Radar Low Altitude / Sidebeam Compensation Switch Clarifications

[Charly_Owl]

Hi folks,

 

Currently doing a bit of research on the MiG-21, and I'm not quite sure what the Low Altitude / Sidebeam Compensation Switch really does. The manual isn't exactly clear on that.

 

• The UP (Low Altitude) position of the switch appears to tilt the antenna up 1.5 deg for Low Altitude. In practice... what is the use of this mode? Is it to be used to avoid scanning ground clutter when you are flying close to the ground?

• The MIDDLE (Sidebeam Compensation) position of the switch appears to "clean" the image of the radar by removing the lower side lobes. Could anyone elaborate how this works practically speaking?

 

Thanks in advance,

 

Chuck

Edited May 10, 2021 by Charly_Owl

[Sideburns]

There is some interesting information in this thread 

 

Also a link to the Polish manuals http://www.muzeumlotnictwa.pl/index.php/digitalizacja/katalog/2309

Edited May 10, 2021 by Sideburns
Corrected German RP21 manual for Polish RP22 manual

[Frederf]

The bottom position of the switch is normal pattern and full gain. The medium position of the switch is normal pattern and reduced gain. The up position of the switch is reduced pattern and reduced gain.

 

The lower two positions do the exact same mechanical pattern of antenna but there is a filter applied. It doesn't remove entirely the side lobe but it makes it not overpowering. Absolute detection range is reduced even for contacts above. A target which is barely able to be seen by unfiltered radar (at high altitude clear of ground return) will not be seen with the switch in the middle position.

 

Normally the scan pattern is 10 lines. In the up switch position the bottom 1 or 2 lines are removed leaving 8 or 9 scan lines. The result is the detection elevation is no longer 1.5 degree below horizon but 1.5~2 degree above horizon. The upper elevation detection angle is unchanged. Combined the compensation channel and removal of the bottom area of the scan sector provides the most protection against ground interference.