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IFC - Tracking Radars


For in introduction to radar or Nike Acquisition Radars, go to .

The controls for these radars were housed in the Radar Control Van, which was located very near the Battery Control Van and the same size. John Porter, manager of SF-88, reports that "The Battery Control Van is 20.5 ft long, 8 ft wide, 7 ft high, with a 6.5 ft tongue."

This is a Nike Hercules tracking radar. It could be a Missile Tracking Radar (MTR), a Target Tracking Radar (TTR), or a Target Ranging Radar (TRR). The details are hidden under the wind shield, which reduces wind pressures and buffeting. The wheeled transportation vehicle is still present, when removed, the antenna is supported by three adjustable legs in a triangle.

This information is grouped into the following sections:

For more details, see
Lesson 4. Track Radar Systems - 2.2 megabytes
Lesson 5. Target Ranging Radar - 0.8 megabytes

Also, TM9-5000-18 "NIKE I SYSTEMS - TTR TRANSMITTER AND RECEIVER CIRCUITRY" is available for another (more detailed) view of some of this material. (The Nike 1 [Ajax] was the predecessor of the Nike Hercules, but the same principles apply.)



From FM 44-1-2 ADA Referennce Handbook, 15 June 1984, see page 21 "Rings of Supersonic Steel"

Tracking Antenna Towers

The Nike tracking antennas need extreme pointing accuracy. The Nike Hercules has a range of over 90 miles and the system should be able to direct a missile to with in 10 or 12 yards of where the Target Tracking Radar says the target is.

This means the Target Tracking Radar (giving target location) and the Missile Tracking Radar (giving the Hercules missile location) must be carefully aligned (discussed below).

Also, the effects of
- the sun's heat distorting the antenna mounts
- the wind's force distorting the antenna mounts
must be minimized also.

To help accomplish this a double tower is used:
- the inner tower supports the antenna
- the outer tower supports the wind screen and shades the inner tower
The photos below are of the IFC area of SF-88, north of San Francisco

Lets start with the inner tower, concrete - with three projections at the top for the three antenna feet.
Photo courtesy of Greg Brown
The outer tower shades the inner tower reducing differential heating on the sun side of the inner tower. It also supports the access ladder, wind screen, working platform and guard rail.
The three pads marked "0" are the pads supported by the inner tower, and support the three antenna pads.
The partial white circle is the remnants of the wind screen bubble support.
This picture shows the two separate base assemblies, the outer rectangle supporting the outer steel tower, the inner round concrete supporting the inner round concrete tower.
Photo courtesy of Greg Brown

Tracking Antenna Base Pictures

Equipment used for BoreSighting
This is the control box and cable used to do fine antenna pointing adjustments during bore sighting and other alignment procedures This is the telescope used in bore sighting and other alignment procedures.
The National Park Service has abscounded with this unit -

Connectors at a tracking antenna
This could be called the connector side of a Nike Tracking Antenna. It also includes two storage compartments for frequently used equipment. Most of the connectors use low current (signal) connectors, here is a sample. The exposed connector is for the three coaxial cables carrying Intermediate Frequency (60 MHz) signals to the Radar Control Van for further amplification. They are the Sum, Azimuth Error and Elevation Error signals.

Tracking Antenna Base Electronics
These are magnetron and other high voltage power supplies, and the amplifiers used to drive the antenna azimuth and elevation motors. They are on the opposite side relative to the connector side.

Target Tracking Radars

These are the Target Tracking Consoles, each with scope and controls as labeled. They looked very similar for both the Nike Ajax and Nike Hercules. In the Nike Hercules, an added (stand-up) position, the Tracking Supervisor, was added to help coordinate activities and operate the anti-jamming controls.
Picture of Radar Control van at Ft. Sill museum from Al Harvard
Tracking Supervisor Controls
This was Nike Hercules only - a forth man stood behind the three tracking operators and used this detachable anti-jamming control panel. I have shown this in great detail as I am fascinated imagining what all could be done to dodge jamming signals.
The first door on cabinet on the left of the Target Tracking Consoles hides the Target Tracking intermediate frequency amplifiers (sum, azimuth error, elevation error), AGC controls, test equipment, and the massive unit at the bottom is the range automatic tracking chassis and potentiometer. This is for the Hercules, but the Ajax was very similar. At one time I could tell you the function and how to adjust/fix everything in here -
The closed door on the left is very similar for the Missile tracking radar.

Beam width
Beam width is usually defined as the width between half power points of the main beam of an antenna.

Wikipedia gives a formula for a typical parabolic beam width as:
    Beam_Width_In_Degrees = 70 * WaveLength / AntennaDiameter
where WaveLength and AntennaDiameter are in the same units.

Using factors of
- wave length = 3 cm
- antenna diameter ( about 5 feet ) = 152 cm
gives a Nike antenna beam width of about 1.4 degrees

A small (narrow) beam width in a tracking antenna is a "good thing", giving:
     - more radar energy on the target and gain (better range)
     - better target angle determination
     - better resistance to off axis jamming
Nike tracking antennas had a beam width of about 1.4 degree, that is, most of the transmitter power was concentrated in about 1.4 degree wide and 1.4 degree high. Although the TRR ( Target Ranging Radar ) had shorter wavelength, it was not used for angle determination.

