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Alternative unsplit-field-based absorbing boundary condition (ABC) computation approach for the finite-difference time-domain (FDTD) is efficiently proposed based upon the deep differentiable forest (DDF) model which is introduced to replace the conventional perfectly matched layer (PML) ABC during the computation process of FDTD. The field component data on the interface of traditional PML are adopted to train the DDF-based model for implementing the perfectly matched monolayer (PMM). The DDF has the advantages of both trees and neural networks. Its tree structure is easy to use and explain for the numerical PML data. Meanwhile, it has full differentiability like neural networks. The DDF can be trained by powerful deep learning techniques. Numerical cases have been carried out to benchmark the performance of the proposed method. Results illustrate that the DDF-based PMM could not only replace the traditional PML but be integrated into FDTD computation process with satisfactory numerical accuracy.

In this letter, a dual-polarized frequency-selective absorptive structure is presented with two wideband transmission windows. The transmission windows are achieved within a wide –10-dB reflection band. At the frequencies of the passbands, the out-of-phase currents are excited without flowing through the lossy elements. Therefore, the passbands can be obtained with high transmittance. Moreover, only four resistors are loaded on each unit cell to consume the out-of-band reflective wave. By combining lossy flower-shaped and lossless arrays together, the desired dual-band and low reflection performances can be realized. Within the operating band, the reflection is below –10 dB with the fractional bandwidth of 127%. Meanwhile, around 6.5 and 12 GHz, the passband widths are 39% and 40% and the corresponding insertion losses are 0.07 and 0.1 dB, respectively. Finally, the fabricated prototype is measured to demonstrate the feasibility of the presented method.

In recent years, two‐dimensional (2D) ternary materials have attracted wide attention due to their novel properties which can be achieved by regulating their chemical composition with a very great degree of freedom and adjustable space. However, as for the precise synthesis of 2D ternary materials, great challenges still lie ahead that hinder their further development. In this work, we demonstrated a simple and reliable approach to synthesize 2D ternary‐layered BiOCl crystals through a microwave‐assisted space‐confined process in a short time (

Incorporating a truncation of the complex-frequency-shifted perfectly matched layer (CFS-PML), the direct-splitting- based Crank-Nicolson finite-difference time-domain (CNDS-FDTD) is developed and applied to the infrared two-dimensional layered material (2DLM) black phosphorous (BP) metasurface implementations on the all-dielectric nanostructure. To improve extremely low efficiencies in solving infrared terahertz (THz) problems with the few-atomic-layer thickness of 2DLMs, the CFS-CNDS-FDTD is proposed in demand due to the fact that it possesses capabilities of implicit FDTD method and unsplit-field CFS-PML truncation, respectively, in completely conquering the Courant-Friedrich-Levy condition (CFL) limit and holding good performance. The temporal incremental in the CFS-CNDS-FDTD can reach 1000 times larger than that in the regular FDTD for infrared nanoscale problems centered at the 2.5 THz and then keep accurate. Three-dimensional (3D) numerical cases have been carried out to corroborate the proposed method. The CFS-CNDS- FDTD can not only achieve high accuracies and then saves several dozen times of CPU time as compared to the regular FDTD, but also pave the way for designing all-dielectric nanostructures with other 2DLM metasurfaces.

A low-profile differentially fed dual-polarized antenna with high gain and isolation is proposed for fifth-generation (5G) microcell communications. By introducing two pairs of symmetrical meandering conductors to connect both ends of the radiating cross slots, a compact-size antenna with wide bandwidth can be achieved. By further adopting an artificial magnetic conductor-backed (AMC) reflector that is arranged below the radiating patches with a distance of 6 mm, the antenna profile can be reduced from $0.25\lambda _{c}$ to $0.13\lambda _{c}$ (where $\lambda _{c}$ is the free-space wavelength at the center frequency), while both the gain and frequency bandwidth are also enhanced. Furthermore, owing to the orthogonal differentially fed structure, the antenna element displays a high port isolation of 37 dB. Finally, by meticulously designing the feeding network, much narrower beamwidth can be yielded, and hence, the unidirectional gain is further improved. The measured results show that a lower-frequency bandwidth of 13.5% (3.26–3.73 GHz) with a gain of 15.7 ± 0.1 dBi and upper-frequency bandwidth of 7.6% (4.68–5.05 GHz) with 15.55 ± 0.05 dBi gain can be obtained by the proposed antenna array. In addition, port isolation better than 28 dB and stable radiation patterns can be achieved. With the aforementioned characteristics, the proposed antenna is a good candidate for future 5G microcell communications.

