PHASES OF RADAR OPERATION

Passive Homing.—Passive homing requires that the target be a source of radiated energy (fig. 1-21, view C). Typical forms of energy used in passive homing are heat, light, and RF energy. One of the most common uses of passive homing is with air-to-air missiles that use heat-sensing devices. It is also used with missiles that home on RF energy that originates at the target (ships, aircraft, shore-based radar, and so forth). An e x a m p l e o f t h i s i s t h e S TA N DA R D A R M (anti-radiation missile) used for both air-to-surface and surface-to-surface engagements. An advantage of this type of homing is that the target cannot detect an attack because the target is not illuminated. Several missiles that normally use other homing methods (active or semi-active) are capable of switching to the passive home-on-jamming (HOJ) mode in a countermeasure environment. That is, if the target detects that it is being illuminated by an active or semiactive guidance radar and initiates jamming (RF interference), the missile will home on the jamming signal if it is unable to maintain track on the reflected illumination signal. Tracking Radar/Fire-Control Radar Radar that provides continuous positional data is called tracking radar. Most tracking radar systems used by the military are also called fire-control radars, the two names being interchangeable. A fire-control tracking radar system produces a very narrow, circular beam. PHASES OF RADAR OPERATION 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, 1-18 A. B. C. Figure 1-21.—Homing guidance: A. Active homing; B. Semi-active homing; C. Passive homing.