There were three types of Nike Target Tracking Radars
- the (earlier) Ajax Target Tracking Radar
- the Hercules Target Tracking Radar
- the Hercules Target Ranging Radar

Ajax Target Tracking Radar

The earlier Nike Ajax tracking radar had an effective range of about 50 miles.
Overview
This antenna (next four pictures) is at the Historical Electronics Museum near Ft. Meade, MD. A great place to visit! :-))
It used a Fresnel lens type of focusing like this. Boresighting was identical with the later Hercules Tracking antennas.
Leveling was of course a big deal. The Target Tracking and Missile Tracking radars MUST have a common vertical reference. Two levels at right angles are used for convenience. This was one leg of the tripod support of a tracking antenna. The cap covers a 1 inch hex bolt head to be turned to level the antenna.
I was really impressed with the smoothness of the rotation in azimuth. The bearing had no apparent play, but was easy and smooth to move. In 2012 I asked Kennith Behr about this. He said this was a Kaydon Bearing and provided this picture.

Bill Shaw Nike website noted an article

showing the evolution of the Fresnel form of the metal plate lens antenna. Chapter 3, METAL-PLATE LENS ANTENNAS by Paul Wade. This contains the following diagrams. Fig. 3-1&2 Fig. 3-1&2 Fig. 3-4&5 Fig. 3-6&7
A discussion of Metalic Delay Lenses, as used by Nike Ajax tracking radars, was presented in this issue of Bell System Technical Journal. Bell and Western Electric (a subsidiary) designed and built the Nike IFC equipment. A Life Magazine photo - at Red Canyon - possibly troops firing their Nike Ajax equipment before taking it to some site at some city. An other possibility is troops back for annual re-fire shooting from resident equipment.

Hercules Target Tracking Radar

The Nike Hercules Tracking Radars had a maximum range of 200,000 yards, a little over 110 miles. (This was a hard limit as the tracking displays and computer scaling had that limit.) For an interesting comparison with the earlier (WWII) SCR-584, click here.

The Nike Hercules systems had two Target Tracking Radars that were externally similar. Internal differences included using different frequency bands. The two radars were used instead of the usual one radar to help fight enemy jamming. A variety of strategies made the life of enemy jammers extremely difficult. (The Nike Ajax systems had one target tracking radar).
Nike Hercules Target Tracking Radar (TTR) (image is 33 K Bytes) (Photo credit Rolf Goerigk) The rope fence and supports are there only during maintenance to reduce accidents - removed during normal operations. During normal operations, a spherical wind screen surrounds the antenna to reduce wind forces and tracking errors. View of electronics (Photo credit Rolf Goerigk)
Gaston Dessornes wants to "... know the approximate weight of the MTR/ TTR mobile tower? (See picture attached) "
The following images are from scans of TM9-1430-253-34 by GoogleBooks
All practical ( and heavy ) electronics were placed in the tripod base. This included power supplies, magnetic amplifiers to drive the drive motor, ... This is the back of the TTR antenna - made as light as practical - Electrical connection, i.e. controls, elevation angle voltages, power, intermediate frequency channels, ... were made with the base via "slip rings".
Here is a slip-ring assembly, electrically connecting the rotating parts, used both in azimuth and another for elevation - The Azimuth Transmitter is a precision sine-cosine potentiometer which helps convert polar coordinates ( angles ) to Cartesian coordinates ( x,y ) :-))
Although there is considerable complexity, we rarely had problems with the radars (or the rest of the Nike IFC system). It was extremely well designed and manufactured :-)) Pretty much a joy to keep running. Unfortunately, Western Electric, the designer and manufacturer has been disassembled by the government -

In special situations, such as typhoon hazard or arctic conditions, a large protective cover was included which could provide additional protection. These covers were shaped like clam shells which could be closed in really bad conditions. See pictures Side view, Quarter view and Alaska location information Site Peter and Site Summit. I am guessing (please correct me) that if the clam shells were closed, the tracking radars could not be used.

From Rolf Goerigk, Specification for the Target Tracking Radar (TTR) include:
Antenna Gain 44 dB = 25,000
Freq. Range 8.5 - 9.6 GHz
Pulse Width Short Pulse (SP) = 0.25 microseconds
Long Pulse (LP) = 2.5 microseconds
RF Peak Power Short Pulse (SP) = 201 kW
Long Pulse (LP) = 142 kW
Average RF Power
LOPAR-Mode
Short Pulse (SP) = 25.1 Watt
Long Pulse (LP) = 177.8 Watt
Instrumented Range
from here
200,000 yards (113 miles)

Hercules Target Ranging Radar

Nike Hercules Target Ranging Radar (TRR) (image is 33 K Bytes) (Photo credit Rolf Goerigk) The rope fence and supports are there only during maintenance to reduce accidents - removed during normal operations. During normal operations, a spherical wind screen surrounds the antenna to reduce wind forces and tracking errors. Note the more pointed cone, this antenna uses a different "optical" system. View of electronics (Photo credit Rolf Goerigk) ..............

