i want install two sextant radio antenna for 5km distance.
one of the tower is (100m+20m for power building) and we install radio antenna on 100m height (for observation Frensel Zone).
i can not install a box on the tower body.
Is 10Ghz allowed in your country? If so, then there are some examples around on the internet for such a system.
Basically its a periscope, you will need to engineer the top reflector carefully and the angles will need to be adjusted by the poor chap that has to install it at the top.
Mesh could be used at the top of the tower as well to lessen the wind loading.
You also might want to research Laser light at that distance..