The geometry of a rectangular microstrip antenna fed by an openend
coplanar waveguide is shown in Fig. 1. We assume that the
substrate and the ground plane extend to infinity in the x and y
directions and that the conductors are perfectly conducting and of
negligible thicknesses. The coordinates are chosen such that the
ground plane coincides with the zy-plane, the coplanar waveguide
is symmetric about the z-axis, and the y-axis is placed along the
edge of the end of the coplanar waveguide. To simplify the analysis,
the patch is also placed symmetric about the z-axis; nevertheless,
our theory can easily be modified to allow asymmetric placement of
the patch.
By invoking the equivalence principle and applying suitable boundary
conditions, the magnetic field H" in the slot aperture and the
electric field Ep on the patch surface can be expressed as