Hello,

I  believe a planar array is a flat array of dipoles. This sort of thing was called a bedspring antenna in WWII. The beam is always aimed normal to the plane of the plate. It is steered mechanically. The dipoles are all fed in-phase to achieve this.

A phased array looks the same, but the phase of each dipole is controllable, so the beam is steered electronically.

Hope this helps you !

All the best!