How does SPECTRA jammer work?

[mrbsct]

How does SPECTRA on the Rafale work?

I heard it uses some sort of active cancellation technology although some people deny this and say it doesn't work. Or is it just a simple deceptive jammer? Can it noise jam? How does it compare to other ECM pods(its rather small)

[wil59]

How does SPECTRA on the Rafale work?

I heard it uses some sort of active cancellation technology although some people deny this and say it doesn't work. Or is it just a simple deceptive jammer? Can it noise jam? How does it compare to other ECM pods(its rather small)

Thales Group and Dassault Aviation have mentioned stealthy jamming modes for the SPECTRA system, to reduce the aircraft's apparent radar signature. It is not known exactly how these work or even if the capability is fully operational, but it may employ active cancellation technology, such as has been tested by Thales and MBDA. Active cancellation is supposed to work by sampling and analysing incoming radar and feeding it back to the hostile emitter out of phase thus cancelling out the returning radar echo.[3]

[wil59]

How does SPECTRA on the Rafale work?

I heard it uses some sort of active cancellation technology although some people deny this and say it doesn't work. Or is it just a simple deceptive jammer? Can it noise jam? How does it compare to other ECM pods(its rather small)

Thales Group and Dassault Aviation have mentioned stealthy jamming modes for the SPECTRA system, to reduce the aircraft's apparent radar signature. It is not known exactly how these work or even if the capability is fully operational, but it may employ active cancellation technology, such as has been tested by Thales and MBDA. Active cancellation is supposed to work by sampling and analysing incoming radar and feeding it back to the hostile emitter out of phase thus cancelling out the returning radar echo.[3]

A Stealthier Rafale?



Our colleagues at Air & Cosmos report that the French government is funding a demonstration of improved stealth technology for the Dassault Rafale fighter, with a focus on active cancellation techniques. The story itself is not online but is being discussed at the Key Military Forum.

Dassault

Active cancellation means preventing a radar from detecting a target by firing back a deception signal with the same frequency as the reflection, but precisely one-half wavelength out of phase with it. Result: the returned energy reaching the radar has no frequency and can't be detected.

It's quite as difficult as it sounds. Some reports have suggested that the so called SP-3 or ZSR-62 "radar jamming device" planned in the early days of the B-2 program was an active cancellation system. It did not work and was scrapped in 1987-88. In 2005, Northrop Grumman paid $62 million to settle a False Claims Act case involving the system.

This may not be the first French attempt to implement AC on the Rafale. At the Paris air show in 1997, I interviewed a senior engineer at what was then Dassault Electronique, about the Rafale's Spectra jamming system. He remarked that Spectra used "stealthy jamming modes that not only have a saturating effect, but make the aircraft invisible... There are some very specific techniques to obtain the signature of a real LO aircraft."

"You mean active cancellation?" I asked. The engineer suddenly looked like someone who deeply regretted what he had just said, and declined any further comment. (As Hobbes once put it after pouncing on an unsuspecting Calvin: "We tigers live for moments like that."*)

The fact that a new demonstrator is being contemplated suggests that the technology may not have been up to the job the first time round - but since AC depends on electronics and processing, that picture may have changed. MBDA and Thales, which absorbed Dassault Electronique and is now the prime contractor on Spectra, have since confirmed that they are working on active cancellation for missiles.

The whole Spectra program has been a major venture, including the construction of four new indoor test ranges, including the colossal Solange RCS range discussed in Ares in 2007. That facility will probably play a major role in the new demonstrator program.

[tritonprime]

A Stealthier Rafale?



Our colleagues at Air & Cosmos report that the French government is funding a demonstration of improved stealth technology for the Dassault Rafale fighter, with a focus on active cancellation techniques. The story itself is not online but is being discussed at the Key Military Forum.

Dassault

Active cancellation means preventing a radar from detecting a target by firing back a deception signal with the same frequency as the reflection, but precisely one-half wavelength out of phase with it. Result: the returned energy reaching the radar has no frequency and can't be detected.

It's quite as difficult as it sounds. Some reports have suggested that the so called SP-3 or ZSR-62 "radar jamming device" planned in the early days of the B-2 program was an active cancellation system. It did not work and was scrapped in 1987-88. In 2005, Northrop Grumman paid $62 million to settle a False Claims Act case involving the system.

This may not be the first French attempt to implement AC on the Rafale. At the Paris air show in 1997, I interviewed a senior engineer at what was then Dassault Electronique, about the Rafale's Spectra jamming system. He remarked that Spectra used "stealthy jamming modes that not only have a saturating effect, but make the aircraft invisible... There are some very specific techniques to obtain the signature of a real LO aircraft."

"You mean active cancellation?" I asked. The engineer suddenly looked like someone who deeply regretted what he had just said, and declined any further comment. (As Hobbes once put it after pouncing on an unsuspecting Calvin: "We tigers live for moments like that."*)

The fact that a new demonstrator is being contemplated suggests that the technology may not have been up to the job the first time round - but since AC depends on electronics and processing, that picture may have changed. MBDA and Thales, which absorbed Dassault Electronique and is now the prime contractor on Spectra, have since confirmed that they are working on active cancellation for missiles.

The whole Spectra program has been a major venture, including the construction of four new indoor test ranges, including the colossal Solange RCS range discussed in Ares in 2007. That facility will probably play a major role in the new demonstrator program.