In this letter, a novel absorptive structure with a high-transmittance bandpass behavior is proposed based on the electromagnetically induced transparency-like effect. The desired response is achieved by employing cascaded lossy π-shaped and lossless dual-band reflective arrays. The lossy array consists of radiative and subradiant resonators. A resistor is loaded on the radiative resonator to consume the excited current within the stopband. The bright-dark mode coupling contributes to a transparency window with an insertion loss of 0.07 dB. By combining with the reflective array, two absorption bands are obtained at both sides of the passband, and the maximum absorptivity is above 98%. Meanwhile, the 10 dB reflection reduction behavior is realized within the operating band, and a good stealth performance is provided. The fabricated prototype is measured, and the simulation and experimental results are in a good agreement.

Graphene, an innovated 2D material with atomic thickness, is a very promising candidate and has drawn great attentions in various applications. Graphene metasurface enables dynamic control of various wavefronts, achieving distinguished functionalities. The flexibility of graphene metasurface makes it possible to implement multifunctional devices with ease. In this work, a novel design of multifunctional graphene metasurface, which can combine the functionalities of generating and steering vortex waves, has been proposed. The multifunctional graphene metasurface consists of a large array of graphene reflective unit cells. Each unit cell is controlled independently by its size and external static gate voltage. By scrutinizing the reflective property of the graphene cell, the graphene metasurface is designed to realize multi-functionalities. Simulation results show that vortex wave can be generated and steered. This work can establish a methodology to design multifunctional graphene metasurfaces, and the tunability of graphene opens the gate to the design and fabrication of reconfigurable graphene devices.

This paper presents a cross dipole antenna for the fifth generation (5G) sub-6 GHz dual-band applications. The proposed antenna mainly consists of eight copper radiating patches, eight parasitic patches, and a reflector. The proposed antenna can achieve a ±45° polarization characteristic. The overlapped bandwidth is 2.77-5.31GHz, and the corresponding gain varies from 7.6 to 8.4 dBi. The gain increases with increasing operating frequency. Besides, the cross polarization level is less than -28 dB while the port isolation is larger than 26 dB.

This paper presents a Ka-band power divider with microstrip branching lines (MBLs) based on a dielectric substrate (RT/duroid 5880 with a thickness of 0.254 mm, permittivity of 2.2, and loss tangent of 0.0009). The proposed power divider consists of two microstrip branching lines and a thin-film resistor of 100 ohm connected to the microstrip branching lines, which leads to high isolation and matching between the two output ports of this power divider. This designed power divider is fabricated and measured. Both simulated and measured results agree well with each other, and show that the insertion loss is less than 4.0 dB, the return loss is higher than 19 dB, and the isolation between the two output ports is higher than 30 dB in the band from 35 – 40 GHz.

In this letter, a new frequency-selective absorber is presented that has wideband transmission/absorption/reflection reduction responses. The presented absorber is completed by lossy cross-dog-bone and lossless second-order frequency-selective surfaces. The modal interaction pole generated by the lossy array is employed to achieve a wideband transmission. Three absorption bands are combined to realize a continuous stopband with high absorptivity. Furthermore, the improved absorber structure is investigated to reduce the strong reflection between the absorption and transmission bands. The 10 dB reflection reduction is obtained with a fractional bandwidth of 126.4%. Meanwhile, the –3 dB fractional passband width is 41.3% with minimum insertion loss of 0.37 dB. The absorption bandwidth of 91.5% is provided with at least 90% absorptivity. The distance between the lossy and lossless layers is only 0.08 $\lambda _{L}$ at the lowest operating frequency. Finally, the proposed design is validated by a good agreement between the numerical simulations and experimental measurements.

