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The integration of multi-standard and multi-band wireless communication system will be the development trend of mine communication. The mine wireless repeater is an important part of the mine communication system. However, the antenna suitable for wireless repeaters is a vertical whip antenna, which greatly limits the size of the antenna in the horizontal direction. In this paper, an ultra-narrow size slotted sleeve antenna is proposed for the RF front end of wireless repeaters for underground mining. The antenna design process can be divided into three steps. First, a flag shaped slot is cut in the rectangular sleeve to increase the impedance bandwidth of the antenna. Second, the reverse branch is loaded on the top of the sleeve, which ingeniously increases the resonant path of the antenna. Moreover, a T-shaped slot is etched on the transmission line, which further improves the overall performance of the antenna. The electrical size of the antenna with this unique structural design is only 0.41λ × 0.048λ, which is much smaller than the lateral size of similar antennas. The simulation and measurement results of the proposed antenna are in good agreement, and the working bands include 0.79–0.82 GHz, 1.42–1.47 GHz, 2.39–2.59 GHz, 2.63–2.91 GHz, and 5.10–5.75 GHz. [ABSTRACT FROM AUTHOR]

This article proposes an eye-shape enclosed split ring resonator (ESE-SRR) based metamaterial absorber for multi-band microwave applications with high absorption levels. Four-fold rotational symmetric eye-shaped electrical resonators form the structure of the proposed metamaterial absorber (MMA) to achieve polarisation-insensitive characteristics. Eight near-unity absorption peaks between S, C, X, Ku, and K-band are achieved, where peak absorptions are attained at 3.349 GHz, 5.06 GHz, 6.829 GHz, 9.178 GHz, 14.54 GHz, 17.96 GHz, 18.89 GHz, and 20.4 GHz with absorption levels of 99.8%, 99.7%, 92.9%, 99.1%, 96.4%, 93.3%, 91.3%, and 99.35%, respectively. The electrical dimension of the unit cell is 0.112λmin × 0.112λmin × 0.018λmin, making it a subwavelength compact structure for oblique incident angle stable absorption behaviour. The absorption characteristics are also investigated with metamaterial properties, surface current, and electromagnetic field distributions. The designed MMA is validated by prototype fabrication and measurement, which shows good agreement with simulation results. Finally, the proposed MMA shows an electrically compact structure with eight near-unity absorption peaks and polarisation insensitivity, which makes it an attractive candidate for absorption, sensing, radar cross-section reduction, etc. [ABSTRACT FROM AUTHOR]

In this paper, a three-layer structure multi-band terahertz (THz) metamaterial perfect absorber (MPA) with the patterned layer formed by a frame graphene and a square copper, the silica dielectric layer and the copper metal bottom layer is designed and investigated. There are four absorption peaks when the Fermi energy level of graphene is 0.4 eV and relaxation time of graphene is 0.1 ps. The absorptivity at the frequencies of 2.77 THz, 5.41 THz, 7.48 THz, and 7.75 THz reached 99.99%, 99.09%, 97.13%, and 99.84%, respectively. The first absorption peak (peak I) of this absorber has a wide range of high absorption, and the second, third, and fourth absorption peaks (peaks II, III, and IV) have a high Q-factor. The absorber is polarization-insensitive, and the absorptivity of peaks I and II is still above 90% even when the incidence angle reaches 70°. Through exploring the absorption curve of different structures and electric field distribution and using impedance matching theory, the cause of absorption peak and the actual operation of the absorber parameter fault tolerance and tunability have been studied. It is found that the proposed absorber has many advantages such as low cost, simple structure, ease to manufacture and tunability. These explored generic properties of the proposed absorber emphasize its development potential in application areas, such as the design of sensors, wireless communication, controllable switch operation, modulators, etc. [ABSTRACT FROM AUTHOR]

Robust edge states and corner states in photonic topological insulators provide effective ways to manipulate the propagation of electromagnetic waves. Bandgaps of the previously reported photonic topological insulators are independent of each other. In this paper, a higher‐order valley photonic insulator composed of arrays of dendritic structure is designed. The band structure shows an overlapped bandgap is observed, and the overlapped bandgap divides the band structure into three bandgaps. The evolution of the overlapped bandgap is investigated by changing the geometric parameters and increasing the fractal to break the C3v symmetry drastically. Besides, it is notable that the band structure of the proposed valley photonic insulator is flat bands. It is demonstrated that undistorted transmission can be observed as a plane electromagnetic wave transmits through the proposed valley photonic insulator. The interface consisting of two valley photonic structures with distinct topological nontrivial phases is constructed. Edge states and corner states with strong energy localization are obtained in multi‐band frequencies. Remarkably, two triangular structures with different Wannier center configurations both have corner states in the same bandgap, which does not obey the valley selectivity. The phenomenon is caused by the weak valley locking property due to the overlapped bandgap. The proposed valley photonic insulators are expected to benefit applications in optical devices such as topological lasers. [ABSTRACT FROM AUTHOR]

This paper presents a novel design method for a tri‐band multiple in multiple out (MIMO) antenna. The antenna consists of four sets of identical antenna pairs arranged on the two side frames. Three resonant modes can be obtained using a microstrip coupling feed structure by employing different branches in antenna unit design. The working frequencies of the modes can be adjusted independently. Moreover, in each pair of antennas, two antenna units were closely arranged and a decoupling grounding branch was employed between the adjacent antennas to ensure good isolation. The tri‐band eight‐element MIMO antenna operates at 3.5, 4.9, and 5.6 GHz and the isolations were better than 14 dB. The proposed antenna had a low profile of 0.06λ0 ${\lambda }_{0}$ and good isolation so it has potential applications in 5G mobile terminals. [ABSTRACT FROM AUTHOR]

Surface soil moisture (SSM) plays an important role in agricultural and environmental systems. With the continuous improvement in the availability of remote sensing data, satellite technology has experienced widespread development in the monitoring of large-scale SSM. Synthetic Aperture Radar (SAR) and optical remote sensing data have been extensively utilized due to their complementary advantages in this field. However, the limited information from single-band SARs or single optical remote sensing data has restricted the accuracy of SSM retrieval, posing challenges for precise SSM monitoring. In contrast, multi-source and multi-band remote sensing data contain richer and more comprehensive surface information. Therefore, a method of combining multi-band SAR data and employing machine learning models for SSM inversion was proposed. C-band Sentinel-1 SAR data, X-band TerraSAR data, and Sentinel-2 optical data were used in this study. Six commonly used feature parameters were extracted from these data. Three machine learning methods suitable for small-sample training, including Genetic Algorithms Back Propagation (GA-BP), support vector regression (SVR), and Random Forest (RF), were employed to construct the SSM inversion models. The differences in SSM retrieval accuracy were compared when two different bands of SAR data were combined with optical data separately and when three types of data were used together. The results show that the best inversion performance was achieved when all three types of remote sensing data were used simultaneously. Additionally, compared to the C-band SAR data, the X-band SAR data exhibited superior performance. Ultimately, the RF model achieved the best accuracy, with a determinable coefficient of 0.9186, a root mean square error of 0.0153 cm3/cm3, and a mean absolute error of 0.0122 cm3/cm3. The results indicate that utilizing multi-band remote sensing data for SSM inversion offers significant advantages, providing a new perspective for the precise monitoring of SSM. [ABSTRACT FROM AUTHOR]

