Principles of Modern Radar - Volume 2 1891121537

544 CHAPTER 12 Electronic Protectiongate pull-in (RGPI) and velocity gate pull-in (VGPI) are used to explicitly distinguish thedirection of the track gate motion, but this distinction is often ignored.Range gate pull-off and VGPO are said to be coordinated when the two techniques areexecuted in a manner that produces a kinematically consistent false target in both rangeand Doppler dimensions, as described in Section 12.2.4.1 for RFTs and VFTs. A simplecoordinated pull-off might use a constant acceleration, a, in which the range is variedparabolically with time (R = at 2 /2), and the velocity is varied linearly with time (v = at).The pull-off is sometimes defined in four phases: dwell, walk, hold, and drop. Duringthe dwell, the jammer turns on with a strong signal in the same cell as the target return.During the walk, the jammer draws the track gate away from the target. During the hold,the jammer stops moving the track gate and pauses at the current location. During thedrop, the jammer turns off. Any of the phases except the walk phase may be omitted inthe sequence. The pull-off sequence is repeated as needed.The range and velocity track gate stealing techniques might be used for several objectives:to induce large track errors, thereby degrading the radar track quality; to break theradar’s track, forcing time-consuming reacquisition; to transfer the radar track to anotherreturn such as clutter or chaff; and to facilitate the execution of EA techniques, such asangle deception, that require a very high jam-to-signal ratio (JSR) (with no target signalin the denominator of the ratio, the JSR becomes infinite).12.2.4.3 Angle Track DeceptionAngle track deception techniques are used by SSJs to create angle track errors or anglebreak-locks (track breaks) against radars supporting weapon system engagement, such asfire-control radars or RF missile seekers. These fall into two broad categories: on-board,in which the EA signal originates from the target itself; and off-board, in which the EAsignal originates from an object spatially separated from the target being protected [1,2,7].Examples of on-board techniques include inverse gain (IG), swept AM (SAM), AGCdeception, image jamming, cross-polarization (XPOL), cross-eye (XEYE), terrain bounce(TB), and jammed chaff (JAFF). Inverse gain and SAM, described in Section 12.5.8, arelimited to conical scan type angle tracking radars. The AGC deception and image jammingtechniques, described in Sections 12.8.3 and 12.8.2, exploit limitations in the radar receiverdynamic range and image rejection, respectively. Cross-polarization, commonly referredto as cross-pol, and XEYE produce distorted responses of a monopulse angle trackingradar. Cross-pol accomplishes this by generating a signal that is orthogonally polarizedto the radar antenna; XEYE accomplishes this by generating a spatial interference patternfrom two widely separated antennas, causing a warped, or distorted, phase front acrossthe face of the antenna. Terrain bounce is achieved by an SSJ that flies at low altitude andilluminates the terrain. If the reflection from the terrain is stronger than the target returnand any direct-path leakage from the jammer, a homing missile will track the reflectionand fly into the terrain. Jammed chaff is an airborne version of TB: the jamming platformilluminates a chaff cloud with sufficient power to create a spatially displaced target fora homing missile. Both TB and JAFF require directional antennas that minimize directpathradiation to the radar. All of the on-board techniques require very high JSR to beeffective.Examples of off-board techniques are chaff, expendable decoy, towed RF decoy(TRD), and cooperative blinking noise (CBN). Chaff bursts consist of huge quantitiesof small reflective material such as wavelength-sized, metal-coated glass filaments, whichare ejected from an aircraft and then bloom into a large reflective, hovering cloud that