Application of Metalines to a Low-Profile Antenna Array for CP Multibeam Generation in the Elevation Plane

A novel application of metalines to a low-profile antenna array is presented, enabling circularly polarized (CP) multiple beams within the elevation plane. The realization is based on five key specifications at the design frequency of fD = 3 GHz: a low-profile antenna structure of less than 0.05 wavelengths, beam directions at elevation angles of approximately θ = −20°, 0°, +20°, and +40, a gain of at least 7 dBic, an axial ratio not exceeding 3 dB in the beam direction, and a reflection coefficient scattering parameter below −10 dB. The realization process consists of three main steps. First, dispersion diagrams are created for four types of CP cells (U1, U2, U3, and U4) in compliance with the specified low-profile structure and beam directions at fD. Second, four metalines M1, M2, M3, and M4 are individually constructed using U1, U2, U3, and U4, respectively, and their radiation characteristics are analyzed to determine the number of cells that meet the specified gain characteristics. Third, the individually constructed metalines are integrated into an antenna array, and simulations are conducted to optimize the space between neighboring metalines, considering the specified axial ratio. Note that the simulated performance, which meets all specifications, is validated through measurements of a fabricated metaline antenna array.