Sweetman, Bill A Stealthier Rafale? Ares Defense Technology Blog, 5 April 2010

[charlielima223]

more information here... I guess...

viewtopic.php?f=22&t=27975

[eloise]

Active cancellation doesn't work, it is the same kind of BS as plasma stealth, which sound very cool in theory but with basic physics knowledge you will know that it not possible
In theory active cancellation rely on destructive interference to work
Firstly, destructive interference is the phenomenon that occurs when two waves meet while traveling along the same medium. The interference of waves causes the medium to take on a shape that results from the net effect of the two individual waves upon the particles of the medium.Consider two pulses of the same amplitude traveling in different directions along the same medium. Let's suppose that each displaced 1 unit ( opposite with the other) at its crest and has the shape of a sine wave. As the sine pulses move towards each other, there will eventually be a moment in time when they are completely overlapped. At that moment, the resulting shape of the medium would be zero
Once the two pulses pass through each other, there is still an upward displaced pulse and a downward displaced pulse heading in the same direction that they were heading before the interference. Destructive interference leads to only a momentary condition in which the medium's displacement is less than the displacement of the largest-amplitude wave. The meeting of two waves along a medium does not alter the individual waves or even deviate them from their path. Yet two waves will meet, produce a net resulting shape of the medium, and then continue on doing what they were doing before the interference.
http://www.physicsclassroom.com/class/w ... e-of-Waves

So the only way for active cancellation to work is if you can transmitting the wave from every where on your aircraft , exact frequency with enemy's radar wave, exactly out of phase by odd multiple of π, and most importantly , in the exact opposite direction with enemy's wave ( otherwise the destructive interference effect would be momentary only) . We're talking about getting a pulse, determining the frequency and phase of pulse at all parts of your aircraft, even where there aren't T/R modules, then determining the frequency and phase it's at when it gets back to all enemy Rxs and cancelling it at that point down to the millimetre, allowing for propagation time, . It's comical. you cant transmitting wave from every part on your aircraft, and not in all directions, unless you make your whole fighter become a big antenna. Even if you can some how cover the whole aircraft with T/R modules , active cancelation would required transmitter, receiver with unrealistic accuracy , and even then active cancellation wouldn't work if radar wave from 2 source hitting the same place on your aircraft

Go try develop a system that cancels random music perfectly to produce complete silence, so that nobody, regardless of where they're standing hears a thing and you see how unrealistic it is to have something active cancellation

( and i have not even mentioned the fact that AESA doesn't use constant frequency, PRF or scan pattern which make active cancellation even more unrealistic)

[wil59]

Active cancellation doesn't work, it is the same kind of BS as plasma stealth, which sound very cool in theory but with basic physics knowledge you will know that it not possible
In theory active cancellation rely on destructive interference to work
Firstly, destructive interference is the phenomenon that occurs when two waves meet while traveling along the same medium. The interference of waves causes the medium to take on a shape that results from the net effect of the two individual waves upon the particles of the medium.Consider two pulses of the same amplitude traveling in different directions along the same medium. Let's suppose that each displaced 1 unit ( opposite with the other) at its crest and has the shape of a sine wave. As the sine pulses move towards each other, there will eventually be a moment in time when they are completely overlapped. At that moment, the resulting shape of the medium would be zero
Once the two pulses pass through each other, there is still an upward displaced pulse and a downward displaced pulse heading in the same direction that they were heading before the interference. Destructive interference leads to only a momentary condition in which the medium's displacement is less than the displacement of the largest-amplitude wave. The meeting of two waves along a medium does not alter the individual waves or even deviate them from their path. Yet two waves will meet, produce a net resulting shape of the medium, and then continue on doing what they were doing before the interference.
http://www.physicsclassroom.com/class/w ... e-of-Waves

So the only way for active cancellation to work is if you can transmitting the wave from every where on your aircraft , exact frequency with enemy's radar wave, exactly out of phase by odd multiple of π, and most importantly , in the exact opposite direction with enemy's wave ( otherwise the destructive interference effect would be momentary only) . We're talking about getting a pulse, determining the frequency and phase of pulse at all parts of your aircraft, even where there aren't T/R modules, then determining the frequency and phase it's at when it gets back to all enemy Rxs and cancelling it at that point down to the millimetre, allowing for propagation time, . It's comical. you cant transmitting wave from every part on your aircraft, and not in all directions, unless you make your whole fighter become a big antenna. Even if you can some how cover the whole aircraft with T/R modules , active cancelation would required transmitter, receiver with unrealistic accuracy , and even then active cancellation wouldn't work if radar wave from 2 source hitting the same place on your aircraft

Go try develop a system that cancels random music perfectly to produce complete silence, so that nobody, regardless of where they're standing hears a thing and you see how unrealistic it is to have something active cancellation

( and i have not even mentioned the fact that AESA doesn't use constant frequency, PRF or scan pattern which make active cancellation even more unrealistic)

you can not know whether or not it works; Northrop Grumman has failed, this does not mean that dassaut Electronic and Thales is ok.DIRCM he really works! these are the point where we can not know! RCS of an aircraft is never published on the internet is the journalist rumor! measurement tables are done by blogger or technician is called to work for different different company! how can he calculated the aircraft rcs if it is never seen prét with very sharp instrument for this is speculation is its stops it!

