur that would result in such a large return. To understand why, some basic information about radar detection and behavior is necessary.

First...Radar detection is a statistical process. If I have ten pulses and only two of them produced returns, the odds are very low that there is 'something' out there. If there are five returns, now I have good cause to be suspicious. If there are seven to eight returns, odss are excellent that there is a body out there. In the early days of radar detection, as in WW II, it was humans who made these statistical determination. The result was many false determinations and wasted resources on wild goose chases. Today we have machines to perform these statistical determinations.

Second...A radar signal always deflect 90deg off an ANGLED surface.

The only time a surface will produce the highest echo energy is when the transmitter is directly facing the surface. Else if the planar surface is off even slightly, the signal will deflect away from the transmitter's direction. If two (or more) surfaces (or edges) meet and formed a corner, we have what is called a 'corner reflector' and this structure also provides the highest echo energy to the receiver section of the radar system. Target corner reflectors are undesirable when the goal is to avoid detection.

But if the goal is to increase radar signature...

Corner reflector - Wikipedia, the free encyclopedia

A corner reflector is a retroreflector consisting of three mutually perpendicular, intersecting flat surfaces, which reflects electromagnetic waves back towards the source. The three intersecting surfaces often have square shapes. This is also known as a corner cube.

Such devices are often used as radar targets or markers and are often employed on ships and, especially, lifeboats; Francis Rogallo invented a target kite incorporating corner reflectors. These normally consist of three conducting metallic surfaces or screens perpendicular to one another.

On an aircraft, where the vertical stab meet the fuselage is a corner reflector, where the pylon meet the wing is another corner reflector. Bombs and missiles have fins and where the fins meet the weapons' bodies are corner reflectors. There are plenty of corner reflectors on an aircraft and all of them contribute to the aircraft's overall RCS average. They are undesirable. But if one surface is off perpendicular even if slightly, then we have decreased the amount of energy that can be reflected back to source direction. The SR-71's inwardly canted vertical stabs are not for aerodynamic purposes but for the elimination of externally facing corner reflectors. Compare them against the F-15's twin straight up vertical stabs for contrast.

In theory, if a surface is perfectly smooth, then as long as the surface is not perpendicular to the transmitting radar, all energy will be reflected away from the transmitter and effectively the surface does not exist as far as the radar is concerned. No surface is perfect. Small and even microscopic imperfections formed corner reflectors and these are what present the aircraft to the radar. If the radar is a ground station, the only time a surface is directly facing the radar antenna is if the aircraft is directly overhead. That situation is more likely at a busy civilian airport. It is high improbability that two opposing fighters will create this situation in their maneuvers to get into favorable firing positions. So it is corner reflectors, large from aircraft structures and small from aircraft surface imperfections, that radars will detect an aircraft.

The F-117 exploit this behavior and this is why we see the F-117's body composed largely of angled surfaces. Those sawtooth patterns where panels meet each other are also because of the desire to eliminate corner reflectors.

The underside of the F-117 is visually deceptive. It is of the 'tapered conductivity' design. Those small reflections have their energy further reduced by radar absorbent materials (RAM), leaving the remaining energy levels be dismissed by the radar as belonging to the 'clutter' region.

But there is the visual difference between the F-117, the first generation of 'stealth' design, to the next generation that has the B-2, F-22 and F-35. The F-117 is retired, not because one F-117 was shot down over Yugoslavia, the Serbs and the Russians would love people to believe that lie, but because there is another type of behavior of radar signals upon a surface that the B-2, F-22 and F-35 now exploit...

Creeping wave - Wikipedia, the free encyclopedia

In radar ranging, the creeping wave return appears to come from behind the target.

When a radar signal impact a sphere or a curved surface, we have this 'creeping wave' effect where most of the wave's energy travels along the surface and finally 'leapt' off the body, hence the echo appears at a distance from the actual body. Only minor surface imperfections at the point of impact produces any reflections that could return straight to the transmitting radar.

A sphere's RCS is constant no matter which direction is the transmitting radar. Some very minor energy will be detected, but most of the signal will travel on the surface of the sphere and eventually meet on the opposite side.

For the B-2, F-22 and F-35, their RAM will reduce this specular energy to the 'clutter' region and be dismissed by the enemy's radar as junk. By the time there is sufficient energy level for the radar to statistically determine that there is an aircraft out there, it would have been weapons release time for these 'stealth' aircrafts. For the F-22, the enemy fighter would not be aware of any threat.

An airliner is a 'cooperative' target. The airliner wants to be seen, not only does its shape is conducive to radar detection, but it also carries a transponder to advertise its presence to all. Military aircrafts are mostly 'noncooperative' because of their mission, which is to try to destroy the enemy. Currently, the B-2, F-22 and F-35 are the least cooperative, or the most noncooperative, shapes in the air. They fly with transponders to assist controllers and to mask their true RCS.

 

[p2prada]

@Gambit:

What would be the case if bistatic radars were used for detection? How would a curved surface prevent detection if there are multiple receivers on the ground and in the air?

Most of what you say is not relevant to antennas transmitting pencil beams(AESA), or is it?

 

[gambit]

@Gambit:

What would be the case if bistatic radars were used for detection? How would a curved surface prevent detection if there are multiple receivers on the ground and in the air?

A bi-static system is the greatest threat to low observables. However, there are limitations on these systems, such as synchronization between transmitters and receivers as to what freq is transmitting at what time. To date, airborne bi-static systems have been tested and found overly complex in high stress, compressed response time situations. The best airborne bi-static system so far remain the simple radar guided missile air-air combat situation...

