What type of cable do I need to connect my Stratus to a remote antenna?

The cable needs to be a 50 ohm coaxial cable.  RG58 will do, but RG400 is better.  Sporty's sells a cable to connect your Stratus to the antenna here:

     10 Ft. Replacement ADS-B Cable For Stratus

If your antenna has a BNC female adaptor, here is a BNC Male to SMA Male Coax Adapter:

     BNC Male to SMA Male Coax Adapter