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.

A circular polarization multiplexing metasurface beam splitter operating at 15 GHz with polarization conversion effect is proposed. The unit cell is formed by alternately stacking 4 layers of metal and 2 layers of dielectric substrates cascaded along the propagation direction, separated by air. The resonant phase of the unit cell can be changed by changing the size parameters of the two arms of the metal cross patch, and the phase coverage of nearly 360° can be achieved in the direction of the two orthogonal linear polarization components, while transmission coefficient is above 85%. The circular polarization geometric phase covering 360° can be achieved by rotating the metal patch. The polarization conversion of the circularly polarized wave can be realized by setting the phase difference of the two orthogonal linear polarization components to 180°, and the polarization conversion ratio (PCR) at the working frequency is greater than 90%. The simulation and test results show that when the circularly polarized electromagnetic wave is perpendicularly incident on the metasurface beam splitter, the transmitted wave is divided into two circularly polarized waves with different exit angles and orthogonal to the polarization direction of the incident wave. This work may provide new ideas for the integration and miniaturization of traditional beam splitting devices and have important application prospects in fields such as multiple input multiple output (MIMO) systems.

A new compact CPW fed dual-band circularly polarized (CP) antenna for a broadcasting satellite application is presented. The proposed dual-band CP antenna consists of modified CPW ground structure by loading stub/slots/inverted L-strip and modified cross-shaped patch. A modified CPW ground structure can generate circular polarization (CP). The proposed antenna design provides the simulated impedance bandwidth (IBW) (S₁₁ < -10 dB) of 81.42% (3.16-7.5 GHz) and 20.53% (11.8-14.5 GHz), respectively, and the 3-dB axial ratio BW (3-dB ARBW) for two bands are 29% (4.18-5.6 GHz) and 8.86% (11.86-12.96 GHz), respectively. The proposed CP antenna provides a maximum gain about 3.8 dBi and 5 dBi in lower and upper bands, respectively, with right hand circular polarization (RHCP) radiations. The overall size of the CP antenna is 27 × 27 × 1 mm³.

Designing a multi-band bandpass filter (BPF) with controllable bandwidths is an alternative process to several technologies suggested by researchers. Hence, this paper presents a tri-band BPF in microstrip technology where T-shaped short-and-open stubs have alternating positions to use the maximally flat theory, based on the overall ABCD parameters of the circuit. The combination of the design Q-factor and the operating frequency to mismatch the design is the technique basis. The proposed structure comprises the quarter wavelength (λ/4) line section to develop a tri-band BPF frequency. All stubs are symmetrical relative to the center axis, while the prototype has been fabricated on a wafer of 22.42x7.62 mm². Using an FR4 HTG-175 with a thickness of 1-mm, dielectric constant ε_r=4.4, and loss tangent tanδ=0.02, the (4.06-4.283) GHz, (5.877-6.408) GHz, and (14.281-14.589) GHz are obtained referring to a 10-dB of the return loss. In contrast, the insertion losses at the center frequencies are 2.107/1.354/4.08 dB and the fractional bandwidths of 2.134%, 5.346%, and 8.645%, respectively. These covers WAS (including RLAN), ISM, and 5G applications. However, the attenuation coefficient is between 1.326 dB and 4.368 dB. The tri-band BPF prototype was validated using the Anritsu MS4642B 20 GHz Vector Network Analyzer. The measured and E-simulated results have been compared with good agreement.