The launch aircraft provides the radar detection signals. The missile is the receiver side that processes any echoes from the target aircraft. The launch aircraft must maintain radar detection on the target at all time. Does this mean the best tactic against low observables is to go back to the semi-active radar guided missile instead of the much touted 'fire-and-forget' type missile? Perhaps, but then this tactic leave the transmitter vulnerable to beamrider missiles. Powerful airborne radar platforms like AWACS are moving towards the bi-static system but more work is still needed on how to coordinate the transmitter, which is the AWACS aircraft itself, with the receivers, which could be anyone that may or may not be capable of performing its role as a passive receiver in this configuration.

For both ground and airborne bi-static systems, there is something called the bi-static triangle for the radar computer to consider...

12.1: HITCHHIKING On GlobalSpec

Furthermore, the bistatic receiver must locate the host radar to solve the bistatic triangle, operate with adequate target LOS and establish time synchronization for range measurements and phase synchronization for coherent operation and clutter suppression.

LOS mean line-of-sight and note the synchronization requirement for best target resolutions. The loss of the bi-static triangle resolution is the cause of many past radar guided missile failures to destroy the target, especially when the target is aware of the imminent danger -- the missile -- and proceed to violently maneuver and deploy distraction/seduction ECM tactics. The ideal bi-static triangle is when the receiver is 45deg off the target and all three elements are equi-distant from each other, like so...

In the above situation, receiver B is the best resolver of both targets with the best resolution on the nearest aircraft. Receiver A is practically worthless for the furthest and highest altitude low observable target. But as both 'stealth' aircrafts move, these bi-static triangle resolutions degrades and if there is a need to track these low observable threats, more transmitters and receivers must be in place. The complexity (and cost) for a ground based bi-static system is obvious.

Most of what you say is not relevant to antennas transmitting pencil beams(AESA), or is it?

It is applicable to the superior AESA system as well.

 

[p2prada]

A bi-static system is the greatest threat to low observables. However, there are limitations on these systems, such as synchronization between transmitters and receivers as to what freq is transmitting at what time. To date, airborne bi-static systems have been tested and found overly complex in high stress, compressed response time situations. The best airborne bi-static system so far remain the simple radar guided missile air-air combat situation...

Considering synchronization is a problem. What if a group of ground radars in one sector are all controlled by a single computer. Will this not ensure the effectiveness of the system?

The launch aircraft provides the radar detection signals. The missile is the receiver side that processes any echoes from the target aircraft. The launch aircraft must maintain radar detection on the target at all time. Does this mean the best tactic against low observables is to go back to the semi-active radar guided missile instead of the much touted 'fire-and-forget' type missile? Perhaps, but then this tactic leave the transmitter vulnerable to beamrider missiles. Powerful airborne radar platforms like AWACS are moving towards the bi-static system but more work is still needed on how to coordinate the transmitter, which is the AWACS aircraft itself, with the receivers, which could be anyone that may or may not be capable of performing its role as a passive receiver in this configuration.

I read somewhere that the Australian Wedgetail needs to be equipped with active ECM like Band track breakers and seduction jammers to beat Russian Long range AAMs in the future. Some analyst.

In the above situation, receiver B is the best resolver of both targets with the best resolution on the nearest aircraft. Receiver A is practically worthless for the furthest and highest altitude low observable target. But as both 'stealth' aircrafts move, these bi-static triangle resolutions degrades and if there is a need to track these low observable threats, more transmitters and receivers must be in place. The complexity (and cost) for a ground based bi-static system is obvious.

It might seem expensive at first. But, if such a system can beat a F-22 this will be cost effective considering the F-22 is not cheap. And it will be far cheaper for countries like India which is still building a robust air defense system.

It is applicable to the superior AESA system as well.

Will the creeping wave effect take place when only a beam is transmitted on an infinitesimally small part of the F-22?

One more question. Modern armies use a large number of ECM equipment like our very own Samyukta system(I cannot guarantee the article is correct with the specifications).
It comprises 145 vehicles tasked to perform ELINT, COMINT and active ECM duties. Considering such systems can be upgraded to capture signals from enemy aircraft, this can also be used as receivers for our own radar signals with the necessary modifications. A follow on system to the Samyukta is also under development. Can such a system plug gaps in the air defense system against F-22 or F-35 considering these systems are robust, also improving the detection of LOs.

 

[gambit]

Considering synchronization is a problem. What if a group of ground radars in one sector are all controlled by a single computer. Will this not ensure the effectiveness of the system?

It might seem expensive at first. But, if such a system can beat a F-22 this will be cost effective considering the F-22 is not cheap. And it will be far cheaper for countries like India which is still building a robust air defense system.

Modern armies use a large number of ECM equipment like our very own Samyukta system(I cannot guarantee the article is correct with the specifications).

It comprises 145 vehicles tasked to perform ELINT, COMINT and active ECM duties. Considering such systems can be upgraded to capture signals from enemy aircraft, this can also be used as receivers for our own radar signals with the necessary modifications. A follow on system to the Samyukta is also under development. Can such a system plug gaps in the air defense system against F-22 or F-35 considering these systems are robust, also improving the detection of LOs.

System effectiveness is one thing, which is about how well all the compnents works together. System effectiveness against the target is a separate issue. It is not merely synchronization but also on how many receivers are you going process since there would be more than one that would detect, or seemingly detect, a target. Let us take just one pulse for now. Because the F-22 is designed to influence the behavior of a radar wave upon its body BEFORE and echo is produced, not all receivers will pick up the echo pulse at the same time and with the same resolution due to differences in the many bi-static triangles present.

