The simplest patch antenna uses a patch which is one half-wavelength-long with the dielectric loading included over a larger ground plane separated by a constant thickness. Electrically large ground planes produce stable patterns and lower environmental sensitivity but of course make the antenna bigger. It isn’t uncommon for the ground plane to be only modestly larger than the active patch. When a ground plane is close to the size of the radiator it can couple and produce currents along the edges of the ground plane which also radiate. The antenna pattern becomes the combination of the two sets of radiators.
The current flow is along the direction of the feed wire, so the magnetic vector potential and thus the electric field follow the current, as shown by the arrow in the figure labeled E. A simple patch antenna of this type radiates a linearly polarized wave. The radiation can be regarded as being produced by the ‘’radiating slots’’ at top and bottom, or equivalently as a result of the current flowing on the patch and the ground plane.