Due to the limitation of low-resolution radar system and the influence of background clutter in the detection process, it is hard for low-resolution radars to classify and identify aircraft targets. To solve the above problems, a classification method for aircraft based on Ensemble Empirical Mode Decomposition (EEMD) and multifractal is proposed, in which the intrinsic modes are obtained by EEMD, and the waveform entropy in the Doppler domain is used to screen and reconstruct the intrinsic modes. The multifractal feature of the target echo data is extracted from the reconstructed signal, and then the aircraft target classification and recognition experiment is carried out with support vector machine. The experimental results show that the feature data extracted by ensemble empirical mode decomposition and multifractal analysis can be used for the classification and identification of civil aircraft and fighter aircraft, and the accuracy rate is about 98.5%, which is higher than that of time-domain multifractal method.

A conformal quasi-isotropic dielectric resonator antenna (DRA) is first investigated for wireless capsule endoscope (WCE) application under the 5.8-GHz industrial, scientific, and medical (ISM) standard. The probe-fed hemispherical DRA (HDRA) is studied to match the shape of the spherical dome end, and the characteristic mode analysis (CMA) tool is applied to analyze the resonant modes of the proposed antenna to reveal the intrinsic behavior of the dielectric resonator. It is found that the quasi-isotropic radiation pattern can be achieved by combining HDRA's TE_111sinφ mode which radiates like a magnetic dipole and a small ground plane's TM₁₀ mode that radiates like an electric dipole. In order to reach the requirement of 5.8 GHz in ISM, a ceramic hemispherical dielectric resonator with dielectric constant of 21.984 is investigated. The radius of the hemisphere is set to 5.35 mm. In free space, the measurement results show that the proposed antenna achieves 3.25% bandwidth, 86% maximum efficiency and 7.2 dB gain deviation. The antenna is also measured in pork to approximate human body environment. The measurement results demonstrate that the antenna achieves 3.20% bandwidth, 8.15% maximum efficiency and 9.0 dB gain deviation. Accordingly, the proposed antenna is suitable for WCE application at 5.8 GHz ISM standard.

Minimum variance distortionless response (MVDR) beamformer is an one of the well-known space-time antijamming techniques for global navigation satellite system (GNSS). It can jointly utilize spatial filter and temporal filter to suppress interference signals. However, the computational complexity is usually so high that it is difficult to apply in engineering problems. In order to solve this problem, a novel MVDR algorithm based on rank-reducing transformation (RRT) and multistage wiener filter (MWF) is proposed for reducing the computational complexity, named as RRT-MWF-MVDR algorithm. Via the characteristics of the oppressive jamming environment and the steering vector of satellite signal, a rank-reducing transformation is given. By the rank-reducing transformation, a rank reduction is realized for the high dimensional received data. Taking these received data with reduced rank as the input of the MWF, the forward decomposition and backward iteration are accomplished. Then the equivalent reduced rank matrix and equivalent weight vector of MWF can be given, respectively. Finally, the space-time two-dimensional antijamming weight vector is given by the mathematical relationship between the reduced-rank matrix and the weight vector.The proposed method can effectively avoid the inverse of high-dimensional matrix. The proposed method offers a number of advantages over the existing algorithms. For example, (1) it has less computational load and is easier to be executed in practical application. (2) It can maintain higher output signal-to-interference-noise ratio (SINR). Simulation results verify the effectiveness of proposed method.

Space-time adaptive processing (STAP) algorithms can provide effective interference suppression potential in global navigation satellite system (GNSS). However, the performance of these algorithms is limited by the training samples support in practical applications. This paper presents an effective STAP based on atoms extension (named as AE-STAP) algorithm to provide better anti-jamming performance even if within a very small number of snapshots. In the proposed algorithm, a spatial-temporal plane is constructed firstly by the sparsity of received signals in the spatial domain. In the plane, each grid point corresponds to a space-time steering vector, named as an atom. Then, the optimal atoms are selected by searching atoms that best match with the received signals in the spatial-temporal plane. These space-time steering vectors corresponding to the optimal atoms are used to construct the interference subspace iteratively. Finally, in order to improve the estimation accuracy of interference subspace, an atoms extension (AE) method is given by extending the optimal atoms in a diagonal manner. The STAP weight vector is obtained by projecting the snapshots on the subspace orthogonal to the interference subspace. Simulation results demonstrate that the proposed method can provide better interference suppression performance and higher output signal-to-interference-plus-noise ratios (SINRs) than the previous works.

In this article, the drawbacks of Li's formula is rectified and extended to compute accurately the resonant frequency of a rectangular patch antenna in multi-dielectric layers. Computed results employing the present model are compared with experimental and simulation results. The present model shows excellent improvement in accuracy compared to the previously reported investigations.