From Rolf Goerigk, Specification for the Target Ranging Radar (TRR) include:
Antenna Gain 49 dB = 79,000
Freq Range 15.7 to 17.5 gHz
Average RF Power Short Pulse (SP) = 15.6 Watt
Long Pulse (LP) = 78 Watt

CW2 Robin E. Smith says that the TRR evolved considerably during its service life.

  • - 1st, manual frequency change (to avoid jamming)
  • - 2nd, automatic and manual frequency change (to avoid jamming)
  • - 3rd, the SAMCAT change, automatic "channel" frequency change, 400 times per second (to avoid jamming)


The Hercules Target Tracking Radar, and the almost identical Hercules Missile Tracking Radar, are diagrammed below

The antenna shown above is pointed roughly level. As per Vasilis Bourantanis, The antenna could be depressed about -204 mils (about 11.6 degrees) at which point a microswitch prevents further motor drive in the down direction. A shock absorber stops further downward physical motion. The antenna can point straight up and a little beyond.

There is a special computer circuit to steer the missile so that it does not pass directly over the Missile Tracking Radar (MTR). This prevents the MTR from having to slew in azimuth at a high rate of speed. This is called an "over-the-shoulder-shoot". (This prevents the need for a special no-launch azimuth.) Although the recommended site configuration suggested the missile launch area be toward the direction of an expected attack, practical considerations sometimes caused the launch area to be "behind" the IFC (radar site).

As the diagram mentions, the fixed base was carefully leveled, and checked daily (or until the cement pad finally showed signs of adequate stability). The level system was extremely sensitive and accurate.
There was a method of "bore sighting" the radar beam to assure that the beam was parallel to a telescope system (with cross hairs). A special microwave transmitter and test mast with optical sights was used in this adjustment.

The telescopes of the missile and tracking radars then were pointer at each other to assure that the elevation and azimuth indicators (potentiometers) were correctly aligned.


Target Tracking Operations

The above Hercules A-Scope type image (thanks to Rick at ShoreRick@aol.com) shows a tracking radar with a single target in the middle of the range notch. This notch gives a range expansion, meaning that although whole base line is 200,000 yards, the lowered section is greatly expanded in range, being about 150 yards in length. This provides a combination of whole picture,
1)the unexpanded base line
2)and the expanded (greater time detail) of the notch.

The lower trace is the error channel signal. This shows the operator the success of the servo system in keeping the antenna pointed at the target. It is extremely useful (required) if the tracking is in "MANUAL" or "AIDED MANUAL" due to ECM (jamming) problems.

In the middle of the range notch is the unseen "range gate" which samples the target information and sends it to the azimuth, elevation and range tracking servo systems. The servo systems use this sample to move the hand wheels controlling the tracking antenna in azimuth, in elevation, or the tracking range systems.

There are three target tracking operators seated in a row. each looking at his own "A" scope. The one on the right is the range operator, the one in the middle is azimuth operator, and on the left is the elevation operator. Between the range and azimuth operator is a PPI scope showing the same picture that the battery commander sees. This helps the tracking operators find the target designated by the battery commander.

Each operator can also look at the error signal (mentioned above) that goes into the servo systems. Each operator can also select to use the following modes of tracking:

In the Hercules, the range operator used a separate antenna TRR (the Target Range Radar). This radar used a selection of different frequencies and had the most extensive anti-jamming equipment.

The three seated tracking operators (range, azimuth, elevation) were assisted/supervised by a Tracking Supervisor who stood behind them and also operated the AntiJamming equipment.

Anti-jamming control box used by tracking supervisor - in the hands of SF-88 site volunteer Ezio Nuriso (who was a tracking supervisor)

from: "Frank E. Rappange" (f.e.rappange@pi.net) " The TTR had 3 different pulse modes: Short pulse, Long pulse, and Multipulse, and the TRR had 2 magnetrons (for eccm reassons). That means that we had to perform the simtrack for: TTR short, TTR long, TRR (both magnetrons) with TTR long and short pulse."

again from: "Frank E. Rappange" (f.e.rappange@pi.net) while discussing Nike sites in Europe " The use of multipulse was strictly forbidden in peacetime, the switch was sealed. By the way we were even supposed to avoid picking up targets in an easterly direction. Before we could fire up the magnetrons we had to check with HQ for the presence of 'Zombies' (= civilian aircraft from Warsaw Pact countries). We had to stay clear 400 mils on both sides with any tracking radar. "

from Rick at ShoreRick@aol.com "The Multipulse mode of the TRR was a ECCM feature that the Tracking Supervisor could select. This was used however in cases of very strong ECM where the operators were having difficulty in tracking. The TRR receiver would "sample" the frequency spectrum and select a frequency that was free from jamming signals and transmit at that freq. The multipulse feature was added later in the life of Nike.

