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Holography has garnered an explosion of interest in tremendous applications, owing to its capability of storing amplitude and phase of light and reconstructing the full-wave information of targets. Spatial light modulators, metalenses, metasurfaces, and other devices have been explored to achieve holographic images. However, the required phase distributions for conventional holograms are generally calculated using the Gerchberg–Saxton algorithm, and the iteration is time-consuming without Fourier transform or other acceleration techniques. Few studies on designing holograms using artificial intelligence methods have been conducted. In this Letter, a three-dimensional (3D)-printed hologram for terahertz (THz) imaging based on a diffractive neural network (DNN) is proposed. Target imaging letters “THZ” with uniform field amplitude are assigned to a predefined imaging surface. Quantified phase profiles are primarily obtained by training the DNN with the target image and input field pattern. The entire training process takes only 60 s. Consequently, the hologram, that is, a two-dimensional array of dielectric posts with variational heights that store phase information, is fabricated using a 3D printer. The full-wave simulation and experimental results demonstrate the capability of the proposed hologram to achieve high-quality imaging in the THz regime. The proposed lens and design strategy may open new possibilities in display, optical-data storage, and optical encryption.

Metasurface antennas (MAs) have been proposed as innovative alternatives to conventional bulky configurations for satellite applications because of their low profile, low cost, and high gain. The general method of surface impedance modulation for designing MAs is complicated, and achieving broad operation bandwidth remains a challenge because of its high dispersion response. We propose a novel and easy technique to control cylindrical surface waves radiated by a phase-tuning metasurface. Simultaneously, this technique exhibits a considerably wide working bandwidth. A detailed analysis of the radiation mechanism is discussed. A left-hand circularly polarized (LHCP) antenna and a right-hand circularly polarized (RHCP) antenna that are based on the phase-tuning metasurface are simulated and measured. The measured fractional 3-dB gain bandwidth and gain are higher than 17% and 15.57 dBi, respectively, which are consistent with the simulated results. Moreover, 30% 3-dB axial ratio is achieved for the LHCP and RHCP antennas. To the best knowledge of the authors, it is for the first time to realize a circularly polarized broadband MA by using the phase-tuning mechanism. The approach can be regarded as a new starting point for antenna design, thereby paving the way for the development of broadband and low-profile antennas for future satellite communication.

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A unidirectional beam-scanning antenna is proposed. The antenna is constructed by placing a series of circular radiating elements on a 2-mm dielectric slab backed by a corrugated metal-insulatormetal (CMIM) ground. The CMIM structure is introduced not only as a ground but also as a waveguide for spoof surface plasmon polaritons (SSPPs). The beam-scanning function is realized through the phase difference of SSPPs fed to the radiating elements. In addition, the CMIM ground reflects downward radiation waves onto upward space, leading to a unidirectional pattern and enhanced radiation gain. Both the numerical simulation and experiment results demonstrate the good performance of the proposed antenna. They validate that the antenna achieves unidirectional radiation and scanning angle of 57 • when the frequency varies from 6.2 to 9 GHz with the frequency sensitivity of 20.4 • /GHz. The realized gains are higher than 8.11 dBi over the entire band. Compared with the published works, this paper provides a novel feed technology, a simpler structure, and higher frequency sensitivity. The high-frequency sensitivity is beneficial to reduce the bandwidth burden of the entire system. The antenna has potential applications in satellite communication. INDEX TERMS Antenna, surface plasmon polaritons, beam scanning.