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.