Say you have a network of five receivers going off one transmitter. Say receiver A picked up a strong return of <something> at 10k ft altitude, 600 mph and heading west. We will freeze this for a moment. If receiver B does detect this <something> it may, or may not, be at the same altitude and speed as what receiver A reported. Same for the other receivers in your network. What if only one of the remaining receivers pick up this <something> but dismissed the signal as clutter? Statistically speaking, you have no valid cause for response due to number of receivers that you use for processing. Your system is working just fine. The problem now is decision making based upon a high degree of certainty from one receiver and decreasing levels of certainty from the other receivers. That is like one guy saying that you will score sex with this one girl but four other guys telling you that you have no chance at all. Who are you going to believe?

You can add more transmitters but that would increase the level of system complexity and cost. Another solution is to have all units be mono-static radar functioning as transmitter OR receiver as situation demands. In other words, one station would act as a source transmission while the other four act as receivers. The moment one of the receiver station detect a suspicious signal, it become a transmitter and the other four changes to receiver mode. The target, if there is one, would be hit from different directions. Now there are correlative signals to support your decision making process. The processing power increases as the transmitter-receiver pairings increases.

Another limitation of a bi-static system is that the transmit-receive pair MUST face each other. Remember that the echo pulse deflects away from source so if the receiver is facing somewhere else, how will it pick up the echo pulse? If there are three receivers to one transmitter, all three receivers must be facing 'inward', in other words, over the area that the system is tasked to provide radar coverage. The transmitter can be just about anywhere but it also must facing that area. In this configuration, a hostile aircraft will not be detected until it is inside the coverage area and is free to deliver ordnance. No matter how many transmitters and receivers you have, all of them must be facing each other to some degree to provide one leg of a bi-static triangle and when there is a target, it will create the other two legs.

Mono-static radars are %99 of radar systems out there, civilian and military. The mode offers mobility and flexibility as situation demands. Limited mobility is why a bi-static system is not the final response despite being more effective at detecting low observable aircrafts.

Will the creeping wave effect take place when only a beam is transmitted on an infinitesimally small part of the F-22?

Upon initial contact with a surface, planar or curve, of whatever size, minor surface imperfections will generate 'specular reflections'. At this moment the creeping wave effect is not even in play.

 

[p2prada]

Another limitation of a bi-static system is that the transmit-receive pair MUST face each other. Remember that the echo pulse deflects away from source so if the receiver is facing somewhere else, how will it pick up the echo pulse? If there are three receivers to one transmitter, all three receivers must be facing 'inward', in other words, over the area that the system is tasked to provide radar coverage. The transmitter can be just about anywhere but it also must facing that area. In this configuration, a hostile aircraft will not be detected until it is inside the coverage area and is free to deliver ordnance. No matter how many transmitters and receivers you have, all of them must be facing each other to some degree to provide one leg of a bi-static triangle and when there is a target, it will create the other two legs.

Ok. So, bistatic and multistatic radars have that limitation. Nevertheless, it gives us the ability to track a LO aircraft within our territory. Gives a target to shoot back rather than have some thing invisible shoot us and leave.

Also, what do you think about forward scattering radars? How effective are they compared to the other bistatic modes.

The area inside the oval is the area where the plane can be detected(but not tracked).

Mono-static radars are %99 of radar systems out there, civilian and military. The mode offers mobility and flexibility as situation demands. Limited mobility is why a bi-static system is not the final response despite being more effective at detecting low observable aircrafts.

Sir, What is the probability of a monostatic radar being able to detect a LO compared to a AWACS considering they are both using the same radar at the same power and the target is flying at 10000ft?

Upon initial contact with a surface, planar or curve, of whatever size, minor surface imperfections will generate 'specular reflections'. At this moment the creeping wave effect is not even in play.

Aren't the specular reflections enough for detection?(Consider bistatic and not monostatic).

 

[gambit]

what do you think about forward scattering radars? How effective are they compared to the other bistatic modes.

The area inside the oval is the area where the plane can be detected(but not tracked).

Forward scatter radar (FSR) is more of a technique than a distinct system, although the elements in a bi-static configuration must be physically deployed in a certain manner to take advantage of the diffraction effect.

Here is why...

Upon impacting a complex body, the wave exhibit four distinct behaviors:

1- Reflection
2- Deflection
3- Creeping
4- Diffraction

Notice I said 'complex body'. Do not confuse symmetry with regularity. Look at your face in the mirror. Your face is symmetrical (I hope) and certainly very handsome. But your eyes, nose, lips, cheekbones and ears are irregular features. They appear nowhere else on each side of your face. An aircraft is symmetrical but like your face -- irregular in its features. A complex body have multiple scattering points as the body itself is one large scattering point. If we record a scattering point's energy level rise and fall over time and plot them out, an aircraft would look something like this...

The radar computer processes all these scattering points, sums and difference them up and display the final result on the scope as a single point of light. The mess as plotted is a profile that we instructed the computer that:

- IF there is X amount of energy states in a cluster

...And...

- IF each point is a certain level over the clutter (junk) threshold

Then consider this cluster a valid 'target'. Those many scattering points come from reflection and deflection off the irregular features. The creeping wave effect contribute to lesser intensity. Even the highly angular F-117 has some curvatures somewhere unseen.

Forward scattering detection is about picking up a portion of the radar wave that managed to 'go around' (diffraction) the body.

Radar Basics

A radio wave that meets an obstacle has a natural tendency to bend around the obstacle as illustrated in the figure. The bending, called diffraction, results in a change of direction of part of the wave energy from the normal line-of-sight path.

This change makes it possible to receive energy around the edges of an obstacle or at some distances below the highest point of an obstruction. Although diffracted rf energy usually is weak, it can still be detected by a suitable receiver. The principal effect of diffraction extends the radio range beyond the visible horizon.