The Boltzmann distribution of electrons sets a fundamental barrier to lowering energy consumption in metal-oxide-semiconductor field-effect transistors (MOSFETs). Negative capacitance FET (NC-FET), as an emerging FET architecture, is promising to overcome this thermionic limit and build ultra-low-power consuming electronics. Here, we demonstrate steep-slope NC-FETs based on two-dimensional molybdenum disulfide and CuInP2S6 (CIPS) van der Waals (vdW) heterostructure. The vdW NC-FET provides an average subthreshold swing (SS) less than the Boltzmann’s limit for over seven decades of drain current, with a minimum SS of 28 mV dec−1. Negligible hysteresis is achieved in NC-FETs with the thickness of CIPS less than 20 nm. A voltage gain of 24 is measured for vdW NC-FET logic inverter. Flexible vdW NC-FET is further demonstrated with sub-60 mV dec−1 switching characteristics under the bending radius down to 3.8 mm. These results demonstrate the great potential of vdW NC-FET for ultra-low-power and flexible applications., The adaptation to atomically thin 2D semiconductors and van der Waals layered ferroelectrics can enable negative capacitance transistors with superior performance and bendability. Here, the authors report flexible negative capacitance transistors based on MoS2 and a ferroelectric dielectric CIPS with a minimum sub-threshold slope of 28 mV/dec and high gain logic invertors.

Since the very recent discovery of ferroic ordering under two dimensional limit, novel devices based on 2D ferroelectricity or ferromagnetism has attracted a lot of interests and are promising for next generation electronic and optoelectronic applications. We find that, below the transition temperature Tc ~320 K, ultrathin CuInP2S6 (CIPS) nanoflakes down to bilayer are still pyroelectric. Changing the temperature will lead to charge modification at the surface of CIPS. 2D pyroelectric nanogenerator is fabricated which can efficiently convert the pyroelectric charges into electrical current. This work will facilitate novel applications of pyroelectric and ferroelectric materials, including pyroelectric devices, thermal sensors, ultrathin nanogenerators and various van der Waals (vdW) heterostructure at room temperature. Ministry of Education (MOE) National Research Foundation (NRF) Accepted version This work was supported by the National Research Foundation Singapore under NRF award number NRF-RF2013-08, Tier 2 MOE2017-T2-2-136, Tier 2 MOE2016-T2-2-153, MOE2015-T2-2-007, Tier 1 RG7/18, Tier 1 RG4/17. X.F.L thanks the support from the Ministry of Science and Technology (2017YFA0205004 and 2016YFA0200700), National Natural Science Foundation of China (21673054 and 11874130), Natural Science Foundation of Beijing Municipality (4182076 and 4184109).

Several configurations of multi-beam reconfigurable THz antennas based on graphene have been investigated. Two modulation mechanisms of graphene-based THz antenna are introduced, one is the reflector-transmission window model, and the other is the reflector-director model (Yagi-Uda antenna). The main parameters, such as main beam direction, resonance frequency, peak gain, and the front-to-back ratio of the proposed antenna can be controlled by adjusting the chemical potentials of the graphene in the antenna. Moreover, this paper provides an easy way to obtain complex graphene-based multi-beam antennas, showing strong potential in the design of other complex graphene-based systems, enabling nanoscale wireless communications and sensing devices for different applications.

This contribution presents a novel 3-D circular conformal MIMO antenna system composed of three magneto-electric dipoles (MED) antennas. The single MED element was delicately designed to include one main (lower-band) dipole and two auxiliaries (upper-band) dipoles in order to achieve the dual-band radiation. The proposed MED owns a low-profile conformal geometry but features a wide H-plane beamwidth (minimum 103°). By embedding the metamaterial of the broadside-coupled E-shaped unit cells into the magnetic dipole, the height of MED can be dramatically reduced by 37.2% as compared with the conventional ones. Meanwhile, the two U-shaped notches together with a rectangular notch were included onto the E-dipole to create a band-notch, which offers the anti-interference capability to the ubiquitous 2.4-GHz signal of the wireless local area network. According to the measurement results, the MED element exhibits an impedance bandwidth of 54.2% (1.68-2.93 GHz) with a stable gain of 6.05± 1.15 dBi in the lower band and 9.2% (3.32-3.64 GHz) with 5.71 ± 0.7 dBi in the upper band, respectively. Moreover, the three-element MIMO system provides quasi-omnidirectional coverage in the H-plane from 1.68 to 3.64 GHz. The outstanding performance metrics validate the proposed ME dipole antenna that is well suited for the future sub-6-GHz fifth-generation MIMO mobile base stations.

