. Airborne radar. Airplanes; Guided missiles. 462 REGULATORY CIRCUITS signal fading period, it is necessary to prevent the antenna from being moved in space away from the target direction by own-ship's motion. Here the stabihzation loop plays a major role in attenuating antenna space motion caused by aircraft motion. Usually, the attenuation needed is not extremely large, because when the radar error signal (which is also the antenna rate command) fades, it is replaced by the thermal noise of the radar receiver. As is shown in Fig. 8-40, this noise causes the antenna in a. Antenna should be wi
. Airborne radar. Airplanes; Guided missiles. 462 REGULATORY CIRCUITS signal fading period, it is necessary to prevent the antenna from being moved in space away from the target direction by own-ship's motion. Here the stabihzation loop plays a major role in attenuating antenna space motion caused by aircraft motion. Usually, the attenuation needed is not extremely large, because when the radar error signal (which is also the antenna rate command) fades, it is replaced by the thermal noise of the radar receiver. As is shown in Fig. 8-40, this noise causes the antenna in a. Antenna should be within the Shaded Area 95% of the Time After the Radar Signal Fades Fig. 8-40 Antenna Drift During Radar Signal Fade. wh( K is per cent modulation/degree tracking error r is time between radar pulses coc is track loop bandwidth, rad/sec / is amount of integration in track loop / is time in seconds Ad is antenna drift angle in degrees Typical Values 50%/deg 1 X 10-3 sec 6 rad/sec > 10 : 1 0 < / < 5 0< 15° typical system to drift away from the desired position by as much as ° in 3 seconds. Thus, even if the stabilization loop operated perfectly, the noise commands would probably drive the antenna off target. Actually, the positional accuracy of the antenna cannot be maintained in space without a radar signal to provide a space reference. Sufficient accuracy for fire-control computation cannot be obtained, and it is only necessary to prevent the antenna from being displaced from the target sight line by more than the antenna beamwidth, which may be between 1° and 15°, to ensure that tracking will be resumed when the target signal strength increases again. Therefore, for the system of Fig. 8-40 it would be well to limit the duration of the fading period to a time less than 3 seconds. If the system is not returned to search at this time, the antenna would probably drift from the target sight line and prevent resumption of tracking. An. Please note that these images
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Keywords: ., bookcentury1900, bookcollectionbiodiversit, booksubjectairplanes