The analogue of an electromagnetically induced transparency (EIT) spectrum is achieved using a metasurface that consists of an array of cross and L-shaped resonators. The mechanism of the EIT-like phenomenon are analyzed, and the influence of geometrical parameters on the effect is discussed. We achieve a multi-band EIT-like through structure configuration. In particular, polarization-independent EIT is realized. A potential application in sensing is suggested and the sensitivity of 65 GHz RIU−1 is obtained. We also investigate the impact of analyte and substrate on the transmission spectrum. We find that when the analyte thickness is higher than 40 μ m, the EIT spectral shift is less affected by the analyte thickness. The thickness insensitive characteristics are beneficial for reducing errors caused by analyte dose, thereby improving the accuracy of sensing. By introducing a phase change material, vanadium dioxide, we obtain active control of the EIT effect. Our results provide valuable insights into the development of multi-band tunable compact devices based on metasurfaces. [ABSTRACT FROM AUTHOR]

The Baihetan reservoir region is characterized by complex geomorphology, significant altitude differences, and rugged terrain. Geological hazards in such areas are often characterized by high concealment, wide distribution, and difficulty in field investigation. Traditional identification techniques are unable to detect and monitor geological hazards on a large scale with high efficiency and accuracy. In recent decades, interferometric synthetic aperture radar (InSAR) techniques, such as small baseline subset InSAR (SBAS-InSAR), have been widely applied to landslide identification. However, due to factors such as vegetation and the degree of landslide deformation, single-band synthetic aperture radar (SAR) still has certain limitations in detecting landslides. In this study, SBAS-InSAR was conducted based on ALOS-2 and Sentinel-1 ascending-descending images covering the Baihetan reservoir region. Deformation identification results were utilized to conduct a statistical analysis of the SAR detection performance and landslide characteristics, and the effect of vegetation on the detection effectiveness of different SAR bands was discussed. The study revealed that when surface vegetation coverage reaches a high degree, the percentage of areas with coverage greater than 0.6 is greater than 95%, the SAR coherence is mainly affected by vegetation thickness; the comparison of the difference change in the average coherence of the C/L bands among the four vegetation types shows that the ratio of the average coherence of the L-bands to the C-bands increases by a factor of three with the increase in thickness and the transition from crops to shrubs and trees. The results showed that the L-band has better detectability than the C-band in alpine-canyon terrain with vegetation coverage and complex vegetation composition. However, considering the high temporal resolution and accessibility of Sentinel-1 SAR data, it is still the main data choice for wide-area identification of landslides in the reservoir area, while other satellite-borne SAR data with different wavelengths and resolutions, such as ALOS, can be used to assist in the identification and monitoring of landslide hazards with significant magnitude of deformations and dense vegetation coverage. Therefore, the combined utilization of multi-band SAR data has the potential to enhance the dependability of landslide identification and monitoring, resulting in more accurate detection results. [ABSTRACT FROM AUTHOR]

A photonic method for flexible multi-band dual-chirped microwave waveform generation is proposed using a recirculating frequency shifting loop (RFSL). The RFSL can be used as an optical frequency comb (OFC) generator with adjustable frequency spacing and line numbers. By heterodyning the OFC with a lightwave modulated by a baseband linearly chirped waveform in a balanced photodetector, a flexible multi-band dual-chirped microwave waveform can be generated. The frequency spacing and the number of the sub-bands can be easily adjusted by tuning the frequency shift and the bandwidth of the optical filter in the RFSL. The bandwidth and duration of each sub-band signal can also be tuned by adjusting the baseband linearly chirped waveform. A numerical simulation is conducted to verify the proposed generator. A flat four-band dual-chirped waveform with frequency spacing of 3 GHz and six-band dual-chirped waveform with frequency spacing of 4 GHz are generated successfully. Due to the flexible reconfigurability and high performance, the proposal may have great potential in multi-band radar systems. [ABSTRACT FROM AUTHOR]

In this study, the electronic band structure and the dynamics of the excited carriers in the formamidinium lead bromide (FAPbBr3) perovskite are investigated by combining the information obtained from steady‐state absorption, photoluminescence, femtosecond transient absorption spectroscopy, photoelectron spectroscopy, and density functional theory calculations. A detailed description of the electronic transitions in the UV–vis energy range has been provided, giving an estimation of the exciton binding energy (40 ± 5 meV), the transition energy from the first valence band (VB1) to the conduction band (CB1) (electronic bandgap at 2.37 ± 0.01 eV) and assigning the broad peak at ≈3.4 eV to the transition from the second innermost valence band (VB2) to CB1. The temporal dynamics of the excited carriers involved in these transitions are investigated using different excitation energies and carrier densities. Different trends are observed in the dynamics of the transient signals associated with the VB1→CB1 (PB1) and VB2→CB1 (PB2) transitions. As the carrier density increased, PB1 exhibited a slowing down of its rise time, while PB2 showed an acceleration attributed to the thermalization of the excited holes in VB2. These valuable findings have the potential to unlock new strategies aimed at maximizing the efficiencies and performance of perovskite‐based solar cell devices. [ABSTRACT FROM AUTHOR]

In this manuscript, an original graphene-based metamaterial perfect absorber (MPA) was suggested and investigated with substituting aluminum with graphene. The proposed structure consists of a gold substrate as a conductive layer, a silicon substrate as a middle insulated layer and the patterned graphene layer as a resonator. The suggested structure, with only one metamaterial layer, has a lot of advantages such as simple implementation, cost-effectiveness, simple design and frequency tunability. The results of the proposed absorber, demonstrate that the absorber can provide absorption close to 100% at the frequencies of 0.56, 0.79, 1.02 and 1.25 THz by 0.9 eV graphene chemical potential (μc). With increasing the thickness of the silicone insulating layer, the absorption peaks number can be increased up to XIII bands. Also, changing the Fermi level can cause an absorption frequency shift. Furthermore, this structure is polarization insensitive and it is tolerating incident angles up to 45°. The recommended absorber is an appropriate candidate for filtering, spectroscopy, imaging and sensing application. [ABSTRACT FROM AUTHOR]

Outphasing power amplifiers (OPAs) can be used in wireless information and power transfer systems due to their excellent conversion efficiency. With the rapid advancement of technology, there is a strong demand for OPAs to achieve wideband and multi-band operations to enhance frequency coverage. This paper provides a comprehensive review of the research progress on the development of broadband and multi-band board-level OPAs. Firstly, the paper introduces the fundamental components of an OPA. Then, the paper delves into a detailed analysis of the load modulation of OPAs. Subsequently, previous works on the circuit topology and design methods for broadband and multi-band OPAs are discussed and compared. The paper highlights various design strategies and their respective advantages and disadvantages. Finally, the paper explores some potential design methods for broadband and multi-band OPAs, discussing emerging technologies and highlighting potential research directions. [ABSTRACT FROM AUTHOR]

