We study TE-wave propagation in a hollow waveguide with a graded transition from a lossy right-handed material (RHM) filling the left-hand half of the waveguide to the impedance-matched lossy left-handed material (LHM) filling the right-hand half of the waveguide. The transition between the two media is graded along the direction perpendicular to the boundary between the two materials (chosen to be the z-direction), and the permittivity ε(ω, z) and permeability μ(ω, z) are chosen to vary according to hyperbolic tangent functions along the z-direction. We obtain exact analytical solutions to Maxwell's equations for lossy media, and the solutions for the field components confirm the expected properties of RHM-LHM structures. Thereafter, a numerical study of the wave propagation over an impedance-matched graded RHM-LHM interface is performed, using COMSOL software. The numerical study shows an excellent agreement between the numerical simulations and analytical results. Compared to other solution methods, the present approach has the advantage of being able to model more realistic smooth transitions between different materials. However, in the limiting case, it includes correct results for abrupt transitions as well. In the present approach we also introduce the interface width as an additional degree of freedom that can be used in the design of practical RHM-LHM interfaces.

The uplink and downlink of modern satellite communication systems operate on different frequency bands. A novel dual-band dual circular polarization filter antenna with a single port is proposed in this paper. The dual-band characteristic of the antenna is obtained by exciting stacked patches. The antenna supports right-handed circular polarization (RHCP) at lower frequency band and left-handed circular polarization (LHCP) at higher frequency band, respectively. The feeding network is realized with a strip line, and the antenna can be equivalent to a parallel circuit. If the lower frequency patch works, the higher frequency patch presents high impedance, and vice versa. Therefore, the antenna has excellent filtering performance. The measurements of antenna prototype are in good agreement with the simulation results. The impedance bandwidth is 5.80-6.10 GHz and 9.20-10.64 GHz, and the axial ratio (AR) bandwidth is 40 MHz for lower band and 180 MHz for higher band, respectively. Meanwhile, the radiation pattern is stable in the operation frequency bands.

In order to solve high torque ripple of permanent magnet synchronous motor (PMSM) for marine electric propulsion under the current control methods, the improved model predictive current control (MPCC) of PMSM for marine electric propulsion based on the mathematical model of three-phase PMSM is proposed. First, the stator current prediction model is derived based on the forward Euler method. Then the first optimal voltage vector is obtained by the value function, and the second optimal voltage vector, and the second optimal voltage vector and the first and second optimal voltage vectors' respective action times are obtained by the q-axis deadbeat control, which are directly fed back to the inverter. The proposed control method is verified by simulation and hardware in the loop simulation experiment. The experiment results show that, in comparison with the direct torque control based on space vector modulation (SVM-DTC) in the case of motor speed and torque mutation, the torque ripple of motor is reduced by 9.40% and 4.80% respectively based on improved MPCC. The feasibility and effectiveness of the proposed method are verified by the simulation and experiment results.

A compact exponentially tapered balanced antipodal Vivaldi antenna for Phased array systems is proposed in this paper. The proposed design implements slots at the edges to improve impedance bandwidth typically at lower frequencies. The antenna is coupled to a 50 Ω microstrip line between the signal conductors of the middle layer and ground plane. A detailed parametric analysis has been carried out to determine the optimized dimensions and to achieve desired antenna performance. A prototype of the antenna (56×28×1.6 mm³) was fabricated and measured to validate the simulation results. It is revealed that the antenna has a wide impedance bandwidth of 120% over 5-20 GHz and measured gain of the antenna increases from 2.6 dB to 8.0 dB in the whole operational frequency band. The small aperture width which is typically 28 mm is the attractive feature of the proposed design. Therefore, compact size, high gain, ultrawide bandwidth, and directional radiation characteristics of the proposed design may be suitable for advance radar systems.

