Heads-Up Display Modes 35 - Metaboli

86 Air-to-Air Missiles
the target’s ability to reflect radio waves; i.e., its radar cross-section (RCS). This
ability significantly depends on the aspect angle of the target. Besides aspect
angle, the reflection of radio waves depends on the size, shape, and details of
construction of the target. The figure below shows a typical diagram of reflected
signal intensity:
Radar Cross-section Illustrated
Although semi-active homing provides acquisition of uncooperative targets and is
good for long distances, one of its major problems is greatly increased complexity,
which results in reduced reliability. Essentially this technique requires two
separate tracking systems to be successful (one in the missile, the other in the
guidance platform). Another serious drawback is the requirement for target
illumination by the guidance platform throughout the missile’s flight. This
requirement makes the illuminator vulnerable to passive-homing weapons, and
with airborne illuminators it often restricts the maneuvering option of the aircraft
providing target illumination.
Although active homing requires a more complex, larger, and more expensive
missile, the total guidance system is no more involved than that of the semi-active
system, and in some ways it is simpler and more reliable. It also gives the
launching platform “fire-and-forget” capability, as do passive systems. One
disadvantage, however, is the possibility of reduced target detection and tracking
ranges. Since the range of target acquisition is proportional to the area of the
illuminating antenna, all other factors being equal, the tracking range of the aircraft
radar greatly surpasses that of the missile. Therefore, semi-active homing is
possible at considerably greater distances than active homing. That is why active
homing is frequently used in a combination with inertial guidance or semi-active
homing and sometimes passive homing.
Target Tracking
A variety of guidance laws are implemented in modern AAMs. Most missiles
that employ proportional navigation techniques require a moveable seeker to
keep track of the target. Such seekers have physical stops in all directions,
called gimbal limits, which restrict their field of vision and therefore limit the
amount of lead the missile may develop. If the seeker hits the gimbal limit, the
missile usually loses its guidance capability, i.e. “goes ballistic”. Such a situation
most often develops when the line of sight to the target moves fast and the
missile’s speed advantage over the target is low.
Using onboard systems, the pilot searches, detects, and acquires a target, then
feeds the targeting data into the selected weapon. The missile can be launched if
the current targeting data fit the characteristics of the guidance system of the