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Laser diode absorption spectroscopy is used to experimentally measure Ar(1s5) metastable density and translational gas temperature within a 94 GHz microplasma. A square two-dimensional photonic crystal (PhC) at this resonance frequency serves to ignite and sustain the plasma from 20 to 200 Torr (2.7 × 103–2.7 × 104 Pa) by using millimeter wave power from 300 to 1000 mW. Metastable density within the plasma is estimated from the absorption line shape of the laser traversing the PhC. The metastable density reaches an order of 1019 m−3 at lower pressure and decreases as pressure increases. From the Lorentzian line shape of the absorption profile at 811.53 nm, the gas temperature is extracted and found to increase from 500 K at 20 Torr to 1300 K at 200 Torr. These data are analyzed and compared with a zero-dimensional plasma model and with previous experimental plasma results at 43 GHz. [ABSTRACT FROM AUTHOR]

Millimeter wave MIMO wireless communication systems are deployed in 5G and next‐generation networks. The effectiveness of deep learning models for improving the performance of these systems has been proven in the literature. However, several deep learning models are vulnerable to security threats, such as adversarial attacks. Therefore, for the deployment of these systems, it is essential to make them resilient to such kinds of attacks for good quality secure communication. Adversarial training is a solution by which deep learning models are trained for adversarial attacks beforehand. Adversarial training for three types of adversarial attacks, that is, Fast Gradient Sign Method, Iterative Fast Gradient Sign Method, and Momentum Iterative Fast Gradient Sign Method is implemented in this paper. The simulation results depict a decrease in the error at the receiving end after adversarial training, even after an adversarial attack has been applied. © 2024 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

Summary: In this paper, a vector‐sum phase shifter (VSPS) integrated with a wideband high‐gain low‐noise amplifier (LNA) for Ka‐band phased‐array receivers is presented. The digitally controlled VSPS based on the RF phase shifting architecture consists of a modified I/Q signal generator with additional inductor resonance and a programmable variable gain amplifier (VGA) based on Four 3 × 4 transistor arrays. Besides the reduced parasitic effect of the I/Q signal generator, an Equidistant Contraction Technology (ECT) is used in the VGA, to maintain higher phase shift accuracy of the VSPS. A multistage LNA with series inductor peaking is adopted to fulfill the flat wideband gain, where LC resonance networks are used as interstage matching to compensate for gain roll‐off at a higher frequency. Based on simulations in 65 nm CMOS technology, the presented LNA‐Phase shifter has achieved an average NF of 3.24–3.66 dB, and an average gain of 13.1–23.6 dB. Moreover, an RMS phase error of 1.1–12.6°, an RMS gain error of 4.2–5.6 dB, and an RMS magnitude error of 2.1–2.8 dB are maintained across 27–40 GHz, with a 360° phase shift coverage in steps of approximately 2.8125°. The chip consumes 16.83 mW from a 1.2 V supply voltage, and the occupied area is 0.65 mm2. [ABSTRACT FROM AUTHOR]

In recent years, the development of intelligent sensor systems has experienced remarkable growth, particularly in the domain of microwave and millimeter wave sensing, thanks to the increased availability of affordable hardware components. With the development of smart Ground-Based Synthetic Aperture Radar (GBSAR) system called GBSAR-Pi, we previously explored object classification applications based on raw radar data. Building upon this foundation, in this study, we analyze the potential of utilizing polarization information to improve the performance of deep learning models based on raw GBSAR data. The data are obtained with a GBSAR operating at 24 GHz with both vertical (VV) and horizontal (HH) polarization, resulting in two matrices (VV and HH) per observed scene. We present several approaches demonstrating the integration of such data into classification models based on a modified ResNet18 architecture. We also introduce a novel Siamese architecture tailored to accommodate the dual input radar data. The results indicate that a simple concatenation method is the most promising approach and underscore the importance of considering antenna polarization and merging strategies in deep learning applications based on radar data. [ABSTRACT FROM AUTHOR]

This paper proposes a 32‐tupling frequency millimeter‐wave (MMW) filter‐free system based on four Mach‐Zehnder Modulators (MZM) connected in parallel and cascaded with a simple radio‐fiber (RoF) link structure. The four MZMs are all at the maximum transmission point (MATP), and the radio frequency (RF) driving voltage phase difference between MZMs is π /2. The center carrier is suppressed by using an optical attenuator (OATT) and an optical phase shifter (OPS). Two parallel MZMs can generate ±8th order and ±12th order optical sidebands, and the ±4th order optical sidebands can be suppressed by adjusting the modulation index m of the MZM, using cascaded two dual‐parallel MZMS(DPMZM) and the phase difference of the RF signal source is π/4 to generate ±16th order optical sidebands. The theoretical analysis and simulation experiments are performed for the scheme proposed in this paper. The results show that the simulated and theoretical values of the optical sideband suppression ratio (OSSR) for ±16th order optical sideband signals are 60.02 and 59.96 dB, respectively, and the simulated and theoretical values of the RF sideband suppression ratio (RFSSR) for the 32‐tupling MMW signal are 56.34 and 53.94 dB, respectively. [ABSTRACT FROM AUTHOR]

Rainfall can reduce the radar signal through a radome. The effects of different water layers on the radome transmission are studied using quasi-optical measurement from 26 to 330 GHz including water permittivity characterization. The water is deposited as drops of different sizes or as a uniform layer while keeping a constant volume, highlighting the importance of the control of the total wet surface for radar applications. A compact model is proposed to predict the signal loss due to water on the radome depending on the rain flow. [ABSTRACT FROM AUTHOR]