The above source very well illustrate diffraction as how it can be exploited in radar detection. You can imagine that 'obstacle' to be the vertical stab, the cockpit bubble, the missile or the small communication antenna. A portion of the impinging wave will exhibit the diffraction behavior on each of these irregular feature. You can also imagine that 'obstacle' to be the entire complex body, aka aircraft, itself. All diffraction points on the aircraft contribute to the overall diffraction behavior on the aircraft itself.

So now we have reflected energy, deflected energy, creeping wave energy and diffracted energy. In theory, all should equal to the original amount that impacted the aircraft, minus atmospheric induced loss during travel, of course. For simplicity's sake, I will classify reflected energy, deflected energy and creeping wave energy as 'absorbed energy'. They are 'absorbed' in the sense that a body is interfering with the wave's travel.

Babinet's Principle has...

Babinet's principle - Wikipedia, the free encyclopedia

In physics, Babinet's principle is a theorem concerning diffraction that states that the diffraction pattern from an opaque body is identical to that from a hole of the same size and shape except for the overall forward beam intensity.

Basically, for forward scattering detection, the fancy explanation above means the amount of absorbed energy equals to the amount of diffracted energy. Sum them together and we have the total amount that impacted the body. The reasoning was that since it is difficult to detect the absorbed type energy, why not use the bi-static configuration to pick up the portion of the original wave that was not so absorbed? Forward scattering detection was not invented because of 'stealth' aircrafts. Rather the technique was adopted out of military necessity.

But the diffraction also imposed limitations on this detection technique.

Gruppo Atmosfera Media e Meteore: Forward-scatter radar system

The above source is for meteor detection using forward scattering detection technique but is applicable to aircrafts as well. In that illustration, Bologna is the transmitter, Modra and Lecce are receivers. Each station is a dedicated platform, meaning Bologna can only transmit, not receive. Same restrictions for the other two stations in their functions. The oval areas are where forward scattering detection techniques can pick up the diffraction energy. That does not mean the receiver cannot process deflected energy. It can process both as both behaviors occurs at the same time. This is why I said forward scattering detection is more technique than an actual system as we can have Modra and Lecce process only deflected energy. Anytime the transmitter and receiver faces each other, the moment a target come directly between them, it does not matter which direction is the transmission, a potential for forward scattering detection exist, but I could be totally ignorant of the diffraction behavior to exploit it.

In your illustration, the detectability area is that oval shape 'fence'. In the meteor detection source above, they drew that detectability area slightly different but it is the same idea as yours. This 'fence' area exist because of the behavior of the wave AFTER leaving the body and its energy level state. Frequency and transmission power level directly influence the size of this detectability area. That is why I used that meteor detection source to illustrate forward scattering detection. They used meters long wavelengths (mhz) over several hundreds km in distance and the size of the detectability area is indicative of this relationship. Outside of the fence and target ambiguity increases as long as you are in forward scattering detection mode. Or let me put it this way: As the target travel inside the fence, and as it approaches the electronic boundaries of this fence, the LEVEL OF CERTAINTY that the target exist decreases -- target ambiguity. Remember that radar detection stands upon a statistical foundation. Once the target is outside of that statistical limit for forward scattering detection technique, what remain viable is deflected energy detection technique. Forward scattering detection has superior target certainty over standard bi-static detection but at the expense of effective coverage area even though they share the same physical configuration.

So far I touched only on basic target detection. Other can of worms are Doppler resolution, the dead zone, equipment stability and many more.

Sir, What is the probability of a monostatic radar being able to detect a LO compared to a AWACS considering they are both using the same radar at the same power and the target is flying at 10000ft?

Not sure what are you trying to get at here, but an AWACS generally operate as a mono-static platform. If you wonder if there are any advantages of an airborne platform over a ground station, in terms of target certainty of an LO aircraft, then there is a slight advantage for the airborne platform in that radar detection is line-of-sight dependent. The higher you are the further you can see. If there is a credible threat of an attack by a flight of LO aircrafts, an AWACS can use long wavelengths (mhz) with being at higher altitude to attempt detection.

Aren't the specular reflections enough for detection?(Consider bistatic and not monostatic).

Yes...And it does not matter the method employed. But there is something called 'clutter', which is unwanted signals, or junk. That said...What is junk to one system is desirable to another. For an AWACS, land mass and clouds are junk. But for a weather radar, the AWACS aircraft itself is junk. The meteorologist want to see only nature-made objects, not metallic ones flying around. The universe is filled with background radiation and that must be included in the clutter region. Specular energy can fall into the clutter region and be dismissed by the radar computer. But how do you know if that particular dismissal was a real bird or an F-22?

Lower the clutter rejection threshold and your scope would be filled with all sorts of signals, from clouds to birds to land and somewhere inside that mess would be that F-22. You could attempt some creative signal processing such as Doppler to filter out anything moving at above so-and-so speed, but then how do you know if what you believed to traveled at several hundreds km/h is not a sudden appearance of a different flock of birds? By the way, we detect birds BY THEIR BEAKS. A bird's body is naturally curvy, remember the creeping wave effect, and the feathers do absorb some freqs. The beak is hard and angular and is the greatest contributor to the bird's RCS. So pelicans with their giant honkers can appear to be several times their individual sizes.

For the X, S and L bands, the F-22 is between the sparrow and the warbler. Unofficially it is even smaller but no one will reveal the true figure. People are misinformed that if a missile's X-band pick up a bird's RCS, it should be able to target a 'stealth' aircraft as well. This belief is true only if missiles will turn and chase birds. But we do not program our missiles to chase birds. No one does. We program our missiles, even though their X-band radars is capable, to ignore any RCS below a certain threshold, else the missile would be chasing everything and anything.

