Compact Loop Antenna Enabling Enhanced Lower-Hemisphere Radiation for Wireless Earphones

Achieving efficient downward radiation within the limited space of wireless earphones remains a significant challenge, which contributes to maintaining reliable links with smartphones. This letter proposes an earphone antenna that realizes enhanced lower-hemisphere radiation on the head by employing an optimized compact loop configuration. The fabricated prototype exhibits a −6 dB impedance bandwidth fully covering the ISM-2.4 GHz band. Measurements demonstrate an average efficiency of −9.1 dB and a lower-hemisphere radiation proportion (LHRP) of up to 71% under on-head conditions. These results verify the feasibility of the proposed design and indicate its strong potential for future development in wireless earphone applications.