A Low-Profile High Gain Circularly Polarized Metasurface Antenna for IoT Applications

This paper proposes a compact, low-profile slot antenna integrated with a metasurface (MS) layer to realize wideband circular polarization and maintain a consistently high gain for IoT applications. The antenna element uses a C-shaped slot in the ground plane, excited by a microstrip feed to generate the circularly polarized waves. The metasurface layer incorporates mushroom-shaped outer cells and centrally placed slanted-slot elements to broaden the axial-ratio (AR) bandwidth and to maintain a consistently high gain. The metasurface consists of twelve adjacent cells arranged in a mushroom-shaped configuration, with a 45° slanted rectangular slots on four central cells. The simulated and measured results demonstrate strong agreement; the impedance-matching bandwidth is 26.7%, and the axial-ratio bandwidth is 15.7% at a central frequency of 6.8 GHz. Finally, the antenna consistently demonstrates a measurement gain exceeding 8 dBic across the AR bandwidth, with a peak measured gain of 9.6 dBic.