Jun Dong

A broadband in-line transition from microstrip line (MSL) to groove gap waveguide (GGW) in Ka-band is proposed. Two matching capacitive posts, a wedge-shaped cavity, and a modified trapezoidal groove etched patch are jointly utilized to achieve a wide operating bandwidth. Furthermore, a tunable notch is introduced using three screws connected to the broad wall of the GGW, which are designed to suppress in-band interference signals. The notch band's dynamic tunability is achieved by adjusting the height of the three metal blocks, covering a tunable range from 26.5 GHz to 40 GHz. Two back-to-back transition prototypes (with and without notch structure) are fabricated and measured. Across the Ka-band, the measured insertion loss is below 0.65 dB and the return loss exceeds 14.5 dB.

This academic paper proposes a terahertz (THz) device featuring dynamic adjustability. This device relies on composite metamaterials made of graphene and vanadium dioxide (VO₂). By integrating the electrically adjustable traits of graphene with the phase transition attributes of VO₂, the suggested metamaterial device can achieve both broadband absorption and dual-band linear-to-circular polarization conversion (LCPC) in the terahertz frequency range. When VO₂ is in its metallic state and the Fermi level of graphene is set to zero electron volts (eV), the device shows remarkable broadband absorption. Specifically, it attains an absorption rate exceeding 90% within the frequency span of 2.28–3.73 terahertz (THz). Moreover, the device displays notable polarization insensitivity and high resistance to changes in the incident angle. Conversely, when VO₂ shifts to its insulating state and the Fermi level of graphene stays at 0 eV, the device operates as a highly effective polarization converter. It attains the best dual-band linear-to-circular polarization conversion within the frequency ranges of 4.31–5.82 THz and 6.77–7.93 THz. Following the alteration of the Fermi level of graphene, the device demonstrated outstanding adjustability. The designed multi-functional device features a simple structure and holds significant application potential in terahertz technologies, including cloaking technology, reflectors, and spatial modulators.

In this paper, a new H-plane horn antenna based on double-sided groove gap waveguide (GGW) is proposed. By employing the double-sided GGW structure, the antenna achieves symmetric radiation in both the E- and H-plane, while the half-height pin structure makes the manufacturing process of periodic pin easier and more accurate. In the proposed structure, two rows of reflector walls are also used on the outer surfaces of the upper and lower horn plates to reduce the backward radiation and improve the gain of antenna. The designed antenna shows proper radiation performance in both E- and H-planes with low sidelobe levels (SLLs). A prototype of the Ka-band H-plane horn antenna is designed, simulated and fabricated. The measured results show that the antenna has the impedance bandwidth of 41%, gain of 11.4–13.4 dBi, and SLL of better than −29 dB.

In the context of real-time video defogging, accurately estimating the transmittance of sky regions and deep fault regions remains a challenging task due to severe color distortion and halo effects. To address this issue, we propose an innovative adaptive wavelet transform defogging (AWTD) scheme aimed at precisely modifying the transmittance of the sky and deep fault regions. Additionally, we present a dedicated field programmable gate array defogging architecture capable of direct application for real-time synchronous defogging of Full HD (1920×1080) videos. Through extensive experiments and comparisons, we demonstrate the effectiveness and practicality of the proposed AWTD approach in mitigating color distortion, halo effects, and other fog-induced artifacts. The results show that the dehazing algorithm attains 60 frames per second for the image resolution of 1920×1080, which is suitable of real time applications.

Bulk Dirac semimetal (BDS) has emerged as a “3D graphene” material for the development of optical devices in the past few years. In this study, a BDS-based tunable highly sensitive terahertz (THz) biosensor is proposed by using a Dirac semimetal/Bragg reflector multilayer structure. The high sensitivity of the biosensor originates from the sharp Fano resonance peak caused by coupling the Optical Tamm State (OTS) mode and defect mode. Besides, the sensitivity of the proposed structure is sensitive to the Fermi energy of Dirac semimetal and the refractive index of the sensing medium. The maximum sensitivity of 1022°/RIU is obtained by selecting structural and material parameter appropriately, which has certain competitiveness compared to conventional surface plasmon resonance (SPR) sensors. From the standpoint of the fabrication facility and integration, we judged that the BDS-based layered structure has the potential application in biosensor field.

In this communication, a novel hybrid decoupler is proposed to reduce mutual coupling for an extremely compact wideband stacked patch MIMO array antenna. The hybrid decoupler consists of a dielectric surface and a metasurface. By using a well-designed dielectric surface, the mode of mutual coupling current on the unexcited antenna can become orthogonal to its polarization mode. Moreover, the electrical distance of coupling wave propagation between two elements is prolonged. Antenna decoupling is naturally achieved. Then, the metasurface, which can reject coupling wave propagation, is a complementary method to further improve isolation. Dielectric rod array is designed by partially hollowing the dielectric surface, which can realize optimized dielectric constant of slab and better combine two decoupling methods. A broadband stacked patch array antenna is chosen as a demonstration to prove that this idea can achieve wide isolation improved bandwidth, as well as high isolation improved degree. Measured results reveal that isolation enhancement ranges from 6 to 21 dB in the frequency band from 1.83 to 2.17 GHz.

This article introduces a novel transition between coplanar waveguide (CPW) and air-filled rectangular waveguide (RWG). A rectangular radiator etched with a semi-elliptic slot is connected to the center conductor of CPW to realize the transition, which broadens the bandwidth. This direct transition does not require intermediate transition or air-bridges. Moreover, the planar circuit of the transition can be designed with high- and low-permittivity materials (ε_r = 10.2 and 2.22), which offer more benefits in both PCB and MMIC design. Two back-to-back transition prototypes at X-band are designed, fabricated and measured. The 15 dB fractional bandwidths are expanded to 44.7% and 47.6% respectively, which have been demonstrated in both of the transitions (ε_r = 10.2 and 2.22). The measurement results agree well with simulation results, which validate the feasibility of this design.

A novel wideband and compact water antenna with optically transparent characteristic is presented in this communication. This antenna mainly consists of a fan-shaped cylindrical radiator, a top disk, a cylindrical base, and a water reflector. Based on two resonant modes, this antenna can achieve wideband characteristic. Meanwhile, when combined with fan-shaped radiator and top disk loading, the overall dimensions can be greatly reduced without compromising impedance matching. The ground made of distilled water is used for full transparency. The proposed antenna covers frequency range from 1.16 to 2.79 GHz for $S_{11} < -10$ dB. As far as we know, the proposed antenna shows the widest relative bandwidth (82.5%) in the field of transparent antennas, without sacrificing size and radiation performance.