[amsat-bb] 2 ghz antenna question

Hello,

I know this is off subject, I am looking for ideas on stacking 2 antennas. I am doing a 25 mile WiFi link on 2 GHz using 1 3 foot grid dish with horizontal polarity. I have a power divider and a second dish that I want to mount directly above the first antenna.

Is the vertical spacing critical? Is there any advantage over close spacing, ie. increase gain or wide spacing to give better path fade protection.

Thanks for your time.

Chris N6ICW