How can we calculate the distances between antennas?

What are the factors and parameters that we should take in consideration when we put adjacent antenna (co-located)?

And how can we calculate the distances between antennas ?

any answer????

well ur question is a bit hard to answer, we dont know either ur are taking about elements of same type or any other antenna is the enviroment

anyways first thing u must consider its spacing, the spacing between to antenna is very important as u increase spacing so does the beamwidth of main lobe decreased and also effect the minor lobes which gain will also increase and becomes nearly equal to main lobe gain.
if u decrease the pattern will become omi directional.
second thing the mutual impedence that will increase or decrease as u increase or decrease spacing. this will lead u to complications in matching with transmission lines
anyways i tried my best to explain if u want more info then post me in detail.

Added after 5 minutes:

the rule of thumb for antenna distance is that use lambda by finding
lambda=(c)/freq
then decide what u want, spacing of what type that suite ur pattern
acutual length of antenna can be find also by
lambda=468/freq(MHz)

with non homegenous type of array its xtreamly difficult to calculte the effects, you can only simulate it, and for homogeneous type it is used for increasing gain, and directivity as saif said to adjust the radiation pattern and main lobe, consult Anteena theory: analysis and design by C. A balanis it has couple of chapters on it

Thank you saif haider & mfarhan1 for your response,

I am sorry about unclear question; I am talking about this structure of antenna (see attached image)

And all antennas are same type.

Should I have the antenna pattern and how can I use it?

Saif (or anyone can help) please explain more about using (lambda) (e.g. how many lambdas, etc.)

And I would to know that should I take in consideration the power or no. of lambda or antenna pattern


please saif, i need some Explanation about this