[eloise]

you can not know whether or not it works; Northrop Grumman has failed, this does not mean that dassaut Electronic and Thales is ok.

None have success with active cancellation yet and it is even harder to do than plasma stealth

DIRCM he really works! these are the point where we can not know!
RCS of an aircraft is never published on the internet is the journalist rumor! measurement tables are done by blogger or technician is called to work for different different company! how can he calculated the aircraft rcs if it is never seen prét with very sharp instrument for this is speculation is its stops it!

theory of DIRCM and aircraft RCS are well known since very long time , and they are much much more simple than trying to make an active cancellation system

[wil59]

you can not know whether or not it works; Northrop Grumman has failed, this does not mean that dassaut Electronic and Thales is ok.

None have success with active cancellation yet and it is even harder to do than plasma stealth

DIRCM he really works! these are the point where we can not know!
RCS of an aircraft is never published on the internet is the journalist rumor! measurement tables are done by blogger or technician is called to work for different different company! how can he calculated the aircraft rcs if it is never seen prét with very sharp instrument for this is speculation is its stops it!

theory of DIRCM and aircraft RCS are well known since very long time , and they are much much more simple than trying to make an active cancellation system

The capacity to deceive a radar LPI (Low Probability of interception) is based on 3 things:-the capacity to listen to simultaneously a very important number of frequencies the capacity to recognize that multiple signals are in fact only one " pulse train " - the capacity treated(manipulated), to reproduce and to put back(hand) the signal on frequencies chosen with intelligence simultaneously .De our days, number of radars "codes" their impulse (s) to return the infalsifiables echos if we can say. Radar AESA is very good in this small game(set,play), returning the even more difficult jamming(blurring). On the other hand, radars equipping missiles are much easier to deceive, being some even monos pulses .Spectra have ways(means) varied to deceive a similar missile. Both main measures are at first to blur the line plane-missile (LAM) then to deceive the radar of the missile and finally (if need be) to release a cloud of glitter in last defense to .Accrocher one gust(burst) in the radar, to pursue him(it) and to pull(fire) at him a missile is not easy thing but in the end, to deceive the missile, it is to survive even if the opponent continues to pursue you to .Tirer a missile on one gust rafale is a thing, to bring(shoot) down him(it) is an other one..

[wil59]

you can not know whether or not it works; Northrop Grumman has failed, this does not mean that dassaut Electronic and Thales is ok.

None have success with active cancellation yet and it is even harder to do than plasma stealth

DIRCM he really works! these are the point where we can not know!
RCS of an aircraft is never published on the internet is the journalist rumor! measurement tables are done by blogger or technician is called to work for different different company! how can he calculated the aircraft rcs if it is never seen prét with very sharp instrument for this is speculation is its stops it!

theory of DIRCM and aircraft RCS are well known since very long time , and they are much much more simple than trying to make an active cancellation system

The capacity to deceive a radar LPI (Low Probability of interception) is based on 3 things:-the capacity to listen to simultaneously a very important number of frequencies the capacity to recognize that multiple signals are in fact only one " pulse train " - the capacity treated(manipulated), to reproduce and to put back(hand) the signal on frequencies chosen with intelligence simultaneously .De our days, number of radars "codes" their impulse (s) to return the infalsifiables echos if we can say. Radar AESA is very good in this small game(set,play), returning the even more difficult jamming(blurring). On the other hand, radars equipping missiles are much easier to deceive, being some even monos pulses .Spectra have ways(means) varied to deceive a similar missile. Both main measures are at first to blur the line plane-missile (LAM) then to deceive the radar of the missile and finally (if need be) to release a cloud of glitter in last defense to .Accrocher one gust(burst) in the radar, to pursue him(it) and to pull(fire) at him a missile is not easy thing but in the end, to deceive the missile, it is to survive even if the opponent continues to pursue you to .Tirer a missile on one gust rafale is a thing, to bring(shoot) down him(it) is an other one..

Assemble An Active Cancellation Stealth System
Modern signal-processing components make it possible to design an active stealth cancellation system to hide a target from an inquisitive radar system, even under changing conditions.ent
Achieving stealth requires minimizing the radar cross section (RCS) of a vehicle or system as it appears to an opponent’s radar detection capabilities. To achieve this objective, an active cancellation stealth system was designed by means of a phased-array technique, digital radio-frequency memory (DRFM), and field-programmable-gate-array (FPGA) technology. The DRFM enables precise replication of stored radar waveforms, while the phased-array technology is used to generate the required waveforms to cancel reflected radar returns. The FPGA is essential for signal analysis, database search, and waveform generation and control.

The system relies on an offline calculation approach in which omnidirectional RCS, clutter, and noise databases are established in advance. The active system’s signal processing and control module analyzes a measured radar signal parameter and then finds the corresponding target echo data in the RCS database, making a real-time adjustment of the coherent echo amplitude and phase parameters. By creating a target scattering field with coherent signal cancellation in the direction of a detecting radar system, the radar receiver remains in a null synthesis pattern. A combination of software and hardware helps realize this active cancellation stealth approach.