Summary: This paper presents a wideband millimeter wave (mmWave) channel model for aerial reconfigurable intelligent surface (ARIS) communications, in which the reconfigurable intelligent surface (RIS) is attached to an unmanned aerial vehicle (UAV) to enable intelligent signal reflections in the air. The model is established according to standard 3GPP channel models and considers important propagation factors, for example, large‐scale fading, small‐scale fading, and radiation pattern of reflection units (RUs). In addition, the model assumes three‐dimensional (3D) rotations of RIS and can capture its effects on channel characteristics. Based on the model, we propose a design method for RIS reflection phases. Statistics including channel amplitude, spatial, temporal, and frequency correlation functions (CFs), and space‐Doppler power spectral density (SD‐PSD) are obtained. The impacts of RU number, UAV height and speed, and RIS rotation on channel statistics are investigated. Results suggest that the designed reflection phases can effectively mitigate multipath fading and Doppler effect. Compared to the yaw angle of the UAV platform, channel characteristics are more sensitive to the roll and pitch angles. [ABSTRACT FROM AUTHOR]

A novel method to generate and two frequency 16-tupling millimeter wave (MMW) and distribute the generated MMW over fiber system (MMOF) with two base stations (BS) by the remodulation with Mach–Zehnder modulators (MZM) is proposed. At the central station(CS), the ± 4th order optical sidebands generated by a dual parallel MZM (DPMZM) are split into two branches, one of which is injected into a photodetector (PD) to generate the 8th harmonic of the RF drive signal of the MZM, which acts as the RF driving signal for the remodulation, and the other acts as the carrier for the remodulation. The remodulation is realized by injecting the outputs of the two branches into an MZM. After remodulation, the signal which contains mainly the ± 20th, ± 12th and ± 4th order optical sidebands is divided into two branches, in which the positive and negative sidebands are filtered out by two optical band-pass filters (OBPF) first and the 4th and − 4th order sidebands are filtered by two fiber Bragg gratings (FBG) later, with which the data of the downlink are modulated on it. At the two BSs, the 12th and − 12th order sidebands in the downlink optical signal are first filtered out by two FBGs, with which the data of the uplink are modulated onto it and transmitted to the CS via optical fibers for carrier reuse; the output signals of the FBGs are injected into two PDs to produce two 16-tupling frequency MMWs with the data of downlinks. The feasibility of our scheme is verified by theoretical analysis and simulation experiments. The main innovations of our designed scheme are that the modulation index of MZM is greatly reduced by using the remodulation method, the power utilization rate is greatly improved by using all the main sidebands and the cost of the system is reduced by using the two BSs structures with carrier reuse. [ABSTRACT FROM AUTHOR]

The location monitoring of underground pipelines is of utmost significance as it helps the effective management and maintenance of the pipelines, and facilitates the planning of nearby projects, preventing damage to the pipelines. However, currently there is a serious lack of data on the locations of underground pipelines. This paper proposes an image-based approach for monitoring the locations of underground pipelines by combing deep learning and visual-based reconstruction. The proposed approach can build the monitoring model for underground pipelines and characterize their locations through their centroid curve. Its advantages are: (1) simplicity: it only requires time-sequential images of the inner walls of underground pipelines; (2) clarity: the location model and the location curve of underground pipelines can be provided quickly; (3) robustness: it can cope with some existing problems in underground pipelines, such as light variations and small viewing angles. A lightweight approach for monitoring the locations of underground pipelines is achieved. The proposed approach's effectiveness has been validated through laboratory simulation experiments, demonstrating accuracy at the millimeter level. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this paper is to illustrate the new technical demands and reliability challenges to printed circuit board (PCB) designs, materials and processes when the transmission frequency increases from Sub-6 GHz in previous generations to millimeter (mm) wave in fifth-generation (5G) communication technology. Design/methodology/approach: The approach involves theoretical analysis and actual case study by various characterization techniques, such as a stereo microscope, metallographic microscope, scanning electron microscope, energy dispersive spectroscopy, focused ion beam, high-frequency structure simulator, stripline resonator and mechanical test. Findings: To meet PCB signal integrity demands in mm-wave frequency bands, the improving proposals on copper profile, resin system, reinforcement fabric, filler, electromagnetic interference-reducing design, transmission line as well as via layout, surface treatment, drilling, desmear, laminating and electroplating were discussed. And the failure causes and effects of typical reliability issues, including complex permittivity fluctuation at different frequencies or environments, weakening of peel strength, conductive anodic filament, crack on microvias, the effect of solder joint void on signal transmission performance and soldering anomalies at ball grid array location on high-speed PCBs, were demonstrated. Originality/value: The PCB reliability problem is the leading factor to cause failures of PCB assemblies concluded from statistical results on the failure cases sent to our laboratory. The PCB reliability level is very essential to guarantee the reliability of the entire equipment. In this paper, the summarized technical demands and reliability issues that are rarely reported in existing articles were discussed systematically with new perspectives, which will be very critical to identify potential reliability risks for PCB in 5G mm-wave applications and implement targeted improvements. [ABSTRACT FROM AUTHOR]

