Check the switch for operation as below before you go replacing it; the mast for the antenna is a much more common trouble spot than the switch, and easily fixed.
The center position is neutral; the antenna will go partway up when the radio's turned on, and down when off.
The first stop to either side, spring-loaded, will move the antenna when the radio's on; left is up, right is down. You can use this to adjust the antenna height for best reception.
The second stop to either side, with the switch staying in place, is full motion. You may simply leave the switch all the way left for the antenna to extend all the way whenever the radio's turned on, or leave the switch all the way right and the antenna won't extend at all when the radio's turned on.
If the antenna's working properly, it will always go all the way down when the radio's turned off, no matter what the position of the switch.

If yours does anything else, post your findings here and we'll see if we can help sort it out.

__________________
Craig Bethune

'97 SL500, 40th anniversary edition

'04 Olds Bravada (SWMBO's)
'06 Lexus ES330
'89 560SL (sold)


SL--Anything else is just a Mercedes.
(Kudos to whoever said it first)