Radar stealth technology can be divided into passive and active techniques. Although passive methods have been traditionally used, the availability of high-speed microelectronic devices, phased-array antenna techniques, and computer processing have made active methods more feasible and practical. An active stealth system can adapt to almost any object that must be protected, such as a power plant or aircraft, and the technology can be retrofit to an existing electronics platform, with lower power consumption and other advantages compared to passive approaches.1

An active cancellation stealth system involves the use of coherent signal interference. For a target to avoid detection, it must emit a cancellation wave that is time-coincident with an incoming pulse, providing the required amplitude and phase to cancel the reflected energy from an enemy radar. This can be an effective means of blanking enemy radar pulses, although the difficulty in implementing such a system lies in the need to obtain cancellation signal parameters in real time, and to achieve precise control of the amplitude and phase of the cancellation waveform.2

Active cancellation stealth depends on adaptive real-time control of electromagnetic (EM) waveforms within a three-dimensional (3D) space. When a radar target is illuminated, return signals are produced by the target’s reflected radiation.

According to EM inverse scattering theory, if the source distribution of the radiation field is known, the properties of the scatterer and the scattering field distribution can also be known. If the radar signals are considered confined within a small solid angle for the sake of EM wave cancellation, a target can made to appear “invisible” or stealth to a radar system.

An important part of developing an active cancellation stealth system is understanding a given target’s RCS, which is a comparison of the scattered power density at the radar receiver with the incident power density at the target. The formal definition of RCS is3:



where:
σ0.5 = the complex root of the RCS
scatterer;
Ei = the electric field strength of the incident wave impinging on the target;
R = the distance between the radar and the scatterer;
êr = a unit vector aligned along the electric polarization of the receiver; and
ĒS = the vector of the scattered field.

Using either active or passive means, the principle of cancellation or reducing the RCS relies on reducing the field strength incident on the target to reduce the power reflected back to the radar receiver. Reducing the target scattering intensity can also reduce the RCS. A target’s RCS can be measured for different scattering directions and, according to Eq. 1, the direction of a radar target’s scattered field can be identified as:

ES = lim [Ei ∙ √σ ∙ êr)2√πR] (2)

Active cancellation methods are based on generating an EM field equal to a target’s scattered field, but with opposite phase. The effectiveness of active radar cancellation depends on the measurement precision of the radar signal, the knowledge of its real-time characteristics, and the accuracy of the generated cancellation field, among other factors. Figure 1 shows the principle of an active cancellation stealth process. The incident radar wave frequency, phase, amplitude, waveform characteristics, polarization, and radar space position are quickly and accurately measured by a reconnaissance antenna and signal processing system on the target platform.

The target reflection characteristics that correspond to the incident radar waveform must then be extracted from the target RCS database under the control of the computer information processing system. By generating a waveform with the appropriate parameters, including frequency, phase, intensity, and polarization, the target echo can be cancelled when the radar wave returns to its receiving antenna.

If a target can be resolved into a collection of N discrete scatterers or scattering centers, then the net radar return at a given frequency is:4



where:
σn = the RCS of the nth scatterer and
φn = the relative phase of the scatterer’s contribution due to its physical location in space.

For a target with a large number of scattering centers, several dominant scattering centers will exist for a specific operating radar frequency and incident signal angle. Reducing the radar returns from these dominant centers can effectively reduce the RCS of the target. If the original target RCS is defined as σ0, an active cancellation system can introduce an equivalent scattering center with effective RCS of σ1. The phases of these scattering centers are φ0 and φ1, respectively. The superposition of both for the target RCS is given by Equation 4:



Namely:



Control of σ1 and φ1can be used to optimize these parameters to obtain:



where parameter σ = 0 indicates having achieved stealth in the direction of the enemy radar.

Compiling a target RCS database is an essential step in designing an active cancellation stealth system. Each RCS entry represents a function, rather than simply a number, varying with different incident signal direction, frequency, and polarization. It may be necessary to establish an RCS database corresponding to different directions, frequencies, and polarizations according to real-time measurements of incident signal direction, frequency, polarization, and power from relevant data. This database must support real-time adjustment of transmitter parameters to generate an effective cancellation wave for transmission.

The capability of making real-time measurements of every radar signal incident on the target is also essential to creating an active cancellation stealth system. Also, the system must be capable of real-time tracking of such things as the relative motion between the detection radar and the desired stealth target, so that the cancellation signal has the proper parameters under dynamic conditions.

A received radar signal can be analyzed in several ways. It can be channeled into the digital-signal-processing and control unit for analysis. Alternately, it can be sent to the forwarding mode active system (used for storage and reproduction of received radar signals), where it can be compared to stored waveforms to find a corresponding signal. Dynamic corrections within the forwarding mode active system can ensure that the echo signal is consistent with the received radar signal. The output signal is then processed by means of Doppler frequency-shift modulation, with coherent superposition of noise and clutter. The power synthesis and beam-forming network and transmitting antenna are then used to form the active cancellation wave.

An active cancellation system structure is shown in Fig. 2. The reconnaissance receiver is used mainly for reconnaissance and reception of radar signals from enemy transmitters. The forwarding mode active system consists of five components: the DRFM, digital phase shifter, digital attenuator, adder, and detector (Fig. 3). The DRFM stores a received radar signal and copies it with high precision. The signal passes through the digital attenuator for amplitude adjustment and the digital phase shifter for phase adjustment. It then travels to the adder to couple with the wave signal produced by the digital-signal-processing and control unit.