The US never claimed our 'stealth' aircrafts to be 'invisible' at any time. If the media decide to use the word 'invisible' we will not make any noise about it. The intention is to insert the B-2, F-117, F-22 and F-35 into the clutter region for as long as possible and let the enemy figure out what to do next while we travel at several hundreds km/h to drop bombs on his head. The American saying 'wild goose chase' is very applicable here.

Ok. So, bistatic and multistatic radars have that limitation. Nevertheless, it gives us the ability to track a LO aircraft within our territory. Gives a target to shoot back rather than have some thing invisible shoot us and leave.

Much misinformation have been made about the single F-117 shoot down over Yugoslavia. The Serbs and the Russians wasted no efforts on crowing how their 1960s era radar supposedly detected, tracked and finally targeted that one F-117. There was some nonsense about long wavelengths to 'defeat' LO aircrafts.

Utter BS.

Over Yugoslavia, NATO flew about 20,000 sorties with about 4,500 Suppression of Enemy Air Defense (SEAD) missions. The SEAD missions were low altitude to entice ground missileers. So out of 20,000 flights, only one F-16 and one F-117 shot down? I would be embarrassed at that kind of combat record. If long wavelengths can defeat US 'stealth' aircrafts, then it stands to reason that whatever was so effective against the F-117, it should be ten times more effective against 'non-stealth' aicrafts, correct? Plus the US had about 60 B-2 missions from Whiteman AFB to Yugoslavia and back to continental US. But only one F-16 and one F-117 shot down?

So here is the truth about Yugoslavia and the F-117...

Over Yugoslavia, NATO operated under very restrictive flight rules. The F-117 sorties ingressed the 'hot areas' at the same time and altitude just about clockwork. There were plenty of Serb sympathizers that had Aviano AB in Italy under 24/7 surveillance. Serb military command received alerts as to when Aviano launched anything in the air. Over time, Zoltan Dani, the famous Serb missile battery commander, figured out the most likely time something would be over his coverage territory. Contrary to myth, Dani did not know about wavelengths behavior on a body. He just used whatever freqs there were on his equipments. That long wavelengths bit came out much later to enhance the myth.

So after a few weeks, Dani began to see a pattern of suspicious echoes on his radar. Nothing concrete but a pattern nonetheless. NATO's predictability assisted him. Dani set the fuses on his missiles to detonate at different altitudes and launch them at one such suspicious echo on that one day. The F-117 pilot, Dale Zelko, reported he had to dodge several missiles before he got caught in the shrapnels of one. What Zoltan Dani did was nothing spectacular -- spray and pray. The North Vietnamese did it enough back in the Vietnam War and most of US air losses in Viet Nam came from missiles, not air-air combat. Zoltan Dani declined to reveal how many missiles he launched in the direction of that suspicious echo that to his good fortune turned out to be an F-117. If it was a British Tornado would so much celebration resulted and a myth created? Probably not. Anyone who has any working knowledge of radar detection quickly dismissed Zoltan Dani as nothing more than a lucky opportunist.

Currently, to increase the odds of detection, not track or target, is to employ several methods against US 'stealth' aircrafts. The preferred method, at least on the ground anyway, is to deploy a bi-static system with forward scattering detection capability. Centralized controlled and data processing. All elements should be non-dedicated, meaning each radar station must be able to change between being a transmitter to being a receiver as needed. And a lot of missiles standing by.

An aircraft is a reusable weapon. Launch it and most likely it will return to be used again. Each time deployed it can deliver multiple types of ordnance, if that is the mission requirement. Unlike an aircraft, a missile is essentially a throwaway weapon. Each time a missile is used, the delivery vehicle and the ordnance is essentially discarded, often with the expectation of no success in its mission. The reason why missiles have a place in our defense system is they are more responsive than manned aircrafts, at the expense of intelligence and reusability. Missiles are less expensive and quicker to manufactured than manned aircrafts. As such, missiles are ideal in a defense network against US 'stealth' aircrafts -- under spray and pray tactic, of course.

The problem for the defenders is that US 'stealth' and 'non-stealth' aircrafts are equally lethal and there are no doctrinal and/or technical issues as to why we cannot use both at the same time against the same target. We demonstrated this coordinative capability with Desert Storm and with a now retired 'stealth' platform. Even if the defenders are aware of the immediate threats from both at that moment, they could still face destruction by one type as they are under pressure and distracted by the other type. Now we have two 'stealth' platforms that are more capable than the retired one and we have another 'stealth' platform on the way.

The US is also not resting on this laurel. This current generation of 'stealth' employ passive RCS reduction measures. We are working on the next generation which will have active RCS control measures. The difference between 'reduction' and 'control' is crucial. The aircraft will be able to emit any or no RCS at will. We will be able to claim with a straight face that the aircraft is 'invisible' to radar.

I know my response is long but you are treading into a very complex topic that require some compromises in explaining technical information involved in language that the average readers can understand.

 

[A chauhan]

USA already possess stealth tech and is probably trying to find how to detect stealth planes (who knows they may have done it)because they know that others will copy stealth feature of F22 & JSF F35.I think stealth feature will not be helpful until we develop it further to make a plane almost invisible on radar, gambit is right F22 & F35 will be nearly invisible on our radars we have to increase radar capabilities and find out alternative ways to detect them.

 

[bhramos]

chauhanji US only has better Stealth tech, but Russia has also done on many research on anti-stealth tech, and knew how to make better stealth then US,

 

[bengalraider]

as long as we are discussing stealth

More recently, a joint team of researchers at Duke University and the Southeast University of Nanjing unveiled a composite material whose properties are invisible to certain microwave bands, which is the first step in developing a structure capable of cloaking.

the above is from
Stealth reform

to tell you the truth; invisible aircraft and china involved , that scares the hell out of me!

