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While F-35 is capable of stand-off jamming for other aircraft — providing 10 times the effective radiated power of any legacy fighter — F-35s can also operate in closer proximity to the threat (‘stand-in’) to provide jamming power many multiples that of any legacy fighter.
The deceptive jammer received enemy incoming RF signal , it analyse , and then re transmitted that signal with different characteristic , like different doppler , pulse width . In contrast to noise jamming, deception jammer tries to mimic the radar echo so that the radar will respond as if it is receiving an echo from another aircraft or ship.
Jamming is likewise much more difficult against an AESA. Traditionally, jammers have operated by determining the operating frequency of the radar and then broadcasting a signal on it to confuse the receiver as to which is the "real" pulse and which is the jammer's. This technique works as long as the radar system cannot easily change its operating frequency. When the transmitters were based on klystron tubes this was generally true, and radars, especially airborne ones, had only a few frequencies to choose among. A jammer could listen to those possible frequencies and select the one to be used to jam.
Most radars using modern electronics are capable of changing their operating frequency with every pulse. An AESA has the additional capability of spreading its frequencies across a wide band even in a single pulse, which equates to lowering the emission power, making jammers much less effective. Although it is possible to send out broadband white noise against all the possible frequencies, this means the amount of energy being sent at any one frequency is much lower, reducing its effectiveness
In general, high PRF radars are more resistant to ECM because their average power is greater. Changing the PRF in a random fashion is an effective counter to deception because deception ECM depends on predictability of the radar. However, because PRF is related to the basic timing of the radar, this technique results in additional complexity and expense. Random PRF has been employed as a very effective ECCM feature in some radars for many years and has the additional benefit of elimination of MTI radar blind speeds.
Scan pattern. The radar scan pattern can influence ECCM capability because it influences the amount of energy directed toward the radar target. An active tracking phased-array radar is quite ECM resistant because of its ability to rapidly scan its radar beam in a random fashion than in the regular circular or sector scan pattern of conventional radars. This irregular beam positioning would give the opposing ECM system little or no warning and make it impossible to predict where and when to transmit false signals. In systems where scanning is performed in the receiver rather than in the transmitted beam, such as those mentioned in the section on angle deception, ECM has no direct access to the radar scan pattern and thus has difficulty using that information to interfere with the radar system operation.
Frequency. Frequency agility is a significant ECCM design feature. Using components such as frequency synthesizers (something like those employed in radio scanners) instead of conventional crystal-controlled oscillators, some radars are able to change frequency within one pulse repetition time (PRT). This makes deception and jamming very difficult. The radar can be designed to change frequency automatically within a certain range, or this can be done manually.
1. RWR antenna typically has a gain of about 0 dB due to wide angular coverage. Fighter AESA radar has a gain of roughly 40 dB. This means instant 40 dB advantage to the radar.
2. Radar can operate at much narrower bandwidth as it knows the frequencies it uses and RWR does not and has to operate at much wider bandwidth. RWR receivers have a sensitivity in the region of -40 to -60 dB while radar receivers have a sensitivity is roughly about -100 dB with digital receivers achieving even better sensitivity like -120 dB.
This can give additional 50 to 80 dB advantage to radar depending on exact design of the systems involved. As AESA has a very wide total bandwidth, RWR must cover that very wide bandwidth leading to much less sensitivity. As the radar signal has a quite narrow bandwidth and radar can process only very narrow bandwidth giving large advantage in sensitivity. For AESA the advantage can be for example in the 60 to 80 dB range.
3. Radar can code or modulate the signal so that it achieves significant processing gain over RWR. Either phase or frequency modulation/coding can be used. As radar knows the coding, it can filter out the signal from noise using matched filters. The RWR can’t know the coding and this gives the radar another big advantage in total gain. This is called Processing gain and it can be tens of decibels. The more complex the coding the larger the processing gain of radar is. Modern AESA radar using Digital Beamforming can use very complex coding schemes and basically only processing power and software is the limit here. A simple calculation about processing gain is dividing the spreading bandwidth (bandwidth where the signal is spread) with actual signal bandwidth.
4. When the radar main beam is not directly pointing towards the RWR, then it will only be seen through sidelobes. Given that sidelobe level can be lower than -50 dB in AESA radars (about -20 to -30 dB in fighter MSA/PESA radars), this gives the radar a healthy advantage against RWR/ESM systems which it’s not painting. This means RWR will only see very short flashes of main beam and makes it more difficult for the RWR to work effectively.