The results from the adder are sent to the detector and a DC voltage is sent to the digital-signal-processing and control unit through an analog-to-digital-converter (ADC) interface. When the detector has measured a minimum output value, the system has achieved a zero balance. At this point, the digital-signal-processing and control unit will send a command to the forwarding mode active system, so that the radar signal is transmitted to the Doppler frequency-shift modulation module.

The system’s memory is mainly used for storing the databases, including the target echo database, the noise database, and the clutter database. The system operates with the assumption that a radar echo consists of three parts: target echo, noise, and clutter. As a result, a radar echo signal can be idealized as follows5:

x(t) = s(t) +n(t) + c(t) (7)

where:

s(t) = the target echo signal;
n(t) = the noise signal; and
c(t) = the clutter signal.

Because a great deal of processing and calculation power is needed to determine the radar cancellation wave, it is difficult to achieve real-time calculations without pipeline delays. For this reason, an offline calculation approach is used to establish a target RCS database. The main RCS prediction method is based on the approximation for obtaining a complex target RCS; the error between the predicted value and the actual RCS value can be minimized within a few decibels.6 Approximate solutions to a target’s RCS can be found in a number of ways, including by geometric optics, physical optics, geometrical theory of diffraction, equivalent currents, and areal projection/physical optics.

The database for clutter and noise usually employs a Gaussian distribution of white noise, which can be generated by the Monte Carlo method. Clutter can include ground, sea, and weather variants, among others. Methods for modeling and calculating clutter and noise are detailed in refs. 7-13.

Clutter data is related to airborne altitude, aircraft speed, radar carrier frequency, radar point, radar pulse repetition frequency (PRF), and distance to target. To reduce this large amount of data when clutter data are calculated, aircraft altitude, speed, and radar frequency are fixed, and only radar point and PRF are changed.

The digital-signal-processing and control unit is an active cancellation system core module that is used mainly for radar signal analysis and processing, database searches, and control of other system modules. It is comprised of field-programmable-gate-array (FPGA) chips, using the design diagram shown in Fig. 4. FPGA1 is used for analysis of a received signal; it sends instructions about a signal to memory via a Peripheral Component Interconnect (PCI) interface control chip. Retrieved data are available to FPGA2 and FPGA3 through PCI connection. Based on the signal information obtained, the target echo and clutter generation module produces a variety of target echo and clutter signals. Because of the range of signals, the computing time may vary, so the first device to complete a calculation will send a data cache to the Double Data Rate 2 (DDR2 ) memory. An output is synthesized once the calculation is completed.

The Doppler frequency-shift modulation unit superimposes the Doppler frequency on the forwarding mode active system output signal to produce an effective Doppler shift in the radar wave. The Doppler unit can be used to reflect the relative position of the target to the incident radar. The power synthesis and beam-forming unit, following instructions from the digital-signal-processing and control unit, can form the desired digital beam. It can also switch off the receiving channel and turn on the transmitting channel, allowing transmission of the modified beam via the transmit antenna.

For the purpose of evaluation, the active cancellation stealth system was simulated using commercial software and the following conditions:

The radar transmit signal is a coherent pulse train with modulation rate of 1 MHz.
The simulation signal has a pulse width of 4 μs and PRF of 1 kHz.
The target moves with uniform speed (in a straight line), with initial distance from the radar transmitter of 100 km, initial radial velocity of 300 m/s; elevation and azimuth angles of both 0 deg.; and target RCS of 2 m2 based on the Swelling II model.
The reconnaissance reference pattern function is described by Eq. 8:


where:
κ0 = (cosΘ0)0.5 = the factor for control of the phased-array antenna beam gain with scanning angle variation;
θ0 = the beam scanning angle;
θ1 = the unbiased-beam mainlobe beamwdth of 3 dB;
θ2 = the unbiased-beam first sidelobe 3-dB beamwidth;
A = the unbiased-beam mainlobe gain value;
B = the unbiased-beam first sidelobe gain value;
a = 2.783;
a1 = πθ1/a = the unbiased-beam first zero (in rads); and
a1.5 = π(θ1 + θ2/a = the unbiased-beam first sidelobe peak point of view (in rads).

The three-dimensional EM pattern can be simplified into an azimuth and elevation pattern multiplication result. Namely:

F(θ, φ) = Fθ(θ)Fφ(φ) (9)

where:
Fθ(θ) = the azimuth pattern and
Fφ(φ) = the elevation pattern.

Assuming that the radar antenna vertical mainlobe beamwidth is 2 deg., the mainlobe gain is 40 dB, the first sidelobe width is 1 deg., and the gain is 9 dB, the 3D antenna pattern shown in Fig. 5 will be produced. The system can also be used for an electronic-countermeasures (ECM) function using an M x N rectangular array antenna with a reference pattern function described as:14

(θ, φ) = G(θ,φ)|E(θ, φ)||e(θ, φ)| (10)

where:
g(θ, φ) = the antenna pattern;
G(θ, φ) = the directivity factor, which only affects antenna gain variations;
E(θ, φ) = the array factor, which determines the beam shape;
e(θ, φ) = the array element factor, with e(θ, φ) ≈ 1;
θ = the azimuth angle on the array of spherical coordinates;
φ = the elevation angle on the array of spherical coordinates;
φ ∈ [0, π/2]; and
Θ ∈ [0, 2π].

