A Dual-Port Dual-Band Dual-Circularly Polarized OAM-Generating Folded Transmitarray Antenna Based on Polarization Conversion of Vortex Waves

In this study, an orbital-angular-momentum (OAM)-generating folded transmitarray antenna is proposed. The antenna is fed by dual probe ports that are excited to generate right-handed and left-handed circularly polarized (CP) vortex waves in the lower and higher frequency bands, respectively. This is principally conducted based on the linear polarization-to-circular polarization conversion of vortex waves, which primarily depends on phase and amplitude control of a transmitarray (TA) and a reflectarray (RA). The linearly polarized (LP) vortex waves are generated from the RA, while the conversion of LP-to-CP vortex waves with OAM mode l = -1 is achieved when the electromagnetic waves pass through the TA. The measured operating bandwidth (|S₁₁| < -10 dB and AR < 3 dB) of the proposed antenna was observed to be 9.1–9.3 GHz (4.4%) and 11.1–11.5 GHz (6.1%) for the lower and upper bands, respectively. The measured antenna peak gain reached up to 12.1 dBi and 15.3 dBi for the lower and upper bands, respectively. The antenna dimensions were maintained at 7.85λ₀ × 7.85λ₀ × 1.41λ₀, where λ₀ represents the wavelength in free space at the center frequency of the lower band, while the profile-to-focal-length ratio was approximately 1/5.4, indicating a large decrease in profile.