Design of Dual-Band Antenna for Metal-Bezel Smartwatches With Negligible Wrist Effects Utilizing Coupled-Feeding Technique

Abstract

Since smartwatches are usually worn on the human wrist, the impact of the wrist on antenna performance (frequency shift and efficiency reduction) is crucial for practical applications. In this communication, a dual-band antenna for metal-bezel smartwatches, which is almost unaffected by the human wrist, is proposed and studied. Unlike traditional smartwatch antenna designs, which directly excite the metal bezel, this work employs a coupled-feeding technique, where the metal bezel is coupled-fed by the coupling metal. The proposed coupled-feeding technique significantly enhances the vertical electric field, making the impact of the wrist on the antenna performance negligible. A prototype demonstrates that, with the coupled-feeding technique, the frequency shift is nearly 0 MHz in the both GPS L1 and Bluetooth (BT) bands. Meanwhile, the efficiency reduction is just 0.3 dB in the GPS L1 band (from −3.8 to −4.1 dB) and 0.2 dB in the BT band (from −3.6 to −3.8 dB). Additionally, with the coupled-feeding technique, the proposed antenna consistently demonstrates stable and reliable performance, whether worn on the left or right wrist or with different coupled-feeding positions. In summary, the proposed antenna, utilizing the coupled-feeding technique, demonstrates slight frequency shift, exceptionally low efficiency degradation, and excellent performance consistency, making it highly promising for practical applications.