Here are some typical XM and Sirius antennas...
http://www.xmradio.com/catalog/product_category.jsp?type=Antenna
http://shop.store.yahoo.com/wvccsi/car.html
http://www.crutchfield.com/S-hYrC4TcW0C5/cgi-bin/prodview.asp?I=019XM5013F
http://www.crutchfield.com/cgi-bin/S-hYrC4TcW0C5/ProdView.asp?s=0&c=3&g=80000&I=113CXSR10&o=m&a=0
http://www.crutchfield.com/cgi-bin/S-hYrC4TcW0C5/ProdView.asp?s=0&c=3&g=80000&I=130AN90XM&o=m&a=0

Some antennas have two jacks - one for satellite, the other for ground signals. FAKRA SMB connectors seem to be what's on the ends.

A little expensive, but worth checking out in more detail.

Konrad