High-gain millimeter-wave antennas based on spoof surface plasmon polaritons (SPPs) are proposed in this paper. Since the dispersion of spoof SPP modes supported by metallic grooves is insensitive to their lateral width, we propose two millimeter-wave antennas with wide SPP grooves, namely, an SPP tapering rod antenna and an SPP leaky-wave antenna. The widened grooves enlarge the aperture size of the antennas, enhancing the antenna gains. Both antennas are fed by a standard waveguide and are fabricated by 3D printing with surface metallization. Based on the similar principle of conventional dielectric rod antennas, the proposed SPP rod antenna achieves broadband and high gain. The measured |S11| is below -16.5 dB from 50 to 75 GHz, and the antenna gain varies from 16.06 to 19.3 dBi. By employing periodic modulation, the SPP leaky-wave antenna operates from 50 to 70 GHz for |S11| below -10 dB. This leaky-wave antenna with 24 modulated periods achieves 20.1 to 23.9 dBi gain in the operating band with a beam scanning range from -39° to -3°.

A circularly polarised (CP) periodic leaky‐wave antenna excited by spoof surface plasmon polaritons (SPPs) is proposed. It is based on an SPP transmission line loaded by periodic rectangular patches on both sides with phase shift, which converts the SPPs mode to CP propagating waves in the air. Due to the dispersion nature of SPPs waveguide, this leaky‐wave antenna exhibits a beam scanning feature. Both simulated and measured results demonstrate that the proposed antenna has an impedance bandwidth of 33% for and a 3 dB axial ratio bandwidth of 15%. The average gain and radiation efficiency are about 10 dBic and 87% from 5.5 to 6.4 GHz, respectively.

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.

Borrowing the idea of amplitude modulation from classical communications theory, this article proposes and demonstrates a new concept of amplitude-modulated (AM) leaky-wave antennas. In the proposed concept, the traveling wave in a wave-guiding structure serves as the carrier wave whose amplitude is spatially modulated by a predefined modulating waveform to generate the desired modulated waves. Two analysis methods are subsequently developed to analyze the amplitude modulation effects. It is demonstrated that spatial amplitude modulation corresponds to shifting the spatial spectrum of the modulating wave up to the carrier spatial frequency. Therefore, one can judiciously design the modulating waveform to control the spatial frequency spectrum of the modulated waves. The spatial frequencies fallen within the radiation region are fast waves, which can radiate into free space. In this manner, the AM structure works as a leaky-wave antenna. To justify the proposed concept, two AM leaky-wave antennas based on corrugated transmission line are designed. The first one is a sinusoidally modulated AM leaky-wave antenna for high-gain application. The second is a beam-forming AM leaky-wave antenna, whose modulating waveform is synthesized to generate flat-top radiation pattern. Both simulated and measured results are given to demonstrate the concept, theory, and design of the AM leaky-wave antennas.

In this paper, a conformal optical transparent metamaterial absorber (COTMA) is proposed based on the circuit analog optimization method (CAOM), which can effectively enhance the optimization speed in the metamaterial absorber structure design by quantifying the equivalent circuit parameters. The operating frequency band can be customized at any band through CAOM, such as microwave, terahertz, and near-infrared frequencies. Here, a five-square-patch structure absorber with transparency and flexible properties is achieved. The simulated and measured incident electromagnetic (EM) wave absorptions of COTMA can reach above 90% in 15.77 - 38.69 GHz band. Meanwhile, COTMA exhibits excellent conformal EM absorption, a thinner substrate (0.078 wavelength at 15.77 GHz), lower structure complexity and polarization independence, and it can also be adapted to the EM absorption of different curved screens. This design is expected to have potential applications for wearable electronics, curved surface screens and OLED displays.