Inverse Gain
![941Inverse Gain](https://www.emsopedia.org/wp-content/uploads/2021/02/Inverse-Gain-Deception-Technique.jpg)
Inverse Gain Technique is a form of angle deception used against Conical Scan Radars and is aiming to mislead the tracker from the actual target angle by means of a false-target modulation in which transmitted peaks fall in the valleys of the real target modulation (Figure 1).
Conical scan is a two-dimensional sequential lobing operation in which a pencil beam with circular symmetry executes a scan about the tracker boresight axis: deceptive angle countermeasures against these radars need to synchronize their modulation patterns with the motion of the radar beam.
Inverse Gain implements the so-called On-Off Keying (OOK) technique: the jammer measures the envelope of the signal transmitted by the radar and synchronizes the transmission of the jamming in counter phase with respect to the received signal: the jammer transmission is maximum during the portion in which the envelope is minimum and vice versa.
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Figure 1: Example of Inverse Gain
In presence of this form angle deception the automatic tracker shifts its boresight axis to a point on the line joining the real target and false target, closer to the stronger of the two.
In case of jammers designed to operate at a fixed (saturation output level) Inverse Gain deception technique can be implemented by transmitting constant amplitude jamming burst (Figure 2) timed to coincide with the valleys of the real target modulation.
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Figure 2: Inverse gain with saturated Jammer