Active protection systems

An active protection system is a system (usually for a military application) designed to prevent line-of-sight guided anti-tank missiles/projectiles from acquiring and/or destroying a target.

Electronic countermeasures that alter the electromagnetic, acoustic or other signature(s) of a target thereby altering the tracking and sensing behavior of an incoming threat (e.g., guided missile) are designated soft-kill measures.

Measures that physically counterattack an incoming threat thereby destroying/altering its payload/warhead in such a way that the intended effect on the target is severely impeded are designated hard-kill measures.

Soft-kill measures are applied when it is expected that a sensor-based weapon system can be successfully interfered with. The threat sensor can be either an artificial one, e.g., a solid-state infrared detector, or the human sensory system (eye and/or ear).

Soft-kill measures generally interfere with the signature of the target to be protected. In the following the term signature refers to the electromagnetic or acoustic signature of an object in either the ultraviolet (wavelength: 0.3–0.4 µm), visual (0.4–0.8 µm), or infrared (0.8 - 14 µm) spectral range as well as cm-radar range (frequency: 2–18 GHz), mmw-radar (35, 94, 144 GHz) and finally sonar range (either 50 Hz – 3 kHz and/or 3–15 kHz).

One or more of the following actions may be taken to provide soft-kill:

Soft-kill countermeasures can be divided into on-board and expendable countermeasures. Whereas on-board measures are fixed on the platform to be protected, expendable measures are ejected from the platform.

Preemptive action of countermeasures is directed to generally prevent lock-on of a threat sensor to a certain target. It is based on altering the signature of the target by either concealing the platform signature or enhancing the signature of the background, thus minimizing the contrast between the two.

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