by October 12, 2002 0 comments



Stealth equipment attempts to bypass detection by either absorbing or scattering the electromagnetic waves thrown at it by radars. However, stealth techniques can only make most craft less detectable to radar and infrared sensors, but not completely undetectable

Stealth techniques were some of the best-kept secrets in the world till the Gulf War. Today these low observed projects are applied to air, sea and ground-force equipment and vehicles.

How far a radar system can detect or track an object depends on its transmitter’s power, antenna size, receiver sensitivity, environmental conditions and, finally, the radar cross-section of the target (RCS). At first glance, sensor designers seem to have an insurmountable advantage in this game of hide and seek. They control most variables, can worry less about space requirements and have a detection range that varies with the fourth root of RCS. So, to halve detection distance, the RCS must be slashed by a factor of 16. If the radar echo of a fighter flying head on is reduced from 5 square meters to 0.5 meter square, all other things being equal, the detection range is cut by 44 percent. However, by increasing the radar’s power and signal-processing ability to gather fainter radar echoes and employing moving target indicator techniques to differentiate stealth aircraft from the slower blips of birds and insect swarms may offer some resistance to stealth techniques. 

The Swedish navy’s ‘Visby Class’ corvette is an example of stealth at sea

Stealthy designs
Normally bypassing radars is done by situational awareness and flying close to unpredictable clutter from ground or sea. In stealth’s case, the goal is to make a fighter plane’s head on RCS that of a bird. So the first step towards making system stealth is to determine what elements contribute to the radar signature. Predicting and analyzing the RCS of a complex object like an airplane is extremely difficult. In general, an aircraft’s frontal RCS can be reduced by using special aerodynamic shapes such as delta wings and blending them into the fuselage. Right angles are anathema. For lower back scatter from ground radars, engine inlets must be placed on the upper side of the body and tailfin stabilizers should be canted inwards. Weapons must be carried internally and reflecting antennas either canted downward or hidden from view behind special radomes. Covering the objects with absorbing material, replacing metallic ports with resistive or composite structures and using honeycombed sections in key areas to trap incoming waves are all techniques for reducing RCS. Also special and precisely-timed response of onboard defensive avionics may become critical to keep the aircraft stealthy or to prevent enemy radar from tracking it.

Typical head on Radar echo at microwave frequencies
OBJECT RCS (sq.
mts.)
35000 ton frigate 10000-30000
Pick up truck  200
Automobile 100
Jumbo jet airliner 100
Large bomber 40
Cabin cruiser boat 10
Large fighter aircraft 5
Small fighter aircraft 3
Adult male 1
Bird 0.01
Insect 0.00001

An important point to note is that designs that give stealth top priority may compromise performance, range and payload.

Reduced detect ability on radar can also be a safety hazard in reduced visibility. These disadvantages can be overcome by some mechanical or electronic means. The degree of stealth depends on many factors, mainly shape, use of absorbent structures, materials and employment of onboard avionics.

Wg Cdr V Kumar (retd) served in Indian Air Force as Aeronautical Electronic Engineer and worked as directing staff in the field of EW. He also served in Embassy of India, Washington DC as Attaché. He is a member
of IEEE, USA

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