Low-Profile Circularly Polarized Metasurface Antenna Based on Characteristic Angle Compensation

A low-profile circularly polarized metasurface (MTS) antenna is proposed for 5G indoor applications. To balance the intricacy of the feeding network design and that of the characteristic mode (CM) control, a novel modal manipulation method is proposed to generate three axial ratio (AR) zeros. A simple feeding network, comprising three T-shaped power dividers and 90microstrip phase delay lines, excites the coupling slots and provides the first AR zero. The width-to-length ratio of the metasurface patches is adjusted to regulate the degenerate broadside modes of the MTS. The second AR zero is achieved by lowering the first MTS mode and cooperating with the coupling slot mode. The third AR zero is generated by controlling the characteristic angle of two MTS modes. The measured results demonstrate that the proposed circularly polarized antenna is capable of covering 42.3% (3.08-4.73 GHz) impedance bandwidth and 32% (3.3-4.5 GHz) 3-dB AR bandwidth (ARBW) with a low profile (0.03λ0).