Almaz S-300: China's "Offensive" Air Defense

Distance from the battlespace means systems like JSTARS, Rivet Joint or the U-2 do not need to be directly in the line of sight or in a sidelobe of a CW radar to detect these. Just as Scratch said, a radar warning receiver or other such detection device will, as a rule of thumb detect the radar in question at a range fifty percent greater than the radar will detect the platform with the detection equipment. The sensor only has to sense an emission while the radar must be able to detect the energy reflected off the platform with the sensor.
As range from the radar increases, the width of the beam likewise increases. For CW fire control radars the target must be close to the center of the beam for accurate information to be generated for the fire control system, or the system will use multiple beams such that the energy reflected from each beam is equal. Rivet Joint does not need to be right in the beam to detect it's presence.
There are several reasons for radars to suppress their side lobes that have little to do with their being detected. Crobato, do you know what "inverse gain jamming" is? This technique exploits the side lobes to create a false echo. CW fire control radars suppress side lobes to prevent ambiguity in the doppler return they use to measure range to the target. What is called "side lobe" ambiguity introduces spurious doppler information and muddies the range reading. A fire control radar can likewise be spoofed by inverse gain jamming and a radar lock broken, so sidelobe suppression employed in these radars has nothing to do with avoiding the JSTARS. CW radars will employ wide beams until a target is detected and locked, then use a narrow beam during an intercept.

The main line of sight is called the main lobe. The sidelobes are the emissions that are out of the line of sight. A radar lobe pattern is similar to a peacock's tail with a big main lob at the main center of the antenna, and smaller lobes protruding to the sides.

If you are trying to detect a search radar, the search radar generally has a large main lobe that sweeps around, so you can generally just detect the main lobe itself.

For an advanced fire control radar, one that uses tight beams, you want to control the side lobes for several reasons, first, less side lobe, you get a stronger main lobe; second, you get less noise and interference especially from side lobe echoes, and third, not and not the last, it reduces detection. Part of LPI in fact, is reducing side lobes and side emissions to the extent its not detectable by receivers.

Side lobe ranges are also much less than that of main lobes. The rule of thumb mentioned above only applies to main lobes.

CW radars will employ wide beams until a target is detected and locked, then use a narrow beam during an intercept.

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Only if you are referring to an integrated set that has both volume search and fire control tracking functions. However, like the S-300 systems, there are sets that have these functions in separate sets.

Sidelobe cancellation defeats inverse gain jamming.

CW radars will employ wide beams until a target is detected and locked, then use a narrow beam during an intercept.

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Or use passive means to locate the target, and then shoot a very narrow beam to provide targeting information for the missiles.

Sidelobe suppression does not deter detection by something like Rivet Joint. It flies so far from the battlespace that side lobe suppression is immaterial. The aircraft can see the whole sweep of the battle from a long ways off.
Systems like S-300 must paint the target with their radar for the duration of the engagement, giving the Rivet Joint plenty to track. LPI does not rely on side lobe suppression to reduce their chances of detection. They use side lobe suppression to some degree but for other reasons such as I mentioned and you simply regurgitated, to reduce side lobe ambiguity and to minimize the opportunities for inverse gain jamming.
LPI functions in part by spreading the energy radiated over as broad a spectrum of wave forms as possible and with phased array radars make the sweeps so fast they RWR has precious little time to detect and classify the threat. It is low probability of intercept however, not no probability of intercept as this paper will tell you.









As you can see students ( mid grade commissioned officers ) of the Naval Post Graduate School in Monterey California have been very busy addressing this issue through several innovative techniques.

RIVET JOINT Joint Airborne SIGINT Architecture (JASA) High Band Sub-System (HBSS) Upgrade and the RIVET JOINT SHF High Gain Steerable Beam Antenna Upgrade I are systems installed specifically to address the characteristics of LPI radars. RIVET JOINT 360º Search, Acquisition, and Direction Finding System is a modification that allows similtaneous 360 degree coverage vice the previous 120 degrees per side coverage of the original Rivet Joint. As expected it is measure, countermeasure and counter-countermeasure. LPI does not guarantee our EW will be ineffective at all, it just changes the parameters of the game.

Sorry but i still think you are contradicting physics. Do you understand how a radar beam is formed do you, and what are main lobe and side lobe patterns are?

Aircraft detect the sweep of the main lobes, and through the side lobes if the main lobes are thin or narrow. Side lobes are generally much weaker than main lobes, and atmospheric attenuation reduces their range like any other EM radiation.