The limited memory retention for a ferroelectric field-effect transistor has prevented the commercialization of its nonvolatile memory potential using the commercially available ferroelectrics. Here, we show a long-retention ferroelectric transistor memory cell featuring a metal-ferroelectric-metal-insulator-semiconductor architecture built from all van der Waals single crystals. Our device exhibits 17 mV dec−1 operation, a memory window larger than 3.8 V, and program/erase ratio greater than 107. Thanks to the trap-free interfaces and the minimized depolarization effects via van der Waals engineering, more than 104 cycles endurance, a 10-year memory retention and sub-5 μs program/erase speed are achieved. A single pulse as short as 100 ns is enough for polarization reversal, and a 4-bit/cell operation of a van der Waals ferroelectric transistor is demonstrated under a 100 ns pulse train. These device characteristics suggest that van der Waals engineering is a promising direction to improve ferroelectronic memory performance and reliability for future applications., The memory retention for a ferroelectric field-effect transistor is limited by the depolarization effects and carrier charge trapping. Here, the authors fabricate a long-retention memory cell with a metal-ferroelectric-metal-insulator-semiconductor architecture built from all van der Waals single crystals.

Novel 2D semiconductors play an increasingly important role in modern nanoelectronics and optoelectronics. Herein, a novel topology designer based on component fusion is introduced, featured by the submolecular component integration and properties inheritance. As expected, a new air-stable 2D semiconductor PdPSe with a tailored puckered structure is successfully designed and synthesized via this method. Notably, the monolayer of PdPSe is constructed by two sublayers via PP bonds, different from 2D typical transition metal materials with sandwich-structured monolayers. With the expected orthorhombic symmetry and intralayer puckering, PdPSe displays a strong Raman anisotropy. The field-effect transistors and photodetectors based on few-layer PdPSe demonstrate good electronic properties with high carrier mobility of ≈35 cm2 V−1 s−1 and a high on/off ratio of 106, as well as excellent optoelectronic performance, including high photoresponsivity, photogain, and detectivity with values up to 1.06 × 105 A W−1, 2.47 × 107%, and 4.84 × 1010 Jones, respectively. These results make PdPSe a promising air-stable 2D semiconductor for various electronic and optoelectronic applications. This work suggests that the component-fusion-based topology designer is a novel approach to tailor 2D materials with expected structures and interesting properties. Agency for Science, Technology and Research (A*STAR) National Research Foundation (NRF) Z.L. acknowledges supports from Singapore National Research Foundation–Competitive Research Program NRF-CRP22-2019-0007 and NRF-CRP21-2018-0007. This research is also supported by A*STAR under its AME IRG Grant (Project No. A2083c0052)

The design of a compact circular polarization (CP) electrically small antenna (ESA) is carried out and presented in this paper. The designed antenna consists of a planar circuit board (PCB) on which two 3-dB hybrid couplers are fabricated for providing left-hand circular polarization (LHCP) and right-hand circular polarization (RHCP) waves, and two ceramic substrates covered by thin metal films with the high dielectric constants of 20.5 and 39 and the sizes of 25x25x6 mm and 18×18×4 mm, respectively. This compact CP ESA can realize a coverage of ±75° elevation angle with gain above -4dB in the frequency band of 1518 - 1525 MHz for RHCP and in the band of 1668 - 1675 MHz for LHCP, and a coverage of ±60°elevation angle with gain above - 2dB in the band of 1575.42±1.023 MHz for RHCP.

Electrically small antennas (ESAs) have been attracting many researchers owing to their compact sizes and potential applications in modern wireless communication systems. Considering that ESAs have high reactance, low radiation resistance and narrow bandwidth, metamaterials (MTMs) structures can be applied to the design of wideband and miniaturized antennas to overcome the above limitations. In this paper, the achievements in MTMs inspired ESAs are summarized, the research status is analyzed, and the future development trend of wideband MTMs inspired ESAs is predicted.

In this letter, A pattern reconfigurable antenna is researched. Using the varactor diode which could be controlled by the voltage, the phase of the circulator could be changed. The principle of phase shift is discussed. The four elements antenna array is designed. Connecting with the phase shifter, radiation pattern is measured. The phase is shifted continuously by changing the voltage, which is add on varactor diode, continuously. The direction of radiation pattern could be changed continuously at the same time.