Adjacent to the array element spacing of d = λ/2 in the x and y directions, E{Θ, φ) can be expressed as:



where:
k = 2π/λ = the wave number;
Imn = the weighting coefficient; and



where:
θ0, φ0 = a beam pointing vector.
If M = 51, N = 21, θ0 = 30 deg., φ0 = 20 deg., the 51 x 21 array antenna pattern shown in Fig. 6 will result. Figure 7 shows the spectrum of a coherent pulse train. Figure 8 shows the coherent pulse train superimposed on the clutter and noise waveform, with the target signal completely submerged under clutter and noise. Figure 9 shows a signal spectrum with the superposition of clutter and noise with the target signal. Figure 10 shows the effects of echo cancellation before (top) and after the cancellation waveform (bottom). The cancellation signal can be defined as:15



where:
ΔĒ = the cancellation residual field and
ĒS = the target scattering field.

When S = 0, complete stealth is realized. From Fig. 10, it can be seen that ΔĒmax = 6 x 10−2 dB and the corresponding cancellation signal, S, is 0.51 dB, so that the maximum radar detection range has been reduced to about 25% of the original value.

In conclusion, these simulation results show that an active cancellation system can greatly reduce the chance that a target will be detected. The approach can be applied to a number of different radio echo scenarios. The active cancellation stealth system presented here has a modular design for simplicity of maintenance.

[eloise]

The capacity to deceive a radar LPI (Low Probability of interception) is based on 3 things:-the capacity to listen to simultaneously a very important number of frequencies the capacity to recognize that multiple signals are in fact only one " pulse train " - the capacity treated(manipulated), to reproduce and to put back(hand) the signal on frequencies chosen with intelligence simultaneously .De our days, number of radars "codes" their impulse (s) to return the infalsifiables echos if we can say. Radar AESA is very good in this small game(set,play), returning the even more difficult jamming(blurring). On the other hand, radars equipping missiles are much easier to deceive, being some even monos pulses .Spectra have ways(means) varied to deceive a similar missile. Both main measures are at first to blur the line plane-missile (LAM) then to deceive the radar of the missile and finally (if need be) to release a cloud of glitter in last defense to .Accrocher one gust(burst) in the radar, to pursue him(it) and to pull(fire) at him a missile is not easy thing but in the end, to deceive the missile, it is to survive even if the opponent continues to pursue you to .Tirer a missile on one gust rafale is a thing, to bring(shoot) down him(it) is an other one..

1) air to air missile are getting AESA seeker
2) monopulse radar are not easy to jam at at all
3) i think you are describing range gate pull off technique ? , cloud of glitter = chaff ? , did you use Google translate ?

Assemble An Active Cancellation Stealth System
Modern signal-processing components make it possible to design an active stealth cancellation system to hide a target from an inquisitive radar system, even under changing conditions.ent
Achieving stealth requires minimizing the radar cross section (RCS) of a vehicle or system as it appears to an opponent’s radar detection capabilities. To achieve this objective, an active cancellation stealth system was designed by means of a phased-array technique, digital radio-frequency memory (DRFM), and field-programmable-gate-array (FPGA) technology. The DRFM enables precise replication of stored radar waveforms, while the phased-array technology is used to generate the required waveforms to cancel reflected radar returns. The FPGA is essential for signal analysis, database search, and waveform generation and control.

The system relies on an offline calculation approach in which omnidirectional RCS, clutter, and noise databases are established in advance. The active system’s signal processing and control module analyzes a measured radar signal parameter and then finds the corresponding target echo data in the RCS database, making a real-time adjustment of the coherent echo amplitude and phase parameters. By creating a target scattering field with coherent signal cancellation in the direction of a detecting radar system, the radar receiver remains in a null synthesis pattern. A combination of software and hardware helps realize this active cancellation stealth approach.

Wil59 , this is exactly what i just described about active cancellation

Radar stealth technology can be divided into passive and active techniques. Although passive methods have been traditionally used, the availability of high-speed microelectronic devices, phased-array antenna techniques, and computer processing have made active methods more feasible and practical. An active stealth system can adapt to almost any object that must be protected, such as a power plant or aircraft, and the technology can be retrofit to an existing electronics platform, with lower power consumption and other advantages compared to passive approaches.

sorry but the red part are bullshit
1 ) it cant not be more flexible than normal passive stealth because wave interference only happened if wave are overlap , aka you have to coated the entire airframe with transmitter
2 ) it cannot have lower power consumption , because to the amplitude have to be equal with the reflection in order to completely cancel the signal
3 ) it doesn't even work again multiple radar like passive stealth

An active cancellation stealth system involves the use of coherent signal interference. For a target to avoid detection, it must emit a cancellation wave that is time-coincident with an incoming pulse, providing the required amplitude and phase to cancel the reflected energy from an enemy radar. This can be an effective means of blanking enemy radar pulses, although the difficulty in implementing such a system lies in the need to obtain cancellation signal parameters in real time, and to achieve precise control of the amplitude and phase of the cancellation waveform.2
Active cancellation stealth depends on adaptive real-time control of electromagnetic (EM) waveforms within a three-dimensional (3D) space. When a radar target is illuminated, return signals are produced by the target’s reflected radiation

if you actually understand the blue part then you will see how unrealistic active cancellation is

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An important part of developing an active cancellation stealth system is understanding a given target’s RCS, which is a comparison of the scattered power density at the radar receiver with the incident power density at the target.

wrong , the most important part is determine enemy radar's pulse frequency, phase, amplitude, waveform characteristics, polarization

The formal definition of RCS is3:
where:
σ0.5 = the complex root of the RCS
scatterer;
Ei = the electric field strength of the incident wave impinging on the target;
R = the distance between the radar and the scatterer;
êr = a unit vector aligned along the electric polarization of the receiver; and
ĒS = the vector of the scattered field.

