Satellite Dish Skirts

[jonovid]

why did this 1960s dish antenna have this skirt?
this antenna is of a satellite navigation system or first generation Global Positioning System

1967 Navy Satellite Navigation; IBM 7094; AN_UYK Computer History Archives
12:46 on the video to see the dish antenna with its skirt

[A.Z.]

wild guess: mechanical reasons ?

[Bicurico]

My guess is that this is a shield against background noise.

https://www.bell-labs.com/about/history/innovation-stories/confirming-big-bang/

[jonovid]

In the meantime  I did some more research.
looks like this is an attempt at weatherproofing the dish.
at a time before the use of weatherproof radomes.
by adding a roof or skirt to keep the weather out of the underside of the dish were the elevation & azimuth tracking geared motors are

so seems to have nothing to do with the radio frequency functionality of the dish.   
its a type of weatherproof skirt.