 

[bengalraider]

an excerpt from force magazine

India Will Be an Equal Partner in All Aspects of the FGFA’
Chairman, Hindustan Aeronautics Ltd, Ashok Nayak

What preparations have you done at HAL regarding the M-MRCA, including talks with competitor companies for absorption of offsets, creation of new or more infrastructures, and hiring of manpower?

It is too early to talk about all this. As you know, the MRCA has six contenders and currently the field evaluation trials are going on. HAL is participating in this to evaluate the maintenance aspects. Regarding the offsets, a clearer picture will emerge after the selection of the aircraft. Once that happens, HAL will initiate talks with the selected company to align its infrastructure to meet the offsets obligation. We have a fairly dedicated export-oriented unit for aerospace structures. We hope to increase this division to meet some of the offset obligations in respect of structures. Depending upon what further needs to be done in this particular area, we will increase the infrastructure.

You mentioned that HAL is looking at the maintenance aspects during the MRCA flight evaluation trials. What is meant by this?

Almost all the aircraft have flown a couple of sorties in Bangalore. HAL has already been looking at various maintenance aspects of these aircraft including what it involves and how easy or difficult it will be to maintain them. Now during the field trials, HAL is working with the IAF as a team to assess the maintenance of these aircraft further. While it will be the IAF that will maintain the selected aircraft in their inventory, HAL will also be assisting them in certain aspects.


What is the status on the first prototype flight of LCH? Considering the LCH model was labelled at HAL stand at MAKS-2009 as an attack helicopter, will LCH compete for the IAF’s RFP for 22 attack helicopters?

The first prototype of the LCH will fly by the end of this year. Work on the prototype is progressing well and I do not anticipate any delays. The LCH is a light helicopter and it is not in the category of the 22 attack helicopters that the IAF is seeking. However, the LCH will definitely be armed when it is offered to the IAF.

Director General Sukhoi, Michail A. Pogosyan said at MAKS-2009 that the Russian fifth generation fighter aircraft (FGFA) prototype’s maiden flight will happen by end-2009 and that the basic version of the Indian and Russian FGFA is similar with software changes only. Is this correct? What does this mean for HAL in terms of sharing work, transfer of technology, intellectual property rights issues, and time-frame for the evolution of the Indian aircraft? He also mentioned that Indians could later look at a two-seat aircraft and a naval version.

I would not like to comment on Mr Pogosyan’s statement and you may take it as the current status. The IAF technical requirements for the FGFA have just been finalised and they are being passed on to the Russians. These technical requirements will include what is needed for a single and a twin seat version and so on. After the technical requirements have been given to them, the technical aspects between the two sides will be discussed in detail. The Indian version obviously cannot be very different from the Russian version. Certain modifications according to the technical requirements will be incorporated in the Indian version and these have already been discussed in detail between HAL and IAF. This then, is the starting point. As you know, it takes a few years between the prototype flight and the acceptance of an aircraft, this time will be utilised between Russia and India to work closely on the Indian version. I can say that metaphorically speaking, India has taken its first step for the fifth generation aircraft. I would also like to dispel a prevalent notion that while India will pay 50 per cent of the money, it may just get about 10 per cent of the work-share. This will not happen. India will be an equal partner in all aspects in the FGFA.

hallelujah to that ! we need the knowledge that such a co-operation could bring.

 

[gambit]

Stealth,radars and discussions on 5TH generation technology

chauhanji US only has better Stealth tech, but Russia has also done on many research on anti-stealth tech, and knew how to make better stealth then US,

Then all the Russians has to do is to deploy just a couple of F-117 equivalent demonstrators. Not an active duty squadron, just a couple of actually flight capable F-117 equivalent aircrafts. The low observability of the F-117, F-22 and B-2 are well known to air traffic controllers. These aircrafts flies with transponders, like the type civilian airliners uses, to enhance their radar returns and to mask their true RCS values.

The above facility is called a 'radar range'. This is where full scale models are tested for their radar returns from various angles.

That is an upside-down test of the A-12/SR-71. Note the vertical stabs are not installed. Why upside-down and no vertical stabs? Depends on the testing criteria on that day. They could be testing for the radar returns on the underside of the aircraft. We do not know. The point here is that the US have extensive knowledge and experience at conducting RCS testing even before the first flight. Radar ranges are often mistaken for airports because of the long strips of concrete. Without full scale facilities like a radar range, the less certainty we have about the radar cross section of a design.

For the Russians and the Chinese...Either put up or shut up.

 

[Vladimir79]

Then all the Russians has to do is to deploy just a couple of F-117 equivalent demonstrators. Not an active duty squadron, just a couple of actually flight capable F-117 equivalent aircrafts. The low observability of the F-117, F-22 and B-2 are well known to air traffic controllers. These aircrafts flies with transponders, like the type civilian airliners uses, to enhance their radar returns and to mask their true RCS values.

The point here is that the US have extensive knowledge and experience at conducting RCS testing even before the first flight. Radar ranges are often mistaken for airports because of the long strips of concrete. Without full scale facilities like a radar range, the less certainty we have about the radar cross section of a design.

For the Russians and the Chinese...Either put up or shut up.

Hate to burst your bubble gambit, but Russia invented the physics used to develop the F-117 before it was even an Amerikan concept. Don't worry about us operating an F-117 equivalent aerocraft... PAK FA will be far superior to that antiquated machine. We will put it up in the next couple of months.