In this paper, a novel three-dimensional (3D) bandpass frequency selective surface (FSS) is presented based on a square waveguide structure using 3D printing technology. The proposed 3D FSS is composed of a periodic array of the square waveguides with dumbbell slots embedded in waveguide walls. The square waveguide of the unit cell provides a propagation path, which can excite two resonant modes, leading to a bandpass response with one transmission pole and one transmission zero below the cutoff frequency of the square waveguide. To explain the operating principle of the proposed 3D FSS, the electric field distributions at the frequencies of transmission pole/zero are analyzed, and an equivalent circuit model is also established. For validation, a practical example is manufactured simply and rapidly, by using 3D printing technology. To verify the performance of the proposed 3D FSS, the frequency selective characteristics of the implemented 3D FSS for both TE and TM polarizations under different incident angles are measured. The measurement results show that the proposed structure exhibits dual polarizations and provides good frequency stability under incident angles from 0° to 40°.

The purpose of this paper is to provide simple analytical homogenization methods for composite materials containing a metallic wire grid. Estimating their effective electrical properties facilitates the numerical simulation of composite structures for shielding applications in the automotive industry. The presented methods are based on surface impedance approaches and effective media theory. The obtained results show that the shielding properties of the described wire grid composites can be accurately estimated and bounded, using the proposed theories in the low frequency range. The frequency limits vary according to the studied sample. For the presented materials, the validity of the results is shown to be up to a few megahertz. The experimental validation is done by measuring the shielding effectiveness of composite samples using a near-field test bench.

Different global and national electromagnetic regulatory standards have been developed based upon significantly diversified premises, developmental backgrounds and objectives to safeguard life. Some standards aim at minimizing short duration thermal effects, some try to mitigate non-thermal effects over prolonged duration and rest have adopted precautionary limits. As a consequence, these global and national electromagnetic standards substantially differ from each other. Moreover, in spite of lossy dielectric nature of plant tissues, electromagnetic energy absorption rate level estimations for a complete plant model have neither been reported in literature nor been considered while preparing safety standards. To this end, Specific Absorption Rate levels have been estimated for a typical Catharanthus roseus plant model --- typical geometric shape of the plant prototype has been modelled considering the most practical scenario. Detailed analyses on variation of Specific Absorption Rate levels due to wide discrepancy among the existing electromagnetic regulatory standards have been reported in a quantitative manner. This particular work encompasses dielectric properties measurement of different Catharanthus roseus plant samples, modelling a typical Catharanthus roseus plant containing leaves, flower and twig with appropriate dielectric properties defined, and finally the simulation-based investigations to estimate the variation in Specific Absorption Rate levels based on the contrasting electromagnetic exposure standards. Specific Absorption Rate levels have been reported at five different telecommunication bands as per two occupational and four public exposure scenarios. Variations among the estimated Specific Absorption Rate levels have been noted to be significant and presented in detail in this article. A total of thirty rigorous simulations have been carried out along with one hundred and twenty Specific Absorption Rate data evaluations to ensure accurate comparison among different electromagnetic standards. Noted vast variations among estimated Specific Absorption Rate levels based on contrasting electromagnetic standards over the frequencies indicate the necessity of re-evaluating all existing guidelines and also call for the need of maintaining a global uniformity among the existing electromagnetic standards worldwide.

The propagated fields within and radiated fields outside a rectangular dielectric cylinder are represented as guided and radiation modes respectively. These fields of the cylinder are related with incident, backward scattered fields at x=0 and transmitted fields at x=a by Mode Matching technique. The expressions for guided and radiation mode amplitudes are derived by applying the orthogonal property of the modes. The unknown functions (mode amplitudes) in each of these equations that are defining discrete functions of the guided modes field and angular spectrum for the radiation field are determined numerically. The powers due to discrete guided modes (even and odd) are calculated. The integrals related with the backward and forward scattered fields and the powers associated with them are approximately evaluated by the method of steepest descents.

An accurate rigorous modal theory has been applied to investigate the propagation characteristics in a rectangular waveguide filled with multilayer left-handed and right-handed metamaterials. It is shown that such a waveguide supports different passbands below the waveguide's cutoff frequency, and the number of passbands is related to the corresponding layers of different left-handed metamaterials (LHMs) filled in the waveguide. The rigorous modal analysis of this structure reveals in detail how the waveguide geometry and left-handed metamaterial parameters may be selected to design rectangular waveguides supporting double or triple below-cutoff passbands. The efficient power transmissions in these below-cutoff passbands are validated by using the full-wave simulation software HFSS. These structures supporting multiple below-cutoff passbands could find applications in waveguide components requiring miniaturization and multiband properties, such as miniaturized multifunctional antennas and filters.