This article reports the Modified Microstrip Feed Hybrid Rectangular Dielectric Resonator Antenna (RDRA). The proposed structure has a ground plane with a plus-shaped slot on an FR4 substrate with a height of 1.6 mm and dimensions of 38 mm x 35 mm. The proposed Dielectric resonator antenna is made of a material with 10 as its dielectric constant, and the dimensions of the DR are 19 x 20 x 18 mm3. The DR is connected to a modified microstrip feed with an octagonal ring through the plus-shaped slot in the ground. The proposed structure operates in frequencies from 2.60 GHz - 2.74 GHz, 3.12 GHz - 3.37 GHz, and 4.25 GHz - 4.37 GHz. The resonant frequency of the final proposed RDRA is 2.68 GHz, 3.26 GHz, and 4.31 GHz, which covers WLAN, WIMAX and Wireless Avionics Intra-Communications (WAIC) applications, respectively. The entire structure was simulated using the CST microwave studio. The simulated results agree with the measured results and both are presented. The compact size, stable radiation pattern and reasonable gain make this antenna suitable for the proposed applications. [ABSTRACT FROM AUTHOR]

This article presents a ±45° dual‐band dual‐polarized filtering antenna. The filtering antenna element is a dual‐polarized patch antenna that loads a parasitic patch with two rectangle slots to achieve compact multi‐array. Multi‐array consists of three 1×2 subarrays arranged, which are designed for 1.8/2.1 GHz FDD band applications. Very close‐arranged antennas exhibit radiation pattern invariance as well as in‐band radiation property. Radiation patterns are conformal with a compact subarray distance of 45 mm (0.29λ0), which is 56% smaller than that of the array using traditional filtering elements. Moreover, the total width is only 180 mm for three subarray‐composed antenna arrays. The average gain is 8.7 dBi with a low profile of 0.069λ0. The proposed array exhibits the filtering property of the subarrays with a very simple structure. [ABSTRACT FROM AUTHOR]

Quasi‐bound state in the continuum (quasi‐BIC) has drawn increasing attention in terahertz biosensing and filtering owing to an extremely narrow linewidth and ultra‐high quality factor. However, it is usually polarization‐sensitive due to broken structure or incidence symmetry and mainly holds for polarization‐dependent single or dual bands, which sets a limitation on practical applications. Here, this article proposes and experimentally demonstrates terahertz multi‐band polarization‐independent quasi‐BICs in tetramer‐based metasurfaces by using the laser etching method. Employing a tetramer cluster with C4v symmetry as the structural unit, which consists of four L‐type copper particles on a flexible and optically‐transparent substrate, the metasurfaces can support dual‐band or tri‐band polarization‐independent quasi‐BICs after performing collective perturbation, specific displacement, or both to the constituent particles. Furthermore, the metasurfaces are integrated with microfluidic channels to explore their potential application in terahertz biosensing. Experimental results indicate that when the concentration of bovine serum albumin solutions is below 4 mg mL−1, both resonance modes of the dual‐band terahertz microfluidic biosensor exhibit a sensitivity of ≈12 GHz mg−1 mL each, and the detection limits reach 0.17 mg mL−1. This work provides a general and simple strategy to construct metasurfaces supporting multi‐band polarization‐independent quasi‐BICs, which have promising applications in biosensing, filtering, and lasing. [ABSTRACT FROM AUTHOR]

The MIMO antenna is one of the essential elements for the implementation of the new fifth-generation (5 G) technologies. The design of the MIMO antenna goes through several steps; the important one is the design of the single-element antenna that resonates at the desired frequency band(s). Its design becomes more difficult if it is a multi-band antenna. In addition, determining the dimensions of multi-band antennas by simulation or mathematical models is both more complicated, difficult, and time-consuming. In this research, different approaches based on artificial neural networks (ANN), radial basis function neural networks (RBFNN), and adaptive neuro-fuzzy inference systems (ANFIS) are used to predict the dimensions of a dual-band circular patch antenna with defected ground structure (DGS) for mm-wave 5 G applications, and then the performances of the three models are compared. To determine the training and the testing data, 280 antennas with different patch values and added slots in the ground plane are simulated. The resonant frequencies of the dual-band circular patch antenna and the height of the substrate are used as the input vector for the ANN, RBFNN, and ANFIS models. Two hundred twenty simulated antennas were used for training, and the remaining 60 data points were used to test the ANN, RBFNN, and ANFIS models. The performance of these models is compared in the training and testing process using some statistical criteria such as MSE, MAE, and RMSE. The proposed dual-band circular patch single-element antenna has a compact size of 5 × 6 × 0.8 m m 3 and exhibits good performance, such as broad band (3.8 and 3 GHz), high gain (6 and 7.1 dB), and high efficiency (99 % and 95 % ) in both operating bands. After studying the single-element antenna and in order to improve its performance, we proposed a 4 × 4 MIMO antenna with a total volume of 17 × 17 × 0.8 m m 3 that was designed by using four copies of the single-element antenna arranged orthogonally on the same low-loss Rogers Duroid 5880 substrate. The suggested 4 × 4 MIMO antenna achieves a high level of isolation (more than - 30 dB in both operating bands), which is obtained by inserting a cross-shaped decoupling structure among elements on the upper and lower sides of the substrate. Moreover, the proposed MIMO antenna has a good gain of 6.4 and 7.5 dB in both bands and a high radiation efficiency of 99.5 % and 99 % at 28 and 38 GHz, respectively. Furthermore, the diversity performance of the MIMO antenna is evaluated using a variety of crucial indicators, all of which greatly surpass realistic norms. The envelope correlation coefficient (ECC) is less than 0.005, the diversity gain (DG) is greater than 9.99 dB, the total active reflection coefficient (TARC) is below 10 dB, and the channel capacity loss (CCL) is no longer than 0.4 bits/s/Hz. In addition, the proposed dual band circular patch single element antenna and the 4 × 4 MIMO antenna are fabricated, and the measured results are in good agreement with the simulated results using HFSS and CST software. [ABSTRACT FROM AUTHOR]