Rotational constants and centrifugal distortion constants of a molecule are the essence of its rotational or rovibrational spectrum (e.g., from microwave, millimeter wave, and infrared experiments). These parameters condense the spectroscopic characteristics of a molecule and, thus, are a valuable resource in terms of presenting and communicating spectroscopic observations. While spectroscopic parameters are obtained from experimental spectra by fitting an effective rovibrational Hamiltonian to transition frequencies, the ab initio calculation of these parameters is usually done within vibrational perturbation theory. In the present work, we investigate an approach related to the experimental fitting procedure, but relying solely on ab initio data obtained from variational calculations, i.e., we perform a nonlinear least squares fit of Watson's A- and S-reduced rotation–vibration Hamiltonian to rovibrational state energies (resp. transition frequencies) from rotational–vibrational configuration interaction calculations. We include up to sextic centrifugal distortion constants. By relying on an educated guess of spectroscopic parameters from vibrational configuration interaction and vibrational perturbation theory, the fitting procedure is very efficient. We observe excellent agreement with experimentally derived parameters. [ABSTRACT FROM AUTHOR]

This paper presents a super wideband and high-gain log periodic dipole array (LPDA) antenna. The overall structure of the antenna was constructed using microwave studio computer simulation technology. The optimal sizes of the planned antenna are 39 × 10× 0.254 mm3. The engineered antenna arrangement is implemented on an RT5880 substrate as a dielectric medium. The LPDA is arranged in four arms that are equally spaced on both lines. The main 50Ω feeder line is partially grounded at the back of the substrate. A combination of circular director units is being studied and tuned in a regular pattern at a predefined distance from the antenna. An improvement in gain of 3 dBi is the response of the director units. The Conformist LPDA is adjusted to achieve a wide range of millimeter wave bands ranging from 40 to over 70 GHz. The antenna resonates at 60 GHz, where the maximum realized gain of 14.97 dBi is attained. The antenna was tested for utilization in the V-band involving wireless personal area network (WPAN) applications recommended by IEEE 802.11ad and IEEE 802.15.3c. The outcomes of the constructed antenna elements' tests and simulations agree fairly well. The proposed layout works better than previous efforts in this field. [ABSTRACT FROM AUTHOR]

Submillimeter wave radiometers are promising remote sensing tools for sounding ice cloud parameters. The Ice Cloud Imager (ICI) aboard the second generation of the EUMETSAT Polar System (EPS−SG) is the first operational submillimeter wave radiometer used for ice cloud remote sensing. Ice clouds simultaneously contain three species of ice hydrometeors—ice, snow, and graupel—the physical distributions and submillimeter wave radiation characteristics of which differ. Therefore, jointly retrieving the mass parameters of the three ice hydrometeors from submillimeter brightness temperatures is very challenging. In this paper, we propose a multiple species of ice hydrometeor parameters retrieval algorithm based on convolutional neural networks (CNNs) that can jointly retrieve the total content and vertical profiles of ice, snow, and graupel particles from submillimeter brightness temperatures. The training dataset is generated by a numerical weather prediction (NWP) model and a submillimeter wave radiative transfer (RT) model. In this study, an end to end ICI simulation experiment involving forward modeling of the brightness temperature and retrieval of ice cloud parameters was conducted to verify the effectiveness of the proposed CNN retrieval algorithm. Compared with the classical Unet, the average relative errors of the improved RCNN–ResUnet are reduced by 11%, 25%, and 18% in GWP, IWP, and SWP retrieval, respectively. Compared with Bayesian Monte Carlo integration algorithm, the average relative error of the total content retrieved by RCNN–ResUnet is reduced by 71%. Compared with BP neural network algorithm, the average relative error of the vertical profiles retrieved by RCNN–ResUnet is reduced by 69%. In addition, this algorithm was applied to actual Advanced Technology Microwave Sounder (ATMS) 183 GHz observed brightness temperatures to retrieve graupel particle parameters with a relative error in the total content of less than 25% and a relative error in the profile of less than 35%. The results show that the proposed CNN algorithm can be applied to future space borne submillimeter wave radiometers to jointly retrieve mass parameters of ice, snow, and graupel. [ABSTRACT FROM AUTHOR]

For the challenges of high-precision mapping in complex terrain, a novel airborne Interferometric Synthetic Aperture Radar (InSAR) system is designed. This system, named ASMIS (Airborne Short-Baseline Millimeter-Wave InSAR System), adopts the coplanar antenna and a pod-type structure. This design makes the system lightweight and highly integrated. It can be compatible with small general aviation flight platforms. The baseline is millimeters in size, which greatly simplifies the unwrapping process. The coplanar antennas have two advantages: they maximize the baseline utilization and minimize the Doppler decorrelation and the motion error inconsistency. Acquisition campaigns of the system have been carried out in Boao, Bayannur, and Chengde, China. In the Chengde experimental area, we designed an antiparallel flight experiment to account for the topographic relief. High-precision Digital Orthophoto Maps (DOMs) and Digital Surface Models (DSMs) at a scale of 1:5000 were obtained. The coordinate Root Mean Square Error (RMSE) of the checkpoints within the obtained DSM is less than 0.82 m in altitude and 3 m horizontally. The RMSE of the Sparse Ground Control Points (GCPs) within the obtained DSM is less than 0.3 m in altitude. Experimental results from different areas, including plains, mountains, and coastlines, demonstrate the system's performance. [ABSTRACT FROM AUTHOR]

