Whole Sub-6 GHz Multiorder-Dual-Degenerate-Modes Loop Antenna in Mobile Smart Devices for IoT Applications

Mobile smart devices, such as smart glasses, smartwatch, smartphone, and uncrewed aerial vehicle (UAV), have rich capabilities of Internet of Things (IoT). They are so handy and ready-to-use that interfacing with the ubiquitous IoT nodes becomes much easier. Mobile smart devices' capability of multiprotocol massive IoT relies on enough bandwidth of their antennas. However, the small size results in a higher quality factor (Q-factor) of the antennas, which severely constrains the bandwidth. In this article, we proposed a novel feeding mechanism that can excite and detune dual-degenerate modes for multiple orders of a loop antenna, compared with present loop antennas' one single mode/resonance for each order. This loop antenna significantly increases the number of the excited modes/resonances up to 12, thus covering 0.73-7.10 GHz, including the whole sub-6 GHz band, which is several times that of the present loop antennas. Further, we demonstrated its size-compressing method. An even smaller folded multiorder-dual-degenerate-modes loop antenna was applied to smartwatch-size devices. It achieves a bandwidth of 1.74-8.87 GHz, which is several times that of the present smartwatch antennas. The proposed method requires no impedance-matching networks, multiports, switches, or tuners, offering ultrabroadband, low-loss, and cost-effective advantages. Because of its ultrabroadband property, it provides a ready-to-use antenna solution to massive IoT, ultrawideband (UWB) energy harvesting, and multiband cellular network communication for mobile smart devices. © 2025 IEEE.