Quad-Band Quasi-Isotropic Antenna for Massive IoT of 6G

Quasi-isotropic antennas are essential to the massive Internet of Things (IoT) of 6G for mobile smart devices, such as uncrewed aerial vehicle (UAV)/uncrewed ground vehicle (UGV) and smart glasses. However, until now, present quasi-isotropic antennas can achieve at most two discrete frequency bands. It is because of the substantially increased structural complexity with the increased number of frequency bands. Since dual-band property is much far from the requirement of massive IoT, we investigated a novel method for multiband (>2) quasi-isotropic antennas. This method combines two inductor-embedded U-radiators, manipulates and purifies the four isotropically radiated modes, and excites all of them simultaneously by wideband-matching capacitive coupling feeding. Consequently, four isotropically radiated frequency bands are produced with a highest-to-lowest frequency ratio up to 3. More importantly, this method has great potential to achieve even more frequency bands for future massive IoT applications. This research releases quasi-isotropic antennas from the constraint of dual frequency bands, which impedes the advances of 6G massive IoT. © 2025 IEEE.