Millimeter-wave (mmWave) communication systems leverage the directional beamforming capabilities of antenna arrays equipped at the base stations (BS) to counteract the inherent high propagation path loss characteristic of mmWave channels. In downlink mmWave transmissions, i.e., from the BS to users, distinguishing users within the same beam direction poses a significant challenge. Additionally, digital baseband precoding techniques are limited in their ability to mitigate inter-user interference within identical beam directions, representing a fundamental constraint in mmWave downlink transmissions. This study introduces an innovative analog beamforming-based interference mitigation strategy for downlink transmissions in reconfigurable intelligent surface (RIS)-assisted hybrid analog–digital (HAD) mmWave systems. This is achieved through the joint design of analog beamformers and the corresponding coefficients at both the RIS and the BS. We first present derived closed-form approximation expressions for the achievable rate performance in the proposed scenario and establish a stringent upper bound on this performance in a large number of RIS elements regimes. The exclusive use of analog beamforming in the downlink phase allows our proposed transmission algorithm to function efficiently when equipped with low-resolution analog-to-digital/digital-to-analog converters (A/Ds) at the BS. The energy efficiency of the downlink transmission is evaluated through the deployment of six-bit A/Ds and six-bit pulse-amplitude modulation (PAM) signals across varying numbers of activated RIS elements. Numerical simulation results validate the effectiveness of our proposed algorithms in comparison to various benchmark schemes. [ABSTRACT FROM AUTHOR]

The success of next-generation Internet of Things (IoT) applications could be boosted with state-of-the-art communication technologies, including the operation of millimeter-wave (mmWave) bands and the implementation of three-dimensional (3D) networks. With some access points (APs) mounted on unmanned aerial vehicles (UAVs), the probability of line-of-sight (LoS) connectivity to IoT nodes could be augmented to address the high path loss at mmWave bands. Nevertheless, system optimization is essential to maintaining reliable communication in 3D IoT networks, particularly in dense urban areas with elevated buildings. This research adopts the implementation of a geometry-based stochastic channel model. The model customizes the standard clustered delay line (CDL) channel profile based on the environmental geometry of the site to obtain realistic performance and optimize system design. Simulation validation is conducted based on the actual maps of highly dense urban areas to demonstrate that the proposed approach is comprehensive. The results reveal that the use of standard channel models in the analysis introduces errors in the channel quality indicator (CQI) that can exceed 50% due to the effect of the environmental geometry on the channel profile. The results also quantify accuracy improvements in the wireless channel and network performance in terms of the CQI and downlink (DL) throughput. [ABSTRACT FROM AUTHOR]

Novel Na 4-x Ag x Co(MoO 4) 3 (x = 0–0.09) compounds were prepared using a solid state ceramic route. The investigation focused on the impact of intrinsic and extrinsic factors on the microwave dielectric properties of the samples. All samples were identified as belonging to the monoclinic structure with the C 2/ c space group. An optimal combination of microwave dielectric properties (ε r = 8.55, Q × f = 30,300 GHz and τ f = –30 ppm/°C) can be obtained for pure Na 4 Co(MoO 4) 3 specimen fired at 660 °C. Partially replacing Na+ with Ag+ in Na 4-x Ag x Co(MoO 4) 3 ceramics resulted in a more stable structure and significantly increased the Q × f value to 64,000 GHz at x = 0.03. Additionally, the study suggested that Na 3.95 Ag 0.05 Co(MoO 4) 3 , sintered at 600 °C, could be a very promising candidate for ULTCC applications at microwave and millimeter wave frequencies due to its high thermal stability. This compound exhibited tremendous microwave dielectric properties (ε r = 9.2, Q × f = 53,000 GHz and τ f = –9.8 ppm/°C), which fit well within the criteria for today's 5G/6G applications, and demonstrated good compatibility with Al pastes. The designed and fabricated hairpin filter on the Na 3.95 Ag 0.05 Co(MoO 4) 3 substrate also demonstrated an excellent frequency response for 5G/6G applications. [ABSTRACT FROM AUTHOR]

Corrosion detection (CD) has become a high priority in chemical industries, defense and transportation sectors to extend the life of existing or new systems while ensuring the safety of the existing components and reducing downtime to minimise economic losses. Here, this article is aimed to review and discuss non-destructive techniques used widely in the industry to detect, monitor and repair corrosion problems early on. The comprehensive review provides a detailed discussion, a functional mechanism, advantages and disadvantages of crucial non-destructive CD techniques widely used in the industry, helping the reader choose the type of corrosion monitoring methods effectively. An extensive literature review of visual and optical testing techniques, acoustic emissions, eddy current, guided wave and equipment, infrared thermography, radiographic, microwave and millimeter wave, and terahertz imaging is discussed. The underlying mechanism, its merits and limitations, along with the usage scenario, is explained that can be related across different areas making it interdisciplinary research for corrosion monitoring techniques. [ABSTRACT FROM AUTHOR]

An optically transparent and angularly stable frequency selective surface (FSS) with a broad stopband is introduced for addressing millimeter wave (mmW) electromagnetic interference. The unique FSS unit cell pattern incorporates a cross patch with Y‐shaped branches, effectively broadening the bandwidth and enhancing the angular stability. Utilizing transparent conductive indium tin oxide deposited on both sides of a glass substrate enables the FSS to reflect and absorb electromagnetic waves. Consequently, the proposed FSS exhibits an exceptionally wide stopband ranging from 18.7 to 40.2 GHz, featuring an insertion loss of 14 dB and maintaining stable angular response up to 60° for both transverse electric and transverse magnetic polarizations. Moreover, an equivalent circuit model is developed to characterize the stopband behavior of the FSS. Finally, measurements conducted on a physical prototype of the proposed FSS validate its effectiveness, showing good agreement with the simulation results. [ABSTRACT FROM AUTHOR]

