In addition to traditional linear Doppler shift, the angular Doppler shift in vortex electromagnetic wave (VEMW) radar systems carrying orbital angular momentum (OAM) can provide more accurate target identification micro-motion parameters, especially the detailed features perpendicular to the radar line-of-sight (LOS) direction. In this paper, a micro-motion feature extraction method for a spinning target with multiple scattering points based on VEMW radar is proposed. First, a multi-scattering-point spinning target detection model using vortex radar is established, and the mathematical mechanism of echo signal flash shift in time-frequency (TF) domain is deduced. Then, linear Doppler shift is eliminated by interference processing with opposite dual-mode VEMW. Subsequently, the shift in TF flicker is focused on the reference zero frequency by the iterative phase compensation method, and the number of scattering points is estimated according to the focusing effect. After this, through the constructed compensation phase, the angular Doppler shift is separated, then the angular velocity, rotation radiusand initial phase of the target are estimated. Theoretical and simulation results verify the effectiveness of the proposed method, and more accurate rotation parameters can be obtained in the case of multiple scattering points using the VEMW radar system.

In this letter, an ultrathin polarization-converting transmissive Huygens element is proposed achieving nearly 100% transmission efficiency for circularly polarized (CP) incident waves. The element consists of a single-layer dielectric substrate with a thickness of only 0.03λ0 and asymmetric S-shaped patches located on both sides. By utilizing surface currents flowing in the reverse direction of the upper and lower patches to form a magnetic dipole, while generating an electric dipole in the orthogonal direction, the electromagnetic response satisfies the Huygens resonance requirement, which makes the transmitarray extremely high efficient for transmission. The independent regulation of CP beam and 360° phase coverage can be flexibly achieved by adjusting rotation angle of the element. The designed element is experimentally integrated to form a metalens antenna to generate directional beam with high gain and low sidelobes. The measured results show that the achieved peak gain of 24.4 dBi at 9.8 GHz with the peak aperture efficiency of 51.3%, which well demonstrated the advantages of low profile, high efficiency, and easy integration of the designed transmitarray structure. Above all, the proposed metalens antenna exhibits superiority for further being applied in device-to-device satellite communications.

A circularly polarized (CP) multiplexing spin-decoupled transmitarray (TA) antenna is proposed, which can realize distinct wavefront manipulation of co-polarized and cross-polarized components under left-handed circular polarization (LCP) and right-handed circular polarization (RCP) incidence, thereby enabling independent beamforming of four CP channels in transmission. By utilizing a receiver-transmitter configuration, the phase shift of each meta-atom can be independently tuned by adjusting the rotation angle of the top and bottom patches, thus achieving complete decoupling of distinct polarization component modulation with reduced complexity. As proof of the concept, a Ku-band aperture-shared TA with quadruplex channels is manufactured and experimentally measured. The measured results demonstrate good agreement with full-wave simulations. For LCP radiation, the measured results indicate that the 2 dB axial ratio (AR) and gain bandwidth for RCP/LCP are superior to 21.8% (11.4-14.2 GHz) and 16.3% (11.8-13.9 GHz), with two independent beams pointing at (10°, 0°) and (20°, 90°), respectively. Similarly, for RCP radiation, the LCP/RCP beams point at (10°, -135°) and (15°, 130°) with the measured 2 dB AR and gain bandwidth exceeding 30.3% (10.9-14.8 GHz) and 14.7% (12-13.9 GHz). In addition, the total maximum aperture efficiencies for LCP and RCP radiations reach 25.4% and 25.3% at 12.7 GHz. The proposed TA offers an alternative avenue for designing a multifunctional antenna for high-throughput satellite communications.