In this work, a substrate integrated waveguide slot array filtering antenna for dual band applications is presented. This novel design performs the functions of both a filter and an antenna simultaneously. The main intention of this work is to design a circuit that separates the frequencies in a dual band operation. The antenna is designed as an integration of two parts; the upper part operates at 10.2 GHz while the lower part operates at 16.4 GHz. In each part, an array of five longitudinal slots is incorporated, as well as a SIW antenna with complementary split ring resonators that operate as a band pass filter at the front end. Each slot array antenna is designed for a specific frequency band, and its function depends upon its preceding band pass filter. The two band pass filters allow only signals from the frequency bands for which they are designed, to their corresponding slot array antennas. This technique, along with properly spaced metal vias of the SIW antenna, prevents any leakage and hence reduces interference in dual band operation. Both the band pass filter and the antenna can be built on the same planar board. The antenna is fed through a microstrip to SIW taper transition. CST Microwave Studio software is used for optimization and simulation of the structure. The antenna was built on an RT Duroid 5880 and tested to investigate practical validation. The antenna has a bandwidth of 1.9 GHz, from 9.2 GHz to 11.1 GHz in the X-band, and 2.2 GHz, from 15.6 GHz to 16.9 GHz in the Ku band. The gain pattern is unidirectional in nature and has low side lobe levels of -24 dB and -21 dB at resonant frequencies. A noticeable difference that is greater than 20 dB between co-polarization and cross-polarization is observed. The dimensions of the antenna are 56 mm x 32 mm x 0.508 mm. There is an excellent similarity between the simulated and measured results.

Volatile organic compounds (VOCs) have received increasing attentions recently. They are important for air quality monitoring, and biomarkers for diseases diagnosis. For the gas sensor community, various detection technologies were explored not only to detect total VOCs, but also aim for sensor selectivity. Commercially available VOC sensors, such as metal oxide based or photoionization detectors, are suitable for total VOCs but lack of selectivity. With the advancement of optical spectroscopy, it provides a good solution for specific VOC detections. In this review, various spectroscopy techniques are summarised focusing on increasing sensor sensitivity and selectivity. The techniques included in the paper are, non-dispersive infrared, multi-pass cell spectroscopy, cavity enhanced absorption photoacoustic spectroscopy and Fourier transform infrared spectroscopy. Each technique has its pros and cons, which are also discussed.

A bat-shaped microstrip patch antenna is proposed with tri-band characteristics (11.0-11.5 GHz), (11.8-12.3 GHz), (13.0-14.3 GHz) and impedance bandwidth 4.4%, 4.1%, and 9.5% at resonant frequencies 11.37 GHz, 12.2 GHz, and 13.5 GHz, respectively. The proposed antenna exhibits peak gain of 2.6 dBi. The proposed microstrip patch antenna shows the dual band circularly polarized characteristics with two bands (11.0-13.0 GHz) and (13.2-14.0 GHz) and 3 dB axial-ratio (AR) impedance bandwidths 15% and 5.2%, respectively. Investigation of proposed antenna is done using evolution technique. The results are verified experimentally in terms of reflection coefficient, gain, axial ratio, and radiation pattern.

Two types of quad-band millimetric-wave four-port MIMO antenna systems are proposed for the forthcoming generations of mobile handsets. A novel printed antenna is introduced to be the single-element of the MIMO antenna system. It is shown that the proposed MIMO antennas are capable to produce both spatial and polarization diversities that enhance the performance of mobile communications. A co-polarized four-port MIMO antenna is proposed to provide spatial diversity whereas another cross-polarized four-port MIMO antenna is proposed to produce both spatial and polarization diversities. It is shown that the two types of MIMO antennas can operate efficiently over the four frequency bands centered at 28, 43, 52, and 57 GHz. Prototypes are fabricated for the proposed MIMO antennas for the sake of experimental evaluation. Both the experimental and simulated results show that the achieved bandwidths, at the four operational frequency bands, are 0.6, 0.6, 1.8, and 1.5 GHz, respectively. Also, the radiation efficiencies calculated at the four operational frequencies are 86.5%, 87.5%, 89.2%, and 90.0%, respectively. The dimensions and the results concerning the performance of the proposed MIMO antennas are compared to those of other designs for MIMO antennas available in some recently published work.