The IF freq of the TTR was still 60 MHz. The TRR operated in the 14 Ghz range, and in fact used three Backward Wave Oscillators (BWO). One for each transmitter, and one for the panoramic receiver. The TRR contained two transmitters and three receivers. Since the TRR had two of everything, it was a simple radar to maintain. (If one unit had trouble, the TRR could still operate.)

The above display shows an a-scope with a single very weak target signal in the range notch. The fuzz or "grass" is primarily receiver noise, similar the "snow" on your TV screen when the TV station received signal is very weak. When the range gated signal is strong, the Automatic Gain Control (AGC) reduces the receiver gain and system and noise tends to disappear. When the range gated signal is weak, the AGC increases the gain and system receiver and other noise is also amplified more, and becomes quite visible.

Enemy or accidental jamming can/will cause these and many other interesting displays on the tracking scopes. Go to jamming for more information.

There are various unverified stories that in practice combat between the Air Force with their jamming equipment, and the Nike with their anti-jamming equipment, that the Nike successfully tracked the Air Force planes and would have had successful intercepts with the Hercules missiles. This was reputed to be true even when the Air Force used their best jamming equipment to try to confuse the tracking.

Return to beginning of Nike Radars


Missile Tracking Radar

As mentioned above, the external appearance of the Missile Tracking Radar (MTR) was identical with the TTR above.

In addition to needing a view of the target volume, into which it guides the missile, the MTR also need a direct view of the missiles on the launchers.
photo courtesy of Greg Brown, of SF-88 launcher from the IFC area.

From Rolf Goerigk, Specification for the Missile Tracking Radar (MTR) include:
Antenna Gain 44 dB
RF Peak Power 158.9 kW
Average RF Power (PRF 520 pps) = 79.4 Watt

There is one missile tracking operator with one a-scope. The missile tracking signal is a radar pulse generated by the missile in response to a pair of radar pulses transmitted by the missile tracking radar. The missile "echo" is quite strong and gives a high "signal to noise ratio" and looks like the strong target tracking signal above. The missile is always tracked in "automatic" mode. When every thing is working correctly, the missile operator observes the equipment for proper operation, but does not have to touch the equipment during missile firing operations.
Missile Tracking is a little different from Target Tracking
  • Automatic Frequency Control tracks missile magnetron not track radar magnetron
  • An automatic range coast function, three seconds (large white box)
  • Missile reject button and signal, request a different missile (small white box)

There is one interesting "got cha" - the MTR can lock on to the *ground reflection* of the missile's transponder. (Radar waves bounce off the ground as well as metal and water.) The missile tracking operator must observe that the elevation angle of the MTR is correct when locking on the missile. This can be called "multi-path, a pest even for FM and TV reception. If locked on the ground reflection, the MTR will slew *down* when the missile is launched - causing loss of tracking of the missile during launch - and things happen so fast that there is no recovery from this error. The missile will go straight up, detect that it is not being tracked, and explode in about 4 seconds. :-((

The only practical thing is to slew to and lock onto the next ready round and fire that. The loss of time should be less than 10 seconds :-((

Since the missile tracking radar is not pointing at the target until the last few seconds, the airborne enemy jammers only "see" the MTR for the last few seconds and have much more trouble jamming it, especially with the high signal strength of the transponder on the missile. The possibility of an enemy plane tracking a Nike missile in order to jam it (cause it to fail to see the MTR or to act on false steering and burst commands) would seem to be slight.

The time delay between the missile receiving the missile tracking radar pulse pair and the generation of the response is fixed, and allowed for in the MTR range system.

Missile Commands - Communication systems to command the missile
The Ajax and Hercules missile systems use different communication systems (using the Missile Tracking Radar) to command the missile.
-
Ajax Command System
- Hercules Command System

Ajax Command System
In the Ajax system, missile steering commands are sent to the missile by the missile tracking radar by changing missile tracking radar pulse rate. You can think of the commands as "tones", one tone range for up/down, another tone range for left/right, another tone for burst. The tone signals are combined and control the generation of radar pulse pairs.

Hercules Command System
In the Hercules system, missile steering commands are sent to the missile as follows:
Pitch, yaw and burst commands are not mixed as in the Ajax but are sent out individually. One command is send out each 2,000 microseconds (500 commands per second). Pitch and yaw commands are sent as two pulse pairs. Lets call the first pulse pair the "start" pulse pair, and the second pulse pair the "command" pulse pair. The "start" pulse pair are separated in time by the site specific delay (called "missile code").

The command is a pitch command if the "command" pulse pair is separated by one missile code plus one microsecond.

The command is a yaw command if the pulse pair is separated by one missile code plus two microseconds.

The delay time between the last pulse of the first pulse pair and the last pulse pair is the value of the command. The delay time for -7 g is 52.5 microseconds. The delay time for 0 g is 87.5 microseconds. The delay time for +7 g is 122.5 microseconds.

The Pitch and Yaw commands are sent alternately during normal tracking until 0.5 seconds before intercept. First the pitch, then the yaw, then the pitch, ... . Due to the coding, the missile knows which command is which type.

During the boost phase (4 seconds) and the roll phase (1 second), zero g yaw and pitch commands are sent to the missile. Then normal steering commands are sent to the missile, which is normally starts as a dive (from vertical) to the predicted intercept point.

