Expendable Active Decoys
Expendable active decoys are designed to lure the tracking gates of an enemy’s radar away from the aircraft.
Expendable decoys are small, active jamming systems designed to be expended by existing aircraft chaff and flare dispensers such as the AN/ALE-40 or the AN/ALE-47.
Decoy ejection typically is initiated by the RWR of the self-protection suite upon detection of the presence of an approaching missile or can be activated directly by the aircraft pilot following a missile alarm.
The Decoy typically begins to radiate the jamming signal to the victim seeker immediately upon ejection and continues to radiate throughout the flight.
Once launched, the Decoy orients itself towards the aircraft’s wake by deploying small aerodynamic drivers to keep it in stable ballistic flight.
The Decoy slowly deviates from the direction of the launcher’s velocity vector by natural deceleration because of friction and gravity.
The dispensing altitude and rate of fall determine the period of effective coverage.
Small parachutes can be employed to slow the rate of fall and increase the time of effective
Expendable decoys can employ noise or deception jamming with noise jamming being the most common.
Deception jamming techniques can be employed to enhance the effectiveness against pulse Doppler radars.
Multiple decoys are sometimes released at a predetermined rate to increase the chances of engaging the missile and, consequently, the aircraft’s chance of survival.
The primary components of an expendable decoy are the transmit and the receive antennas, technique generator, amplifier and power supply.
Some factors limit the effectiveness of an ED and are major challenges in terms of its implementation:
• The small size limits the quantity and type of jammer components that can be packaged in the cartridge.
Therefore the power and frequency coverage of the jammer are limited and the amount of time the jammer is effective is limited as well.
• The geometry of the scenario and of the engagement is not predictable, so a wide antenna beam is required to be sure of the disturbing effect.
The reduction of the antenna directivity and the emitted power means a reduction of the ERP.
The GEN-X Decoy is a small, one shot, expendable terminal, RF threat programmable countermeasure that receives an RF signal from a recognized threat, such as airborne or land-based semi-active radar guided missiles, and then transmits RF power to counter that threat.
The GEN-X Decoy can be launched from the AN/ALE-39 or AN/ALE-47 Countermeasure Dispensers using a CCU-63/B or CCU-136/A Impulse Cartridge.
Figure 1: RT-1489/ALE (GEN-X)
Brite-Cloud is “a self-contained Digital RF Memory (DRFM) jammer for fast jet aircraft”, aiming at providing “an off-board capability to decoy RF-guided missiles and fire control radars”.
More in general, the EAD has been tuned to be effective against surface-to-air and air-to-air threat systems.
Figure 2: Brite Cloud
SPARK is an expendable active RF decoy based on a Digital Radio Frequency Memory (DRFM).
The SPARK “payload” is housed in a flying body (“platform”) contained in a “2-1-8” cartridge compatible with a standard Counter-Measures Dispenser System (CMDS).
Figure 3: SPARK