In the antenna design we used both theoretical
(infinite ground) and experimental (finite ground)
approaches. It was found that in order to obtain a
favorable coupling between the patch and the
feeding line, as well as to increase isolation,
displacements of the slots off the patch principal
symmetry axes were hard to avoid. Improvements
were obtained when the coupling slot in the ground
was arranged partially out off the patch outline (ref.
Fig. 2). An obvious drawback of this solution is the
extension of the area that must be reserved for each
element. However, the benefit is that enough space
is available for mounting a wideband directional
coupler under the patch.
The effect of slot displacement along the x and y
axes on the center frequency and bandwidth shows
when the slot is hidden entirely under the element,
the impedance match deteriorates (see Fig. 4).
Pushing the slot part out the patch results in