The proliferation of wireless communication technologies has led to a surge in the need for multiband antennas. This study introduces an innovative multiband antenna design that incorporates a 4 × 4 Artificial Magnetic Conductor (AMC) surface to achieve reduced Specific Absorption Rate (SAR), high gain, and improved Front to Back Ratio (FBR). The multiband antenna design presented in this study spans a wide range of wireless frequency bands, including ISM, WLAN, WiMAX, Wi-Fi 6E, and 7. The antenna offers comprehensive coverage for various wireless communication applications with resonating frequencies at 2.4 GHz, 3.2 GHz, 5.5 GHz, 7.5 GHz, and 10 GHz. The AMC unit cell generates four zero-degree reflection phases with Double Negative (DNG) properties at 2.5 GHz, 3.8 GHz, 5.5 GHz, and 7.5 GHz. The compact design measures 29 × 37 × 1.6mm3 and is placed 13 mm above an AMC surface of size 64 × 64 × 1.6mm3. The proposed antenna design achieves an increase in gain of up to 8.55dBi at 6.01 GHz and a notable improvement of 31.5 dB in FBR at 4.5 GHz. The proposed antenna design achieves a -10 dB impedance bandwidth for a range of frequencies, including 2.34–2.43 GHz (3.77%), 2.81–3.83 GHz (30.72%), 4.82–6.21 GHz (25.20%), 7–7.65 GHz (8.87%), and 8.06–10.31 GHz (24.5%). An average percentage reduction in SAR at these frequencies with the AMC structure is 96.11%. The antenna sample was successfully fabricated, and the experimental results have been found to match well with the simulation results. Consequently, this design offers a promising solution for wearable off-body communication devices that require low-SAR, high-gain, and multiband functionality. [ABSTRACT FROM AUTHOR]

In this article, a multiple input multiple output quadrate frequency bands modified PIFA antenna is introduced for 4G LTE and WLAN applications. The quadrate proposed antenna covers LTE 1800 (1.71-1.88 GHz), LTE 1900 (1.85-1.99 GHz), UMTS (1.92-2.17 GHz), LTE 2300 (2.305-2.400 GHz), LTE 2500(2.50-2.69 GHz), WLAN (2.400-2.484 GHz5.15-5.75 GHz) specified by IEEE 802.11a/b/g/n/ac and WiMAX (3.3–3.6 GHz). Then, the PIFA antenna is used as 2×1 MIMO antenna as a radiation element. The overall dimensions of the single antenna are 50×35×0.8 mm³ and the MIMO antenna is 50×70×0.8 mm ³ while both are realized on FR4-epoxy substrate. To reduce mutual coupling between PIFA antennas at MIMO configuration, Defected Ground Structure (DGS) along with parasitic double split ring resonator is used. The antenna performance is confirmed by the construction of the antenna prototype and measuring its characteristics in terms of reflection loss coefficient, gain, and radiation properties. The extracted outcomes show a good correlation between the simulation and experimental results that candidate it to satisfy mobile communication requirements. [ABSTRACT FROM AUTHOR]

In this article, a low-profile quad-port wideband and multiband printed conformal antenna for 4G/5G WLAN/Wi-Fi 6E applications is presented. The designed antenna is printed on a 0.5 mm thick transparent polymide substrate with dimensions of 112.8 × 112.8 mm2. Over a 10 dB impedance bandwidth, the slotted ground plane antenna can operate in the following spectrums: 2.2–2.6 GHz (Bluetooth, ISM band, Wi-Fi), 3–5.59 GHz (LTE band 42, New radio bands 77, 78, and 79), and 5.8–7.1 GHz (5G WLAN, Vehicular Band, Wi-Fi 6E band). Therefore, the antenna presented in this research has versatile operation, almost covering existing and upcoming frequency bands for 4G and 5G applications, respectively. The proposed conformal antenna also provides superior performance in terms of isolation—better than 20 dB—even after antenna elements are kept with a minimum distance between them. Because of such isolation improvements, it is possible to achieve a radiation efficiency of up to 93 percent with an overall gain of around 4.8 dBi over the desired operating band. Further, MIMO characteristics including channel capacity, Envelope Correlation Co-Efficient, Channel Capacity Loss and Diversity gain have been calculated to validate the MIMO performance of the proposed antenna. More studies have shown that the suggested antenna works well enough for both multi-band and wide-band applications. [ABSTRACT FROM AUTHOR]

The rapid growth of the communication frequency band leads to the diversity of receiving frequency bands of smart devices. This paper proposes a reconfigurable wireless superheterodyne receiver for multi-standard communication systems. The receiver is designed through architecture design, chip selection, layout drawing, and physical measurement. The designed receiver consists of receiving module, local oscillator module, and control module. Unlike previous receivers, the proposed receiver selects the frequency channel, local oscillator frequency, and link gain through the control module in the current scene. The control module consists of a single-chip microcomputer and computer. The receiver can work in application scenarios including 2.4–2.5 GHz, 3.3–3.6 GHz, and 4.8–6.0 GHz. This paper discusses the design process of the proposed reconfigurable receiver in detail. Compared with the traditional receiver, the proposed receiver can change its working mode by software and has the characteristics of flexible reconfiguration. In addition, it has the advantages of a large link gain range and good demodulation performance. Moreover, the receiver is low in design cost and easy to manufacture. Therefore, it can be widely used in receiving modules of WLAN and 5G communication systems. [ABSTRACT FROM AUTHOR]

In this paper, one of the necessary and fundamental conditions for using an additional layer to obtain more absorption bands in metamaterial absorbers is determined. We consider the case in classical 3-layer absorbers (usually made of metal-dielectric-metal) that use graphene in their upper layer. If the form or pattern of the upper layer has cross-symmetry, a dual-band or multiband absorber will be achieved by adding another layer. In the present literature, there is no specific regulation for improving the absorption performance of terahertz absorbers by adding a layer, and there are only ad hoc working examples. Because the multi-band absorbers have greater tuneability and are more efficient than the single band absorbers, the ability to design for a higher number of bands is of practical significance. Note that this phenomenon is achieved only by adding one layer of graphene-shaped structures on the surface without manipulating the dimensions of the unit cell or the material of each component. This concept has been studied on the absorption performance of three basic structures. This increment in the number of absorption bands is true for all absorbers with cross-symmetry forms. [ABSTRACT FROM AUTHOR]

• Polarization-insensitive UCSRR-MMA is proposed, featuring the characterization of the concentration of the substances. • The proposed UCSRR-MMA achieves six near-unity absorptions in the X, Ku, K, and Ka-band for both TE and TM modes. • The proposed UCSRR-MMA emerges as a strong candidate for hexa-band absorbing and solid material sensing applications. A U-coupled split ring resonator-based metamaterial absorber (UCSRR-MMA) is presented in this article. The proposed UCSRR's unit cell comprises a fourfold rotationally symmetric structure with a cubic-shaped resonator wrapped in two square rings, which are positioned at every quarter of the MMA. The compact structure is designed with dimensions of 0.293λmin × 0.293λmin utilizing an FR-4 substrate, where λ min at the lower absorption frequency. The proposed MMA achieved high absorption of 99.68 %, 95.13 %, 99.88 %, 93.88 %, 99.8 %, and 96.4 % at 8.8 GHz, 10.512 GHz, 13.87 GHz, 16.084 GHz, 22.048 GHz, and 28.348 GHz, respectively, in the X, Ku, K, and Ka-band frequency regions. The absorption characteristics are also investigated using an equivalent circuit model with metamaterial properties, surface current, and electromagnetic field distributions. The permittivity, permeability, and absorption exhibit similar results for both TE and TM polarization modes. Furthermore, this study examines the sensing performance of the UCSRR-MMA with three distinct concentrations of solid mixer: 25 % cement, 40 % cement, and 55 % cement etc. Finally, the effectiveness of the S 11 and absorption characteristics are validated by the fabrication of a physical prototype array. Therefore, the proposed multi-band electrically compact and polarization-insensitive MMA is an attractive candidate for absorption, sensing, and radar cross-section reduction applications. [ABSTRACT FROM AUTHOR]

