The three sequential phases of radar operation (designation, acquisition, and track) are often referred to as modes and are common to the target-processing sequence of most fire-control radars.

Designation Phase

During the designation phase, the fire-control radar is directed to the general location of the target.

Acquisition Phase

The fire-control radar switches to the acquisition phase once its beam is in the general vicinity of the target. During this phase, the radar system searches in the designated area in a predetermined search pattern until it either locates the target or is redesignated.

Track Phase

The fire-control radar enters into the track phase when it locates the target. The radar system locks on to the target during this phase.

Typical fire-control radar characteristics include high pulse-repetition frequency, a very narrow pulsewidth, and a very narrow beamwidth. A typical fire-control antenna is shown in figure 1-22.

Detect-to-Engage Sequence

The basic sequence can be divided into six fundamental operations: detection, acquisition and tracking, prediction, launcher/gun positioning,

Figure 1-22.-Typical fire-control radar.

guidance (missiles), and evaluation (intercept and target destruction). Figure 1-23 illustrates the fire control problem sequence.

DETECTION.-In this phase, the radar looks for a target. After the radar (usually a search radar) detects a target, the system obtains precise target position information. This information can be provided by the same source that detected the target, or it can be provided from some other source, such as another radar. In the majority of the cases, a second radar, a fire control radar, is used.

The search radar establishes the target's initial position and transmits this information to the designated fire control system.

ACQUISITION AND TRACKING.-During this phase, the fire control radar director/antenna is aligned with the search radar's target position information until it locks on the reflected target signal (acquisition). Either an operator or an automatic control circuit maintains that alignment (track) while the ship and target are moving. In this way, continuous, accurate target position information is available to the weapon system for processing. Not only is the continuous present position of the target obtained, but its movement (course and speed) is also determined.

Data other than target data is equally important for weapon flight path (trajectory) determination. Wind, for example, could blow the weapon off its flight path. Appropriate corrections would require that wind direction and velocity be determined. The course and speed of the launching ship and its motion, because of the sea (pitch and roll), are also important considerations. If this type of data is not included in the flight path determinations, it could cause large errors in the flight path (trajectory).

Data of this nature, along with target data, is transmitted to the fire control system's computer. The computer performs the necessary calculations for computing the launcher or gun mount position angles and the weapon's flight path.

After target detection and target acquisition have occurred, the fire control system provides three operations for the tracking, computation (prediction), and positioning functions.

The first operation tracks the target and provides all necessary data on the target. The fire control radar performs this function by establishing a tracking Line Of Sight (LOS) along which it receives the returned or reflected energy from the target. It also provides accurate range data.

Since the speed of the propagated RF energy is about 186,000 miles per second (the same as the speed of light), and since the target ranges involved are relatively small, the time for the energy to travel to and from the target can be considered as instantaneous. Therefore, the radar indications of the target can be considered as instantaneous, present-target positions.

PREDICTION.-The second operation of the fire control problem that must be performed is the computation of the gun/launcher positioning angle (line of fire) and the weapon flight path trajectory. This operation consists of two parts. First, the system processes received data into a usable form. Then the fire control computer performs arithmetic operations to predict the future position of the target.

Figure 1-23.-Fire-control problem sequence.

LAUNCHER/GUN POSITIONING.-The third operation that must be performed is the positioning of the gun/launcher, based on the calculated line of fire to the future target position. This amounts to using the gun/launcher drive mechanism to offset the gun/launcher axis from the LOS by the amount of the predicted lead angle. In some cases, the missile is positioned (guided) in flight by the fire control system.

GUIDANCE (MISSILES).-For the Guided Missile Fire Control System (GMFCS), additional functions must be performed during the time the missile is in flight. Prior to launching, the fire control computer performs certain computations to provide the missile with information about the target and its own flight path. If the target maneuvers during the missile's flight, the computer can send course correction data to the missile via the fire control radar or the missile can correct itself.

EVALUATION.-The fire control radar displays are used to evaluate the weapon's destruction of the target. If the missile misses the target or causes only minor damage, additional weapons can be used. In missile fire control, another missile is fired. In gun fire control, corrections are made to bring the fall of shot onto a target using the radar indicators, optical devices, or spotter corrections. Normally, a target will be fired at until it is evaluated as either destroyed or damaged to the point it is no longer a threat.

Q10. What type of radar system provides early warning of approaching enemy aircraft or missiles?

Q11. What phase of guidance is NOT necessary for some missiles

Q12. What are the three types of homing guidance used for missiles?

Q13. What are the three sequenti8al phases of radar operation?

Q14. In what phase of the fire control problem sequence does fore control radar first play a part?