You wouldn’t use CAT6 to a microwave antenna.
It would be something like LMR400 or LMR600 cabling (very thick).
If you would run CAT6, then the radio transmitter must be mounted on/near the antenna, the antenna would hook to the transmitter and the CAT6 is just carrying ethernet traffic to that device from your networking device, (router, etc.). in that scenario the CAT5/6 cabling would still have to follow the standard 100 meter, (328 feet) rule of thumb.
this information was supplied to me via a very good friend, Randy Perry, at Domain Logic
Carrie Higbie says:
If you are looking at Cat 6 for data – you are limited to 100m. However in some situations, category 6 won’t reach 100m (for 10GBASE-T) or if you are planning on supplying a proprietary amount of Power over Ethernet. The distance of 100m includes the equipment cords at both ends and needs to be decreased as the cord length increases.