The burst command is a special series of pulses starting 0.5 seconds before predicted intercept. No steering is performed during this final 0.5 second interval.

The Missile Tracking Radar (MTR) pointing system had an added circuit to automatically point the the MTR at the designated missile. If the MTR was not tracking a launched missile, and this circuit was engaged, the MTR would slew (in azimuth, elevation, and range) to the position of the designated missile. The Launch Control Officer would select the next missile to be fired based on:

The position (range, azimuth, elevation) of each launcher was dialed into the MTR system.

Return to beginning of Nike Radars


How The Tracking Radar Points at an Object - Monopulse

The tracking radars use the system called monopulse. First Reference? In this system, each returning radar pulse provides pointing information by being focused at the antenna onto a group of 4 radar openings. The focusing can be done by either a simple radar lens, as in the original Nike Ajax system (similar to the long refractor telescope of newspaper cartoon fame) or a more complex Cassegrain (folded) system used in the Hercules, similar to many modern optical telescopes.

Looking at it from the transmitter out, the Magnetron generates a high power pulse, it travels down the waveguide of the sum channel, hits the comparator, gets broken up equally into each port, and travels out the 4-port feed as horizontally polarized RF.

The pulse of radar waves strike the hyperbolic sub-reflector, (which has horizontal wires so that it reflects horizontially polarized radar waves),

and reflect back to the parabolic reflector, (which is a twist reflector), gets rotated 90 degrees in phase, and is now vertically polarized RF. (There is a trick, wires at 45 degrees one-half wave length from a reflecting surface twist the polarity of the radar wave.)

The now vertically polarized reflected pulse then travels through the horizontally polarized wires of the sub-reflector, and propagates as a vertically polarized wavefront out into space.

This design is beautiful in that you have basically no aperture blockage by the sub-reflector, and the radome design of the antenna means there are no spars to cause aperture blockage and defraction.

The vertically polarized returning radar signal is gathered, the polarity rotated to horizontal, and is focused onto the four windows shown in the above diagram. The four windows are connected to complicated microwave "plumbing" (discussed in the Wave guide section) which gives the following 3 outputs:

  • Sum of the inputs
  • Elevation difference, top 2 windows subtracted from bottom 2 windows
  • Azimuth difference, left 2 windows subtracted from right 2 windows.
The following diagram is a much simplified schematic of the method of detecting pointing errors in the left/right (azimuth) direction. The up/down (elevation) is similar.

The Sum video signal is sent to the range servo system and is the signal usually displayed on the a-scopes.

The elevation difference and the azimuth difference radar signals are processed by the receiver circuits, and available to be gated into the servo system by the range gate circuits to control the antenna elevation angle and the azimuth angle. The goal of the servo systems is to reduce the pointing error to zero (and also to remain stable - not oscillate about the zero error signal).

The antenna pointing controls the elevation and azimuth potentiometers which feed position information into the computer.


There are several advantages (and no disadvantages that I know of) of Monopulse pointing system over the older (?original?) nutating radiating dipole pointing system.

  1. No nutating moving mechanical parts to wear, get sloppy, cause vibration, ...
  2. Highly variable radar returns from a target (normal as the target wiggles due to air turbulence, will cause "rough tracking" errors.
  3. A jammer, observing the nutation characteristics, can counter by jamming in synchronization with the nutation rate and cause wild pointing errors in the servo system of the nutating antenna.
The Wikipedia monopulse article is reasonably accurate until it gets to its History section where it states that monopulse was "very expensive, labor intensive, and less reliable". Simply not true - I contend the nutation system had those negative characteristics vs the monopulse system. Once you fabricate the wave guide system in monopulse (which has no moving parts and in the X band fits in a cube 10 inches on a side) you are home free. The few extra tubes (if any) involved hardly ever fail. Consider that the nutation detection system is replaced by a simpler synchronous detector and added IF strip. (I have no clue how the wave guide assembly was fabricated.)

Monopulse Wave Guide Schematic
Please note, this is a schematic drawing, actually the feed horns (left) are very close together.
This is a more detailed diagram from TM9-5000-18 (available on this web site) showing the complete wave guide detail. Unfortunately, the Tracking Radar at the SF-88 restoration is missing this unit (actually the entire RF section) so I cannot show a picture.
The exit labled "AFC" goes to the Automatic Frequency Control circuitry so that the receiver can track the magnetron in frequency (the magnetron is tuneable about +=10% nominal frequency).
This drawing ( from Hercules ) ( maybe more realistic than the schematic above ) is from GoogleBooks. You better believe we on site never got in this far - something for Ordnance ;-))

Comments from the designer of the Hercules tracking antenna.

Return to beginning of Nike Radars


Multi-path Problems & Work-arounds

OK - You can get most of the above from any serious radar book. Now for a gory practical detail :-((

Radar waves are just a (VERY) low frequency light wave. This is both good and bad news.

