If you really do have an RP-SMA connector on the end of your antenna
cable, then it appears that you will need one of these:

http://www.wirelessnetworkproducts.c...ROD&ProdID=912

I have a couple of RP-SMA adapters that came with antennas. They
adapt an RP-SMA antenna (made for most routers) to a RP-TNC (your
Linksys).

But you probably want a pigtail.