 

[Quickgun Murugan]

Hate to burst your bubble gambit, but Russia invented the physics used to develop the F-117 before it was even an Amerikan concept. Don't worry about us operating an F-117 equivalent aerocraft... PAK FA will be far superior to that antiquated machine. We will put it up in the next couple of months.

Vladimir,

Can you pls give me a gist about this video?

http://translate.googleusercontent....le.com&usg=ALkJrhiLCuRKwo_ciSEZpS8Nilvl_5-fUw


I remember reading in some serbian defence forum about the same topic you raised. I did not understand much though due to poor translation!

 

[gambit]

Hate to burst your bubble gambit, but Russia invented the physics used to develop the F-117 before it was even an Amerikan concept. Don't worry about us operating an F-117 equivalent aerocraft... PAK FA will be far superior to that antiquated machine. We will put it up in the next couple of months.

Sorry to burst YOUR bubble but the Soviets did not 'invent' anything remotely resembling 'stealth'. Ufimtsev created the PREDICTIVE equations on wave behavior on a surface. He taught electromagnetic theories at UCLA for a while before retirement. When asked about his equations and why it was the Americans who recognized it for what it was, he had no answer. He could only speculated on why the Soviets were so shortsighted at that time.

If I can predict what something will do, I can certainly engineer or create or alter the environments that will compel that 'something' to do as I wish. From this we have the F-117 which exploited reflective and deflective behaviors of Ufimtsev's equations. The F-117 was designed when engineers were still proficient with sliderulers. Only senior project leads had access to something exotic called 'personal computers' which hardly was 'personal' by today's standards. Without a strong engineering foundation that the F-117 provide, whatever Russia and China create runs high the risk of being an inferior specimen to the F-22, whose design was based upon the experience from the F-117.

Fly MiG and Sukhoi Fighter Jets in Moscow!

The PAK-FA project is forever in 'development'. Look at the source above. When Russia has to resort to renting out its top of the line fighters for tourist flights to raise money to sustain its decrepit military, I would not place too much faith on what this project can produce to achieve parity with US 'stealth' fighters.

 

[Vladimir79]

Sorry to burst YOUR bubble but the Soviets did not 'invent' anything remotely resembling 'stealth'. Ufimtsev created the PREDICTIVE equations on wave behavior on a surface.

Of which US scientists were able to programme computers to predict them.

He taught electromagnetic theories at UCLA for a while before retirement.

The ninties were hard times.

When asked about his equations and why it was the Americans who recognized it for what it was, he had no answer. He could only speculated on why the Soviets were so shortsighted at that time.

Good ole Amerikan ingenuity... steal somebody elses idea and make it your own.

If I can predict what something will do, I can certainly engineer or create or alter the environments that will compel that 'something' to do as I wish. From this we have the F-117 which exploited reflective and deflective behaviors of Ufimtsev's equations. The F-117 was designed when engineers were still proficient with sliderulers. Only senior project leads had access to something exotic called 'personal computers' which hardly was 'personal' by today's standards. Without a strong engineering foundation that the F-117 provide, whatever Russia and China create runs high the risk of being an inferior specimen to the F-22, whose design was based upon the experience from the F-117.

Hate to burst your second bubble, but Russia has super computers second to none. We also have experience with Su-35BM and LO technologies. Even using the outdated frame of the Su-27 were able to reduce the RCS by over ten times. Altering inlets, introduction of nano composites, and nano RAM coatings have enabled this at very little cost. Our tech level is far superior to when you were making stealth calculations with rulers. We have access to all the testing and computations we need and our scientists and engineers are among the brightest in the world. That is why your nation's companies try to grab them at every opportunity. Not to mention we have the greatest minds in India on this project. PAK FA will be far superior to F-117 as it is based on a whole new generation of technology, the same as that used in the F-35.

The PAK-FA project is forever in 'development'. Look at the source above. When Russia has to resort to renting out its top of the line fighters for tourist flights to raise money to sustain its decrepit military, I would not place too much faith on what this project can produce to achieve parity with US 'stealth' fighters.

Rather reminds me of our space tourism and how NASA's decrepit space programme has to pay us to launch their astronauts into space.

DailyTech - NASA to Pay Russia $51M Per Manned Launch

Needless to say, I am not concerned for our aerospace tourism when it is bringing in billions of USD. It is a market your capitalists have failed to garner and we reap the benefits. BTW, I am going up in a MiG-31 for Christmas so you are really complaining to the wrong person about that.

 

[gambit]

Good ole Amerikan ingenuity... steal somebody elses idea and make it your own.

You mean the Soviets were so innocent of the same? Wonder who got the USSR on the fast track to becoming a nuclear weapons state. Got news for you, tovarisch, not trying to downplay Ufimtsev, but what he did was to create the predictive equations, he did not discover the behavior itself, which was discovered prior to WW II, which ended with the world's first wide deployment of a functional radar system -- Chain Home and Chain Home Low -- which gave Britain the edge over the Germans. If it was not Ufimtsev, it would have been someone else. In fact, there are credible evidences that the equations were co-created, albeit at different countries, because the behaviors are the same in communication. Ufimtsev happened to have a large organization, the Soviet academic institution, to publish and professionally archived his knowledge.

Hate to burst your second bubble, but Russia has super computers second to none. We also have experience with Su-35BM and LO technologies. Even using the outdated frame of the Su-27 were able to reduce the RCS by over ten times. Altering inlets, introduction of nano composites, and nano RAM coatings have enabled this at very little cost. Our tech level is far superior to when you were making stealth calculations with rulers. We have access to all the testing and computations we need and our scientists and engineers are among the brightest in the world. That is why your nation's companies try to grab them at every opportunity. Not to mention we have the greatest minds in India on this project. PAK FA will be far superior to F-117 as it is based on a whole new generation of technology, the same as that used in the F-35.

