A Wideband Millimeter-Wave Metal-Only Dual-Mode OAM Transmit-Reflect-Array Antenna

In this communication, a wideband metal-only dual-mode orbital angular momentum (OAM) transmit-reflect-array (TRA) antenna is proposed. The transmission and reflection modes of the antenna are dependent on the polarization of the incident wave, and a cascaded metal waveguide structure consisting of a square waveguide and a dual-cavity waveguide is designed as the element. The element not only allows for a wideband polarization selective performance of transmitting x-polarized incident wave and reflecting y-polarized incident wave but also provides independent phase control capability for the transmitted and reflected waves. To validate the proposed methodology, four TRA antennas generating OAM beams with different modes are designed and discussed first, and a prototype with transmitted ${l} = +1$ OAM mode beams for x-polarized incidence and reflected ${l} = 0$ OAM mode beams for y-polarized incidence is fabricated and measured. The measured results agree well with the simulated ones, demonstrating that ${l} = +1$ OAM mode beams can be generated from 23 to 34 GHz with a peak gain of 22 dBi, and ${l} = 0$ OAM mode beams can be generated from 24.5 to 34 GHz with a peak gain of 28.6 dBi. The calculated mode purities for both transmission and reflection modes are more than 0.93.