A novel design of a 4x4 miniaturized UWB-MIMO (multiple-input, multiple-output) antenna with isolation improvement is proposed in this paper. The designing procedure of a flower-shaped MIMO antenna is done using characteristic mode analysis (CMA). The flower shaped UWB-MIMO antenna is made up of four symmetrical flower-shaped radiating elements that are isolated using an orthogonal method. The flower antenna's dimensions are 40x40x1.6 mm³ (0.44λ₀x0.44λ₀x0.017λ₀). A flower-shaped radiator is used to get good the isolation in MIMO elements. Further isolation is enhanced by inserting a swastik-shaped stub on the ground to get return losses of S₁₁<-10 and isolation of S₁₂<-18 dB. The designed antenna covers the entire UWB (3.1-14 GHz) spectrum for impedance matching, including (10.7 to 11.7 GHz), 11 GHz (10.7 to 11.7 GHz), and 13 GHz (10.7 to 11.7 GHz) (12.75 to 13.25 GHz). Good diversity performance is achieved in the UWB and ITU range. The designed antenna has a gain of 5.5 dB, an efficiency of 89%, an impedance bandwidth of 123.61%, an envelope correlation coefficient of 0.0012, a diversity gain of nearer to 10 dB, a capacity channel loss of 0.29 bps/Hz, and a mean effective gain of less than -3.1 dB. The designed antenna is fabricated and tested. These simulated results are validated in state-of-the-art laboratories. According to the simulation and measurement results, this antenna is well suited for reliable wireless communication systems. The potentiality of the designed antenna is high, and the antenna is compact and portable.

A deep learning-based approach in conjugation with Fourier Diffraction Theorem (FDT) is proposed in this paper to solve the inverse scattering problem arising in microwave imaging. The proposed methodology is adept in generating a permittivity mapping of the object in less than a second and hence has the potential for real-time imaging. The reconstruction of the dielectric permittivity from the measured scattered field values is done in a single step as against that by a long iterative procedure employed by conventional numerical methods. The proposed technique proceeds in two stages; with the initial estimate of the contrast function being generated by the FDT in the first stage. This initial profile is fed to a trained U-net to reconstruct the final dielectric permittivities of the scatterer in the second stage. The capability of the proposed method is compared with other works in the recent literature using the Root Mean Square Error (RMSE). The proposed method generates an RMSE of 0.0672 in comparison to similar deep learning methods like Back Propagation-Direct Sampling Method (BP-DSM) and Subspace-Based Variational Born Iterative Method (SVBIM), which produce error values 0.1070 and 0.0813 in the case of simulation (using Austria Profile). The RMSE level while reconstructing the experimental data (FoamDielExt experimental database) is 0.0922 for the proposed method as against 0.1631 and 0.1037 for BP-DSM and SVBIM, respectively.

To reduce the computational complexity of traditional model predictive torque control (MPTC) and improve the sensitivity of predictive control to disturbances, an improved three vector model predictive control strategy applied in permanent magnet synchronous motor (PMSM) is proposed. First, the principle of deadbeat synchronization between torque and flux linkage is adopted to reduce six candidate vectors in traditional torque prediction to two, and the cost function is designed to select the optimal voltage vector. In addition, disturbance observation compensation is introduced to compensate for the influence of load disturbance on the control performance of the predictive model. As experimental results show, the proposed three-vector model predictive torque control can obtain small torque ripple and current harmonics both in steady state and dynamic state.

Since massive multiple-input multiple-output (MIMO) array and beamforming significantly improve spectrum efficiency, where beamforming adapts the radiation pattern of the massive array, most previous studies focus on the MIMO beamforming optimization problem to maximize the utility of the system by assuming that a massive array consists of an isotropic antenna. This research work was conducted to investigate the beamforming optimization problem with practical elements in a MIMO array. By inserting the effect of a practical antenna array gain in the channel model, the impact of array elements feeding on the beamforming optimization problem could be illustrated. Furthermore, the beamforming optimization, non-convex issue, is reformulated to synonymous convex optimization issue, through a weighted minimum mean square error (WMMSE) technique. Consequently, a conformal array (CfA) with a half wavelength dipole element is proposed at the base station (BS). The simulation results display that the suggested WMMSE-beamforming technique performance with considering antenna array gain effect can yield much better and accurate system performance than the other algorithms. Eventually, to analyze the impact of array gain on the optimization problem solution in addition to boot the network capacity, a curl antenna array in octagonal prism geometry is created. The curl antenna is circularly polarized and has a high gain compared to the half-wavelength dipole.