Wireless communication plays a vital role in transmitting information from one point to another. Wireless devices have to be smart, intelligent, compact in size and cost effective to meet the demand of wireless communication. A multi-layered, Split Ring Resonator (SRR), negative permeability material inspired antenna has been designed, analyzed, fabricated, and measured. The developed antenna resonates at 1.13 GHz, 2.47 GHz, and 2.74 GHz frequencies with gain of 3.73 dBi, 6.18 dBi, 1.35 dBi, and bandwidth of 2.10%, 2.81%, and 2.09%, respectively. The structure utilizes FR4 material as a substrate. The engineered model has applications in navigation, WiFi, and satellite communication applications.

This paper presents a fifth-generation (5G) wireless smart antenna for performing both power substation communication (in space domain beam-steering) and electrostatic discharge (in time domain Ultra-high Frequency ``UHF'' impulse) detection. The same smart antenna used to communicate with other wireless antennas in the switchyard, as well as with the control room is utilized to cyclically gather data from power apparatus, busbars and switches where electrostatic discharge (ESD) may occur. The ESD poses a major threat to electrical safety and lifetime of the apparatus as well as the stability of the power system. The same smart antenna on which beam rotation in space-domain is designed by implementing an artificial neural network (ANN) is also trained in time-domain to identify any of the received signals matching the ultra-high frequency band electrostatic discharge pulses that may be superimposed on the power frequency electric current. The proposed system of electrostatic discharge detection is tested for electrostatic pulses empirically simulated and represented in a trigonometric form for the training of the Perceptron Neural model. The working of the system is demonstrated for electrostatic discharge pulses with rising times of the order of one nanosecond. The artificial intelligence system driving the 5G smart antenna performs the dual role of beam steering for 5G wireless communication (operating in the space domain) and for picking up any ESD generated UHF pulses from any one of the apparatus or nearby lightning leaders (operating in the time domain).

In this paper, a substrate integrated waveguide (SIW) quasi-uniform leaky-wave antenna (LWA) is proposed for a dynamically steerable beam design at a single frequency through the use of a thin layer of nematic liquid crystal (LC) underneath the substrate. The orientation of the LC molecules, and therefore the effective dielectric properties of the LC cell, is controlled via an externally low-frequency, low-strength bias voltage. The radiation occurs through a series of closely placed transverse slots etched on the top plane of the SIW. This antenna was designed to operate based on the fundamental space harmonic (n=0) in the frequency range between 24.25 GHz and 29 GHz, which covers one of the future 5G frequency bands to be deployed in some parts of the world. This novel antenna design concept was verified numerically using a commercial software based on the Finite Element Method (FEM), and the results are presented and discussed herein.

For the first time, a real sized complex target that is coated with an absorber material is discriminated from the uncoated one using an aspect independent discrimination method based on natural resonances. This resonance based technique provides a real-time, accurate and aspect independent solution for stealth target discrimination. First, the discrimination is studied for a complex shaped aircraft of electrical size 1.5λ. The Perfectly Electrically Conducting (PEC) target is coated uniformly with sintered nickel-zinc-ferrite, a magnetic Radar Absorbing Material (RAM) with complex dielectric and magnetic properties. The resonant range Radar Cross Section (RCS) of the aircraft for different coating thicknesses is computed using the Method of Moments (MoM). The resonances contained in the RCS are extracted using the vector fitting method, and the dominant resonances representing the target are determined by applying the power criteria. The variation in the pole placements with the increasing coating thickness is also studied. A one number quantifier of discrimination --- ``Risk'' in dB is defined to express the amount of mismatch between the compared targets. Further, the discrimination technique is also studied for an aircraft of electrical length, 7λ. A Risk value of 2 dB and more is obtained in this study at all aspects. This demonstrates the capability of the algorithm to discriminate between targets of identical structure but with different material compositions.

In this article, a meander line dipole antenna for radio frequency identification (RFID) tag is presented. The loaded meander antenna has a simple meander line structure with a spiral inductor at the end for size miniaturization, a T-match structure and an inductively coupled parasitic element for impedance matching with the tag IC. The antenna is designed to operate in North American UHF RFID frequency band of 915 MHz. The size of the proposed tag antenna is 50 mm × 12 mm and has good impedance matching with Alien Higgs IC chip of 13.5-j111 Ω at the desired frequency band. The proposed tag antenna provides omnidirectional radiation pattern with a maximum read range of 3.5 m at an effective isotropic radiated power of 4 W. Simulation results are in good agreement with measurement results.