A circularly polarized (CP) antenna based on metasurface with simple structure is proposed for 5G millimeter-wave (mmw) applications. This antenna mainly consists of three layers. Square patches with periodic rhombus grooves are placed on the top of the first layer. A pair of substrate integrated waveguide (SIW) feeding networks are orthogonally arranged in the second layer and third layer, respectively. Simulated experiments demonstrate that an overlapped frequency bandwidth of 5.4% (27.1-28.6 GHz) as well as a 3-dB axial ratio (AR) bandwidth of 7.9% (26.8-29 GHz) can be achieved in dual circularly polarized directions.

An ultra-wideband double-ridged horn antenna is proposed in this paper. By utilizing the ridge structure, the bandwidth of the horn antenna is broadened. Prototype of the horn has been fabricated to verify the performance. The horn antenna impedance bandwidth (VSWR

A rectangular filtering dielectric resonator antenna (FDRA) based on the metamaterial (MMT) with a low profile and high gain is investigated in this paper. The proposed antenna consists of a FDRA fed by a microstrip-coupled slot from bottom and a 3×3 array of the near-zero-index MMT on the top of FDRA. The reflection coefficient of the antenna is better than -10 dB in the band from 5.1 to 5.9 GHz, and it has an average gain of 8.3 dB over the band of 5.4~5.9GHz.

In this paper, a double-mode orbital angular momentum (OAM) antenna is proposed. By using an octagonal microstrip ring antenna with a matched load can generate orbital angular momentum (OAM) beams with different OAM modes at the same frequencies. When the inner ring is fed, this antenna can generate an OAM mode of $l=1$ at 5GHz. Similarly, when the outer ring is fed, vortex waves with $l=2$ can be generated. Because of its low profile and small size, this antenna is more potential in wireless communication, mobile devices, remote sensing and so on.

A beam deflection reconfigurable antenna based on the metamaterial is proposed for macro station or integrated small base station applications. The proposed antenna consists of a cylindrical dielectric resonator antenna (CDRA) and a reconfigurable 2 × 2 array of metamaterial. The proposed antenna can steer the main beam by 20°, 43°, −26°, −48° in the E-plane over 3.6-3.8 GHz according to the simulation results.

Mid-infrared (MIR) light-emitting devices play a key role in optical communications, thermal imaging, and material analysis applications. Two-dimensional (2D) materials offer a promising direction for next-generation MIR devices owing to their exotic optical properties, as well as the ultimate thickness limit. More importantly, van der Waals heterostructures—combining the best of various 2D materials at an artificial atomic level—provide many new possibilities for constructing MIR light-emitting devices of large tuneability and high integration. Here, we introduce a simple but novel van der Waals heterostructure for MIR light-emission applications built from thin-film BP and transition metal dichalcogenides (TMDCs), in which BP acts as an MIR light-emission layer. For BP–WSe2 heterostructures, an enhancement of ~200% in the photoluminescence intensities in the MIR region is observed, demonstrating highly efficient energy transfer in this heterostructure with type-I band alignment. For BP–MoS2 heterostructures, a room temperature MIR light-emitting diode (LED) is enabled through the formation of a vertical PN heterojunction at the interface. Our work reveals that the BP–TMDC heterostructure with efficient light emission in the MIR range, either optically or electrically activated, provides a promising platform for infrared light property studies and applications., Thin-film semiconductors enhance black phosphorus mid-infrared light emission Layering thin films of semiconducting transition metal dichalcogenides with thin-film black phosphorus enhances its ability to emit mid-infrared (MIR) light, which could facilitate MIR light emission investigations and applications. Xiaolong Chen of China’s Southern University of Science and Technology and colleagues layered thin flakes of black phosphorus (BP) with one or the other of a monolayer of tungsten diselenide (WSe2) or a thin film of molybdenum disulfide (MoS2). Thin-film BP is considered a promising MIR material, with potential applications in MIR photodetection and optical modulation. WSe2 efficiently transferred light energy to the BP, enhancing its MIR photoluminescence by up to 192%. On the other hand, the interface created by layering BP with MoS2 enabled the formation of a MIR light-emitting diode at room temperature.

