Radar_jamming_and_deception

# Radar jamming and deception **Radar jamming and deception** is the deliberate use of radio-frequency signals, or of extra false echoes, to stop a [[Radar|radar]] from detecting, ranging or tracking a target correctly. The two halves of the name mark a real distinction even though "jamming" is often used loosely to cover both: jamming saturates a radar's receiver with enough noise or clutter that its display becomes unreadable, while deception feeds the receiver a plausible but false signal, a decoy range, bearing or velocity that the radar accepts as genuine. A three.js companion sketch, built for the aviation portal's coverage of radar jamming and reused here, renders this same idea in more depth than a static description can. Radar jamming falls into two broad families. Mechanical jamming manipulates what a radar sees by physical means, dispensing reflective decoys or shaping a target to return a false or oversized echo, without the jammer transmitting any signal of its own. Electronic jamming transmits: a jammer radiates its own radio energy, either as broadband noise meant to bury the true echo or as a shaped, timed signal meant to be mistaken for one. Countermeasures against jamming, the electronic counter-countermeasures a radar designer builds in, and the complementary, passive approach of reducing what a radar has to detect in the first place, are each treated in turn below. ## Mechanical jamming The oldest and simplest countermeasure needs no transmitter at all. Chaff, thin strips of metal foil or metallised fibre cut to a length that resonates strongly at the radar's wavelength, is dispensed in a cloud that presents a very large [[Radar_cross_section|radar cross-section]] of its own, either masking a real target flying through or near it or standing in for a target that is not there. A corner reflector, three mutually perpendicular reflecting surfaces meeting at a point, returns an incoming beam back toward its source from a wide range of angles, which makes a small, cheap decoy fitted with one reflect far more strongly than its size would suggest, a trick also used defensively to make a small boat or a lightweight target more visible to a radar looking for it. Chaff was first used operationally in the Second World War, dropped by bomber crews to blind ground-based tracking radars during major raids.[^chaff] Because none of these techniques transmits, they cannot be direction-found the way an active jammer can, but they also cannot adapt to what a radar does next: once released, a chaff cloud drifts and thins on its own schedule, not the target's. ## Electronic jamming Electronic jamming instead puts a transmitter on the problem, and splits again into two strategies that trade off against each other: overwhelming the receiver with noise so nothing can be read, or feeding it a false signal precise enough to be read as the real target. A repeater jammer follows the second strategy by intercepting the radar's own pulse and retransmitting a delayed, amplified or otherwise altered copy of it, timed or [[Amplitude_modulation|amplitude-modulated]] to drag a tracking radar's range, angle or velocity gate away from the true target before the jammer cuts the false signal loose, leaving the radar tracking nothing at all. ### Noise jamming Noise jamming instead abandons any pretence of mimicking a real echo and simply raises the noise a radar's receiver has to work against. A radar recognises a target only once the wanted echo clears the noise referred to the receiver's input by a sufficient margin; barrage noise jamming spread across the radar's whole tuning range adds directly to that noise power, in much the same bookkeeping a receiver's own noise figure already accounts for, so that echoes which would otherwise clear the detection threshold are buried before any signal processing downstream ever sees them.[^ell99] Spot jamming concentrates the same transmitter power onto the radar's actual operating frequency instead of spreading it thin across a wide band, which jams far more effectively if the jammer can find and track that frequency, and far less effectively the moment the radar moves off it. To an operator watching a [[Radar_display|radar display]], heavy barrage jamming looks like the screen filling with a bright, textureless wash that swallows whatever real returns were there. ### Radar burn-through Because a genuine echo's power falls off with the fourth power of range while a stand-off jammer's power at the radar's receiver falls off only with the square of its own, generally much greater, range, closing distance eventually favours the target: at some range the true echo grows fast enough to climb back out of the jamming, the radar's burn-through range. A jammer therefore buys the defended target time and distance rather than permanent concealment, and the same arithmetic sets how much jammer power, or how much stand-off distance, is needed to hold burn-through range below whatever range actually matters, whether that is a fire-control radar's lock-on range or a search radar's