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#1
Old 09-12-2002, 08:37 AM
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what does it mean when a radar "locks on"?

Several times the US has used as an excuse to bomb iraq that their planes were "locked on" by the iraqi radar. What happens when a radar "locks on", how does the plane know? I presume the Iraqis are allowed to use "non-locked on" radar whatever the difference is.
#2
Old 09-12-2002, 08:54 AM
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At a non-technical level, 'locked-on' means that the radar has acquired a target and is actively tracking it. This is a Bad Thing as it may indicate that a surface-to-air missile could be on the way shortly thanks to information from the radar.
#3
Old 09-12-2002, 09:01 AM
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At a non-technical level, 'locked-on' means that the radar has acquired a target and is actively tracking it. This is a Bad Thing as it may indicate that a surface-to-air missile could be on the way shortly thanks to information from the radar.
#4
Old 09-12-2002, 09:05 AM
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from http://fas.org/man/dod-101/navy/docs/fun/part01.htm

Components


All modern naval weapons systems, regardless of the medium they operate in or the type of weapon they employ, consist of the basic components that allow the system to detect, track and engage the target. Sensor components must be designed for the environments in which the weapon system and the target operate. These components must also be capable of coping with widely varying target characteristics, including target range, bearing, speed, heading, size and aspect.


Detecting the Target


There are three phases involved in target detection by a weapons system. The first phase is surveillance and detection, the purpose of which is to search a predetermined area for a target and detect its presence. This may be accomplished actively, by sending energy out into the medium and waiting for the reflected energy to return, as in radar, and/or passively, by receiving energy being emitted by the target, as by ESM in our scenario. The second phase is to measure or localize the target's position more accurately and by a series of such measurements estimate its behavior or motion relative to ownship. This is accomplished by repeatedly determining the target's range, bearing, and depth or elevation. Finally, the target must be classified, that is, its behavior must be interpreted so as to estimate its type, number, size and most importantly identity. The capabilities of weapon system sensors are measured by the maximum range at which they can reliably detect a target and their ability to distinguish individual targets in a multi-target group. In addition, sensor subsystems must be able to detect targets in a medium cluttered with noise, which is any energy sensed other than that attributed to a target. Such noise or clutter is always present in the environment due to reflections from rain or the earth's surface or as a result of deliberate radio interference or jamming. It is also generated within the electronic circuitry of the detecting device.


Tracking the Target


Sensing the presence of a target is an essential first step to the solution of the fire control problem. To successfully engage the target and solve the problem, updates as to the target's position and its velocity relative to the weapon system must be known or estimated continuously. This information is used to both evaluate the threat represented by the target and to predict the target's future position and a weapon intercept point so the weapon can be accurately aimed and controlled. In order to obtain target trajectory information, methods must be devised to enable the sensor to follow or track the target. This control or "aiming" may be accomplished by a collection of motors and position sensing devices called a servo system. Inherent in the servo process is a concept called feedback. In general, feedback provides the system with the difference between where the sensor is pointing and where the target is actually located. This difference is called system error. The system then takes the error and through a series of electro-mechanical devices moves the sensor and/or weapon launcher in the proper direction and at a rate such that the error is reduced. It is the goal of any tracking system to reduce this error to zero. Realistically this isn't possible so when the error is minimal the sensor is then said to be "on target." Sensor and launcher positions are typically determined by devices that are used to convert mechanical motion to electrical signals. Synchro transformers and optical encoders are commonly used in servo systems to detect the position and control the movement of power drives and indicating devices. The power drives then move the radar antennas, directors, gun mounts, and missile launchers.
#5
Old 09-12-2002, 09:15 AM
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In short, it's complicated...tons of data is being evaluated by a series of computers to make sense out of reflections so that a certain reflection (or series of) can be tracked.....considered 'locked on' ...and that locked on target provides more info that can go into detemining what to fire upon it and how.

Locked on means the target has been evaluated and has a high probability of being hit if fired upon.