A four-level iterated cantor set fractal antenna for Internet of Things (IoT) applications is proposed in this work. The proposed antenna operates at 2.4 GHz and for the range of 5 GHz to 8.5 GHz. In the 5 GHz to 8.5 GHz range it covers a Wi-Fi802.11 Standard (4.9 GHz, 5 GHz, 5.9 GHz, 6 GHz), 6.56 GHz, and at the lower band it covers WiMax (2.5-2.7 GHz). The proposed antenna offers a gain up to 4 dBi with an efficiency up to 90%. The designed antenna is experimented with a partial ground plane, with and without notch to perceive its effects on S₁₁ parameters. The antenna and its feed location is optimized for improved performance. The proposed antenna is analysed using the theory of characteristics mode analysis. The antenna is fabricated on a low-cost FR4 substrate with a dielectric constant of 4.4 anda substrate height of 1.6 mm. The antenna performance in terms of S₁₁, VSWR, and Gain is validated by measuring the performance in an anechoic chamber with Agilent N5247A Vector Network Analyser (VNA). The antenna is designed and optimized in mentor graphics software and CST Studio. The results show good agreement between the simulated and measured performances of the antenna. The optimized geometry of the antenna is compact having overall dimensions of 32 mm×22 mm×1.6 mm and suitable for short-range IoT applications.

Magnetic gear has high torque density and efficiency, and has a good application prospect in the field of low speed and high torque transmission. Accurate calculation of its air gap magnetic field is the key to analyze and design the magnetic gear. In order to improve the output torque of magnetic gear, the inner rotor is slotted, and copper bar is added in this paper. The air gap magnetic field of magnetic gear with rotor copper bar is calculated by two-dimensional analytical method. The solution domain is divided into four sub-domains, i.e., permanent magnets, air gaps, slots, and rotor copper bars. The solutions of Laplace's equation, Poisson's equation, and Helmholtz's equation are obtained by boundary conditions and continuity conditions. The distributions of air gap magnetic field, the induced current of rotor copper bars, and electromagnetic torque are obtained. The calculation results of this method are basically consistent with those of the finite element method, which proves the correctness and rationality of the analytical model.

To further improve the sensitivity of liquid dielectric constant measurements, a cylindrical container-type dielectric constant sensor is proposed in this paper. The container of the sensor consists of a substrate integrated waveguide (SIW) loaded with complementary split ring resonators (CSRRs) and a microstrip line. In order to solve the problem that the electric field distribution of the traditional container liquid dielectric constant sensor is only in a single plane, which cannot obtain good resonance characteristics, the sidewall of the sensor container is surrounded by a flexible material loaded with CSRR-SIW. Higher sensitivity can be obtained from measuring dielectric constant with more concentrated electric field distribution. The simulation results show that when the permittivity of the liquid under test (LUT) changes from 1 to 10, the resonance frequency of the sensor changes from 4.50 GHz to 2.94 GHz. The resonance frequency shift with unit dielectric constant greater than 150 MHz is realized. Using the relationship between the fitting permittivity and resonance frequency, the measurement of the known liquid permittivity of the standard sample is carried out. The test results show that the relative error is less than 2%, and the test sensitivity is 3.85%.

This paper proposes a dual-band circularly polarized antenna with ``X'' parasitic structures applied in the Beidou satellite navigation system. The innovation of this paper is to introduce the radome with ``X'' parasitic structures to broaden the beam width of the L-band and to improve the low-elevation gain of the antenna. Furthermore, high dielectric constant materials are used to realize the miniaturization and embedded application of the antenna. The measured results show that the VSWR of the L-band is 1.09 at 1616 MHz, and the VSWR bandwidth (VSWR<2) is 45 MHz (1589 MHz-1634 MHz). The VSWR of S-band antenna is 1.24 at 2492 MHz, and the VSWR bandwidth (VSWR<2) is 54 MHz (2471 MHz-2525 MHz). By adding the designed radome, the 20-degree elevation gain of the L-band is increased by 3.755 dBic. The measured results show that the gain variation at 20-degree elevations of the antenna at 1616 MHz and 2492 MHz are 4.981 dBic and 3.7 dBic, respectively. Moreover, the beam widths of the antenna at 1616 MHz and 2492 MHz are 130 degrees and 104 degrees, respectively. The antenna has an improved gain and a good roundness at low elevation angles, thus providing a favorable choice for navigation antenna solutions.