  • The good news is that radar waves reflect off of conductive surfaces, like aircraft.
  • The bad news is that radar waves reflect off of surfaces you wish they wouldn't, like earth or water (with different dielectric constants relative to air) between you and the aircraft you are trying to track. Here are two stories one story and another story involving the Missile Tracking Radar "Locking-On" the reflection of a missile.

This is a visualization of the problem and a graph showing tracking errors of a plane at unspecified height with a radar at unsspecified height and frequency with beam width about 3 times Nike 3 centimeter wavelength. This edition goes on for about 3 more pages about this effect.
The above "sample" is from the 1980 edition of "Introduction to Radar Systems" by Merrill I Skolnik. While trying to contact the author for permission to publish, (no contact yet) I found that he is alive, still lecturing and authoring. According to http://www.radarcon2008.org/bio_Skolnik.html , "Dr. Merrill Skolnik served as superintendent of the Radar Division at the US Naval Research Laboratory in Washington, D. C. from 1965 to 1996." and has all sorts of accolades. If you are seriously interested in modern radar (including Lidar) you should get one of his more modern books.
The above paragraph indicates a reason that the Nike mission was against "high flying" aircraft, and some motivations for developing homing missiles such as HAWK, and the more sophisticated methods in PATRIOT.

Good News

The chart can be interpreted to indicate that the error between two closely spaced radars, involved with low angles of elevation of the target, will have similar errors - that the error of the MTR tracking the missile into the Intercept Point will be largely compensated by the error of the Target Tracking Radar tracking the target into the same Intercept Point. - The two errors largely cancel -

Bad News

If the Missile Tracking Radar tracks the reflection or image - it will lose track of the missile, and there is no practical way to regain track before the missile self destructs after losing the tracking/command signal from the MTR.
Good News ;-))
The effect was known and corrected for until judged "not a problem". This was usually easy in the U.S. Rolf Goerigk reports from Germany
... A good example was the daily MSL {Missile Tracking Radar} acquire procedure. Because of the usually low grazing angle of the antenna beam, multipath effects were monitored in elevation. By using NIKE amplitude monopulse there was no cure. The MSL was rated non-operational. Just imagine, looking thru the mounted telescope seeing some cows instead of the auto tracked missile!

But the view-point or directing point was not the reflection point, instead it was the sum of the direct and indirect RF energy from the MSL. The "reflection point" was changing with season and daytime and sometimes gone at all. It was a really interesting case and I learned a lot. I was engaged (again) in that "secret" story. That case was really hot and sensitive. This matter is discussed in some radar books.

The wartime solution! Moving trucks between the MTR and MSL, it worked!


Radar Aiming Alignment including boresighting

A quick Wikipedia introduction

Radar alignment is reasonably complex. Each radar (target tracking & missile tracking) must be individually leveled and boresighted. Then the two radars must be aligned so that their potentiometers read the same when both are pointed in the same direction. Then the position difference of the missile tracking radar from the target tracking radar must be placed into the computer for that correction.
This is a bore site mast (15 K bytes). The test signal radar waves come out of the feed horn at the center of the X on top, and the 4 side things of the X on top are optical targets for the telescopes on the radars (TTR, TRR, and MTR).
More details here
A little reflex klystron, such as this, was used to generate the echo pulse via the feed horn to the tracking antenna being boresighted. The radar receiver sensitivity could also be checked by attenuating the output of this tube. The tube is about 3 inches, 8 centimeters, from tube base to top. The long "pin" below the base is the coaxial output structure feeding a wave guide.

This is a bore site mast (34 K bytes) being lowered. When in place, the long pole is vertical. Image from Rolfs NIKE Pages by goerigk@onlinehome.de.

In list fashion, it can be organized into the following major steps:

  • Individual leveling (all tracking radars)
    The level indicating instrument was a ruggedized version of the Precision engineers level mounted on the rotating part of the antenna. The instrument alignment was checked by leveling the antenna then rotating the antenna 180 degrees and assuring that the instrument still indicated level. If not, you readjusted the level until it indicated the same error "forward" and "backward". You then re-leveled the antenna and checked again. (This adjustment was quite stable.) The level of the antenna was generally not stable.
  • Individual bore sighting (all tracking radars)
    • Turn on Bore Sight Test Mast oscillator
    • - When the test mast control box senses X-Band pulses,
    • -- it will generate echo pulses on the same frequency from the feed horn
    • Lock on oscillator
    • Track in automatic
    • Set telescope into mount, position 1, observe target
    • Set telescope into mount, position 2, observe target
    • Adjust telescope (not radar!) for correct bore sight
    • Shut down the Bore Sight Test Mast oscillator
  • Aim missile and target tracking telescopes at each other's crosshairs
  • Adjust potentiometer alignments
  • Make sure the missile tracking radar position offset was in computer
The leveling adjustment was the most troublesome at many new sites. It would drift about quite a bit (require releveling several times a day) until the concrete pads settled down into the ground. Then the adjustments would not be required more than once a day.



