Integrated GPS Antenna with Circular Polarization for Metal-Rimmed Smartwatch Applications

An integrated GPS antenna with circular polarization (CP)is proposed for smartwatches with an unbroken metal rim. By utilizing a small feeding structure in the ground plane, two dominant characteristic modes of the metal rim along the x-axis and y-axis are simultaneously excited for radiation. For CP operation, the time-phase difference between the two modes can be provided by adjusting their resonant frequencies to be inductive and capacitive, which can be further tuned by changing the values of loaded capacitors between the metal rim and ground plane. The proposed technique can generate a 3-dB axial ratio bandwidth of 10 MHz with left-hand circular polarization (RHCP)and right-hand circular polarization (LHCP)at the front side and back side, respectively.