element spac
svarun:
Getting multiple beams out of an antenna array usually requires elements to be spaced apart by at least 1/2 wavelength (element phase center to phase center).
Array designers will sometimes develop antenna arrays with larger element-to-element spacing (or lattice spacing for 2D arrays) so that you get natural grating lobes in visible space. Then they will take the signals off of each element separately and use adaptive signal processing (I think they usually use digital signal processing and do the combining in a signal processor) to synthesize multiple beam directions for the purpose of focusing the array on 2 or more desired signals. In this way, they can also control and place antenna pattern nulls on noise, jammer or clutter sources in order to maximize the overall SNR.
If you have some code for antenna array pattern visualization, try an experiment where you start with either a 1D or a 2D array with center-to-center spacings of about 1/4 wavelength, and then move them apart. You should see the antenna pattern show a grating lobe at the edges of visible space (the horizon) as the elements reach 1/2 wavelength spacing.
You can also achieve multiple beams if you influence the element-to-element phase to "steer" the main beam off of boresight. This can make grating lobes (or you can think of them as extra main beams, depending on your application) appear in the visible space as well.
Good luck,
--Max