Fire control radars do not need to sweep the battle space if another radar does it for them.



Low Probability of Intercept (LPI) radars are military radars which are designed for the modern electronic combat environment. More or less successfully, they try to avoid being detected by ELINT sensors by using any combination of the features outlined in this Entry.

Multistatic Radar

Common radars are monostatic - that is, their transmitter and receiver are located in the same place. An ELINT sensor can only detect transmitters and once the transmitter has been located, the whole radar can be engaged by jamming or by other means such as artillery or anti-radiation missiles.

Bistatic radars have the transmitter and receiver at different places. Therefore, the transmitter may be located, but destroying the transmitter won't lead to much damage as the receiver and signal-processing equipment makes up the more expensive part of a radar. It doesn't make sense to direct a jammer against the transmitter because only a receiver can be susceptible to jamming. A special case of bistatic radar is the pair that is made up by a target illumination radar and the seeker head of a radar homing missile. Attempting to jam the illuminator won't affect the seeker-head. Even worse, doing so would provide it with a beacon signal.

Multistatic radars are the extension of bistatic ones. They've got a single transmitter but have several receivers distributed over an area of interest. The receivers deliver their findings to an evaluation centre where powerful computers are busy correlating the results and putting together an air picture. Transmitters are much cheaper than all this equipment and if a transmitter was to be destroyed, it would be fairly easy to replace it.

Ultra-low Sidelobe Antennae

Ordinary radar antennae feature sidelobes which are weaker by a factor of, for example, 100 times than the main lobe. That is, they are giving away their position not only in the intended direction but also to anybody who cares to listen from somewhere else. Ultra-low sidelobe antennae are designed to change that by featuring sidelobe levels in the ranges of one ten-thousandth of the power of the main lobe and even less. Thus, the chances of intercepting a signal from a position outside the main beam are significantly reduced.

Ultra-wide Band Signals

Long pulse duration means that a given amount of energy is distributed over time. Ultra-wide band signals distribute a given amount of energy over frequency, with the same effect of hardening an ELINT receiver's task of detecting them. The radar itself knows which signal it is looking for, and the receiver circuitry has been matched to the signal properties. This knowledge gives the radar receiver a distinct advantage over an ELINT receiver.

Long Pulse, Low Power

A radar receiver needs a distinct amount of energy in order to detect a radar return. This energy can be contained in a short but powerful pulse, in a weak pulse with correspondingly longer duration, or ultimately in a continuous wave signal with even less power. ELINT receivers rely on some minimum ratio of power to noise in order to identify a radar signal. Low power signals are designed to evade detection by lowering this ratio and trying to hide within the noise.

No Power At All: Passive Radar

A passive radar like Silent Sentry [Note: This is a PDF document, requiring the free Adobe Acrobat Reader to be installed on your machine. The software can be downloaded for free from Adobe] is a multistatic radar - without the transmitter. The receivers pick up reflections that are caused by background illumination provided by commercial TV or radio stations. Enormous computer power is engaged to correlate them against a master copy that was received via some direct propagation path and to calculate target flightpaths and positions. As this type of radar doesn't have any transmitter, it is obvious that an enemy's ELINT assets are confronted with the problem of finding something that doesn't actually exist.

