SLB

Radar Glossary

Radar — SLB

 

 

 

 

 

 

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Information on SLB

Antennas with poor sidelobe performance can be improved by using SLB techniques. Even antennas with good sidelobe performance can benefit from SLB especially in the presence of jamming. In SLB, a second antenna (an omnidirectional antenna) is set-up near the main radar antenna.
     The role of this second antenna is to alert the system to the presence of jamming. An important point to note is that the omnidirectional antenna has a gain higher than that of any of the radar antenna sidelobes. The main antenna drives the radar display through a switch arrangement. If more energy is coming through the omnidirectional antenna than through the main antenna, the switch prevents any radar information from being displayed.
     The following sections describe three broad scenarios and explain how the SLB circuit responds.
    

  • No jamming present. Under normal circumstances, the radar signals coming through the main lobe of the radar antenna system are much stronger than the same signals coming through the omnidirectional antenna.

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  • Jamming through the main lobe. Note that if jamming is coming through the main lobe of the radar antenna, the SLB circuit still believes everything is normal because the condition it is designed to detect is not apparent. That is, if the jamming signal comes through the main lobe, the signal received by the radar antenna is stronger than the signal from the omnidirectional antenna. In this case, the jamming signal is passed through to the processor and display. The receiver may well be saturated and the display affected, but at least the operator can be confident of the direction of the jamming signal.

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  • Jamming through a sidelobe. If jamming starts to come in through one of the radar antenna's sidelobes, the omnidirectional antenna receives a stronger signal than the main radar antenna. In this case, the summing point detects the unusual situation and feeds into the switch to stop momentarily the main radar antenna signal from passing to the processor and display. This continues until the situation returns to normal (main radar antenna signal strength is greater than omnidirectional antenna signal strength). The receiver may not receive a signal for some time in this case, especially if the jammer can maintain jamming throughout the scan of the radar. In this case, the switch is "off" until either the jamming stops, or passes through the antenna’s main beam.

    •      Jamming may interfere with the radar operation for an extended period of time if SLB is used. This is a problem as the radar system is incapable of detecting valid target returns during the jamming period. The main advantage of SLB in this situation is that the operator knows from which direction the jamming is entering the radar, allowing some action to be taken.


    Other topics in our resources on Radar related to SLB include: 
     
  • sidelobe cancellation (SLC)
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  • sidelobe control

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