MICROSTRIP PATCH DESIGNS THAT DO NOT EXCITE SURFACE-WAVES

Two variations of a circular microstrip patch design are presented which excite very little surface wave power. Both of the proposed designs are based on the design principle that a ring of magnetic current in a substrate (which models the patches) will not excite the dominant TM0 surface wave if the radius of the ring is a particular critical value. Numerical results for radiation efficiency and radiated field strength from a ring of magnetic current are shown to verify this basic design principle. The proposed patch designs are chosen to have a radius equal to this critical value, while maintaining resonance at the design frequency. These patch designs excite very little surface-wave power, and thus have smoother radiation patterns when mounted on finite-size ground planes, due to reduced surface-wave diffraction. These new patch designs also have reduced mutual coupling, due to the reduced surface-wave excitation. Measured results for radiation patterns and field strength within the substrate are presented to verify the theoretical concepts.