Lateral heterostructures of two-dimensional transition metal dichalcogenides (TMDs) have offered great opportunities in the engineering of monolayer electronics, catalysis and optoelectronics. To explore the full potential of these materials, developing methods to precisely control the spatial scale of the heterostructure region is crucial. Here, we report the synthesis of ultra-long MoS2 nano-channels with several micrometer length and 2–30 nanometer width within the MoSe2 monolayers, based on intrinsic grain boundaries (GBs). First-principles calculations disclose that the strain fields near the GBs not only lead to the preferred substitution of selenium by sulfur but also drive coherent extension of the MoS2 channel from the GBs. Such a strain-driven synthesis mechanism is further shown applicable to other topological defects. We also demonstrate that the spontaneous strain of MoS2 nano-channels can further improve the hydrogen production activity of GBs, paving the way for designing GB based high-efficient TMDs in the catalytic application., Controlled growth of heterostructures within 10 nm scale is crucial for potential applications of transition metal dichalcogenides. Here, the authors report strain-driven synthesis of ultra-long MoS2 nano-channels having several micrometers length and 2–30 nm width embedded within MoSe2 monolayer.

A novel magneto-electric dipole antenna with wide H -plane beamwidth, triple-linear polarisation and frequency reconfiguration is proposed for 5G communications. In this study, the radiated dipoles are designed with the arc-shaped planes to exhibit wide H -plane performance. A bent cross-dipole feed with PIN diodes and varactor diodes inserted into its four arms at different altitudes is utilised to excite and control the antenna. Consequently, a measured wide beamwidth ranging from -67° to 67° can be achieved in H -plane. In addition, the height of the proposed antenna decreased about 30% due to the bent designs. Finally, by controlling the PIN diodes and varactor diodes, the three kinds of linear polarisations and frequency reconfiguration functionalities for 2G/3G/LTE/5G applications can also be easily obtained. With the above-mentioned features, the proposed antenna well suits for intelligent base-station communications.

In this paper, we present the first millimeter-wave GaN HEMT monolithic integrated circuit (MMIC) amplifier with an operating frequency at 220 GHz. This MMIC has a small-signal gain well above 11 dB at 222 GHz. Moreover, the use of gallium nitride technology allows for achieving state-of-the-art saturated output power, up to 14dBm at 222 GHz. To our knowledge, the measured gain and output power levels are the best among any of the GaN MMICs beyond 200 GHz reported to date.

In this paper, a dual-polarized wide-beamwidth magneto-electric (ME) dipole antenna for the fifth generation (5G) mobile communications is proposed. The proposed ME dipole antenna is printed on several dielectric substrates for easy fabrication. By applying a quadrate fence around the ME-dipole antenna, wide-beamwidth characteristics for both E- and H-planes can be obtained in dual linearly polarized directions. The proposed antenna realizes a half-power beamwidth (HPBW) of 129.1 ° in E-plane and another 100.4° in H-plane at 3.4 GHz, while 151.6° in E-plane and 94.2° in H-plane at 4.9 GHz can also be achieved. An overlapped impedance bandwidth (

In communication systems, the nonlinear effect of waveguide flanges, coaxial connectors, antennas and other passive devices produces passive intermodulation (PIM). The mechanism for the nonlinear effect of the PIM is very complicated, which mainly comes from two sources: contact nonlinearity and material nonlinearity. PIM caused by contact nonlinearity at metal junctions of microwave devices is studied in this paper. According to the geometrical configuration and mechanical properties to characterize the contact surface, and the mechanical model of the metal contact surface is established. The microscopic physical effect of metal contact surfaces is analyzed and the equivalent circuit model is obtained. Moreover, the power series model is used to describe the nonlinear voltage-current relationship in the circuit. The model is verified by two-tone simulation, and the spectrum characteristics of PIM are obtained. Finally, the multi-carrier simulation of the equivalent circuit combined with the search method is conducted, predicting the intermodulation products under multi-carrier quickly and accurately.