In this paper, a novel construction method for a single hybrid cavity is proposed for the first time, which integrates a quarter-mode substrate integrated waveguide structure into a patch cavity (QMSIWP), and a novel single-cavity multi-mode resonator is realized through the incorporation of cross-slot lines. A detailed analysis of its characteristics, combined with a specialized feed structure, leads to the design of multiple dual-band quasi-elliptic bandpass filters (BPFs) with varying frequency ratios and a triple-band quasi-elliptic BPF. The finite frequency transmission zeros (FTZs) and bandwidths (BWs) can be controlled by adjusting various parameters. For the demonstration, a triple-band quasi-elliptic BPF is fabricated and measured to validate the performance and design method of the proposed QMSIWP hybrid cavity and feed structure. The measured results agree with the synthesized and simulated results, confirming the proposed method's feasibility and universality. The proposed filter exhibits advantages such as compact size, high selectivity, and excellent group delay, which expands its application prospects and potential value. [Display omitted] [ABSTRACT FROM AUTHOR]

In recent years, the electromagnetically induced transparency-like (EIT-like) of metamaterials has been widely concerned due to obtain high Q , which has potential applications in the field of sensing and slow light. In this paper, an EIT-like metamaterial structure in the microwave band was investigated, which can realize to multi-band EIT-like phenomena. The equivalent circuit method and the electric field distribution are used to study the EIT -like effect' mechanism, and the multi-band EIT-like phenomenon is discussed by analyzing its structural parameters. The results show that the multi-band EIT in the proposed structure is obtained by coupling multiple bright modes to multiple dark modes. The change of transmission spectrum is discussed by changing the environmental permittivity. The results have potential applications in areas such as refractive index sensing, filters. • A five-band electromagnetically induced transparency-like on microwave is investigated. • The equivalent circuit method is used to analyze the principle of multi-band EIT. • In the structure, multiple bright modes will result in the generation of EIT-like multi-frequency band phenomena. [ABSTRACT FROM AUTHOR]

In this research, a double negative (DNG) metamaterial is proposed for C, X, and Ku frequency bands applications. The two − layer DNG metamaterial comprises of a copper resonator patch and a FR − 4 substrate material with a thickness of 1.6 mm. The novel unit cell structure consists of a triple T − shaped resonator within the square split-ring resonators (SRR). The proposed metamaterial exhibits negative permittivity and permeability for multi-band operation which provides more control of electromagnetic waves for multi-band operation. The presented design resonates at four resonance frequencies of 4.65 GHz, 9.08 GHz, 11.02 GHz, and 12.03 GHz, which is validated through simulations in the CST Microwave Studio and measurements of the fabricated DNG metamaterial. The detailed parametric analysis of the effects of geometric modifications on the S-parameters is presented. An effective medium ratio (EMR) of 6.4 confirms the potential of the proposed metamaterial for practical use, such as in telecommunications, radars, and antennas for achieving advancements in miniaturization, performance improvement, absorption efficiency, radar signature enhancement etc. [ABSTRACT FROM AUTHOR]

Bismuth-doped fiber amplifiers offer an attractive solution for meeting continuously growing enormous demand on the bandwidth of modern communication systems. However, practical deployment of such amplifiers require massive development and optimization efforts with the numerical modeling being the core design tool. The numerical optimization of bismuth-doped fiber amplifiers is challenging due to a large number of unknown parameters in the conventional rate equations models. We propose here a new approach to develop a bismuth-doped fiber amplifier model based on a neural network purely trained with experimental data sets in E- and S-bands. This method allows a robust prediction of the amplifier operation that incorporates variations of fiber properties due to manufacturing process and any fluctuations of the amplifier characteristics. Using the proposed approach the spectral dependencies of gain and noise figure for given bi-directional pump currents and input signal powers have been obtained. The low mean (less than 0.19 dB) and standard deviation (less than 0.09 dB) of the maximum error are achieved for gain and noise figure predictions in the 1410–1490 nm spectral band. [ABSTRACT FROM AUTHOR]

In this paper, a multi-band acoustic topological insulator based on the Valley Hall effect is designed. Based on the mirror symmetry in the C 3 v point group phononic crystal, by changing the parameters of the primitive cell, the phononic crystal simultaneously has multiple linear Dirac degenerate points at the K point of the Brillouin zone, which can realize multi-band topology valley transmission. The whole triangular multi-band acoustic topological valley insulator system has C 3 v symmetry. By rotating the clover-like scatterer, the mirror symmetry of the structure can be broken, thereby opening the degeneracy at the Dirac point. The energy band is reversed at the K point, realizing the Valley Hall phase transition. By connecting different structural systems, boundary states are constructed to simulate topologically protected edge acoustic transmission. Different phonon crystal structures are further constructed, and their acoustic transmission characteristics are verified by finite element algorithms. This paper can provide guidance for the design and engineering application of multi-band acoustic antennas, acoustic logic control gate circuits, and other functional devices for acoustic communication. [ABSTRACT FROM AUTHOR]

In this article, we have managed to achieve a quad-band perfect classical absorber in the terahertz band. In this proposed structure, which consists of three layers that the top and bottom layers made of gold and a dielectric layer, is located in middle layer. The results show that this structure has four perfect absorption bands with an average absorption of 98.22% at frequencies of 1.36, 2.6, 3.68, and 4.36 THz. To better understand the absorption mechanism, an equivalent circuit related to the proposed structure is presented. We have also shown that the percentage of absorption of the proposed absorber has increased due to the loss of the middle layer. Finally, the distribution of the electric fields is shown at each of the absorption frequencies. Due to its four bands, this absorber has potential in imaging, selective sensing, and photodetector applications. [ABSTRACT FROM AUTHOR]

High-performance metasurface refractive index sensors are extremely promising for biosensing, petroleum, agricultural production, and security detection fields. We theoretically propose a terahertz refractive index sensor based on absorption mechanism, which can achieve an excellent triple-band absorber and high-performance refractive index sensor. The proposed triple-band absorber may achieve 90.22%, 98.87%, and 99.91% at 0.93, 1.12 and 1.45 THz, respectively. Multi-band response promises multi-point matching of the resonant frequency between the sensor and the measured substance, thus enabling a high-accuracy terahertz sensor. The refractive index sensor has the maximum sensitivity (S), quality factor (Q), and figure of merit (FOM) of 420 GHz/RIU, 71.54, and 21.4 RIU−1, respectively. The triple-band absorber is achieved by the combination of electric and magnetic dipole responses and the sensing performance is determined by localized electromagnetic field distribution. The proposed terahertz refractive index metasurface sensor has a promising application prospect in biosensing and critical parameter measurement for oil and gas wells. [ABSTRACT FROM AUTHOR]

