A Subwavelength Transmit-Array Lens Element Combining Functions of Phase Modulation and Polarization Conversion

Abstract

Advanced applications require transmit-array lenses featuring low profiles, covering 360° phase modulation, and, potentially, polarization conversion. Subwavelength metamaterial elements with multilayers manipulate electromagnetic waves with predesigned phase shifts, resulting in the transmit-array lens’s low profile and light weight. Conventional designs separate the transmit-array lens and polarization converter with two functional devices and suffer from high profiles and complicated mechanical assembly. In order to resolve these issues, a subwavelength lens element combining the functions of phase modulation and polarization conversion is proposed. The metamaterial lens element consists of phase modulation, linear-circular polarization conversion modules, and a metallic via structure electrically connecting these two modules. The multifunctional lens element modulates the transmitted phase with a three-bit phase shift and operates in the frequency range from 24.5 to 27 GHz, with less than −10 dB reflection coefficient, 1 dB transmission loss, and a 2.5 dB axial ratio. A transmit-array lens antenna with the proposed element is implemented to validate the abilities of beam focus and polarization conversion. The gain of the lens antenna reaches 26.3 dBi, with a 3 dB beamwidth of 6.7° and −18 dB sidelobe level, and the axial ratio of the converted circular polarization is below 1 dB. The aperture efficiency of the antenna is 45.2%.