In this letter, a wideband cavity‐backed filtering antenna based on 3‐D printing technology is proposed for millimeter wave applications. This antenna is made up of an air‐filled metal cavity, attached with two transverse slots on its upper surface. By exciting one TE110 cavity mode and two slot modes simultaneously, wideband performance can be obtained. Besides, by properly bending one slot into U‐shape, two radiation nulls appear at two sides of the passband, yet causing the increase of the cross‐polarization in H‐plane. To remedy this, the U‐shaped slot is further bent at its ends, successfully suppressing the cross‐polarization by 7 dB. The final proposed filtering antenna is implemented and measured, showing a wide bandwidth of 37.3%, covering from 21.4 to 31.2 GHz. And the measured maximum gain is 6.6 dBi in band, with two radiation nulls at 14.6 and 40 GHz. [ABSTRACT FROM AUTHOR]

The millimeter‐wave radar sensor is widely used for urban traffic surveillance because of its weather resistance and high detection accuracy. Methods such as fuzzy theory, pattern recognition, and artificial neural networks have been integrated into the research of traffic state discrimination. However, research on systematically describing the fusion of sensors and traffic state discrimination algorithms to alleviate urban road congestion is still lacking, especially based on millimeter‐wave radar. Thus, the authors propose an urban traffic congestion alleviation system framework. First, the design and deployment of the millimeter‐wave radar system, including waveforms, signal processing flow, and target tracking, are demonstrated to achieve vehicle information acquisition and output. Then, the appropriate traffic parameters are obtained by analysing traffic state influencing factors and the radar data characteristics. Finally, a traffic conditions identification algorithm combining spectral clustering and neural network algorithm is presented to realise road congestion level classification. The system is applied to real urban intersections rather than simulation or approximate real simulation. According to the current road congestion level, regulate the traffic light state to achieve road vehicle driving command. Experiments show that the proposed system can effectively reduce road congestion by 20% compared to the current fixed traffic light system. [ABSTRACT FROM AUTHOR]

We proposed a newly devised method for measuring the complex permittivity of high-loss materials at the millimeter wave frequency range. In this paper, we employed a geometrical gap between samples, which allows us to evaluate the complex permittivity of high-loss materials. By introducing this gap, we obtain a characteristic shape of the transmittance, which enables us to fit the data and obtain a more precise complex permittivity value. The proposed method has been supported by experimental results with a very low error bar compared to the existing fundamental transmission line method. We measured diverse samples including alumina, Teflon, Vero family, and AlN-SiC, and confirmed that the proposed gap method achieves much higher precision than the existing method by 3 to over 10 times. Particularly for high-loss materials like the AlN-SiC sample, the average error of the relative permittivity evaluated by the existing transmission line method is 2.05% whereas the error by the proposed method is 0.05%. Moreover, the average error of the loss tangent measured by the existing method and the suggested method is 1.85% and 0.3%, respectively, which confirms the superiority of the proposed method. [ABSTRACT FROM AUTHOR]

The millimeter wave spectrum fulfills the demand for higher data rates with low latency. Moreover, futuristic wearable gadgets demand flexible antennas operating at these frequencies, such that they can easily be accommodated. Therefore, the article focuses on designing a compact and highly flexible antenna with the aid of characteristic mode analysis (CMA). A thin polyimide substrate of 0.1 mm thickness is used to maintain flexibility. The overall antenna profile is 0.61 λ 0 × 0.61 λ 0 . The design evolves through four stages, where, in each stage, the solution to the surface current through eigenvalue leads to significant modes. The final stage design generated Mode 2 fundamental mode at 30.5 GHz along with contributing Modes 3 and 5 with a bandwidth range of 28-31.5 GHz. Further, the design is simulated using electromagnetic simulation software, and the prototype is fabricated. The simulated and measured reflection coefficient |S11| > 10 dB in 28.72-32 GHz and 28.9-31.75 GHz. The CMA analyzed, simulated, and measured gain is 4.82 and 5.6 dBi, respectively. The proposed antenna has a stable response for conformal orientations along the x and y-axis. The antenna has resulted in bidirectional radiation in the XZ plane with simulated and measured half-power-beam-width (HPBW) of 58° and 54°. In the YZ plane, it resulted in omnidirectional radiation. The simulated and measured results are in good agreement. The article also performs the link budget analysis. It suggested that the antenna can communicate 100 Mbps of data to a distance of 100 m and 1 Gbps of data up to 70 m. Thus, the proposed antenna structure is suitable for wearable, IoT, and other 5G wireless applications. [ABSTRACT FROM AUTHOR]

Many vehicle applications requiring large capacity, minimal latency, and excellent dependability are anticipated to be made possible by 5G. To help with this, 5G suggests using highly focused mmWave networking implementation, denser, more minor cell innovation, and various new sophisticated communications techniques to increase networking bandwidth, lower latency, and offer high dependability. Robust mobility managing strategies are needed in these networks to enable automotive connection wherein the points are very dynamic to reduce transmission costs and disruptions during periodic transfers. Engineers working on technology for communication have to tackle this significant obstacle to fulfil the potential of 5G networks enabling V2X and comparable purposes. Therefore, a new implementation strategy is essential to support 5G functionalities. A possible approach for the 5G system installation optimization challenge is predicted to involve using meta-heuristics. To reduce the number of basis stations (BSs) as well as optimize the assignments in millimetre wave (mmWave) frequency ranges (such as 28 GHz as well as 38 GHz) within the framework of such 5G system while fulfilling customer data rates requirements, a deployment regarding a meta-heuristic method depending upon swarming intelligence is presented in this paper. After that, a sequential procedure is used to eliminate unnecessary BSs. [ABSTRACT FROM AUTHOR]