The F-117's method is effective but dated. You can make all the claims you want out of nationalistic pride, but -- put up or shut up.

Rather reminds me of our space tourism and how NASA's decrepit space programme has to pay us to launch their astronauts into space.

DailyTech - NASA to Pay Russia $51M Per Manned Launch

We pay Russia to launch because our REUSABLE SPACE VEHICLE fleet is worn out, not because we are behind Russia in space technology. The future is in reusable launch vehicle (RLV), not in expendable (ELV). An RLV is infinitely more versatile than an ELV. Our experience in this will allow the US to build the next generation of RLV that will be more capable than the current shuttle fleet design and keep US several steps ahead of Russia. This is about finance, not technology or experience.

Needless to say, I am not concerned for our aerospace tourism when it is bringing in billions of USD. It is a market your capitalists have failed to garner and we reap the benefits. BTW, I am going up in a MiG-31 for Christmas so you are really complaining to the wrong person about that.

Russia entered this 'market' out of dire financial necessity. It demean the Russian military, as if the state of the Russian military is not sorry enough already. Your flight in the -31 will be enjoyable, I am certain, but I doubt that it will be more interesting than what I had in the F-111. We flew hard ride terrain following (TF) over the English hills and later simulated a very low altitude bomb run over the Channel for the French to test their radars. We flew at 50ft over the water and I set the TFRs sensitive enough to pick up surface waves. It made for a very choppy flight. French air defense never pick our flight up until we broke horizon, which usually is weapons release. Then we had an air refueling stop before returning to Upper Heyford.

 

[p2prada]

Not sure what are you trying to get at here, but an AWACS generally operate as a mono-static platform. If you wonder if there are any advantages of an airborne platform over a ground station, in terms of target certainty of an LO aircraft, then there is a slight advantage for the airborne platform in that radar detection is line-of-sight dependent. The higher you are the further you can see. If there is a credible threat of an attack by a flight of LO aircrafts, an AWACS can use long wavelengths (mhz) with being at higher altitude to attempt detection.

You answered my question anyways.

Yes...And it does not matter the method employed. But there is something called 'clutter', which is unwanted signals, or junk. That said...What is junk to one system is desirable to another. For an AWACS, land mass and clouds are junk. But for a weather radar, the AWACS aircraft itself is junk. The meteorologist want to see only nature-made objects, not metallic ones flying around. The universe is filled with background radiation and that must be included in the clutter region. Specular energy can fall into the clutter region and be dismissed by the radar computer. But how do you know if that particular dismissal was a real bird or an F-22?

Will faster processing not solve this problem? AESAs are meant to preform better classification of targets too.

Lower the clutter rejection threshold and your scope would be filled with all sorts of signals, from clouds to birds to land and somewhere inside that mess would be that F-22. You could attempt some creative signal processing such as Doppler to filter out anything moving at above so-and-so speed, but then how do you know if what you believed to traveled at several hundreds km/h is not a sudden appearance of a different flock of birds? By the way, we detect birds BY THEIR BEAKS. A bird's body is naturally curvy, remember the creeping wave effect, and the feathers do absorb some freqs. The beak is hard and angular and is the greatest contributor to the bird's RCS. So pelicans with their giant honkers can appear to be several times their individual sizes.

Out of the topic. I believed the other parts of the bird cannot be detected easily because they are organic rather than their distinct shape.

At the same time, can a sky diving human be detected by a radar? Consider he is in his birthday suit.

For the X, S and L bands, the F-22 is between the sparrow and the warbler. Unofficially it is even smaller but no one will reveal the true figure. People are misinformed that if a missile's X-band pick up a bird's RCS, it should be able to target a 'stealth' aircraft as well. This belief is true only if missiles will turn and chase birds. But we do not program our missiles to chase birds. No one does. We program our missiles, even though their X-band radars is capable, to ignore any RCS below a certain threshold, else the missile would be chasing everything and anything.

Will doppler resolution not solve the same problem again? Nothing in the air flies faster than an airplane, and definitely not a bird(max 200km, probably lesser).

Much misinformation have been made about the single F-117 shoot down over Yugoslavia. The Serbs and the Russians wasted no efforts on crowing how their 1960s era radar supposedly detected, tracked and finally targeted that one F-117. There was some nonsense about long wavelengths to 'defeat' LO aircrafts.

I have always thought of it as a fluke. He took a chance and it worked. Thanks for making it clear.

Now we have two 'stealth' platforms that are more capable than the retired one and we have another 'stealth' platform on the way.

Sir, how do you rate the 2 birds? My opinion is the F-22 is more stealthy, faster, more agile etc; but it will be the F-35 which will be the superior fighter considering its avionics.

Also, how will 2 stealth platforms engage each other? Let's say Greece and Turkey have F-35s and they are at war. How will the F-35 engage the other F-35. Consider both have the same avionics and the pilots have the same skill level.

The US is also not resting on this laurel. This current generation of 'stealth' employ passive RCS reduction measures. We are working on the next generation which will have active RCS control measures.

Are you referring to active cancellation or plasma stealth or something more elusive?

The difference between 'reduction' and 'control' is crucial. The aircraft will be able to emit any or no RCS at will. We will be able to claim with a straight face that the aircraft is 'invisible' to radar.

I would suggest a spherical fighter.

I know my response is long but you are treading into a very complex topic that require some compromises in explaining technical information involved in language that the average readers can understand.

In 3 posts you have provided enough information that I will never find in any text book or from my professors. Thank you for that sir. I am a student studying electronics(bachelor's degree).