Design of Quad-Band Antenna for Metal-Bezel Smartwatches With Triple-band Circular Polarization in GPS and Tiantong Tx/Rx bands

Since the demand for global connectivity continues to grow, enabling satellite communication in smartwatches has become crucial. Integrating a satellite communication antenna into smartwatches extends their functionality beyond traditional GPS positioning and BT connectivity, ensuring reliable connectivity in emergencies. This work proposes a quad-band antenna covering the GPS L1, Tiantong TX, Tiantong RX, and BT bands, with triple-band CP in GPS L1 and Tiantong TX/RX bands, which is suitable for integration into metal-bezel smartwatches. The CP operation in the three bands is investigated through characteristic mode analysis (CMA), with one inductor enabling CP in the GPS L1 band and two inductors achieving CP in the Tiantong TX/RX bands. Besides, three bandpass filters are integrated to isolate the GPS and Tiantong bands while distinguishing between the Tiantong TX and RX bands. A fabricated prototype demonstrates right-hand circular polarization (RHCP) in the GPS L1 band and left-hand circular polarization (LHCP) in the Tiantong TX/RX bands, achieving 3-dB axial ratio (AR) bandwidths of 74 MHz (1536–1610 MHz) for GPS L1, 40 MHz (1978–2018 MHz) for Tiantong TX, and 35 MHz (2163–2198 MHz) for Tiantong RX. Additionally, the measured average efficiencies on the wrist for GPS, Tiantong Tx, Tiantong Rx, and BT bands are 11.7%, 17.8%, 17.8%, and 15.8%, respectively. With the CP performance in the GPS, Tiantong Tx/Rx band, the designed quad-band antenna presents a promising solution for next-generation smartwatches supporting satellite communication.