Design of Triple-Band Antenna for Metal-Bezel Smartwatches With Circular Polarization in Both GPS L5/L1 Bands

A triple-band antenna, operating in the global positioning system (GPS) L5/L1, and BT bands with circular polarization (CP) for the GPS L5/L1 bands, is proposed for metal-bezel smartwatches. The proposed antenna consists of two metal rings, two stubs, a plastic insulator, three capacitors, and a substrate with ground and matching network (MN). The operation across three bands with CP for GPS L5/L1 bands is analyzed using characteristic mode analysis (CMA), where two capacitors for achieving CP in the GPS L5/L1 bands and a third capacitor for extending the bandwidth in BT band. An antenna prototype shows that the −6-dB impedance bandwidths on the wrist model (WM) for the GPS L5, L1, and BT bands are 53 MHz (1146–1199 MHz), 170 MHz (1494–1664 MHz), and 245 MHz (2287–2532 MHz), respectively. Average efficiencies are −9 dB (12.6%) for GPS L5 band, −6.4 dB (24.6%) for L1 band, and −6 dB (25%) for BT band. Also, the prototype demonstrates robust RHCP performance within the GPS L5/L1 bands, achieving 3-dB AR bandwidths of 20 MHz at both 1168–1188 MHz (for L5) and 1570–1590 MHz (for L1) on the WM. This triple-band design, featuring wide bandwidths in the GPS L5/L1, and BT bands and effective AR for GPS L5/L1 bands, shows promise for practical application.