Polarization is an essential feature of electromagnetic (EM) waves, and the variety and simplicity of polarization conversion have substantial demands in wireless systems. Metasurfaces, two-dimensional artificial electromagnetic structures, are emerging as novel modulation solutions for EM waves. In this work, a multifunction polarization converter based on a transmissive metasurface (MPC-TMS) is suggested. This planar structure is made up of a copper-clad dielectric substrate with top and bottom orthogonal slotted sheets joined by a metal via. With frequency selectivity, x- and y-linear cross-polarization transformations are efficiently achieved between 8.04-8.82 GHz (9.25%) and 7.04-9.07 GHz (25.19%), respectively. Meanwhile, the presented microstructure is capable of rotating a circularly polarized incident wave into its opposite handedness from 8.16 to 8.87 GHz (8.46%). Both peak transmission efficiency and the polarization conversion ratio exceed 0.95 simultaneously. In addition, resonance superposition and coupling effects are investigated to explain the operating mechanism. This microstructure not only has a simple construction with an ultra-thin thickness (0.06λ), but also reveals superiorities in bandwidth, transmission, and efficiency. To verify the above quadruple polarization conversion, measurement has been implemented, and the results are reasonably accordant with simulation, suggesting that the low-profile converter is conducive to future telecommunication design where polarization diversity is needed.

Wearable textile antenna is most appropriate for Wireless Body Area Network (WBAN) applications due to its flexibility, compactness, and user compatibility. Dual band antenna has advantage in duplex communication, hence it is desirable. In this paper, a dual band microstrip antenna is designed using textile material as a substrate with a circular patch and a rectangular patch Methods from literature and experimentation are compared based on performance parameters. Slots are loaded on the patch to achieve dual-band characteristics. HFSS software has been used to simulate the proposed antenna, and the results are compared with the fabricated antenna based on Voltage Standing Wave Ratio (VSWR), directivity, return loss, gain, impedance, and radiation pattern. Since the antenna operates with close proximity to the human body, the Specific Absorption Rate (SAR) is also calculated using the CST software and is found within the prescribed limits.

This paper presents a method based on the elliptical representation of D-Q currents to detect and quantify an Inter-Turn Short-Circuit (ITSC) fault in windings of a Doubly Fed Induction Machine (DFIM). ITSC is said to be an evolving fault, so it is essential to detect it at an early stage to avoid damage on the machine. Therefore, the method should be able, on the first hand, to detect the defect and, on the second hand, to quantify its severity. Moreover, this study requires less computation time than classical methods such as harmonic analysis. In this paper, current data are acquired at a sampling frequency of 1 kHz. This method is successful with this low data sampling rate. In order to validate this study, a theoretical analysis with two models of different DFIM powers (0.3 kW, 0.25 kW and 11 kW) is carried out (healthy case and faulty case: presence of ITSC), and these results are confirmed by using platforms including Doubly Fed Induction Machines (DFIMs) and Data Acquisition (DAQ) system.

In this paper, the authors propose a small substrate integrated waveguide (SIW) slot antenna for future fifth generation (5G) communication systems. It works at 28 and 38 GHz. The proposed geometry consists of horizontal and vertical vias as well as a central circular ring. The cut slots in the etched center circular ring create a significant capacitive loading effect, lowering the lower resonating mode. Further, the introduced circular ring slot resonates on TE₁₀₁ and TE₁₀₂ modes at 28 and 38 GHz, respectively. The measured impedance bandwidths are 27.77-28.02 GHz and 37.99-38.10 GHz. Peak gains in the lower and upper bands are measured to be 6.96-7.15 dBi and 8.10-8.22 dBi, respectively. At 28 and 38 GHz, the observed half-power beam-widths (HPBWs) are 74.5˚ and 79.2˚, respectively. Considering these performance results, such as single-layer dual-bands, high gain, small size, and good radiation efficiency, the designed SIW slot antenna is suitable for future millimeter-wave 5G applications.