Data Unit Adj

Elevation BoreSight

Azimuth BoreSight

This yielded a bore sight accuracy between the Missile Tracking Radar and Target Tracking Radars of about 1.5 inch in a thousand yards (assuming the bore site mast was at about 250 yards from the radars). At 110 miles (200,000 yards) that would be about 300 inches or on the order of 25 feet. There are many more error sources in the system - of course - but the system was/is interestingly accurate. In angular measure, the boresight error was about 0.0025 degrees For an interesting comparison with the earlier (WWII) SCR-584, click here.

Frank E. Rappange points out that there is a check that demonstrates that all of the adjustments REALLY WORK. " ...the main test (that had to be performed every 6 hrs, when on 30' SOA) was the 'Simultaneous Tracking Test'. In this test the MTR was set to 'skin track mode' and both TTR (and TRR) and MTR locked on the same target. The BCO could read the voltage difference for the positions of the respective radars in the BC Van. Readings were made for both TTR and TRR in the difference pulse modes. It was the decision of the BCO to accept the system or not."

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Radar Range Determination

Radar waves (and light and other electromagnetic waves) travel through air almost as fast as in a vacuum. Fortunately for engineers and users, air pressure, humidity, and other atmospheric variables do not affect the speed of travel very much. To make matters even easier for the Nike problem, any variations that do occur are largely canceled out at the end of the flight, as both the radar beams are traveling through very similar air conditions. Errors due to refractive effects due to differences in air pressure along the beams cancel out. So a common crystal oscillator was used to calibrate the range systems of both the missile and target radars. This adjustment was fortunately very stable, rarely needed tweaking unless a component was changed.

There is a circuit called a "phantastron" that has a remarkably linear pulse delay time from a voltage input. The Range Operator (or range tracking servo system) operates a linear potentiometer which provides the range voltage for:

  • elevation potentiometers, see Height Determination below)
  • phansitron (supplies range gate for displays and for servo gating)

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Radar Height Determination

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Radar Azimuth (horizontal direction) Determination

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Tracking Radar Physical Support

One of the many keys to precision tracking between the target and missile tracking radars is the fact that (small) identical errors of tracking by both the target and missile tracking radars "cancel out". Example, if both the target and missile tracking radars say that their respective tracks are both 100 yards higher than absolute height, the actual miss distance (if every thing else was perfect) would be 0 yards. **Very Interesting and Useful**

This way, errors due to radar wave (like light wave) refraction in the atmosphere cancel out if both radars are tracking the same point in space (in this discussion we ignore the slightly different paths due to the slightly different physical location of the two radars.

The Nike Ajax system "assumed" that wind buffeting of the two tracking radars would be sufficiently similar so that accurate enough tracking could be accomplished.

Since the Nike Hercules had an "effective" range more than 3 times the Ajax, and a real range more than 4 times the Ajax, errors due to wind buffeting and similar errors could be 3 or 4 times larger, and possibly render Hercules ineffective (too inacurate) at longer ranges.

Bubbble surrounds each tracking antenna
To counter the wind buffeting, the tracking radars were enclosed in an air inflated fabric "bubble". This greatly reduced the wind forces on the tracking antennas. Even if the wind gust shifted the bubble a few inches, the air forces on the antennas would be greatly reduced during the shift of the "bubble".

The "bubble" also protected the antenna from much of the differential heating due to the sun heating (expanding) one side of the mount and antenna relative to the other side (shady side) of the mount and antenna. Although both tracking antennas would likely be illuminated by the sun the same way, vertical alignment was usually made by one person at slightly different times (an error source) and one was never confident that everything was identical anyway.

Wind Force and Sun Heating on Tower Mount
Ideally, the radars could be located on high ground, well above surrounding trees, buildings, ... . However, in flater areas, towers had to be used to get the tracking radars high enough.

The wind also supplies forces and torques on radar towers. The forces and especially the torques shift the top of the tower in space, and shift its angle with the vertical. The shift in space (inches) is much much smaller than other errors, but the shift in angle from vertical could result in much more severe errors.

To provide improved resistance to angle errors due to torque in the tower, the tower was actually a double tower.

The outer tower was buffeted by the wind, and also the differential expansion due to the sun light heating it. The platform at the top of the outer tower also supported the bubble that protected the antenna from the wind.

The inner tower supported the antenna. The inner tower was largely isolated from the wind and the sun which resulted in much more stablity.


Image of tower showing:
- outer tower platform
- bubble base
- foot pad from inner tower

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Simultaneous Tracking Test (the proof)

Did all of the above boresighting adjustments and alignments REALLY yield a system that could get a missile within kill distance of the target? There is a way to check!

Have BOTH the target tracking radars and the missile tracking radar track the same target (aircraft). If both radars say the aircraft is in the same place, the tracking system is correctly aligned. Period. No guess work, no theory, no "it oughta", the tracking system IS correctly aligned. Assuming the computer works, the missile takes commands, etc., that NIKE system is capable of guiding the missile to the target!

However, you remember that the Missile Tracking Radar (MTR) tracks a beacon in the missile, not the skin of the missile. So, (FOR THIS TEST) the MTR is set to:

  • a mode to track the MTR radar reflection from a target, not the missile beacon
  • remove the delay of the beacon (a fixed delay between receiving the MTR radar signal and the firing of the beacon) from the MTR range system
The above two changes permit MTR to track the aircraft just the same as the TTR system.