Summary: The hybrid precoding problem is considered a Frobenius norm reduction problem for the narrowband channel in a millimeter wave (mmWave) with multiple inputs and outputs (mmWave MIMO). This work proposes a hybrid distributed online and alternating convex optimization (HDO‐ACO) algorithm to improve hybrid precoding (HP), interpreted as a trace minimization problem. HDO‐ACO alternately determines the digital and analog precoders to reduce the trace by keeping the other constant. Initially, HDO‐ACO uses Lagrange's method to determine the digital precoding subproblem. Then, it uses the integrated distributed online convex optimization and alternating minimization algorithm in the analog precoder design. In the HP method, the digital and analog precoders are iteratively updated until the highest number of iterations or convergence is reached. But this hybrid precoding method requires an initial analog precoding matrix input to begin the iteration. The algorithms converge gradually and fall into a suboptimal solution when the initial analog precoding matrix is set randomly. Hence, an initial value acceleration‐based heuristic approach is used in the HDO‐ACO alternating minimization algorithm that calculates the initial feasible value of an alternating minimization method using channel conditions. The simulation results of the proposed HDO‐ACO algorithm are presented under bit error rate (BER), spectral efficiency (SE), and convergence behavior by comparing it with modified block coordinate descent–HP (MBCD‐HP), manifold optimization–alternating minimization (MO‐AltMin), and semi‐definite relaxation‐based alternating optimization (SDR‐AO). The proposed HDO‐ACO attains maximum SE and less BER than other hyper‐precoding designs. [ABSTRACT FROM AUTHOR]

Most calibration laboratories prefer the Direct Comparison Transfer Method (DCTM) for a reliable and accurate calibration of power sensors in the radio frequency (RF) scope. Most studies suggest using this calibration method, with its automatic power level control (APLC) of RF signal generators. The APLC is preferred to keep the output power level of the signal generator the same, while the power sensor is calibrated and the reference power sensor is connected to the measurement system. The known APLC mechanisms are also explained for the DCTM, and a comparison of the calibration factor values carried out with and without the automatic power level control process in the DCTM is also given in this study. RF power sensor calibrations with coaxial and waveguide connector types are examined with DCTM in this study as well. This study shows that the DCTM, unless with APLC, should be applied for the waveguide power sensor's calibration at millimeter wave frequencies. [ABSTRACT FROM AUTHOR]

During the COVID-19 pandemic, the number of cases continued to rise. As a result, there was a growing demand for alternative control methods to traditional buttons or touch screens. However, most current gesture recognition technologies rely on machine vision methods. However, this method can lead to suboptimal recognition results, especially in situations where the camera is operating in low-light conditions or encounters complex backgrounds. This study introduces an innovative gesture recognition system for large movements that uses a combination of millimeter wave radar and a thermal imager, where the multi-color conversion algorithm is used to improve palm recognition on the thermal imager together with deep learning approaches to improve its accuracy. While the user performs gestures, the mmWave radar captures point cloud information, which is then analyzed through neural network model inference. It also integrates thermal imaging and palm recognition to effectively track and monitor hand movements on the screen. The results suggest that this combined method significantly improves accuracy, reaching a rate of over 80%. [ABSTRACT FROM AUTHOR]

The attachment of 5G with millimeter wave (mmWave) frequencies offers massive capacity and low latency to reveal the full 5G experiences. High directive gain and beamforming are considered essential for mmWave 5G systems. The main requirements of the beamforming network for 5G mmWave applications are the scanning coverage of ± 60° and SLL > 10 dB in a wide operational bandwidth over the standard 5G frequency bands. In this paper, a novel PCB-based wide-angle Rotman lens beamformer is designed, simulated, and successfully measured to meet the mentioned requirements for 5G mmWave applications. A comprehensive improved design methodology is provided for all components of the Rotman lens to reach a wide scanning angle, enhanced sidelobe level, and low scan loss. The end-fire Vivaldi antenna is selected as an array element for easy integration to the beamforming network as well as its capability to use in dual-polarization configuration. The proposed Rotman lens is operational in the 24–30 GHz frequency band covering 5G n257, n258, and n261 frequency bands. The results show a nearly constant 8 beams across the whole bandwidth steering from − 53° to 53° in 15° increments to provide ± 60° coverage with the SLL > 10 dB and scan loss < 1.9 dB. The retrieved novelties from this work contain an effective design methodology for an optimized Rotman lens with wide-scan angle and low phase and amplitude error, non-uniform distribution based array ports, and integration with end-fire antenna for possible dual polarization and 2-D beamforming capabilities. The comparison of the proposed beamformer with the most recent works shows several advantages in terms of integrated structure and performances including bandwidth, wide scanning angle, SLL, and scan loss. With such performances, this beamformer can be used for various mmWave and 5G applications such as advanced antenna systems, massive MIMO systems, and hybrid beamforming systems. [ABSTRACT FROM AUTHOR]

The existing frequency bands, such as the C-band and L-band, are becoming increasingly crowded and cannot meet the growing demand for high-speed data rate services. To overcome spectrum congestion, meet future business needs, and overcome the bottlenecks of traditional electronic methods, we have modified an approach for generating W-band mm-wave signals with octupling frequency without the need for an optical filter. One integrated modulator consisting of two push-pull Mach-Zehnder modulators (MZM) in series is employed to achieve W-band signal generation. The octupling frequency signal generation depends on ±4th optical sidebands to beat frequency in the photodetector. For capturing ±4th optical sidebands, the bias point of the two push-pull MZMs needs work at the peak point, and the modulation index of the two MZMs should be simultaneously set to 2.4. We have conducted detailed mathematical derivation and computer simulation for the scheme, demonstrating its correctness. The results show that the optical sideband suppression ratio is not less than 45.73 dB, and the RF sideband suppression ratio can reach 37.64 dB. [ABSTRACT FROM AUTHOR]

