A Compact Quasi-Isotropic Shorted Patch Antenna

A compact shorted patch antenna with quasi-isotropic radiation pattern is proposed in this paper. The antenna consists of a radiating patch, a small ground plane that has the same dimensions with the top patch, and a metallic sidewall which connects the former two. A coaxial probe is used to feed the antenna and excite its fundamental TEM mode, whose magnetic field generates surface electric current on the shorted sidewall and electric field generates surface magnetic current on the open-ended aperture. Due to the inherent properties of the electric and magnetic fields, the corresponding currents are found not only perpendicular but also quadrature with each other, and, therefore, the patch antenna can provide a quasi-isotropic radiation pattern without involving complex feeding circuit. To verify the theory, a prototype operating at 2.4-GHz WLAN band was designed, fabricated, and measured. Reasonable agreement between the calculated, simulated, and measured results is obtained. It has been shown that the difference between the maximum and minimum radiation power densities is ~2 dB over the entire spherical radiating surface, and the difference can be further reduced to ~0.9 dB by using a lower profile.