Crobato, did you even bother to read the links regarding Rivet Joint, or about the research accomplished way back in the 1990's on this issue. LPI radars are tougher to detect, but not impossible. We know a lot about side lobe suppression and passive radar. Aegis has both features. This is all normal stuff for us. Side lobe suppression does not mean they are completely eliminated. If you have sensitive enough equipment with a sufficient signal to noise ratio they are still detectable.
Passive radar has serious limitations but is used when we are Emcon. However if a threat is detected you have to light off the radar and emit. Passive radar can tell you something might be out there and give some general information about where, but not nearly enough to generate an accurate picture of the battlespace much less provide targeting information. If you can imagine ships sailing Emcon, no emitters except directional data links like Link 11 or 16, using signal lights to communicate ( even in the landing pattern at the carrier ), the Aegis and other radars are on in a passive listening mode. This is routine during Emcon for two reasons. One, if a threat emerges you need to emit right away. Second, you can obtain some imprecise direction information on aircraft and surface targets, and maybe listen to their emissions to try to determine what it is ( might just be a passing airliner ). That is about all passive radar will get you. This is real life Crobato, what we do in the Navy at sea. Have you been there yet? I have. You cannot develope a fire control solution off of passive radar. You have to emit.
Again, at the ranges Rivet Joint flies from the battlespace it does not have to be in the direct line of sight of the radar. Same for the U-2. Scanning search radars scan wide swaths of the sky, and CW radars that use very short waves have limited range and their signals scatter at the sort of ranges systems like the U-2 and Rivet Joint fly. The modifications to Rivet Joint I gave you the links to allow the necessary sensitivity and wide band signal reception necessary to receive an LPI signal. Did you read them Crobato or not? From there it is up to powerful computers and advanced math algorithms to recognize the radar signal from other electronic noise. This is doable. The idea of LPI is not new to us. We build them and understand the principles of their operation, so why is it such a struggle for you to understand the US has some ability to locate and classify them? The signal is spread over a wide band of freqs with low energy emitted on each band. Some very complex math is used to integrate these signals into something useful to an operator. These signals, while low, are not immune to being DF'ed. The difficulty is to re-integrate perhaps many LPI radar signals to see what is a radar sweep and what is noise. It is a tough math problem, but not beyond our scientists. Computers do the calculations. Does this surprise you? It doesn't hurt that we take every opportunity to record the emissions of any and all radars in the world for analysis by our scientists. Again this has been done. That is in part what those two papers from the Naval Postgrad School are about, developing the mathematical models of LPI radars for use in EW. This is the old unclassified stuff.

I am quite aware of methods and programs undergoing to detect LPI and by the way, its not confined to the US, its worldwide, including Europe, China, and Russia.

What seems to be the problem is that you don't seem to know the meaning of the world "attenuation".



Add inverse-square law geometric spreading to that mix too.

Try to understand this, if you want to gain signal, the size of the array is also important. There is an apparent limitation in array size you can stuff in an aircraft, and even less on the strike aircraft, and finally the missile seeker's array.

And here is the other problem too, you can't put your scientists and all that equipment on board a SEAD aircraft, much less a missile. Here is another problem too, the more signals you get in the environment, the greater the magnitude the number of signals you have to process and identify. Sure it can be done by computers, eventually if you stay long enough, or carry enough computers, but this kind of equipment can;t be carried on strike aircraft and much less the seekers of HARMs. The third catch is trying to process hundreds if not thousands of signals in less say, 20 seconds. Yeah, remember the radars can shut down, and they can shut down before you can even manage to process the signal background fast enough.

Sigh.

Here is what is in the links I posted. Maybe you can read these this way.

"On February 12, 1997 Sanders, a Lockheed Martin Company, was selected by the Joint Airborne Signals Intelligence (SIGINT) Program Office for development and demonstration of the Joint SIGINT Avionics Family (JSAF) Low Band Subsystem (LBSS). Major subcontractors include: Radix Technologies, Inc. of Mountain View, Calif.; Applied Signal Technologies (APSG) of Sunnyvale, Calif.; and TRW System Integration Group, also of Sunnyvale. Radix will provide radio frequency (RF) and digital signal processing subsystems; APSG will develop special signal processing subsystems; and TRW will be responsible for high speed networking and computing subsystems. The JSAF low band subsystem is a platform-independent, modular, reconfigurable suite of hardware and software that can address multiple mission scenarios aboard a variety of aircraft. It will significantly enhance the ability of reconnaissance platforms to detect and locate modern enemy communications systems and provide real time intelligence on enemy intentions and capabilities to the warfighter. Initially, JSAF LBSS will be deployed on U.S. Air Force RC-135 Rivet Joint aircraft and other special Air Force platforms as well as the U.S. Army's RC-7 (Airborne Reconnaissance Low) and the U.S. Navy's EP-3 aircraft. JSAF LBSS will also be capable of deployment on unmanned air vehicles (UAVs) in the future. JSAF collection systems intercept, exploit, and report on modern modulation and low probability of detection communications and radar signals. It permits the collection of signals in the presence of co-channel interfering signals, and provides interoperability between primary DOD airborne collection platforms, establishing the infrastructure to support near-real-time exchange of information for rapid signal geolocation and targeting. Provide compliance with DOD directed Joint Airborne SIGINT Architecture (JASA)."

