Dear Cadi

This is a signal processing based approach: 

http://publications.lib.chalmers.se/records/fulltext/95362.pdf

this may not be so applicable, but still interesting

http://www.mathworks.com/company/user_stories/delphi-develops-radar-sensor-alignment-algorithm-for-automotive-active-safety-system.html

regards

Gerro

Matlab 2013 has a phased array tool box which can give direct functions for your purpose.

may have a look into:

Mahafza, B.R. Radar Systems Analysis and Design using Matlab, Chapman & Hall/CRC, 2nd Ed., 2005

Dear Dardi,

If you know what is the feeding function of the array element and only interested to see the radiation behaviour, then the suggested resources by other experts are usefull. You can also write your own program to find the radiation. it is not that much difficult.

However, if you have a desired radiation pattern in mind and eager to find the appropriate feeding of the array element (array synthesis), then it is another stroy. 

Normally the classic ways of feeding would not be very effecient (Dolfchebychef, fourier, ...). In this case you should look at the global optimization techniuqes.

Hope to be usefull.

Mohammad