High-Isolated Coplanar-Fed Circularly Polarized 2×2 Curl Antenna for MIMO Applications

This paper proposes a coplanar-fed circularly polarized curl antenna for MIMO applications, whose feeding element consists of a metal strip and an inner conductor of coaxial line to match the 50Ω system and to ease the fabrication process. The radiation element including a horizontal strip and a curl strip is etched on the Rogers4003C substrate to enhance the robustness of the antenna system. Besides, a design guideline of a high-isolated 2×2 MIMO antenna is provided such that the antenna isolation of > 25 dB can be obtained theoretically. Both the simulation and measurement results are quite in agreement with each other, indicating that the isolation of > 22 dB is achieved within the axial ratio bandwidth of ~ 4%.