"The RIVET JOINT Joint Airborne SIGINT Architecture (JASA) High Band Sub-System (HBSS) Upgrade procures and installs upgrades to the RIVET JOINT’s high band antennas, RF distribution network, and software to intercept, exploit, and report on modern modulation and low probability of detection communications and radar signals. It permits the collection of signals in the presence of co-channel interfering signals, and provides interoperability between primary DOD airborne collection platforms, establishing the infrastructure to support near-real-time exchange of information for rapid signal geolocation and targeting. Provide compliance with DOD directed Joint Airborne SIGINT Architecture (JASA). The JSAF CRD (CAF 002-88 Joint CAF -USA, USN, USMC CAPSTONE Requirements Document for JOINT SIGINT AVIONICS FAMILY) requires all airborne reconnaissance aircraft to migrate to JASA compliance by 2010."

"The RIVET JOINT SHF High Gain Steerable Beam Antenna Upgrade I will procure and install a new antenna array in the cheek to provide increased sensitivity and signal separation for selected frequency bands. It provides an increased number of steerable beams in bands that currently have steerable beams, and provides steerable beams in bands not currently steerable beam capable. Increases the number of signals that can be processed simultaneously and increases signal selectivity against co-channel signals. Increasing number of low power signals and increased signal density have decreased the ability to collect tasked targets due to co-channel signal interference. Antenna improvements permit deeper target penetration against low power emitters or increased standoff ranges."
In other words your concerns were being addresses as far back as the end of the last decade. The quotes are from the Federation of American Scientists link I gave you to read a couple of posts ago. It should be pretty clear that a decade ago the US was addressing these same things you claim erroneously are not possible to overcome.
You need to keep in mind that the US throws extrordinary amounts of resources at such problems. There are no other air forces with the sorts of integrated sensors the US has with JSTARS, the U-2, Global Hawk, Rivet Joint and the EP-3. This is a level of resources no other military brings to battle specifically to exploit the electronic spectrum to our advantage. For 99% of all the other military's out there an AESA radar is invisible to any RWR. A JSTARS or Rivet Joint can do this mission due to their great size, multiple sensors and vast onboard processing capability. A lone F-16J flying around with a Harm under the wing could not do the job alone, that is correct. But with all the other resources backing that F-16J up it can find and kill a SAM site. We have done this successfully in actual wars.

Sigh.

Read it from an engineer.



"This paper discusses the current and projected future capabilities of “Low Probability of
Intercept” radars and of the intercept receivers used by Electronic Support Measures (ESM) systems. Indiscussing the possible future sensitivity of the latter it makes use of the Matched Incoherent Receiver to show how the intercept ranges may be able to increase in the future. It then discusses future radar tactics which can make interception harder, and concludes that there is no overwhelming advantage to one side or the other, but the balance will depend on the particular tactical situation."

There is some math here involving a hypothetical baseline radar, and the calculations produce this.

"These tables show that the radar can detect its target at 20km range, whilst its emissions can only be intercepted at 2.5km range, which confirms that, at least in this scenario, the radar is “tactically indetectable.” Its conclusions have also been given, for example, in reference (2) ."

"This is about 20dB better than a current “state of the art” channelized receiver and would allow the free-space interception range to be increased to 280km against the main beam of the “baseline” radar whose parameters are shown in table 1, but the range against sidelobes 40dB below the main beam would still be only 2.5km and the range would only be 8km if the transmitter power could be reduced to 1mW. Obviously, other variations of these figures are possible."

Crobato, I suggest you get well acquainted with the evidence you produce to back up your POV before posting them. Simply quoting "This is about 20dB better than a current “state of the art” channelized receiver and would allow the free-space interception range to be increased to 280km against the main beam of the “baseline” radar whose parameters are shown in table 1, but the range against sidelobes 40dB below the main beam would still be only 2.5km and the range would only be 8km if the transmitter power could be reduced to 1mW. Obviously, other variations of these figures are possible." without understanding whether it applies universally would only mislead the uninitiated.

That paper chose to use the Scout as an example of LPI radar, what it failed to mention is that Scout/Pilot are quite unique among radars. Unlike other radars, they use FMCW technology, which is the basis of their LPI properties. Why FMCW? That's because using FMCW allows for minimisation of peak transmission power, which is the parameter ESMs use for detection. That is how Scout/Pilot can achieve detection ranges beyond that of ESMs. But if FMCW was so good, why isn't every radar utilising it? The flipside is that FMCW severely restricts range. That's why it is not used widely. So this paper presents only a unique case that doesn't even have anything to do with sidelobe suppression. Incidentally, Thales is the producer of Scout.