Fully Printed 3-D Antennas With Wideband Radiation Isotropy Based on Annular Currents Models

Internet of Things (IoT) devices require orientation insensitive communication and a small footprint. Wireless communication should be maintained across the whole operation band, hence electrically small antennas (ESAs) with wideband radiation isotropy are also desired. This paper proposes a theoretical model based on annular ring currents to synthesize quasi-isotropic antenna radiation patterns. The theoretical model shows that wideband radiation isotropy can be achieved by optimizing the combination of azimuthal currents. We subsequently present spherical and cubical ESA designs that achieve measured wide impedance and radiation isotropy bandwidths exceeding 10% for the GSM900 band. The ESAs were fully printed, with substrates 3D printed and metallization applied using screen printing. Despite the electrically small sizes and low cost fully printed fabrication, the antennas achieved approximately 90% radiation efficiencies. The proposed designs are low cost because of additive manufacturing, can have embedded electronics because of their 3D structure and have the largest radiation isotropy bandwidth for an electrically small antenna in published literature.