Missile lock and radar lock are oversimplificaions of a sophisticated set of calculations being made by computers.
#6
Old 09-12-2002, 10:46 AM
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Quote:
Originally posted by Philster
Missile lock and radar lock are oversimplificaions of a sophisticated set of calculations being made by computers.
How does a targeted plane know it has been locked on to? Does the radar tracking the plane start behaving differently through its different tracking phases? Do some radard not let the plane being tracked that it is has locked on to it (e.g. phased array radars or the radar dome on an AWACS)?
#7
Old 09-12-2002, 11:07 AM
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In many air defense systems, like the ones we regularly bomb in Iraq, there are two basic types of radar; Searching and Tracking (my terms). Search radars generally sweep around 360 degrees and send out either “pings” or “continuous wave” (CW) energy as they rotate. When a “ping” bounces off a target and returns to the radar receiver, the radar can figure out range (from the time it takes for the “ping” to return) and azimuth (from the orientation of the antenna when the “ping” went out). Multiple returns gives it the data to gather speed and direction of motion.

When the CW radar sends out the continuous energy as it rotates, it also waits for the return signal that bounces off the target, also gets range from the time span, but it looks at the Doppler Shift in the frequency it sends off to determine axial speed immediately. Multiple returns and it can figure true speed and direction of motion.

So now we know where the bugger is and where he is going. Now, how do we splash him?

If the missile has a passive guidance system, the seeker head in the missile looks for the reflected energy sent from a Tracking Radar that bounces off the target. Once the Search Radars locate the aircraft, they send the location info to the Tracking Radar, which has a much more powerful and focused energy, but kind of in a doughnut shape. It “looks” in the area of sky the plane is reported to occupy until it gets a strong radar energy signal. It refines the location by finding the slightly weaker return from the “doughnut hole” in the center of the radar signal, then ensures the signal is stronger on all sides. Ther target is now “locked on”. This continuous energy illuminating the target is very different from the Search Radar energy, and the pilot’s “RAW Gear” tells him he is “painted”.

They can also tell when a missile is launched because the radar “powers down” momentarily when the missile goes off the ground, so as to avoid burning up the seeker head and giving it a change to clear all the side lobe energy. This quick dip in power tells the flyer he’s in deep.
#8
Old 09-12-2002, 11:10 AM
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Quote:
If the missile has a passive guidance system…
Pardon me, I meant to say “semi-active homing”, not “passive guidance”. Passive means there is no emission from the ground or missile, (a heat-seeker, for instance). Semi Active needs a radar energy source other than the missile, and Active means the missile itself emits and receives the energy (fire and forget).

I also misspelled "chance" in the last paragraph.
#9
Old 09-12-2002, 11:20 AM
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Quote:
Originally posted by Whack-a-Mole


How does a targeted plane know it has been locked on to? Does the radar tracking the plane start behaving differently through its different tracking phases? Do some radard not let the plane being tracked that it is has locked on to it (e.g. phased array radars or the radar dome on an AWACS)?
IAMAE but... Radars work by bouncing radio waves off of the target and detecting the bounce. Aircraft systems can detect that bounce when it hits them and realize that they might be detected. IIRC one of the crewmembers on B-1 bombers was assigned to monitor enemy radar sources and advise the pilot of best courses to avoid detection. This is also why millitary combat flights fly with their radar off to avoid passive detection. If they are detected and engaged they will then turn their radar on for targeting and tracking enemy planes.

Also some radar systems can focus on an area or emit more energy to try and elicit a more solid return. If a plane is detecting higher energy radar waves hittiing them, or hitting them more often, the system alerts the pilot that they have been detected.
#10
Old 09-12-2002, 11:27 AM
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Quote:
Originally posted by Whack-a-Mole
How does a targeted plane know it has been locked on to? Does the radar tracking the plane start behaving differently through its different tracking phases? Do some radard not let the plane being tracked that it is has locked on to it (e.g. phased array radars or the radar dome on an AWACS)?
Former F-14/AWG-9 weapons system specialist here.

