A Frequency-Reconfigurable Antenna With Cavity-Backed Annular Architecture for Smartwatches

A frequency reconfigurable antenna with a cavity-backed annular that can switch multiple bands is proposed. The compact size of the antenna allows its structure to be integrated into the housing of a smartwatch. This model is a circular watch with a cylindrical housing. The annular structure has seven controlled grounding branches, which can be adjusted to vary the current distribution by different grounding combinations to produce 18 resonant frequencies. The frequency reconfigurable antenna design for the smartwatch was simulated and measured for each of the 18 resonant bands. The frequency reconfigurable antenna design of this smartwatch was investigated in the simulation and measurement sections for each of the 18 resonant bands, and both results were very similar. The frequency bands cover 2.0-2.36, 2.52-3.14, 3.29-3.47, 3.84-6.42, and 7.22-7.41 GHz, all bands with reflection coefficients below −10 dB. The antenna can work in the 5G NR and IoT bands. The simulations and measurements of antenna gain and radiation efficiency at each resonance point are consistent, with most antennas achieving more than 3 dBi gain and more than 70% of radiation efficiency, showing good performance. This article also analyzes the antenna design structure, operation mechanism, and evaluation of electromagnetic energy absorption. The proposed antenna has reasonable gain, significant bandwidth, and efficient direction performance.