Achieving modulation of visible and infrared spectra is an important task for applications in the field of smart thermal management. In the application area of smart thermal management, modulating the visible and infrared spectra can dramatically improve energy efficiency and flexibility in temperature control. By modulating the spectral properties of materials, we can enable buildings, vehicles, and a wide range of electronic devices to automatically respond to environmental changes and optimize thermal management. Electrochromic materials have the property of actively adjusting their color and infrared emittance. Based on this, this paper prepares Al-WO 3 thin films with Fabry-Perot structure by magnetron sputtering, and modulates the color and infrared emissivity of the films by adjusting the thickness of the WO 3 films therein. The reflectance modulation performance of the film shows an increasing and then decreasing trend with the increasing thickness of the WO 3 film, and it has the best performance when the thickness of the WO 3 reaches ∼1080 nm, and the average modulation amplitude of its reflectance can be up to 0.32 (400–700 nm), 0.38 (3–5 μm) and 0.25 (8–14 μm). On this basis, flexible sandwich devices were prepared, which have the advantages of simple preparation, fast response and multi-band modulation. The coloring time and bleaching time of the device are 2.7s and 1.9s, respectively, while the reflectivity modulation range can reach 0.33 (400–700 nm), 0.13 (3–5 μm) and 0.19 (8–14 μm). In addition, the temperature difference between the original state and the colored state of the device under infrared thermal camera is 5.4 °C. • We design a novel device structure that features tungsten oxide in the top layer to investigate changes in emissivity. • The dynamic modulation of multi-band infrared emissivity of tungsten oxide is achieved by adjusting the thickness. • The color modulation of the film showcases a dynamic shift between greenish and reddish hues. [ABSTRACT FROM AUTHOR]

By utilizing the monolayer graphene, we propose a reconfigurable multiband EIT 3D structure in the THz region, which exhibits eight consecutive transparency windows spanning from 1.16 to 2.80 THz, and the according transmission intensities were in the range of 0.75–1.0. Furthermore, with the help of graphene and VO 2 , the transmission curves can be modulated efficiently. The research results demonstrate that the structure proposed can generate high-intensity slow light effects at multiple frequency points within the terahertz range. Compared to existing research on EIT metamaterials, this structure offers advantages such as operation in multiple frequency bands, high transmission coefficients, and flexible modulation capabilities. Therefore, this study helps design novel tunable THz devices. [Display omitted] [ABSTRACT FROM AUTHOR]

In this paper, a highly efficient tree-shaped fractal antenna with multi-broadband resonance characteristics is proposed. The proposed antenna exhibits broad operating bandwidth, high gain, and high efficiency characteristics due to the suggested modifications in the antenna geometry. The suggested circular patch is modified by introducing slots in the form of a tree-shaped fractal structure, and the partial ground plane is modified by incorporating a narrow rectangular slot. The proposed antenna is designed on an FR4 substrate of 4 0 × 2 5. 0 5 × 1. 6 mm3. The prototype of the proposed antenna has been fabricated and tested to justify the simulation results. The measurement results are in good agreement with the simulation that validates the multi-broadband design approach of the proposed fractal antenna. As per the measurement results, the proposed antenna operates at four distinct bands with − 10 dB impedance bandwidths of 600 MHz (2.2–2.8) GHz, 1070 MHz (3.3–4.37) GHz, 2550 MHz (4.75–7.3) GHz, and 2200 MHz (9.7–11.9) GHz. Furthermore, a high peak gain of 10.23 dB and a peak radiation efficiency of 96.65% are recorded for the suggested fractal antenna. The suggested compact bandwidth enhanced multi-band antenna can be useful for several wireless communication systems such as wireless fidelity (Wi-Fi), wireless local area network (WLAN), Bluetooth, long-term evolution (LTE), C, S and X bands. [ABSTRACT FROM AUTHOR]

In this paper, we present and investigate a multi-band metamaterial perfect absorber based on the heterogeneous structure of graphene with Cu and SiO2 substrates. The top layer of structure consists of one graphene disk at the center and four graphene solid triangle with semicircular cuts on them that surround the central disk. This heterogeneous structure causes us to achieve 99.5%, 99.7%, 94.71% and 97.06% perfect absorptions peaks at 4.24 THz, 5.89 THz, 9.66 THz and 10.62 THz, respectively. The absorption mechanism based on electric fields has been investigated. We can shift the wavelength of absorption peaks to our required wavelength by changing the Fermi level (µc) of graphene. Two absorption peaks of this absorber remain unchanged in different light incident angles. In addition, very important point about this structure is that it is not sensitive to polarization and this feature makes the proposed absorber very suitable for applications such as imaging, filtering, sensing and detecting applications. [ABSTRACT FROM AUTHOR]

In the microwave band, we designed a new multi-band metamaterial absorber (MMA) consisting of a Buddhist logo metal resonator enclosed by a non-closed rectangular frame and a metal soleplate, separated by a dielectric layer. Through calculation, five near-perfect absorption peaks were obtained at 5.24, 8.84, 14.28, 15.96 and 18.6 GHz, with absorption rates of 96.39%, 98.13%, 98.26%, 98.07% and 99.75%, respectively. By analyzing the distribution of electromagnetic field and surface current, the absorption mechanism is further explored. Experimental results are consistent with the calculated results. Furthermore, how design parameters affect absorb property has been studied. The MMA has the characteristics of flexible structure and relatively higher absorption rates, which makes it have good potential in stealth materials, radar detection, electromagnetic sensing and other fields. [ABSTRACT FROM AUTHOR]

A design method of five-band polarization-insensitive metamaterial absorber (MMA) based on the slotted structures and the magnetic rubber is proposed for L-, S-, C-, X-, and Ku-band applications. The slotted structures of the top layer, which evolved from two square rings, are used to excite multi-resonance. The range of the electromagnetic (EM) parameters of a magnetic rubber substrate, which is used to adjust the equivalent impedance of the absorber to match the free space impedance in different bands, is estimated using the impedance matching principle. A series of magnetic rubber substrates based on the estimated EM parameters are prepared and measured, whose thickness is only 0.7 mm, meeting the thin design requirements. The absorption of the proposed absorber greater than 90% at 1.7 GHz, 3.87 GHz, 5.96 GHz, 9.4–10.4 GHz, and 14 GHz is achieved when the doping amount of the carbonyl iron powders is 200%. The absorbing performance of the absorber with measured EM parameter agrees well with the theoretical estimates, which validates the accuracy of the proposed design method. [ABSTRACT FROM AUTHOR]