As other posts have said there are multiple forms of "locking on" and tracking. Radar can track the angle of the target, distance and relative velocity.

The AWACS example is a bit misleading. The target may not know it's being tracked not becuse of the type of antenna array but because it;s being tracked by a search rader rather than a fire control radar.

The antenna of the AWACS points to the side through the rotodome as it rotates. As the antenna rotates return signals from targets will indicate the bearing of each. Each target will only be illuminated once every time the antenna rotates. In between each return from a particular target the track will have to be extrapolated from the position and velocity vector from the last time it was painted. If the target maneuvers between that time the tracking system won't know it.

Fire control radar for the most will perform a single target track where they stay aimed at the target. In cases like that it's pretty easy to surmise that you're being tracked when an energy source stays at maximum intensity. Different types of fire control rader use different methods to maintain angle track and sometimes this can be used to detect a track and defeat it.
#11
Old 09-12-2002, 11:28 AM
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Unclebill has explained it in more detail and depth than I could have hoped to. I didn't know about the "donut" effect myself....learn something new every day.
#12
Old 09-12-2002, 12:35 PM
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thanks for the info. Why do you think the iraqis then are actively tracking the US warplanes when they know there will be a armed response? Is it to actually provoke a response, or to test their radar or something else? I presume they are not about to launch a missile (yet)
#13
Old 09-12-2002, 01:34 PM
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Iraq has fired missiles every so often at or in the vicinity of coalition aircraft operating in Operation Southern Watch and Operation Northern Watch. 470 seperate incidences of Iraqi AAA firings or missile firings are reported for the period of Dec 98 to May 00 here
#14
Old 09-12-2002, 04:37 PM
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so, does anybody have a functioning passive radar set yet?

(not to change the subject, or anything...)
#15
Old 09-12-2002, 04:58 PM
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Virtually every radar set is capable of operating in passive mode. It has limited usefulness for search or fire control though as you don't see anything unless a transmitting radar is aimed at you. It is used to detect possible threats. F-14As had a detection device that was was less sophisticated than a fuzzbuster to suppliment other countermeasure systems.
#16
Old 09-12-2002, 05:25 PM
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Thanks for the info and I apologize for my hideous grammar and spelling (worse than usual).

No one mentioned what a phased array radar does. Take the system on a Ticonderoga class cruiser with the Aegis system. Since a phased array radar doesn't 'sweep' the sky in the same fashion that a rotating radome does is it possible that an enemy wouldn't know the system had a lock on him? Certainly he will know he's been painted but I'm wondering if the phased array radar never changes its behavior such that the systems aboard an enemy craft couldn't tell there was now a missile gunning for him (assuming the missile was passive or semi-active).

Also, for passive missiles, why do you see in movies that they need a lock as well to fire accurately? I mean, say I pop-off a sidewinder without any lock. Why would it be hard at all for the missile to look ahead and 'see' the only thing that is considerably hotter than the surrounding sky?

Finally, movies again have it that a plane will warn the pilot with an ever increasing beep or tone that a missile is closer and closer. A) Is that really possible and B) Can it do the same if a heat seeker (or other passive or semi-active) missile is in pursuit?

NOTE: I realize that extracting reality from movies is always a dicey business at best.
#17
Old 09-12-2002, 08:29 PM
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The easiest answer to the OP is that our military has thoroughly catalogued every radar system type that Iraq has, and they know what the purpose of each one is. And, as drachillix explained, search and tracking behaviors are very different.

To get to Whack-a-Mole's questions: No, a phased array radar isn't constrained in its scan patterns as a mechanically-steeered antenna is, but a search radar isn't much use if it isn't scanning its search volume periodically. And, in track or fire-control mode, the radar still needs to get a certain amount of energy on the target at a certain revisit rate. The flexibility inherent in a phased array antenna is exploited to make the radar harder to jam, but I'm not familiar with any system trying to disguise its basic intent.

