Patch antennas on a spherical body

The far field radiation patterns of wraparound, circular disk and annular ring microstrip patch antennas mounted on a sphere are studied theoretically. The patches are replaced by equivalent magnetic currents based on cavity model theory. The radiation fields are then determined using the modal expansion technique in spherical co-ordinates. Results for a wraparound antenna of a half-wavelength in width, for the broadside TM₁₁ mode of a circular disk antenna and for the TM₁₁ and TM₁₂ modes of an annular ring antenna are given. The accuracy of the simple theory is confirmed by a more rigorous but complicated theoretical approach based on electric surface current model.