A sequence of anisotropic and isotropic materials of dielectric constant 12 and 10 respectively have been stacked alternatively to form a four-layer stack structure with aperture coupled feed mechanism for excitation. Applying this excitation, orthogonal mode pair TE_δ21^x and TE_2δ1^y has been excited at frequencies 7.54 GHz and 7.8 GHz, respectively in YZ and ZX planes to generate circular polarization. A circularly polarized bandwidth in the region (7.54 GHz-7.92 GHz) in conjunction with impedance bandwidth in the region (5.23 GHz-5.52 GHz) with a gain of 5.2 dBi has been accomplished. The designed antenna is appropriate for C-band and weather radar applications. The design assessment has been done using Ansys HFSS. The three stages of antenna design are examined. Further, the design is investigated with a 6-layer structure and an 8-layer structure.

In this paper, a triple-band reflective polarization converter with high efficiency for both linear-to-linear and linear-to-circular polarizations based on a metasurface is proposed, which can rotate a linearly polarized (LP) incident wave into its orthogonal direction with over 90% polarization conversion ratio (PCR) in the bands of 5.5-5.9 GHz (relative bandwidth of 7%) and 12-17.7 GHz (relative bandwidth of 38.4%). Besides, the proposed converter can also transform a linearly polarized incident wave to circularly polarized (CP) wave in the band of 6-12 GHz (relative bandwidth of 66.7%). Additionally, the performance of proposed polarization converter stays in considerable stability with the incident angle increasing 60˚ in circular polarization and 30˚ in linear polarization. Moreover, the physical mechanism of multiple resonances is discussed based on surface current distributions and equivalent circuit model. A prototype of the proposed converter is fabricated and measured, and the experiments and simulations are in great agreement. This polarization converter can be employed to manipulate the polarization of the signal in microwave communication.

The manuscript presents a log-periodic microstrip antenna with a defective ground structure (LPMADGS). The antenna is simulated, designed, and validated for C-band applications. The design of the antenna consists of three layers with upper most layer consisting of log-periodic, copper patches with a thickness of 0.035 mm; the middle layer is a 2 mm thick dielectric layer of FR-4 substrate; and the bottom layer is a defected ground structure (concentric ring resonators of 0.035 mm thickness). The suggested antenna design is simulated with a complete ground plane, without ground plane, and with a defective ground plane. The proposed antenna with optimized design is fabricated by wet etched method. The simulated results are approximately similar to the experimentally measured results. The experimentally measured results show transmission peaks at 7.65 GHz and 7.90 GHz. The resonating effect of log-periodic patches with a defected ground structure results in wide-band of 0.91 GHz (-10 dB bandwidth). The proposed antenna structure exhibits a wide bandwidth transmission which mostly resonates in frequency range that lies in C-band. It has future applications for mobile as well as wireless communication.

The goal of vector control of interior permanent magnet synchronous motor (IPMSM) is to make IPMSM have excellent dynamic and steady-state performance, but there is coupling between the d-q axis in the synchronous rotating coordinate system, which affects the torque response performance. In view of the fact that the traditional voltage compensation strategy is sensitive to the change of motor parameters, genetic algorithm is introduced to identify the parameters, and a feedforward voltage compensation control based on genetic algorithm parameter identification is proposed. The compensation voltage is calculated by the inductance and flux value of the motor identified by genetic algorithm. Compensation voltage is used to counteract the change of feedback voltage caused by the change of motor parameters in feedforward decoupling control. Simulated and experimental results show that the proposed strategy can effectively achieve d-q axis current decoupling, improve the dynamic performance of the system, and have excellent robustness.

This paper presents a multi-sections broad-band radio-frequency (RF) to direct-current (dc) power rectifier for pulsed signal transfer. The power transfer using a pulse allows to use a signal with low power spectral density. The optimal distributed configuration with critical parameters is studied to enhance the efficiency over broadband frequency and wide power range. A five stage distributed RF-dc converter arrangement with micro-strip transmission line ensures the power harvesting from 100 MHz to 11 GHz. The designed and fabricated circuit is characterized at multi-frequencies of ultra-wide band (UWB). The distributed harvester significantly improves the detected voltage over a wide bandwidth compared to conventional RF detectors. The achieved efficiency with optimized parameters is 48% with five-stage harvester. A maximum dc output of 956 mV is reached at 8 dBm of input power of sinusoidal single tone signal at 1 GHz of frequency. The designed prototype is associated with a square wave signal to show the circuit potential in terms of power transfer. The output voltage can be controlled with input signal level, frequency as well as the pulse width. For the power transfer circuit, 996 mV of maximum dc output voltage is reached for 1 V of input amplitude at 1 GHz with duty cycle of 50%. The efficiency increases significantly with duty cycle ratio of the input signal. The power harvester associated with a UWB antenna confirms the benefit of using a square wave signal in the case of power harvesting or transfer.