detection range. ## Inadvertent jamming Not every burst of interference is meant as an attack. A nearby transmitter operating on or near a radar's frequency, another radar's own pulses arriving out of step with the victim's timing, or ordinary spectrum congestion in a crowded band can all degrade a radar's picture exactly as deliberate noise jamming would, without anyone intending it. Distinguishing an inadvertent source from a deliberate one matters operationally, since the response, retuning, filtering or simply waiting out a transient source, differs sharply from the response to an adversary actively working to blind the radar, even though the raw effect on the [[Radar_display|display]] can look identical in the moment. ## Countermeasures A radar designer answers jamming with electronic counter-countermeasures built into the set itself rather than relying only on operator skill. Pulse-to-pulse frequency agility, hopping the transmitted frequency, and [[Pulse-repetition_frequency|pulse-repetition-frequency]] agility, varying the interval between pulses, both deny a spot jammer a fixed target to track and defeat a deception jammer's assumption that the next pulse will look like the last one. Sidelobe blanking and sidelobe cancellation use an auxiliary antenna to recognise a jamming signal arriving through the main antenna's sidelobes rather than its narrow main beam, and suppress it before it reaches the operator's display, while a home-on-jam mode turns a jammer's own transmission into a bearing to steer toward, so that jamming hard enough to blind a radar's receiver can still hand that radar a target to home on. [[Monopulse_radar|Monopulse]] angle tracking, which compares signals arriving in several simultaneous beams rather than scanning one beam around a cone, closes off much of the angle-deception repertoire that worked against older conical-scan trackers, and [[Pulse_compression|pulse compression]]'s processing gain concentrates a long transmission's energy into an effectively short pulse on receive, improving the odds of pulling a genuine echo out from under noise that a simple, uncompressed pulse could not match. Modern [[Active_electronically_scanned_array|active electronically scanned array]] radars fold several of these tricks into routine operation, reshaping and resteering their beam electronically, pulse to pulse, in ways a mechanically scanned dish never could.[^aesa] ## Stealth Jamming and deception are active countermeasures: they work by transmitting or by throwing up a decoy, and can in principle be detected as such. [[Stealth_technology|Stealth]] takes the complementary, passive route of giving a radar less to see in the first place, shaping and coating a vehicle to return only a small fraction of the energy that strikes it. The two approaches compound rather than compete: a low-observable aircraft that also carries a jammer needs less jamming power to disappear from a screen than a conventional one would, because there is less real echo for the jamming to bury, and a radar already fighting to see a small return has correspondingly less margin left to fight through noise as well. In practice the two approaches are often assigned to different aircraft in the same strike package rather than combined on one airframe: a stealth design typically favours strict emission control over carrying its own powerful jammer, since transmitting anything at all works against the whole point of being hard to see, while a force of conventional, non-stealthy aircraft more often relies on dedicated escort-jamming aircraft flying alongside to blind the defending radars for everyone at once. ## Interference Radio regulators draw a line between deliberate jamming and the broader category of interference, unwanted energy in a receiver's passband whatever its source or intent. Harmful interference, in the sense used by international radio regulation, is interference that endangers a safety-of-life service such as radionavigation or seriously degrades or repeatedly interrupts it; deliberate jamming of a radar is one especially serious case of harmful interference, but the same regulatory category also covers accidental sources with no intent to disrupt anything at all.[^itu-interference] The distinction matters for enforcement as much as for engineering, since a regulator's response to a faulty, unlicensed transmitter differs from its response to a deliberate attack even where the signal received looks the same. ## Jamming police radar Traffic police radar measures a vehicle's speed from the [[Doppler_effect|Doppler]] shift of its own transmitted signal reflected back from the car, and the same countermeasure logic that applies to a military radar scales down to that far smaller problem. A passive radar detector, which only listens for a police radar's transmission and warns the driver, is legal in most jurisdictions, though banned in a few; an active radar jammer, which transmits its own signal to swamp or spoof the police unit's receiver, is illegal in most places that regulate radio spectrum at all, treated as unlicensed interference with a government radio service rather than as a private countermeasure a driver is free to deploy.