Calculated together, radar can suddenly have well over 100 dB advantage over RWR system through mainlobe and over 150 dB advantage otherwise. There are ways for RWR/ESM systems to get some of that back and of course the race is never ending. RWR/ESM system can use more directional antenna, more sensitive receivers and higher processing power.[code][/code]
eloise wrote:
To effectively jam an AESA radar, you would need to use noise jamming. For a noise jammer to be effective , the signal to noise ratio that enemy received must be less than 1. To achieve that you either have to increase your jamming power or reduce your reflected signal , or both. F-35 use APG-81 to jam, AESA have very narrow beam, as a result jamming power are more focused at enemy's place. It's also have a tiny RCS, thus reducing the reflected signal significantly
Even if we assume both side use the same kind of jammer, it still much easier for a stealth fighter to jam a normal fighter's radar than the other way round. Here is why :
mrbsct wrote:^Doesn't F22 RWR ALR-94 have 360 coverage? A read by Military Expert and Aviation magazine editor Bill Sweetman, the ALR-94 can not only passively receive but cue the APG-77 to make it even more LPI, and even lock on to targets whether they are generating radar or not.
mrbsct wrote:So stealth fighters not having dedicated jammers but use their own radar to jam are more effective than dedicated jamming systems like the SPECTRA?
mrbsct wrote:I believe the F22's RWR the ALR-94 can provide accurate data for attack.
Journal of Electronic Defense; Bill Sweetman
The F-22 represents a radical departure from the traditional approach to EW. Passive systems, once considered to be defensive in nature, are now critical to detecting, tracking and even attacking the target.
High-priority emitters -- such as fighter aircraft at close range -- can be tracked in real time by the ALR-94. In this mode, called narrowband interleaved search and track (NBILST), the radar is used only to provide precise range and velocity data to set up a missile attack. If a hostile aircraft is injudicious in its use of radar, the ALR-94 may provide nearly all the information necessary to launch an AIM-120 AMRAAM air-to-air missile (AAM)
mrbsct wrote:But aren't radar based jamming more prone to be detected by RWR and can risk an attack from anti-radiation missile?
Here is a quote from Air Power Australia:
Currently classified capabilities such as the use of the APG-79 or APG-81 AESA radar as an X-band high power jammer against the Russian BARS or Irbis E radar are not a panacea, and may actually hasten the demise of the F/A-18E/F or F-35 JSF in a BVR shootout. This is for the simple reason that to jam the Russian radar, the APG-79 or APG-81 AESA radar must jam the frequencies being used by the Russian radar, and this then turns the APG-79 or APG-81 AESA radar into a wholly electronically predictable X-band high power beacon for an anti-radiation seeker equipped Russian BVR missile such as the R-27EP or R-77P. The act of jamming the Russian radar effectively surrenders the frequency hopping agility in the emissions of the APG-79 or APG-81 AESA radar, denying it the only defence it has against the anti-radiation missile. A smart Russian radar software designer will include a "seduction mode" to this effect, with narrowband emissions to make it very easy even for an early model 9B-1032 anti-radiation seeker.
mrbsct wrote:I
But aren't radar based jamming more prone to be detected by RWR and can risk an attack from anti-radiation missile?
Here is a quote from Air Power Australia:
Currently classified capabilities such as the use of the APG-79 or APG-81 AESA radar as an X-band high power jammer against the Russian BARS or Irbis E radar are not a panacea, and may actually hasten the demise of the F/A-18E/F or F-35 JSF in a BVR shootout. This is for the simple reason that to jam the Russian radar, the APG-79 or APG-81 AESA radar must jam the frequencies being used by the Russian radar, and this then turns the APG-79 or APG-81 AESA radar into a wholly electronically predictable X-band high power beacon for an anti-radiation seeker equipped Russian BVR missile such as the R-27EP or R-77P. The act of jamming the Russian radar effectively surrenders the frequency hopping agility in the emissions of the APG-79 or APG-81 AESA radar, denying it the only defence it has against the anti-radiation missile. A smart Russian radar software designer will include a "seduction mode" to this effect, with narrowband emissions to make it very easy even for an early model 9B-1032 anti-radiation seeker.
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