Theory and Design of a 3-D Antenna With Wideband Radiation Isotropy

Internet of Things (IoTs) applications require compact antennas with quasi-isotropic radiation patterns to maintain orientation-insensitive communication. Moreover, IoT devices have operational bandwidth requirements and they operate at multiple frequency bands. Therefore, an antenna that can maintain radiation isotropy for a wide bandwidth is promising for IoT applications. In this communication, we present the theory of two orthogonal annular currents with first azimuthal harmonics to obtain wideband quasi-isotropic radiation patterns. Based on the proposed synthesis approach, we determine the optimal phases and magnitude ratios between the currents. This optimized model provides 0.73 dB gain variation at the center frequency and 60% of −7 dB radiation isotropy bandwidth. The sensitivity of the radiation isotropy bandwidth to deviations of the model’s parameters is investigated. Inspired by the proposed theoretical model, we also present an antenna design consisting of four dipoles bent around a sphere with an electrical size (
$ka$
) equal to 1. The fabricated prototype, which is fully printed, demonstrates a measured impedance bandwidth of 70%, a radiation isotropy bandwidth of 33.6%, and an average radiation efficiency of 90.7%. This is the largest reported radiation isotropy bandwidth in the literature.