A Wideband Millimeter-Wave Dual-Mode OAM Metal Lens Antenna

This article introduces a novel dual-mode orbital angular momentum (OAM) metal lens antenna for millimeter-wave applications. The proposed lens antenna enables the independent mode manipulation of the transmitted OAM beams for respective left-handed circularly polarized (LHCP) and right-handed circularly polarized (RHCP) illumination within a wide frequency range. Such functionality is achieved by designing a novel quadruple-ridged waveguide element with the capability of providing the simultaneous geometric phase and propagation phase control of the transmitted waves by rotating the ridges and tuning the waveguide height, allowing for the irrelevant synthetic phase profiles of the transmitted waves for LHCP and RHCP incidences. For demonstration, four lens antennas with different OAM modes are designed and discussed first, and a lens transmitting $l =0$ OAM mode beams for RHCP excitation and $l = +1$ OAM mode beams for LHCP excitation is fabricated and measured. A dual-circularly polarized (dual-CP) horn with two ports for respective LHCP and RHCP wave generation is used as the feed. Both simulated and measured near- and far-field results validate the effectiveness of the proposed dual-mode OAM lens antenna. The measured effective bandwidths with joint −10-dB impedance, 3-dB axial ratio (AR), and 3-dB gain bandwidths are 33.3% from 22.5 to 31.5 GHz with a peak gain of 22.6 dBi for $l = +1$ OAM mode beams and 37.8% from 22.5 to 33 GHz with a peak gain of 28.5 dBi for $l =0$ OAM mode beams. The obtained mode purities are both more than 0.97 for two states. Due to the merits of wide bandwidth, dual-mode OAM generation, and high-power handling properties, the demonstrated dual-mode metal lens antenna is a promising candidate in millimeter-wave high-capacity communication systems.