Design of Dual-Band Antenna for Metal-Bezel Smartwatches with Circular Polarization in GPS Band and Low Wrist Effect

A dual-band antenna with circularly polarized (CP) in GPS band and low wrist effect for metal-bezel smartwatches is proposed and studied in this article. The proposed antenna consists of a metal ring, a capacitor, a system ground plane with a feeding network, and a metal plane. The dual-band operation with CP in the GPS band is analyzed based on the theory of characteristic mode (TCM), where the CP is achieved by the capacitor. The low wrist effect, which is analyzed based on the electric-field distributions, is realized by a metal plane. On the wrist, with the help of the metal plane, the antenna efficiencies are improved from -9.8 to -6 and from -7.3 to -4.6 dB in the GPS and WiFi/Bluetooth (BT) bands, respectively. In addition, the AR in the GPS band is improved from 4.5 to 2.4 dB. A prototype shows that, on the wrist, the measured return loss is better than 8.6 and 6.7 dB in the GPS and WiFi/BT bands, respectively. The measured efficiencies are -6.6 and -5 dB, respectively, in the two bands. The measured 3-dB AR bandwidth is 30 MHz (1558-1588 MHz). In addition, the proposed antenna has a stable performance on the wrist. The dual-band antenna with high efficiencies in the GPS and WiFi/BT bands, good AR in the GPS band, and stable performance on the human wrist, is promising for practical application.