This paper introduces a new absorber that can effectively absorb millimeter wave frequencies. The design involves stacking foam, plasma, and laminated graphene sheets on a perfect electric conductor substrate. The absorber can generate a wideband effect on electromagnetic waves by combining graphene layers and a plasma medium. The absorption and bandwidth of the plasma slab depend on various parameters like plasma frequency, collisional rate, and thickness. By tuning the plasma frequency ω p (rad/s), average collision frequency υ p (Hz), Fermi energy of graphene sheets, and thickness of the foam and plasma layers, the benefit of wideband and good absorption considering reflection amplitude lower than −15 dB, an ultra-bandwidth from 32 to 150 GHz can be achieved. This structure has multiple layers that have bandgap and band-stop regions. These regions are associated with the cavities of dielectric slabs that have graphene sheets. These regions are identified as coupled Fabry–Pérot resonances, which can induce multiple interference effects in multi-reflection for the incident electromagnetic waves, resulting in high-level absorption. Understanding and controlling these resonances is crucial for optimizing the performance of such systems. An equivalent circuit model has been used to predict the absorber's performance. The proposed absorber has a symmetrical structure that reacts similarly to transverse-electric and transverse-magnetic waves. The frequency range of the absorber has been studied to determine the effects of the graphene sheets' relaxation time and voltage biasing. The absorber offers advantages such as being thin, having a wide bandwidth, and being insensitive to polarization. [ABSTRACT FROM AUTHOR]

The traditional algorithms for generating 3D human point clouds often face challenges in dealing with issues such as phantom targets and target classification caused by electromagnetic multipath effects, resulting in a lack of accuracy in the generated point clouds and requiring manual labeling of the position of the human body. To address these problems, this paper proposes an adaptive method for generating 3D human point clouds based on 4D millimeter-wave radar (Self-Adaptive mPoint, SA-mPoint). This method estimates the rough human point cloud by considering micro-motion and respiration characteristics while combining the echo dynamic with static information. Furthermore, it enhances the density of point cloud generation. It reduces interference from multipath noise through multi-frame dynamic fusion and an adaptive density-based clustering algorithm based on the center points of humans. The effectiveness of the SA-mPoint algorithm is verified through experiments conducted using the TI Millimeter Wave Cascade Imaging Radar Radio Frequency Evaluation Module 77G 4D cascade radar to collect challenging raw data consisting of single-target and multi-target human poses in an open classroom setting. Experimental results demonstrate that the proposed algorithm achieves an average accuracy rate of 97.94% for generating point clouds. Compared to the popular TI-mPoint algorithm, it generates a higher number of point clouds on average (increased by 87.94%), improves the average accuracy rate for generating point clouds (increased by 78.3%), and reduces the running time on average (reduced by 11.41%). This approach exhibits high practicality and promising application prospects. [ABSTRACT FROM AUTHOR]

In this article, the problem of achieving the minimum backbone connectivity cost while simultaneously maximizing user coverage for 5G millimeter-wave (mmWave)-based networks is considered. Let G = (N , E) be an input graph instance with a set of nodes N (base stations) and a set of edges E. It is assumed that G represents a wireless backbone network. Let M represent a set of users to be covered by G. Note that mmWave technology has been considered in the literature as an important candidate solution for 5G networks due to its low latency. However, there remain some problems to be addressed before using this technology. A serious one is that millimeter waves cannot cover large transmission distances. In this article, the proposed methodology consists of formulating mixed-integer programming models to deal with the problem from a management point of view. Our models allow the determination of which of the nodes of G should be active and connected while simultaneously maximizing the total number of covered users. The models are solved with the CPLEX solver using its branch and cut and automatic Benders decomposition algorithms. For this purpose, symmetric complete and sparse graphs are considered. Using the symmetry concept, it is considered that the distances between base stations and users and between base stations themselves are symmetrical. Finally, an efficient local search meta-heuristic is proposed that allows for finding near-optimal solutions. Our numerical experiments indicate that the problem is hard to solve optimally. Thus, instances with up to 40 nodes and 500 users have been solved to optimality so far. In particular, it is observed that one of the models presents slightly better performance in terms of CPU time. Finally, the heuristic approach allows us to obtain tight solutions with less computational effort when dealing with even larger instances of the problem. [ABSTRACT FROM AUTHOR]

A high‐gain high‐selectivity 4 × 4 metasurface (MS) filtenna array is presented in this paper for 5G millimeter‐wave (mmW) applications. The TE20‐mode substrate integrated waveguide (SIW) with two parallel coupling slots is applied as the differential feeding structure, which can produce a wide impedance bandwidth and good radiation performances, simultaneously. Additionally, the TE20‐mode SIW feeding line is well designed to operate as a λ/2 short‐circuited line at the upper edge frequency to gain a radiation null. Meanwhile, a folded U‐shaped slot is etched on each MS unit to generate a radiation null at the lower edge. As a result, a passband which covers our 5G mmW band (24.25–29.5 GHz) of interest can be realized. To validate the design, a 4 × 4 MS filtenna array was manufactured and measured. The simulated and measured results are in good agreement, demonstrating a −10 dB impedance bandwidth of 19.8%, a flat gain variation with a maximum value of 19.82 dBi, symmetrical radiation patterns, low cross‐polarization levels of –30 dB, and high out‐of‐band rejection levels of 25 dB. [ABSTRACT FROM AUTHOR]