The deformation behaviors of a droplet on surface of composite insulator can strengthen local electric field, which could finally lead to flashover. Both experiments and numerical simulations for dynamic behaviors of a droplet on the surface of a composite insulator under applied AC voltage are investigated in this paper. Experiments are performed to study the influences of water droplet's volume and conductivity on the dynamic behaviors. Two critical parameters are proposed to describe the morphological change process of water droplet, and it is shown that the process can be divided into three stages. Moreover, these motion laws are explained by establishing theoretical factors and physical influence models. In addition, we perform computer simulation to study the dynamic behaviors of a water droplet under AC field, and the findings are in good consistency with our experimental results, proving the rationality of the theoretical physical model. It is found that the vibration frequency of droplet changes regularly with at different stages under the AC electric field.

A new method for obtaining an orthogonal system of eigenwaves of an open cylindrical waveguide filled with a gyrotropic medium and located in free space is presented. The advantage of the method is that it enables one to explicitly represent the fields of eigenwaves, which correspond to the discrete and continuous parts of the eigenvalue spectrum of such a guiding structure. Orthogonality relations for the eigenwaves and the procedure of expanding an electromagnetic field in terms of these modal solutions are discussed. The limiting transition from the case of a closed cylindrical waveguide with a perfectly conducting wall and a coaxial cylindrical gyrotropic core to the case of an open waveguide is considered. To illustrate the completeness of the obtained system of eigenwaves, a given field is expanded in terms of the found discrete- and continuous-spectrum waves and then resynthesized by evaluating the corresponding expansion numerically. Perfect coincidence between the initially specified field and the result yielded by this evaluation is demonstrated.

In order to solve the problem of the low direct control accuracy of permanent magnet assisted bearingless synchronous reluctance motor (PMa-BSynRM), which caused by transmission delay, the predictive control is applied to direct control of PMa-BSynRM. Meanwhile, in view of the disadvantages of large ripple (torque ripple, flux linkage ripple) and poor robustness in traditional predictive direct control (PDC), a fractional super twisting sliding mode controller (FSTMC) is proposed. Firstly, the mathematical models of torque and radial suspension force of PMa-BSynRM are derived. Secondly, the torque and flux controller based on FSTMC are designed, and the stability is verified. Thirdly, the torque predictive controller and levitation force predictive controller are designed, and the algorithm of PDC is described. Finally, the FSTMC-PDC system of PMa-BSynRM is built and simulated by Matlab/Simulink module. The simulated and experimental results confirm the validity and superiority of the proposed method.

A multiband hexagonal ring-shaped fractal antenna with stubs and slits loaded partial ground plane has been presented in this manuscript. The proposed antenna is compact in size 24×30×1.6 mm³ and exhibits enhanced bandwidth, gain, and reflection coefficient. Measured results exhibit that the proposed antenna resonates with impedance bandwidth (S₁₁ ≤ -10 dB) in the frequency ranges 1.0-2.75 GHz, 4.74-8.70 GHz, 11.04-12.76 GHz, 14.97-16.62 GHz, and 19.70-22.0 GHz. These frequency ranges cover distinct wireless standards such as 1800 MHz 2G spectrum of GSM band (1.71-1.88 GHz), LTE 2300/LTE 2500 (2.3-2.4 GHz/2.5-2.69 GHz), RFID/Bluetooth (2.4 GHz), 5G spectrum band (5900-6400 MHz) adopted by European Union, Long Term Evolution (LTE) band 46 (5150-5925 GHz), RFID (5.4 GHz), WLAN (5.15-5.35 and 5.72-5.85 GHz), Wi-MAX (5.25-5.85 GHz), FSS (11.45-11.7/12.5-12.75 GHz), defence systems (14.62-15.23 GHz), aeronautical radio navigations (15.43-17.3 GHz), and fixed/mobile satellite communications (19.7-20.1 GHz and 20.2- 21.2 GHz). The proposed antenna reveals the positive value of peak realized gain with almost omnidirectional radiation patterns in E- and H-planes for all the resonant frequency bands. The performance of proposed antenna has been realized by using HFSS V13 simulator based on FEM (Finite Element Method), and the results are compared with the experimental results which are in good agreement with each other.

