distance between antennas on the tower

Please let me know if there is some sources to help me to determine the minimum safe distance between two antenna on the tower, depending on parameters such as antennas' patterns, carrier frequencies, and ....
Thank you very much!

Hi farfar

look at http://wireless.fcc.gov/siting/

and the pdf

PL

Each nation has it's own laws and regulations.
Usually US laws are more permissive than Russian one.
In Europe the limits fixed by the law of each nations are more similar between them but not exactly the same.
In the country where i'm living, Italy, for professional operator the limit is max 20 V/m (under certains conditions) and an "attention" level has been set to 6 V/m.

I prefere the 6V/m limit.

To convert V/m to W/m^2 use the 377 Ohm.

To calculate the distance, take care if you are on far field (use Friis formula) or Fresnel region (E field change very little vs. distance)