Quantum Radar, a brief description of anti anti radar counter measure

Quantum radar is a hypothetical remote-sensing method based on quantum entanglement. One possible implementation of such technology has been developed and patented by defense contractor Lockheed Martin. It intends to create a radar system which provides a better resolution and higher detail than classical radar can provide.

Radar and lidar (Light Detection And Ranging) systems bounce radio or light signals off an object and measure how long they take to return. The returning information can be used to determine the object's position and height, or to calculate its speed.
Meanwhile Mehul Malik and colleagues at the University of Rochester, New York, utilized a special encryption from quantum cryptography. A polarized outgoing photon in one of two ways according to a sequence.
Their radar system measures the polarisations of the returning photons, using conventional algorithms to measure speed direction. But also checking the encrypted polarized sequence for proof of original signal, forcing anyone wishing to create a false beam to polarise the photons in the same sequence. But if that person tries to measure the photons arriving from the radar transmitter, quantum mechanics ensures that many of the true polarisations get lost.
So a false signal always has more wrongly polarized photons than the true beam, which would probably indicate as enemy signal and easily distinguishable. In a lab test, photons reflected from a model of a stealth bomber had an error rate of less than 1 per cent. When the team tried to spoof the photons as if they were reflected off a bird, over half had the wrong polarisation. The same principle can also be used to reveal if photons encoding a secret key have been intercepted.


For example if a stealth aircraft attempts to intercept these photons and resend them in a way that disguises its position, it would inevitably change the photons' quantum properties, revealing any interference. In order to jam our imaging system, the object must disturb the delicate quantum state of the imaging photons, thus introducing statistical errors that reveal its activity. Traditional methods of evasion include the use of chaff to generate extra noise, as a radar countermeasure.

In early 1942, a Telecommunications Research Establishment (TRE) researcher named Joan Curran investigated the idea and came up with a scheme for dumping packets of aluminium strips from aircraft to generate a cloud of false echoes. An early idea was to use sheets the size of a notebook page, these would be printed so they would also serve as propaganda leaflets. However, it was found the most effective version used strips of black paper backed with aluminium foil, exactly 27 by 2 centimetres (11 in × 0.79 in) and packed into bundles each weighing 1 pound (0.45 kg). The Head of the TRE, A. P. Rowe, code-named the device as "Window".

Meanwhile in Germany, similar research had led to the development of Düppel. The systems were all essentially identical in concept: small aluminium strips (or wires) cut to one-half of the target radar's wavelength. When hit by the radar, such lengths of metal resonate and re-radiate the signal. Opposing defences would find it almost impossible to distinguish the aircraft from the echoes caused by the chaff. Alternatively Electronic counter measures work by Jamming transmitting signals on the radar frequency to produce a noise level sufficient to hide echoes.
The jammer's continuous transmissions will provide a clear direction to the enemy radar, but no range information. Deception may use a transponder to mimic the radar echo with a delay to indicate incorrect range. Transponders may alternatively increase return echo strength to make a small decoy appear to be a larger target. Target modifications include radar absorbing coatings and modifications of the surface shape to either "stealth" a high-value target or enhance reflections from a decoy.

The new system of radar effectively renders all forms of radar counter measure useless. Despite passive radar using the subtle method of terrestrial signals from public transmission, which hides the knowledge of possible transmitters. The Quantum radar will accurately record height direction and speed, but at the cost of knowing radar is being used. Although  enemy aircraft will be able to detect the radar, it is unlikely that they can provide any countermeasures to quantum encryption radar scanning. This also makes the current fleet of stealth aircraft useless, which in retrospect seems like a regrettable avenue of research considering the program for the Northrop Grumman B-2 Spirit bomber was US$44.75 billion (through 2004).