An inset-fed planar MIMO antenna array design has been presented for dual-band 5G applications. The proposed MIMO array offers numerous advantages such as compact size, planar structure, and high isolation. The single element of the array comprises an inset-fed rectangular patch and open circuit stubs designed on the top side of the substrate, while the bottom layer consists of a partial ground plane. Simulated and measured results show that the proposed antenna offers dual-band characteristics at 28 GHz and 38 GHz frequency bands, respectively. It has also been observed from the results that the proposed inset-fed planar antenna offers good radiation characteristics, and acceptable gain and radiation efficiency. Furthermore, four-elements based MIMO antenna array has been designed for its possible use in 5G enabled communication devices. It has been demonstrated that the proposed MIMO antenna provides high isolation between array elements without disturbing the return loss of an individual element. The proposed MIMO antenna array has been fab- ricated and measured for the validation of simulation results, and it has been observed that both the results are in good agreement.

This paper shows a dual-band frequency and pattern reconfigurable antenna. The proposed antenna is designed on an FR4 substrate of thickness 1.6 mm and size 25×15 mm². Depending on the ON/OFF states of the PIN diode, the proposed antenna resonates at two distinct frequencies, i.e., 3.5 GHz, and 5.2 GHz, and has a pattern tilt from -170˚ to +160˚ in yz plane. In HFSS simulation, lumped RLC elements are used to reconfigure the antenna frequency and pattern. For switching, the PIN diode is used for frequency and pattern reconfiguration in the fabricated antenna to verify the simulated performance. In the simulated and measured performance, the proposed antenna shows reasonable matching. The proposed antenna is suitable for WiMAX and WLAN applications.

An inline quarter-mode substrate integrated waveguide (QMSIW) filter with controllable finite transmission zeros (FTZs) is presented based on a novel frequency-dependent coupling structure, which is constructed by a microstrip line with a pair of symmetric metallized via/buried holes and a magnetic coupling iris between two resonant cavities. FTZ can be independently introduced and controlled on both sides of passband to achieve high selectivity while keeping the filter compact configuration unchanged. For demonstration, the proposed structure is analyzed in detail. An inline fourth-order QMSIW bandpass filter (BPF) with two upper FTZs is designed, fabricated, and measured. The synthesis results, EM results, and measured results are in accordance with each other, which confirms the effectiveness of the proposed method.

The junction temperature change of SiC MOSFET will change its switching process, and then affect the electromagnetic interference (EMI) characteristics of the system where the device is located and the safe operation of the surrounding equipment. Therefore, it is of great significance to research the temperature dependence of its EMI characteristics. In this paper, a buck converter composed of SiC MOSFET is taken as the research object to study the temperature variation characteristics of the conducted EMI spectrum during the switching process. Combined with the specific circuit connection form of the buck converter, the coupling paths of the conducted EMI are determined, and then the influence mechanisms of temperature change on the differential mode (DM) interference and common mode (CM) interference are analyzed. The theoretical analysis and experimental results show that the DM interference of the buck converter composed of SiC MOSFET increases with the increase of temperature, and the CM interference is almost unaffected by temperature. When the working temperature increases from 25˚C to 145˚C, the peak value of DM voltage increases by 6.7 dBμV, and the peak value of CM voltage changes less than 1.4 dBμV.

The problem of direction of arrival (DOA) estimation based on a polarization sensitive array (PSA) is considered in this paper. In the environment of the mixture signal, a novel DOA estimation for both the independent signals and the coherent signals is proposed. The process of estimation is divided into two steps. First, the root-multiple signal classification algorithm is employed to estimate the DOAs of the independent signals. Then, the data covariance matrix which only contains the information of the coherent signals is estimated with improved vector reconstruction technique. Theoretical analysis and simulation results show that the proposed method can expand the array aperture and has small computation load as well as excellent estimation performance.

This paper presents a dual-band eight-element multiple-input multiple-output (MIMO) antenna for 5G applications. The 8-element antenna is formed into two 4×4 MIMO systems that operate at 2500-2600 MHz and 1800-2200 MHz bands. The antenna elements are mounted along the perimeter of a rectangular ground plane with a total size of 110 × 80 mm² and are printed on both sides of a low-profile PCB material. Elements radiate through open rectangular slots etched on the antenna's ground conductor. The open slots are excited by T-shaped microstrip lines fed by 50-Ω coaxial connectors. The size of the ground plane's slots, and the T-shaped radiators control the resonance of the antenna's elements. The proposed design employs orthogonal elements to mitigate mutual coupling. The isolation between ports is less than -10 dB. The radiation efficiency ranges from 40% to 65% across operating frequency bands.

