Design of a 2.5-D 2-Bit Reconfigurable Transmitarray Element for 5G mmWave Applications

The design of a novel reconfigurable transmitarray (RTA) element with 2-bit phase resolution is proposed. The 2.5-D receiver-transmitter transmitarray structure is adopted. In addition to the 1-bit current reversible dipole, it fully utilizes the longitudinal space for housing an additional 90° digital phase shifter based on a quadrature hybrid coupler with two PIN diodes. Full wave simulations under normal and oblique incidence show that the transmission insertion losses for four phase states are 1.1-1.2 dB at 26 GHz, with a 3-dB transmission bandwidth of 18.3%. The RTA element is able to generate stable performance under large incident angles, which makes it suitable for two-dimensional wide-angle beam scanning. The proposed element design has good 2-bit phase tuning capability. The simple structure with only two metallic layers and four PIN diodes effectively reduces the cost. It is believed to have great potentials for future 5G millimeter-wave applications.