This equation served no purpose here really

Active cancellation methods are based on generating an EM field equal to a target’s scattered field, but with opposite phase

Not opposite phase but out of phase by half a wavelength

. The effectiveness of active radar cancellation depends on the measurement precision of the radar signal, the knowledge of its real-time characteristics, and the accuracy of the generated cancellation field, among other factors. Figure 1 shows the principle of an active cancellation stealth process. The incident radar wave frequency, phase, amplitude, waveform characteristics, polarization, and radar space position are quickly and accurately measured by a reconnaissance antenna and signal processing system on the target platform.

The target reflection characteristics that correspond to the incident radar waveform must then be extracted from the target RCS database under the control of the computer information processing system. By generating a waveform with the appropriate parameters, including frequency, phase, intensity, and polarization, the target echo can be cancelled when the radar wave returns to its receiving antenna.

If a target can be resolved into a collection of N discrete scatterers or scattering centers, then the net radar return at a given frequency is:4



where:
σn = the RCS of the nth scatterer and
φn = the relative phase of the scatterer’s contribution due to its physical location in space.

For a target with a large number of scattering centers, several dominant scattering centers will exist for a specific operating radar frequency and incident signal angle. Reducing the radar returns from these dominant centers can effectively reduce the RCS of the target. If the original target RCS is defined as σ0, an active cancellation system can introduce an equivalent scattering center with effective RCS of σ1. The phases of these scattering centers are φ0 and φ1, respectively. The superposition of both for the target RCS is given by Equation 4:



Namely:



Control of σ1 and φ1can be used to optimize these parameters to obtain:



where parameter σ = 0 indicates having achieved stealth in the direction of the enemy radar.

Compiling a target RCS database is an essential step in designing an active cancellation stealth system. Each RCS entry represents a function, rather than simply a number, varying with different incident signal direction, frequency, and polarization. It may be necessary to establish an RCS database corresponding to different directions, frequencies, and polarizations according to real-time measurements of incident signal direction, frequency, polarization, and power from relevant data. This database must support real-time adjustment of transmitter parameters to generate an effective cancellation wave for transmission.

The capability of making real-time measurements of every radar signal incident on the target is also essential to creating an active cancellation stealth system. Also, the system must be capable of real-time tracking of such things as the relative motion between the detection radar and the desired stealth target, so that the cancellation signal has the proper parameters under dynamic conditions.

A received radar signal can be analyzed in several ways. It can be channeled into the digital-signal-processing and control unit for analysis. Alternately, it can be sent to the forwarding mode active system (used for storage and reproduction of received radar signals), where it can be compared to stored waveforms to find a corresponding signal. Dynamic corrections within the forwarding mode active system can ensure that the echo signal is consistent with the received radar signal. The output signal is then processed by means of Doppler frequency-shift modulation, with coherent superposition of noise and clutter. The power synthesis and beam-forming network and transmitting antenna are then used to form the active cancellation wave.

An active cancellation system structure is shown in Fig. 2. The reconnaissance receiver is used mainly for reconnaissance and reception of radar signals from enemy transmitters. The forwarding mode active system consists of five components: the DRFM, digital phase shifter, digital attenuator, adder, and detector (Fig. 3). The DRFM stores a received radar signal and copies it with high precision. The signal passes through the digital attenuator for amplitude adjustment and the digital phase shifter for phase adjustment. It then travels to the adder to couple with the wave signal produced by the digital-signal-processing and control unit.

The results from the adder are sent to the detector and a DC voltage is sent to the digital-signal-processing and control unit through an analog-to-digital-converter (ADC) interface. When the detector has measured a minimum output value, the system has achieved a zero balance. At this point, the digital-signal-processing and control unit will send a command to the forwarding mode active system, so that the radar signal is transmitted to the Doppler frequency-shift modulation module.

The system’s memory is mainly used for storing the databases, including the target echo database, the noise database, and the clutter database. The system operates with the assumption that a radar echo consists of three parts: target echo, noise, and clutter. As a result, a radar echo signal can be idealized as follows5:

x(t) = s(t) +n(t) + c(t) (7)

where:

s(t) = the target echo signal;
n(t) = the noise signal; and
c(t) = the clutter signal.

Because a great deal of processing and calculation power is needed to determine the radar cancellation wave, it is difficult to achieve real-time calculations without pipeline delays. For this reason, an offline calculation approach is used to establish a target RCS database. The main RCS prediction method is based on the approximation for obtaining a complex target RCS; the error between the predicted value and the actual RCS value can be minimized within a few decibels.6 Approximate solutions to a target’s RCS can be found in a number of ways, including by geometric optics, physical optics, geometrical theory of diffraction, equivalent currents, and areal projection/physical optics.

The database for clutter and noise usually employs a Gaussian distribution of white noise, which can be generated by the Monte Carlo method. Clutter can include ground, sea, and weather variants, among others. Methods for modeling and calculating clutter and noise are detailed in refs. 7-13.

