Unbalanced Current Mode Predistortion Inspired Design Approach to Self-balanced Planar Semi-Isotropic Magnetic Dipole Antennas

A novel design approach to circumferentially short-circuited, circular sector magnetic dipole antenna with nearly upper hemispherical coverage property is proposed. By extending the circumference of the ground plane of a planar magnetic dipole antenna, the unbalanced electric currents are manipulated to flow in the circumferential direction, such that the unbalanced sheath currents flowing on the vertical feed cable can be effectively suppressed to yield a self-balanced operation. Based on the idea of unbalanced current mode predistortion, external sleeve choke is eliminated and a simple closed-form formula is derived to empirically estimate the extended angle of ground plane. Two prototypes with different flared angles are investigated and validated at 3.6GHz band. The proposed antennas exhibit nearly hemispherical coverage characteristic in the upper spherical zone. Good agreement among the theoretical, simulated, and measured results has evidently verified the proposed antenna design approach.