A scheme of generating millimeter‐wave signals with 16 times frequency using a cascaded Mach–Zehnder modulator (MZM) is proposed. Optical delay lines (ODLs) are used to place between cascaded MZMs, two MZMs work at the maximum transmission point. By controlling the modulation index of the MZM and the delay of the ODL, 0‐order, ±8 $\pm 8$‐order, and ±12 $\pm 12$‐order sidebands can be generated. The optical phase shifter and attenuator are adjusted to eliminate the 0‐order sideband, and the photodetector output generates a frequency 16‐tupling millimeter wave (MMW). In the simulation platform, a 160‐GHz MMW signal can be obtained by taking a 10‐GHz radio frequency signal as the driving signal of two MZMs. The optical sideband suppression ratio is 29.92 dB, and the radio frequency sideband suppression ratio is 24.89 dB. Further, the effect of system performance on optical devices under nonideal conditions is also discussed. [ABSTRACT FROM AUTHOR]

Hybrid precoding is an emerging solution for millimeter wave massive MIMO system to achieve reduced complexity and enhanced spectral efficiency. Hybrid precoding fully exploits spatial information to achieve high channel gain which reduces excessive path loss. The research presented in this paper is aiming at the design of optimal precoder which is based on Logarithmic hyperbolic cosine cost function with ZA and RZA criterion and has the advantage of reduced RF Chains. The channel state information (CSI) is generated by using random values of angle of arrival (AoA) and angle of departure (AoD) information. This CSI information is crucial to generate the precoding matrices and the row wise elements of the digital precoding matrix are recursively updated by using hyperbolic cosine filtering algorithm. Proposed precoder achieves spectral efficiency of 13 bps/Hz with 20 dB SNR which is comparatively higher than the precoders designed using other state of art methods. The performance is tested by varying base station antennas, mobile station antennas and number of users. The achievable spectral efficiency with variation of antenna elements and users establish the superior performance of the precoder. Thus the design can be suitable for fifth and next generation wireless communication systems when higher data rate is the requirement in millimeter wave band. [ABSTRACT FROM AUTHOR]

Massive multiple-input multiple-output (MIMO) systems at millimeter wave have been touted as a possible technology for 5 G wireless communications. The massive MIMO systems, gathering channel information using a beam tracking approach is crucial for tracking user movement. Conventional beam tracking algorithms for narrowband systems using the classic hybrid precoding framework suffers from the beam split effect and hence cannot be effectively adapted to wideband massive MIMO systems. To address this problem, we describe a long-short term memory (LSTM) network for detecting user movement and calibrating beam direction based on received signals from earlier beam training to improve noise resilience. Simulation findings demonstrate that the proposed approach may reach near-optimal achievable sum-rate performance with little beam training overhead. [ABSTRACT FROM AUTHOR]

A dark photon is one of the simplest extensions of the Standard Model of particle physics and can be a dark matter candidate. Dark photons kinetically mix with ordinary photons. The mass range from 10−4 to 10−3 eV of such dark photons is underconstrained by laboratory‐based experiments and a new search is therefore motivated. In this mass range, dark photons behave like waves rather than particles and the corresponding electromagnetic waves are in the millimeter‐wave range. The technical difficulties of the millimeter waves have prevented so far dark photon experiments in this mass range. The use of coherent millimeter waves to search for dark photons in a Light‐Shining‐through‐a‐Wall (LSW) experiment is proposed. The merits and limitations of coherent wave detection are clarified and the potential of single photon sensors at microwaves is investigated. Development of millimeter‐wave technology is not only limited to dark photons. Technically, an experiment for dark photons by using electromagnetic waves resembles that for axions, another light dark matter candidate, with static magnetic fields. This paper represents an essential step toward axion LSW in the millimeter‐wave range (Sub‐THz‐AXion experiment; STAX) as a potential successor of an on‐going experiment in infrared. [ABSTRACT FROM AUTHOR]

Radio Frequency (RF) Nano Electro Mechanical Switches (NEMS) using Carbon Nanotube (CNTs) are preferred for electronic switching due to its high stiffness, switching speeds and ultra-low mass over several GHz range. CNT switch for microwave and millimeter wave applications utilizing a maximum of three CNTs with fixed starting positions of CNTs from zero level offset to obtain better isolation (S21) of the switch in DOWN State has already been studied. The motive of this paper is to obtain better RF performance in terms of return loss (S11) and isolation loss by modelling the switch in DOWN-state by varying the random positioning of CNTs, interelement spacing between CNTs, number of CNTs and frequency is predicted and reported using XG—Boost approach. Time-consuming optimization methods to predict the S-parameters in customized Electromagnetic (EM) simulators such as HFSS (High Frequency Structure Simulator) have been resolved using the proposed XG-Boost regression approach. In this paper, the proposed XG-Boost approach minimizes the switch design time with random placement of CNTs by 99.81% compared to the conventional EM simulator which requires about 120 h for 400 simulations in an Intel-Core processor (2.50 GHz) with 8 GB RAM. To validate the results, they are compared to the HFSS model, and a high degree of agreement is found. Mean Square Error (MSE) of the switch in the DOWN- state after comparing the EM simulation values and XG-Boost regression values is 6.832e−03. [ABSTRACT FROM AUTHOR]