Yes, there is a 2 port circulator on every waveguide. One for the 5.8 and one for the 6.5. We recently tested TrangoLink45 units in an underbuild scenario and it worked well without any filtering, etc. Our 6GHz microwave equipment did not suffer any ill-effects… they are old-school analog video microwaves and I suspect they can take whatever the puny 5.8 equipment can dish out. I have another thread discussing this and the problems I am experiencing with trying to underbuild the Mikrotiks here.
http://forum.mikrotik.com/t/42km-ptp-link-problems-rb433ah-r5h/30277/1
Right now, I am ordering some bandpass filters for 5.8Ghz in hopes that keeping the 6GHz signal away from the 5.8 equipment will improve performance of the Trango and help get the Mikrotiks working on the links (can’t afford 7 sets of Trangos for this project.) Though if you check out that thread you will see in my testing of the R5H units I may have blown them up. So there is much left to isolate and test here. If you have any input on the matter I would love to hear it.
As for my 5.4GHz idea, that is a moot point now. I have decided not to get greedy.