Interception by radar

By Jan Meyer

Whoever wants to keep an eye on large sections of airspace needs suitable "eyes", like an early warning and controll chain. Such a chain consists of a number of powerful ground based radars suitably located in highe places in such a way that they provide continous coverage of the airspace that is beeing watched.

The radars are usually placed in solid rock, only the antennae see daylight. Within the mountain there are operations rooms containing radar screens and plotting aids to maintain a view over the situation. The guardian needs a hand and a weapon to wield to maintain his authority over said airspace - one or more squadrons of fighters. The allweather fighter is thus a component in a larger weapons system and is capable of finding, intercept, identify or even destroy a target as the name implies, in darkness or low visibility.

The radar is an important component

of the allweather fighter´s equipment. It is the fighter´s eyes making it possible to see and track a target regardless of visibilty or light. The aircraft, it´s radar and weapons constitute a system. F-86K was an all weather fighter in this respect, but even seen through eyes of the early sixties, with very limited performance. When the F-104 arrived in 1963 it meant a large leap in the posibilities to guard the airspace over and around our country. But the aircraftÕs performance alone wouldnÕt be of much help without a capable radar.

The F-104 radar had several functions:

  • It could be an aid to navigation and draw a map of the terrain ahead of the aircraft. It could also be used for terrain avoidance during low flying.
  • It was a search radar that could search for targets.
  • It was a means to tracking and intercepting a target.
  • It was an aiming system for the aircaft´s weapons.

The radar could operate in several modes

The antenna was located in the nose cone and moved freely from side to side in an azimuth sector of 45 degrees to each side. It could also be tilted 40 degrees above and below the horisontal plane. The screen that was centrally loacted in the cockpit would usually work in Plan Position Indicator mode (PPI) and the screen picture would be a map of the terrain ahead. Targets would show as blips. The sweep on the screen would look like a windshield wiper moving back and forth. The map would be in polar coordinates with the aircraft at the apex and corespond to what you could see from the cockpit. The screen could also show concentric circles that would mark range (range circles). The range might be adjusted as the the aircraft approached the target. The antenna could also be steered to limit itÕs scan both in asimuth and elevation.

When approaching the target, the blip would disappear in the pointed part of the display, and the picture would be difficult to read. The display could then be altered to B-screen. The picture would then be rectangular with course information across the screen (x-axis) and distance along the y-axis as before. The sweep would change to a vertical line that moved back and forth across the display.

With a little stick

on the left side of the cockpit, behind the throttle we could move a marker (pipper) on the screen. When approaching the target we could put the pipper on the target and press a button on the stick. The radar would cease scanning and point at the target and lock on it. The radar display would change to weapons guidance. The display would now consist of a range circle that showed distance to the target and had an indicator of closing speed along the edge. The speed mark would be closer to six o´clock on the left the faster the target was overtaken. As overtake speed was reduced the marker would move counterclockwise towards twelve o´clock. At twelve o´clock the speeds would be equal and on the right side the target would move away. The range circle would decrease in size as we approached the target. In addition there was a steering circle. The pipper should be within the steering circle and it was used as directional guidance, that is, the fighter would maneuver such that he kept the pipper centered in the steering circle. At minimum distance the display would change again and give a break away signal to warn against collision with the target.


Robert L. Shaw, an American fighter- and test pilot has written a special book, " Fighter combat, tactics and maneuvring". It´s a treatise for fighter pilots and systemizes tactics, maneuvres and aerodynamics behind all known kinds of aerial fight. It also explains the tactics used by allweather fighters armed with missiles. If the purpose of the intercept is identification, only one of these tactics are useful, what Shaw terms stern conversion. It entails the fighter positioning itself such that the target may be overtaken from behind to be formated on and identified. This tactic is the base for the pattern that we describe here, was usually (and still is) empolyed during intercepts of unknown air trafic along our coast. This procedure means that the fighter is positioned on opposite course to the target with a few miles offset to one side.

Profile of a typical intercept. Scramble and takeoff is followed by climb, accelleration, flight to position, turn towards taget and target acquisition (radar picture with B-screen) followed by attack/identification (radar screen with lock-on) and return to base and landing or intercept of another target.


At a given angle to the target the fighter commences a turn towards the target and rolls out with an intercept angle of 70 degrees to the target´s track. During this turn the fighter´s radar usually aquires the target. When the fighter gets close enough to the targte´s track he contiues his turn and rolls out behind the target with overtaking speed. The radar´s B-mode is used in this phase and the display develops as shown in the figure. When the fighter gets to missile range the fighter will lock his radar on the target and the display changes again. He will use his radar in missile mode till he reaches minimum missile range and then change to gun mode and use this and the infrared sight to maneuvre all the way up to the target to make an identification. .

The radar pictures are drawn on screen and simplified to show essential traits. The screen pictures on an actual mission will only occationally be as clean as shown here.


The range circle displays a moderate overtake speed and that the fighter is slightly to the right of the target´s track. A small turn to the left will bring the pipper into the center of the steering circle and the circle will move towards the middle of the screen as the fighter approaches the targetÕs track. The range circle will shrink simultaneously.


This picture shows the outer limits of the sweep and a fixed symbol of the aircraft in the middle of the screen. It also shows a series of blips the way they will occur as the intercept proceeds (Only one at a time will show). The sequence spans from target acquisition during turn-in to the target till the fighter is astern the target ready to lock on.


The antenna is tilted far enough down to paint parts of the terrain and a target blip. The screen also displays the outer limits of the sweep and a single range circle. The picture is simplified, none of the fixed screen marks are displayed.

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