In this work, a novel multi-tracks wideband and multi-band miniaturized antenna design for implanted medical devices biomedical telemetry is proposed. This antenna entirely covers seven frequency bands which are the bands (401-406) MHz of the Medical Device Radiocommunications Service (MedRadio), the three bands (433.1-434.8), (868.0-868.6), and (902.8-928.0) MHz of the Industrial, Scientific, and Medical (ISM), and the three bands (608-614) MHz, and (1.395-1.400) and (1.427-1.432) GHz of theWireless Medical Telemetry Service (WMTS). The antenna possesses a compact full size of (19.5 × 12.9 × 0.456) mm3. The antenna miniaturization and impedance bandwidth enhancement are achieved using two techniques: the patch slotting and insertion of open-end slots in the ground plane, respectively. Prototype of proposed antenna with multi-tracks has been fabricated and tested in free space. The comparison between the simulated and measured reflection coefficient has been done and found in good agreement with each other. Furthermore, simulations of the proposed antenna implanted in the underneath the scalp in a realistic human model shows a wideband operation from 0.19 to 0.94 GHz, and from 1.38 to 1.54 GHz corresponding to return loss (S11 = -10 dB). Link budget calculation is performed to specify the range of telemetry considering both Specific Absorption Rate (SAR) restrictions and effective isotropic radiated power (EIRP) limitations. The designed implantable antenna with full ground plane presents an appropriate reflection coefficient for muscle implantation. Furthermore, the designed implanted muscle antenna may be also suitable for skin implantation. [ABSTRACT FROM AUTHOR]

Polarization and infrared imaging technology have unique advantages for various applications ranging from biology to ocean remote sensing. However, conventional combined polarization camera and infrared camera have limitations because they are constrained to single-band imaging systems with rotating polarizers and cascaded optics. Therefore, we propose a common-aperture mode based on multi-band infrared guided polarization imaging system (IGPIS) in this paper, which consists of infrared wide-area sensing and polarization features acquisition for accurate detection of ship targets. The IGPIS can provide images in visible polarization (0.45–0.76 μm), near-infrared polarization (0.76–0.9 μm), and long-wave infrared (8–12 μm) bands. Satellite attitude parameters and camera optical parameters are accurately calculated by establishing a dynamic imaging model for guidance imaging. We illustrate the imaging principle, sensors specifications and imaging performance analysis and the experimental results show that the MTF is 0.24 for visible and near-infrared, and 0.13 for long-wave infrared. The obtained multi-band images have an average gradient of 12.77 after accurate fusion. These results provide theoretical guidance for the design of common-aperture cameras in remote sensing imaging field. [ABSTRACT FROM AUTHOR]

In this study, we implemented a triplexer using a 65‐nm CMOS process. The triplexer was composed of a low‐pass filter (LPF), bandpass filter (BPF), and high‐pass filter (HPF). Each filter was designed with a Chebyshev structure to obtain a sharp skirt characteristic and series‐first structure to achieve impedance matching in a common terminal, reduction of insertion loss and compact size. The proposed triplexer operates at 0–2 GHz, 5.8–6.5 GHz, and 10.7–14 GHz. In addition, the triplexer shows that the return loss of all ports is more than 10 dB in the bandwidth used. The insertion losses in the passbands, LPF, BPF, and HPF were less than 2.5, 5.55, and 4.4 dB, respectively. The attenuation levels in the stopbands of the LPF, BPF, and HPF are over 47.6, 33.6, and 43.7 dB, respectively. The active area of the triplexer is 0.7 mm × 0.67 mm. To our knowledge, this circuit is the first implementation of a CMOS on‐chip triplexer. [ABSTRACT FROM AUTHOR]

Dipole antenna is the simplest type of antenna from the theoretical point of view. However, the majority of the research on it focuses on adding supplementary structures to produce more resonant modes to achieve more functions. Here, we focus on the inherent modes of the dipole itself. Dipole antenna has alternating odd and even modes. In classical antenna theory, only odd modes are excited. The even modes are difficult to be excited due to their very high input impedances. In this article, both odd and even modes of the dipole antenna are excited simultaneously by a single port with a novel feeding structure. Moreover, to tune the resonant frequencies of such multiple modes, a method by combining antithetical structures of indentations and outdentations is proposed. Its principle is explained intuitively by eigencurrent distribution. By these new techniques, all the first six modes of a dipole are excited, among which five modes are used for Internet of Things (IoT) applications. The antenna can cover industrial, scientific, and medical (ISM) bands of 868 and 2450 MHz, global navigation satellite system (GNSS) band of 1575 MHz, and 5G bands of 3500 and 4900 MHz. This research could broaden the application of this classic antenna. [ABSTRACT FROM AUTHOR]

A differential four-way power divider for 24 to 30 GHz and a frequency reconfigurable differential four-way power divider for 24 to 30 GHz and 37 to 43.5 GHz are presented. The differential structure provides sound virtual grounds in a multiple-channel chip. Both circuits have a four-way Wilkinson power divider (WPD) configuration based on lumped elements that provide small chip sizes. The first one has a small core chip area of 0.09 mm2, a small insertion loss of 0.93 to 1.94 dB, and the port-to-port isolation of 19.1 to 25.6 dB from 24 to 30 GHz. It has a small amplitude and phase differences at four outputs. The second one allows frequency-reconfigurable operation by switching inductances and capacitances to cover widely separated frequency bands (5G NR n257-n261 bands). In addition, switched capacitors (SCs) are inserted to resonate out the parasitic series inductances in isolation resistors at both bands of 24–30 GHz and 37–43.5 GHz. It has a core chip area of 0.168 mm2, insertion losses of 1.65–1.89 dB at 24 to 30 GHz and 2.04–2.70 dB at 37 to 43.5 GHz, respectively. The port-to-port isolations are 23.4–37.6 dB at 24 to 30 GHz and 22.6–28.4 dB at 37 to 43.5 GHz. [ABSTRACT FROM AUTHOR]

In this paper, a compact reconfigurable tri-band/quad-band monopole antenna is presented. To achieve the multi-band behavior, two right-angled triangles were etched in a conventional rectangular patch, and a partial ground plane is used. Moreover, the proposed multi-band antenna is printed on a low cost FR4 epoxy with compact dimensions of 0.23 λ 0 × 0. 2 3 λ 0 × 0. 0 1 2 λ 0 , where λ 0 is calculated at the lowest resonance frequency. To provide frequency agility, a metal strip which acts as PIN diode was embedded in the frame of the modified patch. The tri-band/quad-band antenna performance in terms of reflection coefficient, radiation patterns, peak gain and efficiency was studied. The measured results are consistent with the simulated results for both cases. The simple structure and the compact size of the proposed antenna could make it a good candidate for multi-band wireless applications. [ABSTRACT FROM AUTHOR]

The main advantage of multi-band (MB) networks is to provide more capacity than C-band networks by using other unused bands like the L- and S-bands and, in this way, postpone the announced optical network capacity crunch. However, MB nodes have a more complex structure than C-band nodes, impacting their cost and enhancing their induced physical layer impairments (PLIs). The main goal of this paper is to analyze the impact of several MB node architectures (namely baseline, common-band and compact MB node architectures) on the total network capacity and total network cost-per-bit, using a routing, modulation format, and spectrum assignment (RMSA) network planning tool based on a Monte–Carlo simulation that also incorporates the impact of network PLIs. When the PLIs are neglected, the common-band architecture presents the lowest cost-per-bit compared to the remaining MB architectures, since only lower cost C-band components are used. However, with the PLIs impact, the common-band architecture leads to the lowest total network capacity and highest cost-per-bit due to additional noise coming from all-optical wavelength converters. In particular, the common-band total network capacity is less than half the baseline and compact total network capacities for a blocking probability of 1%, considering the best channel launch power. Also, the common-band cost-per-bit is almost twice the baseline and compact cost-per-bit due to the PLIs-induced degradation. • Four multiband nodes are compared in terms of cost and capacity in a network scenario. • Common-band node loses the cost advantage in presence of physical layer impairments. • Common-band node capacity is less than half the baseline and compact nodes capacity. • Baseline and compact nodes have similar costs and capacities. [ABSTRACT FROM AUTHOR]