Wireless power transmission system (WPTS) based on near-field inductive coupling is an effective way to provide power for gastrointestinal micro-robot. WPTS is normally realized by a Helmholtz coil outside the body and a three-dimensional receiving coil in the micro-robot. Helmholtz coil has two types, circle and square. However, a quantitative comparison for them in the application of WPTS has not been available yet. In this paper, the calculating models of the electromagnetic field intensity (EMFI) for the circular Helmholtz coil (CHC) and square Helmholtz coil (SHC) are built. With the built model, the uniformities of the electromagnetic field (UEMF) of two Helmholtz coils are calculated. The actual coil system is built to verify the correctness of the built models. When the diameter of the CHC and the side length of the SHC are both 40 cm, the available areas (UEMF ≥ 90%) for powering the robot supplied by the CHC and SHC are 39% and 56%, respectively. Also, the consumed powers of the two coils, when identical EMFI is excited, are compared. When the EMFI at the center of the CHC and SHC are both 1 Gs, the consumed powers are 5.09 W and 4.62 W, respectively. The above results show that compared to the CHC, the SHCnot only has better uniformity, but also consumes less power. Thus, it is more suitable for the WPTS.

The aim of this paper is to prove that the power generated by a wearable textile patch antenna experiences reduced absorption in the phantom when the antenna ground-plane is increased. First, the dedicated human torso-equivalent phantom and two antennas were fabricated, which are multi-layered, with orientation normal to the body and made of the same materials. One of the antennas has a double in size ground-plane with regards to the other antenna, while the rest of their dimensions are identical. According to the proposed measurement procedure, once the radiation efficiencies of both antennas are measured in free space and with the phantom, the total absorption coefficient and the phantom losses are evaluated. The comparison of the measurement results proves that the increased ground-plane reduces the absorption on the phantom body of the antenna EM power (by 30.5%). Simulations and measurements were found in good agreement, with maximum deviation between the two up to 6% in terms of radiated efficiency. Hence, the proposed experimental evaluation of the impact of the ground-plane size of a wearable textile patch antenna on the reduction of the power absorbed by the user's body can be considered as a simple, reliable and cost-effective measurement method.

In this paper, a novel compact single element G-shaped Asymmetric Coplanar Strip (ACS) fed antenna and its four-element printed multiple-input multiple-output (MIMO) antenna have been presented with multi-band frequency characteristics. The proposed MIMO antenna has been fabricated on an FR-4 substrate (46 × 46 × 1.6) mm³ with dielectric constant ε_r = 4.4. The desired isolation between the elements (-18 dB) is achieved by placing the antenna elements orthogonal to each other. Simulated and measured results show that return loss (S₁₁) for the proposed MIMO antenna is less than -10 dB in the operating bands, with frequency ranging 2.30-2.45 GHz, 3.36-3.65 GHz, and 4.53-5.88 GHz, respectively, which ensures its operation in multiple frequency bands. Moreover, these bands are obtained for 2.3 GHz WiBro, LTE and 5G NR to cover B40/B42/N30/N40/N97 together with 3.5 GHz/5 GHz WiMAX/WLAN band applications. Meanwhile, the diversity performance characteristics like ECC (Envelope Correlation Coefficient), MEG (Mean Effective Gain), DG (Diversity Gain), Total Active Reflection Coefficient (TARC), and Channel Capacity Loss (CCL) have been calculated and are presented in this paper. The correlation coefficient is found to be less than 0.001 with a diversity gain greater than 9.95, and an acceptable channel capacity loss is less than 0.4 bits/s/Hz.

This paper proposes a dual-polarized and high gain, four-element based compact multiple-input-multiple-output (MIMO) antenna operating at 5.2 GHz. First, a hammer-shaped antenna has been designed with a gain of 5.3 dBi, impedance bandwidth of 400 MHz, and broadside radiation. A mathematical analysis for radiated electric field and an equivalent circuit model for the hammer-shaped antenna are developed. Using the hammer-shaped antenna as an element, four element MIMO design with shorting walls is proposed. The shorting walls near non-radiating edges improve isolation between the elements by changing the direction of the major lobe. The proposed design has an envelope correlation coefficient (ECC) < 0.15, measured gain of 5.5 dBi, and mean effective gain (MEG) ~ -3 dB. This design has a low profile and single layer planar structure of area 65 mm x 65 mm, which makes it a good contender for portable devices or low-profile hand-held applications in WLAN band.

A high selectivity microstrip dual-mode diplexer with a stepped-impedance opened-end structure is implemented to reduce the size of a dual-mode resonator and suppress the harmonics. The proposed dual-mode resonator structure consists of a microstrip half-wavelength resonator and an open-circuited stepped-impedance stub. The stepped-impedance opened-end structure can control an even mode in the upper and lower desired bands to improve the cutoff responses. The sharp cutoff selectivity of the filter is created to improve the diplexer performance and wide suppress harmonics. The dual-mode diplexer prototype is analyzed, fabricated, and measured. The measured result agrees well with the analyzed result. The simulated and measured dual-mode diplexers are designed at the operational frequency of Tx/Rx at 1.95 GHz and 2.14 GHz, respectively. It is shown that the dual-mode filter has a wide stopband, including the first spurious resonance frequency due to the stepped-impedance stub.