Communications, Radar & Electronic Warfare (201.. - Index of

336 Communication, Radar and Electronic Warfare18.2.5 Inverse Gain JalnmingInverse gain jamming is a method of denying the target radar angle information. In thiscase, the jammer does not produce a single alternate target but rather blocks all angles.Figure 18.8 illustrates again the scenario. Diagram (a) shows the signal from the radaras perceived from the target. Each of the pulse trains will be received not only tlu-oughthe main lobe but also via all of the sidelobes at a lower level. If the jammer transmitseither noise or replicates the incoming signal with the opposite gain applied, it canconfuse the enemy radar. This is shown in Diagram (b). Diagram (c) shows the nonjammedsituation, where the target is clearly seen. If the jammer were to sendadditional replications of the original signal with the same delay from each transmissionbut during the radar sweep, the display on the radar would be as seen in Diagram(d). If the pulse trains are sent at other intervals, then targets would appear at otherranges and bearings. If noise is sent instead, then the radar would be de-sensitised andthus may not be able to detect any targets.The main problem with inverse gain jamming is the power required to overcome theradar antenna directionality. This is likely to result in very low sidelobes and thusthe jammer has to be very powerful. Additionally, the radar can be designed with(a)(c)c·CiiOJOJ>a;a:Radar screen (no Jamming)(b)(d)c·CiiOJOJ.:::roa;a:Radar screen (Inverse gain jamming)Figm·c 18.8Inven,c gain jamming.