selective ac/dc coupling of GBps+ signals

Hello gang, Suppose I wanted a 6GBps+ serial line to be AC or DC coupled to its receiver under software control. What kind of circuit could act as a short-circuit from DC-18GHz or as a coupling cap? I'm thinking maybe some sort of diode switch system but I can't see it. Anything I add to the cap (like a parallel reed relay) will add parasitics when it's deselected. Oh and this has to be small, fit on maybe 1in sq. of PCB real estate. We can already do this job with big microwave relays. Of course insertion loss, etc. has to be small. I'm hoping for 0.1 dB vs a regular coupling cap. This is perhaps optimistic... TIA