Clutter data is related to airborne altitude, aircraft speed, radar carrier frequency, radar point, radar pulse repetition frequency (PRF), and distance to target. To reduce this large amount of data when clutter data are calculated, aircraft altitude, speed, and radar frequency are fixed, and only radar point and PRF are changed.

The digital-signal-processing and control unit is an active cancellation system core module that is used mainly for radar signal analysis and processing, database searches, and control of other system modules. It is comprised of field-programmable-gate-array (FPGA) chips, using the design diagram shown in Fig. 4. FPGA1 is used for analysis of a received signal; it sends instructions about a signal to memory via a Peripheral Component Interconnect (PCI) interface control chip. Retrieved data are available to FPGA2 and FPGA3 through PCI connection. Based on the signal information obtained, the target echo and clutter generation module produces a variety of target echo and clutter signals. Because of the range of signals, the computing time may vary, so the first device to complete a calculation will send a data cache to the Double Data Rate 2 (DDR2 ) memory. An output is synthesized once the calculation is completed.

The Doppler frequency-shift modulation unit superimposes the Doppler frequency on the forwarding mode active system output signal to produce an effective Doppler shift in the radar wave. The Doppler unit can be used to reflect the relative position of the target to the incident radar. The power synthesis and beam-forming unit, following instructions from the digital-signal-processing and control unit, can form the desired digital beam. It can also switch off the receiving channel and turn on the transmitting channel, allowing transmission of the modified beam via the transmit antenna.

For the purpose of evaluation, the active cancellation stealth system was simulated using commercial software and the following conditions:

The radar transmit signal is a coherent pulse train with modulation rate of 1 MHz.
The simulation signal has a pulse width of 4 μs and PRF of 1 kHz.
The target moves with uniform speed (in a straight line), with initial distance from the radar transmitter of 100 km, initial radial velocity of 300 m/s; elevation and azimuth angles of both 0 deg.; and target RCS of 2 m2 based on the Swelling II model.
The reconnaissance reference pattern function is described by Eq. 8:


where:
κ0 = (cosΘ0)0.5 = the factor for control of the phased-array antenna beam gain with scanning angle variation;
θ0 = the beam scanning angle;
θ1 = the unbiased-beam mainlobe beamwdth of 3 dB;
θ2 = the unbiased-beam first sidelobe 3-dB beamwidth;
A = the unbiased-beam mainlobe gain value;
B = the unbiased-beam first sidelobe gain value;
a = 2.783;
a1 = πθ1/a = the unbiased-beam first zero (in rads); and
a1.5 = π(θ1 + θ2/a = the unbiased-beam first sidelobe peak point of view (in rads).

The three-dimensional EM pattern can be simplified into an azimuth and elevation pattern multiplication result. Namely:

F(θ, φ) = Fθ(θ)Fφ(φ) (9)

where:
Fθ(θ) = the azimuth pattern and
Fφ(φ) = the elevation pattern.

Assuming that the radar antenna vertical mainlobe beamwidth is 2 deg., the mainlobe gain is 40 dB, the first sidelobe width is 1 deg., and the gain is 9 dB, the 3D antenna pattern shown in Fig. 5 will be produced. The system can also be used for an electronic-countermeasures (ECM) function using an M x N rectangular array antenna with a reference pattern function described as:14

(θ, φ) = G(θ,φ)|E(θ, φ)||e(θ, φ)| (10)

where:
g(θ, φ) = the antenna pattern;
G(θ, φ) = the directivity factor, which only affects antenna gain variations;
E(θ, φ) = the array factor, which determines the beam shape;
e(θ, φ) = the array element factor, with e(θ, φ) ≈ 1;
θ = the azimuth angle on the array of spherical coordinates;
φ = the elevation angle on the array of spherical coordinates;
φ ∈ [0, π/2]; and
Θ ∈ [0, 2π].

Adjacent to the array element spacing of d = λ/2 in the x and y directions, E{Θ, φ) can be expressed as:



where:
k = 2π/λ = the wave number;
Imn = the weighting coefficient; and



where:
θ0, φ0 = a beam pointing vector.
If M = 51, N = 21, θ0 = 30 deg., φ0 = 20 deg., the 51 x 21 array antenna pattern shown in Fig. 6 will result. Figure 7 shows the spectrum of a coherent pulse train. Figure 8 shows the coherent pulse train superimposed on the clutter and noise waveform, with the target signal completely submerged under clutter and noise. Figure 9 shows a signal spectrum with the superposition of clutter and noise with the target signal. Figure 10 shows the effects of echo cancellation before (top) and after the cancellation waveform (bottom). The cancellation signal can be defined as:15



where:
ΔĒ = the cancellation residual field and
ĒS = the target scattering field.

When S = 0, complete stealth is realized. From Fig. 10, it can be seen that ΔĒmax = 6 x 10−2 dB and the corresponding cancellation signal, S, is 0.51 dB, so that the maximum radar detection range has been reduced to about 25% of the original value.

In conclusion, these simulation results show that an active cancellation system can greatly reduce the chance that a target will be detected. The approach can be applied to a number of different radio echo scenarios. The active cancellation stealth system presented here has a modular design for simplicity of maintenance.

ok Wil , your post is very long ,but you havent really said anything new , if you actually understand what you posted , you will see that it doesn't really disagree with anything that i explained
Active cancellation isnt realistic , but to understand why , first you have to understand the physics behind it ( aka wave interference )