In this brief, an ultra-vast stopband lowpass filter with miniaturized circuit size for 26th harmonic suppression using poly-resonators and an inclined stepped-impedance transmission line (ISTL) is developed. The poly-resonators such as radial stub resonator and resonator modules constitute the significant part of the filter, and the discontinuity in the inclined angle of the ISTL is balanced by 75% chamfering. The coupling with ISTL has influence over the stopband behavior, and the equivalent circuit for the first transmission zero is analysed. The normalised circuit size is reduced to 16.6%, and additional frequency rejection is achieved using resonator modules RM1 and RM2. The relative stopband width of 185.4% is attained with a 3 dB cut-off frequency of 1.51 GHz. L band communication applications having circuit area limitations can make use of the Poly-resonator ISTL filter for achieving high-frequency noise rejection.

This paper outlines the design characterization and the electromagnetic performance of a millimeter-wave high power combining structure, which exploits the spatial power combination technique. The input matching is always below 10 dB over the entire Q band, and the overall weight of the structure is about 500 g. Multiphysics simulations show how this structure is suitable for the most challenging space missions that will arise in next few years. In fact, 100 W of RF power above the frequency of 40 GHz can be delivered while all the specifications for satellite payloads are complied. Other Spatial Power Combiner structures, such as Radial ones, cannot be implemented in space missions since they are much less compact and much heavier than the one presented in this article, and this is the major advantage of this configuration which was specially designed for a space project.

A novel EBG structure in the form of a square spiral cell with a via at its middle is presented in this work to improve the isolation between the antenna elements and also enhance the overall parameters of the proposed MIMO system. Wide BW is achieved for the 6-elements MIMO system operating in the frequency range from 3 GHz to 5 GHz which is suitable for 5G mobile applications. The single antenna element consists of four coupled sections printed on an FR4 substrate. To improve the performance and maintain the BW, the EBG structure is employed to increase the isolation between the antenna elements. The proposed EBG is designed to have a bandgap from 2.5 GHz to 6.5 GHz. The addition of the EBG structure between the radiating elements reduces the envelope correlation coefficient across the whole operating BW. SAR calculations are also performed using head and hand models. The performance of the proposed EBG loaded MIMO antenna is suitable to be a potential competitor for future 5G applications.

Arc synthetic aperture radar (ArcSAR) forms the synthetic aperture through uniform circular motion with antenna pointed outwards circular trajectory, so the point target response is different from traditional linear SAR and Circular SAR (CSAR). Due to the unique imaging mode, ArcSAR has the characteristics of large field of view and constant azimuth angular resolution. The ArcSAR system is built by vector network analyzer (VNA), rotating platform, standard gain horn antenna, and computer, and the system transmits stepped frequency continuous wave (SFCW). A Qt-based GUI is designed to realize the accurate and convenient remote control of the system. An outdoor imaging experiment was carried out with a corner reflector to investigate the point target response of SFCW-ArcSAR which has unique forms in Cartesian coordinate and cylindrical coordinate systems. In order to avoid the additional phase error introduced by coordinate transformation based on interpolation, back projection (BP) algorithm is applied in Cartesian coordinate system and cylindrical coordinate system, respectively. The point target response presents a 2-D sinc function in cylindrical coordinate system. The azimuth angular resolution is 0.0175 rad under the experimental condition of 1.9 m-rotating radius and 16˚ antenna beamwidth. The simulation results agree with measured ones, which prove the validity of SFCW-ArcSAR system and correctness of theoretical analysis. The imaging result based on BP algorithm and corner reflector can be used to evaluate other ArcSAR imaging algorithms.