An aircraft flies about, and the computer voltages representing N-S, E-W, UP-DOWN for the MTR and the TTR are compared. They ideally should be identical. Placing a sensitive volt meter between say the target radar N-S and the missile radar N-S should ideally yield zero at all times while tracking the same aircraft. In practice they rarely are completely identical due to at least the following error sources.

  • different parts of the aircraft reflect (glint) differently at different angles
  • different pointing servo gains and damping
  • actual level errors
  • actual boresight and alignment errors
  • errors in the range, elevation, azimuth potentiometers
  • errors in components in the computer
  • a wide variety of mechanical errors such as binding, looseness, ...

In spite of the above long list of possible error sources, people at NIKE sites had to and did prove - frequently - that the tracking system errors were very few yards at ranges in excess of 50 miles. Unbelievable but true!


Simulated Tracking (and jamming)
using the T-1 System

Tracking aircraft with a NIKE system is trivial if the aircraft is not using jamming.

With no jamming, you can easily teach your junior high school kid to be a good NIKE radar operator in an afternoon. A group of afternoon trained junior high kids could do all the NIKE aircraft radar tracking operations necessary to shoot down a non-jamming aircraft.

The airforces of the world spend a great deal of time and money to try to defeat radar - and many interesting jamming methods have been developed and are used. How do you train NIKE people to track aircraft that are using Electronic CounterMeasures - ECM (jamming)? How do you maintain and enhance this difficult skill?

Using friendly aircraft for this training and skill maintenance has many disadvantages, including:

  • The friendly air force is unlikely to wish to fly aircraft for hours per day around the various sites to assist in trainning and honing the friendly anti-aircraft forces. Occasional tests may be OK, but almost every day?
  • The friendly air force may not wish to turn on their latest and greatest ECM (jamming) equipment for analysis by non-friendly agents.

I presume these, and other, reasons led to the development of the AN/MPQ-T1 Electronic Warfare Simulator (developed by ITT Baltimore, MD ) which was housed in one very large trailer. The operators in the T-1 trailer could exercise the radar operators in both

  • the Battery Control (BC) van (acquisition operators and battery commander)
  • and the Radar Control (RC) van (Target Tracking operators (azimuth, elevation, range) and Missile Tracking operator.
with many types and quantities of "interesting" ECM (jamming) problems.

For more details on the T-1 unit, see

Lesson 8. Target Simulation - 1.2 megabytes

There is a T1 manual on-line at T1 AN/MPQ-T1 (another site)(.zip -> .pdf files)(10 files totaling 6 Mbytes)

For a more general discussion of jamming, go here.

From Steve Johnson
LOPAR/HIPAR target video and ECM was created using sync and preknock signals from the radar. Antenna rotation was slaved to the radar by a device called a "flying spot scanner" and video was triggered using a system called an "antenna pattern generator" which simulated not only the main antenna lobe but side lobes as well. By changing the position of the main lobe, the target could be moved in azimuth at will and the ECM would also be positioned along the main lobe.

TTR and MTR video was generated {by the T-1} much the same as the IF test pulse except that the TTR was given sum, azimuth and elevation signals and long and short pulse. Azimuth and elevation signals were controlled through servos which were slaved to the antenna and range simulation was done by delaying the video from sync.

The system could generate 6 independent targets with 4 types of Electronic jamming on 4 different carriers in addition to Acq and track chaff and angle deception.

From Bert Belfer
Army Navy Mobile Radar Signal Simulator. I worked on them for about 10 years, a great training device. Simulated up to 6 targets, ECM, and ground clutter. The Chaff cabinet was a bitch to maintain. The T1 also had a reusable missile. The T1 was heat sensitive and the IF strips had to be retuned as the trailer got warmer. The Simulations were injected at the RC & BC Vans not at the radars.


Resistance to ECM (Jamming)

from Doyle Piland < dpiland@zianet.com > his Nike ordnance web site
First, let me say something about analyzing the ECM/ECCM situation for Nike or any other system. That is somewhat akin to painting a moving train. Technology advances tend to make the advantage shift between ECM and ECCM. So, Iím not surprised that some point in time the SSKP was as low as 85%.

However, I have watched as Air Force planes tried to break Hercules System lock after the TRR was added to the system and they could not do that. I have even read letters from Air Force organizations requesting that Nike not track their planes using their ECCM, because it tended to undermine the confidence of their pilots in their ECM equipment.

I donít know the time period that the simulations were done. Ability to do meaningful simulations developed as technology did, so the sophistication (accuracy) of the simulation could be called into question. Second, all simulations involve some approximations and assumptions. Thus, simulations have to go through a validation process to determine the accuracy of the simulation. I have never heard of any meaningful simulations involving the Nike Hercules systems. That doesnít mean there werenít any, just that if the 20+ or so years working with and around Nike, I would have expected to see something about it.

I hope this helps.

Doyle


If you have comments or suggestions, Send e-mail to Ed Thelen

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Updated March 2, 2014