[^policejam] The asymmetry mirrors the military case in miniature: listening is broadly tolerated, transmitting to defeat another party's radar is not. Some jurisdictions have shifted enforcement toward laser-based speed measurement partly for reasons unrelated to jamming, but the practical effect is the same one seen in the military case: a narrow, aimed optical beam is far harder for a driver's receiver to detect in advance, and offers no broad radio-frequency band for even a legal detector to listen across, let alone for an illegal jammer to swamp. ## Jamming in nature Jamming is not only a human invention. Some tiger moths respond to an attacking bat's echolocation calls with their own rapid train of ultrasonic clicks, and at least one well-studied species has been shown experimentally to jam the bat's own sonar with those clicks, reducing the bat's ability to home in on the moth in the final stage of an attack.[^mothjam] The parallel with an aircraft's noise jammer is close enough to be more than a metaphor: both the moth and the jammer answer an active, echo-based sensor with their own emission timed to arrive exactly when the predator's receiver, biological or electronic, needs a clean echo most. The finding was not obvious in advance, because ultrasonic clicking is common across tiger moths and had usually been read as a warning that the clicking species tastes bad, an acoustic analogue of a wasp's bright colouring rather than a countermeasure; only the unusually high click rate of the species studied was shown, by testing bats against moths whose clicks were disabled and restored, to jam rather than merely warn. ## Microsims This article carries no p5.js sketch of its own. A three.js companion, already built for the aviation portal's coverage of radar jamming and reused on this page, renders the idea in more depth than a static description can. The neighbouring Radar, Doppler effect and Sonar articles carry sketches that model pieces of the same trade-off in ordinary, non-hostile ranging, which the *Try* lines below draw on directly. *Try:* in the [[Radar]] sketch, raise the pulse-repetition frequency and watch the dashed unambiguous-range ring shrink until a distant target folds back as a ghost at a much shorter apparent range; a deception jammer that retransmits a delayed copy of the radar's own pulse is deliberately creating exactly that kind of false, displaced echo. *Try:* in the [[Doppler_effect]] sketch, raise the source speed and read the two observer markers' frequency shifts; a velocity-deception jammer works by gradually sliding a false echo's apparent Doppler shift away from the target's true one, in the hope that a tracking radar's velocity gate follows the false shift instead. *Try:* in the [[Sonar]] sketch, raise the noise implied by a weaker, more distant target and compare it with a stronger, closer one on the same A-scan; the same climbing-echo-over-a-noise-floor picture is what a radar's burn-through range describes as jamming and target range change together. ## Wikipedia : Wikitube **Strict pair:** [Wikipedia](https://en.wikipedia.org/wiki/Radar_jamming_and_deception) : [Wikitube](https://en.wikitube.io/wiki/Radar_jamming_and_deception) Skeleton mirrored at revision 1358533784. Prose, emphasis and the microsims are Wikitube's own. ## See also - [[Stealth_technology]] - [[Active_electronically_scanned_array]] - [[Radar_cross_section]] - [[Radar_display]] - [[Doppler_effect]] - [[Pulse-repetition_frequency]] - [[Noise_(electronics)]] - [[Radar]] ## References Standard radar-range-equation reasoning, that a genuine echo's power falls as the inverse fourth power of range while a stand-off jammer's one-way path falls only as the inverse square, is textbook material and is not separately footnoted, per the Wikitube style guide's §6.1. Page numbers below are PDF pages of the open edition linked in the Ellingson citation. [^chaff]: Citation needed: a primary operational history of the first wartime use of chaff, with the specific raid, date and units involved, has not been pinned to a source in this pass. [^ell99]: Ellingson, S. *Radio Systems Engineering, Revised First Edition*. 2023, pp. 96-103 (PDF pages). Open Textbook Library: https://open.umn.edu/opentextbooks/textbooks/radio-systems-engineering . CC BY-NC. [^aesa]: Citation needed: a specific active electronically scanned array radar's documented electronic counter-countermeasure modes would give this claim a concrete, dated example. [^itu-interference]: Citation needed: the current International Telecommunication Union Radio Regulations definition of harmful interference would confirm the exact wording paraphrased here. [^policejam]: Citation needed: a specific national regulator's rule prohibiting radar-jamming devices, with its exact statute or rule number, would confirm the legal claim made here. [^mothjam]: Corcoran, A. J.; Barber, J. R.; Conner, W. E. "Tiger moth jams bat sonar." *Science*, vol. 325, no. 5938, July 2009, pp. 325-327.