A novel synthesis method is proposed to design multi-band bandpass filters (BPFs) using an L-C ladder prototype lowpass filter loaded with two symmetric shorted stubs. The transmission zeros (TZs) are produced by the shorted stubs, which are used to realize multiple passbands. By controlling the number of the open stubs loaded on the shorted stub, the number of TZs is exactly determined. Therefore, multi-band BPF is easy to be obtained by increasing the number of the open stubs. The TZs can be adjusted by optimizing the L-C values of the equivalent circuit of the proposed filter to tune the center frequencies of each passband independently. The proposed BPF also has wide upper stopband. For demonstration, an octa-band BPF is designed and manufactured. The measured results show good agreement with the simulated ones. [ABSTRACT FROM AUTHOR]

This article presents a quad‐band multiple‐input multiple‐output antenna with two‐element. Its radiator, composed of four rings, realizes multi‐band function, and isolation between the two antenna elements is improved by using the cross‐shaped defective ground structure and the goblet shaped stub at the center of the back ground plane. The total size of the design is only 25 mm × 32 mm, but it can obtain good performance in the four frequency bands (4.6‐5.0 GHz, 6.82‐7.83 GHz, 10.3‐10.8 GHz, and 14.1‐16.96 GHz), which can be concluded from the simulation and measurement results on the desired bands: (a) the input reflection coefficient (S11) less than −17 dB, (b) the isolation (S21) better than −15 dB, (c) the envelope correlation coefficient below 0.04 and the peak gain greater than 1.23 dBi. The proposed antenna is suitable for wireless communication of small unmanned aerial vehicle operating in the beyond‐line‐of‐sight range. The first of the four bands (4.6‐5.0 GHz) is used for 5G cellular network communication and the other three bands can be applied for downlink of X‐band (7.25‐7.75 GHz) satellite communication, X‐band (8‐12 GHz) and Ku‐band (12‐18 GHz) satellite communication, respectively. [ABSTRACT FROM AUTHOR]

A passive terahertz security screening system utilizes the contrast of imaged targets in the terahertz band to identify concealed contraband. The variety of covered clothing textures presents a wide distribution of transmission characteristics, resulting in the diversity of high-contrast detection frequencies within the terahertz band. Thus the commonly used single operating band system modelled under one clothing texture is inadequate in multi-type clothing scenarios in practical applications. In this study, the concept of relative contrast is proposed for the detection of concealed metal contraband, and the relationship between the operating band and relative contrast is revealed. Two novel operating band design schemes, a reconfigurable multi-band single-system design and a fixed multi-band dual-system design, are presented. Computer simulation results show that these two design schemes can effectively improve the imaging contrast and enhance the detection effect of passive terahertz security screening systems. [ABSTRACT FROM AUTHOR]

A new multiband circular polarized rectenna is implemented as a radio frequency (RF) power harvesting system tuned for the quad bands of 1.8 GHz (GSM 1800), 2.4/5.8 GHz (WLAN), and 3.6 GHz (WiMAX). An innovative monopole antenna is made for the rectenna; consisting of an octagonal shaped microstrip patch, loaded with an I‐shaped rectangular slot and three L‐shaped stubs so that the antenna creates circular polarization at the quad bands. The second part of the rectenna is a multi‐frequency impedance matching network (IMN) set between the antenna and the rectifier circuit. The IMN includes some parallel shunt stepped impedance stubs (SIS), which provides eight‐band matching network and connected to the rectifier, functioning at the frequencies of 0.84, 1.29, 1.68, 3.08, 3.45, 4.31, 5.11, and 5.49 GHz. Simulation and experimental results verify that the system operates well and deliver proper DC power. For input power of 0 dBm, the peak RF‐to‐DC power conversion efficiencies are 62.69%, 63.28%, 46.94%, 30.23%, 45.69%, 16.42%, 8.13%, and 19.61% at the eight frequency bands, which is higher than the recently reported rectennas. [ABSTRACT FROM AUTHOR]

This article proposes and designs a multi‐band antenna that imitates banana leaves structurally. The edge structure of the antenna radiator is a mirror‐symmetrical trapezoid, and four patches of different sizes are used as leaf veins inside. The feeding mode is coplanar waveguide feeding with a trapezoidal structure. The electromagnetic simulation software HFSS is used for antenna modeling and parameter optimization. The test results show that the antenna can cover 0.79 to 3.18 GHz, 3.29 to 3.98 GHz, and 4.98 to 7.62 GHz and produce six main frequency points: 0.9, 1.5, 2.4, 3.8, 5.6, and 6.9 GHz. The antenna has omnidirectional radiation characteristics and can be widely used in the future mobile communication network coverage field. [ABSTRACT FROM AUTHOR]

We design a structure to achieve a function of polarization-independent multi-band unidirectional reflectionlessness in a non-Hermitian metamaterial system based on the Fabry-Pérot resonance. All contrast ratios of reflectance at 198 THz, 214.2 THz, and 232.65 THz are 0.99. The unidirectional reflectionless peak position remains almost unchanged with increasing polarization angles. Besides, the structure can also be used to realize the unidirectional reflectionless phenomenon in the incident angle range of 0–30 ∘ , which may provide great convenience for experimental operations. [ABSTRACT FROM AUTHOR]

In this study, multi‐band antenna for LTE wearable device with shared slots and radiators for smart watch was present. This study incorporated 4G communication frequency bands, a GPS positioning system, and BT/Wi‐Fi in a 43.6 × 43.6 × 5.8 mm3 metal case to achieve satisfactory radiation fields and performance efficiency within a small space. This article presents an overview of the theory. There are four ports in the system. Frist, Port 1 is a low‐frequency antenna offering LTE 700 and GSM 850/900. The maximal gain and efficiency are respectively 3.9 dBi and 82%. Second, Port 2 is a high‐frequency monopole with a winding long path on the side of the frame to achieve a reflection loss bandwidth that fully encompasses GSM 1800/1900/UMTS and LTE 2300/2500. The maximal gain and efficiency of this port are respectively 5.3 dBi and 92%. There are also have GPS (Port 3) and Wi‐Fi (Port 4) antenna implement IFA and loop excitation mechanisms, respectively. This antenna system can fulfill the market demand. As confirmed through both simulation and measurement, the antenna can cover LTE bands. Increasing the path capacity of a MIMO system to increase the transmission speed is a crucial focus in mobile communication research and development. [ABSTRACT FROM AUTHOR]