I'm not a missile expert, but I'd think that you wouldn't fire your air-to-air missiles without their being locked-on because they might never lock on. You've wasted a very expensive missile, as well as part of your self-defense, if you let it fly without a target. And, the "only thing that is considerably hotter than the surrounding sky" is maneuvering furiously and possibly firing flares to confuse your heat-seeking missiles.

I don't know about the ever increasing beep, but a radar-guided missile should know the range to its target with a great deal of accuracy. It doesn't matter whether the missile is active or semi-active; semi-active missiles receive a reference signal from the illuminating radar, so they can measure range as accurately as an active seeker. Passive missiles might know the range to the target when they're fired, but they'd have to extrapolate from that point, making the range measurement shaky at best.
#18
Old 09-12-2002, 10:19 PM
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Hoo boy. I thought I'd get to bed at a decent hour.

Phased Array? I'll skip on that one. It floats.

Passive missiles needing lock I can handle. Stingers, at least. Let me explain. No, there is no time, let me sum up. You can fire the missile without having a lock, but the search pattern the missile goes into is wide and varying, and rumors are it can then find and lock onto objects behind the gunner, which is bad. I imagine the problem is exacerbated when the launcher is doing 500 knots, like a fighter that just popped off a Sidewinder. I do not know if the Sidewinder requires a lock to fire or not. But not only do you not want to waste the missile, you don't want to waste a Friendly, or yourself.

The Field of View (FOV) of the seeker head is classified, and I don't remember it anyway, but suffice it to say it is very small, anglewise. VERY small. Once the target is locked, the gunner releases the gyroscopic seeker head so it can maintain it's "look" at the target while the missile launch tube is moved about a bit. When the missile is launched, it actually has two motors. One is like a shotgun shell, while kicks the missile out of the tube and is burned out by the time the ass end clears, then the missile coasts, in freefall ballistic motion, until it gets out a bit from the gunner. Then the flight motor kicks in. During this time the seeker head needs to stay locked on, or the chances of getting a hit are slim to none. The search pattern is funny to see, but scary, because it happens not all that far away.

Passive does not just mean heat seeking. Some missiles can aim for the shadow caused by the target against the background UV radiation, defeating flares quite nicely.

And the range estimation of passive missiles is quite a bit better than shaky. They have proximity fuses. They fly to an intercept point. Getting there is very hard math, and more classified than the FOV, I'm sure.

Major UncleBill
USMCR
formerly at 2nd LAAD Bn (Stingers)
and 3rd LAAM Bn (HAWK Missiles)
#19
Old 09-13-2002, 03:04 AM
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Reading the answers, I take it that an active radar tracking requires a movable antena system to point at the target. Is that also true of plane born system? It must be tricky if the plane is manouvering at the same time, as in a dog fight?
#20
Old 09-13-2002, 03:10 AM
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Quote:
Originally posted by happyheathen
so, does anybody have a functioning passive radar set yet?

(not to change the subject, or anything...)
A small addition to the answer by Padeye.

All radars I have had experience with can function in a passive mode.

A search radar can turn of the emitter and just keep the receiver open. This will as pointed out limit what you hear as you wont get as many echos back (after all you are not emitting anything). Some form of detection is still possible if other radars in the area are emitting you may pich up echoes from them, but this is very limited.

What you can see very well however is the signal from a jammer. So if a large strike force is heading your way with radar jammers blazing making your screens go wild so that you can´t see individual planes you may as well turn of your emitter and just see what bearing the jamming signal comes from. If you have two or more radars cooperating and feeding eachother information you can triangulate the position of the jammer giving you some kind of indication of where the attacking aircraft are.

Then you send this data to your firing units so that they can be prepared for incoming targets in that area.

This will of course not be as accurate as if you were active but you do increase the survivability of your radar station. Because if you are not emitting the anti-radiation missiles wont have anything to follow.

When you see the target getting closer it may be worth it to turn on the emitter again since you may be able to burn through the jamming when the range decreases, giving your shooters better targeting data.

As a radar commander I would prefer not going active until it is absolutely neccessary so that the enemy wont know where I am.

2nd Lt Coil 9th Armoured AA Company
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