In this paper, a tri-polarized MIMO antenna with diverse radiation properties for the 5G-V2X vehicular communication is proposed. The design consists of an omnidirectional monopole unit and two pairs of loop radiator dipoles. By loading eight pairs of double inverted L-shaped elements, the directional dipoles get wide-beamwidth characteristic for both E-plane and H-plane. Moreover, the larger inverted L elements lower the elevation angle of the main radiative direction of the monopole, which results in gain enhancement in the azimuth plane. For the directional cross-dipoles unit, two impedance bands reach 34.36% and 19.62% (VSWR

A novel linearly dual-polarized antenna array with triple elements is proposed for beamwidth reconfigurable base-station communications. By cutting off the arc-shaped corners on the radiated patches, the single dual-polarized antenna unit can obtain a wide bandwidth of 78.4% for SWR ≤ 2, ranging from 1.63 to 3.73 GHz for 2G/3G/LTE and 3.5-GHz C -band (3.4–3.6 GHz) applications. In addition, with the box-shaped reflector and the inherent characteristic of the ME dipole antenna, the average gain of the dual-polarized antenna element is about 11.5 dBi. Finally, by employing a two-stage circuit with several power dividers, a three-element antenna array with a widely adjustable beamwidth in both the $E$ -plane and $H$ -plane is investigated, which could meet the demand of the future smart applications.

This paper presents a frequency-selective rasorber whose transmission window locates at the higher frequency of absorption band. The accomplished rasorber is composed of dipole-like and slot arrays, and has realized the transmissive/absorptive performance. In every unit cell, each pair of dipole-like elements connected by vias is printed on the two sides of the substrate, and the coupling between long and short dipoles is suppressed by this structure. A guiding circuit is studied based on the analysis of the current path, and the insertion loss of transmission window is significantly reduced by the surface current at the pass-band that is hindered to pass through lossy elements. The presented rasorber acts as an absorber at the low frequencies, while providing a high transmittance window at 5.6 GHz. This design is elaborately optimized to achieve low reflection and angle-insensitive performance. Finally, the presented structure is validated by numerical simulations and experimental measurements. This rasorber could be used for secrecy communications among stealth facilities while providing stable broad-band absorptive properties.

This paper presents a design method of wideband Fabry–Perot resonator antennas (FPRAs) with two layers of electrically thin dielectric superstrates. The bandwidth enhancement mainly benefits from the superstrate structure with reflection phase increasing with frequency, which is used as a partially reflective surface. The proposed method is validated by a design example in ${X}$ -band. Experimental results of the FPRA prototype demonstrate that the 3-dB gain bandwidth ranges from 8.5 to 11.2 GHz (relatively 28%) with a peak gain of 14 dBi and coincides with the impedance band for ${S} _{11}\leqslant -10$ dB. Compared with the existing methods of gain bandwidth enhancement, the one presented in this paper does not need dielectric substrates with a large or fixed electrical thickness, improving cost performance and design flexibility.

A low-profile metamaterial loaded antenna array with anti-interference and polarization reconfigurable features is proposed for base-station communication. Owing to the dual notches etched on the radiating electric dipoles, an impedance bandwidth of 75.6% ranging from 1.68 to 3.72 GHz with a notch band from 2.38 to 2.55 GHz can be achieved. By employing the metamaterial loadings that are arranged in the center of the magnetic dipole, the thickness of the proposed antenna can be decreased from 28 to 20 mm. Furthermore, a serial feeding network that consists of several Wilkinson power dividers and phase shifters is introduced to attain the conversion between dual-linear polarization and triple-circular polarization. Hence, the antenna could meet the demand of the future 5G intelligent application.

The 2D transitional metal oxides/transition-metal dichalcogenides vertical heterostructures of MoO3–MoS2 are successfully synthesized on SiO2/Si substrates via one-step chemical vapor deposition process. The vertical MoO3–MoS2 heterostructures exhibit the average size of ∼20 μm and the thickness down to ∼10 nm. Moreover, the phototransistor device based on MoO3–MoS2 heterostructures presents responsivity of 5.41 × 103 A W−1, detectivity of 0.89 × 1010 Jones and external quantum efficiency of 1263.4%, respectively, under a 532 nm wavelength light. This study affords a new path to simplify process of fabricating MoO3–MoS2 vertical heterostructures for electronic and optoelectronic applications.

This paper presents a novel resistance-type sensor based on chipless radio-frequency identification. It consists of a scatterer and the resistor to be detected. The scatterer is designed to be V-shaped. The angle $\theta $ between two arms is used to encode the address data of sensor. The resistor to be detected is loaded in the middle of the two V-shaped arms. The sensor is excited by the plane wave. By measuring the scattered fields in two orthogonal polarization directions, the angle $\theta $ and the value of resistor can be identified. Compared with the normal resistance-type sensor, the novel sensor can transform the resistance value and its address into the wireless signal which can be received directly by the reader. Another advantage of angle-based sensor is that every element can encode multibit data. This is helpful to achieve higher capacity. Also, for different codes of one element, the proposed sensor uses the same spectrum. This is beneficial to improve the efficiency of the spectrum. The realized sensor has the identification errors less than 3° in the angle and less than $1.5~\Omega $ in the resistance value.

