Phased array minimum size
Just like lens apertures and loadspeaker arrays, a phased array antenna needs physical width to be able to focus a tight beam.

The tightest beam you can form is limited by the diffraction limit for that width, in the ballpark of wavelength/array_width. To get a 'reasonably' focussed beam, you will need an array width 'many' wavelengths.

I notice from the comments that you want to use 24GHz, which has a free-space wavelength of 12.5mm, which suggests that on the face of it, the physical width of the array you need is going to be the least of your problems. Then you want 1 wavelength width at 10m, or about 1mradian beam width. That's going to need an array width of the order of 1000 wavelengths or >12m, which is totally impractical (not that 24GHz is practical for an amateur). You may need to rethink your specifications.