In this article, a novel broadband end-fire circularly polarized antenna is presented. It comprises a diamond-shaped shorted parallel-plate cavity (DSPC) and planar symmetrical conductor arms (PSCA). The DSPC and PSCA serve as the electric and magnetic dipole, respectively. By adjusting the aperture of DSPC and bending angle of PSCA, the impedance bandwidth and the axial-ratio bandwidth are greatly improved. Meanwhile, the end-fire circles are employed to improve the gain of an antenna. The overall size of the antenna is 35.5 mm × 38.2 mm × 2 mm, equal to 0.98 λ0 × 1.05 λ0 × 0.055 λ0. The measured results show that the realized impedance bandwidth for S11 ≤ –10 dB is 14.1% (7.63–8.79 GHz) and 3-dB AR bandwidth is 16.4% (7.57–8.92 GHz). A good agreement between the simulated and measured results is obtained.

A dual-band beam-sweeping antenna based on two independent cylindrical active frequency selective surfaces (AFSSs) is proposed in this paper. This antenna is composed of a dual-band omnidirectional monopole antenna operating at 2.45 and 5.2 GHz and two cylindrical AFSS screens. The dual-band omnidirectional monopole antenna is designed as a radiating source and surrounded by the proposed two cylindrical AFSS screens. The unit cells of the two proposed AFSS screens consist of two metallic crosses connected by a pin diode vertically. By switching the pin diodes, the transmission and reflection characteristics of unit cell of the two AFSS are investigated, respectively, at their own operating frequency. This leads to the variation of the radiation pattern when the cylindrical AFSS screens are loaded around the monopole antenna. Therefore, by switching the pin diodes with specified combinations, the dual-band beamforming antenna with multiple discrete states can be achieved at 2.45 and 5.2 GHz.

A beam-tilting antenna with negative refractive index metamaterial (NRIM) loading is proposed for WLAN applications. The proposed antenna is composed of a double-feed dielectric resonator antenna (DRA) and 1 × 4 NRIM array, which are fixed over and in the middle of the DRA. The proposed NRIM unit cell comprises a fractal cross-ring resonator structure and performs a negative refractive index in the band from 5 to 5.5 GHz. When the electromagnetic (EM) waves enter a medium with a negative refractive index, the direction of propagation of the EM wave can be changed. Therefore, beam-tilting can be implemented by using the DRA cooperating with the proposed NRIM array. The simulation and experimental results show that the beam-tilting antenna can steer the main beam by ±38° in the xoz -plane over 5–5.5-GHz band. The reflection coefficient of the antenna is better than −10 dB in the band from 5 to 5.5 GHz. Furthermore, the measured results have a good agreement with simulated ones.

A novel wideband antenna array with coplanar waveguide series feed is proposed in this letter. By etching a symmetrical circular slot (SCS) structure on the bottom metallic layer, the impedance characteristic of the antenna array is greatly improved. Meanwhile, the gain of the antenna array at the lower band is improved by inserting another SCS in the center of the two array elements. The measured results show that the impedance bandwidth of the proposed antenna array is from 2.04 to 3.74 GHz (the relative bandwidth is 58.8%). Moreover, the maximum gain reaches 6.9 dBi.

In this paper, a microstrip array antenna with orbital angular momentum is proposed. Twelve identical printed dipole antennas with microstrip balun feeder are arranged in a dodecahedron cylindrical substrate. By changing the value of the phase difference between successive elements, five kinds of electromagnetic waves of different modes of orbital angular momentum are generated. The simulation results show that the expected results have been achieved with the modalities of OAM 0, 1, 2, 3, 4. Consequently, the proposed orbital angular momentum antenna has a promising prospect.

This paper proposed a dual-polarized broadband horn antenna for mm-wave 5G application. The operating frequency of the antenna proposed in this paper is 18 to 40GHz. The antenna with VSWR 10dB and HPBW>20° is presented, and the radiation patterns maintain a good symmetry in full band. And this antenna has been tested and used in practical applications.