A novel computational technique is proposed for heat conduction analysis. The heat transfer equation is expanded in the complex frequency domain and solved using the finitedifference method (FDM). The results in the complex frequency domain are transformed into the time domain via fast inverse Laplace transform. In the proposed approach, the instantaneous temperature at a specific time can be easily obtained. Moreover, the computational time for the conventional explicit FDM is reduced by employing the time-division parallel computing method.

A meshless method for fast solution of the electromagnetic scattering problem related to arbitrary shaped radially inhomogeneous cylinders is proposed. This is an important problem since radially inhomogeneous circular cylinders are common in various engineering applications, and deformations such as notches, grooves and noncircular holes on such cylinders are required for different purposes. This approach is basically an extension of the previously proposed method, which is based on Fourier series representation of the electric field on boundaries. In the original method, a multilayer cylinder with arbitrary shaped homogeneous layers is considered, and accordingly, the general solution of the cylindrical wave equation in homogeneous medium is used. Here we modify the method by considering the general solution in radially inhomogeneous medium, and derive compact expressions for the field.

As ionosphere is one of the most prominent sources of error, ionospheric TEC and scintillation studies are necessary for improving the performance of a navigation system. In this paper, the behavior of the correlation coefficient (ρ) between Rate of TEC Index (ROTI) and amplitude scintillation index (S₄) over low latitude station Hyderabad (Latitude: 17.44° (deg.) N, Longitude: 78.74° (deg.) E) for different seasons is analyzed. Also, the analysis is extended for nearly same longitude stations like Trivandrum, Bangalore, Bhopal, Delhi and Shimla for the higher values of total K_p index for 60 days (most disturbed 5 days per month). For Trivandrum (lowest latitude station), it is observed that both S₄ and ROTI are high as compared to Bangalore, Bhopal, Delhi, and Shimla. It is found that there is a good correlation between the temporal variations of ROTI with S₄ after post sunset hours. The confidence intervals for computed correlation coefficients at 95% confidence level are also given.

Non-contact vital sign detection using radar is relevant for many applications. In search and rescue missions in disaster-stricken areas, this technology can be used to non-invasively detect live survivors on the ground. However, in a very large disaster area, a fast and effective detection approach is required. This need has suggested radar mounted on a flying platform such as a drone as the most feasible approach. This task is challenging, since human respiration is weak, and the signal recorded is easily affected by disturbances such as noise and movement of the platform. Therefore, in this study, we propose a signal processing technique to deal with this problem. Human respiration signals modulate a hyperbolic pattern recorded by moving radar because of distance projection, leading us to applying sequential image processing steps and hyperbolic pattern reconstruction to extract respiration signals. A Fourier transform is then applied to seek the respiration frequency component. The results of laboratory experiments show that the proposed method can detect human respiration. As an important note, the flying speed of the platform should be determined carefully to cope with slow human respiration.

The performance of direction-of-arrival (DOA) estimation algorithms degrades when a partly calibrated array is adopted due to the existing unknown gain-phase uncertainties. In addition, the spatial discretized searching grid also limits the performance improvement and effectiveness of subspace-based DOA estimation algorithms, especially when the true angles do not lie on the grid points which is referred to the off-grid problem alike. In this paper, a self-calibration DOA estimation algorithm is proposed which solves the array calibration and off-grid problems simultaneously. Firstly, the signal model for a partly calibrated array with gain-phase uncertainties is established. To suppress the off-grid errors, an optimization problem for joint parameters estimation is constructed by substituting the approximation of the steering vector into a newly constructed objective function. The alternative minimization (AM) algorithm is employed to calculate the joint DOA and gain-phase uncertainty estimations. Within each iteration step of the optimization problem, a closed-form solution is derived that guarantees the convergence of the proposed algorithm. Furthermore, the Cramer-Rao bound (CRB) for the partly calibrated arrays with unknown gain-phase uncertainties is also derived and analyzed in the paper. Simulation results demonstrate the effectiveness of the proposed algorithm.

An efficient field-to-circuit hybrid method is presented for the electromagnetic interference (EMI) analysis of penetrated wire of an electronic device excited by ambient wave, which consists of finite-difference time-domain (FDTD) method, transmission line (TL) equations, Thevenin's theorem, and circuit analysis method. The significant feature of this method is that it can avoid modelling the structures of penetrated wire and terminal circuit directly on the premise of guaranteeing sufficient accuracy. At first, the whole model of penetrated wire of an electronic device is decomposed into external and internal regions according to the shielded enclosure of the device. Then, the FDTD method combined with TL equations is applied to build the coupling model of external transmission line with the shielded enclosure and extract the equivalent circuit model of an external region based on Thevenin's theorem, which is further imported into the internal region as excitation source. Finally, the EMI analysis of internal region is executed by constructing the transmission parameter matrices of the two-port cascade network, which is contributed by the penetration node, internal transmission line and terminal circuit. Then the interference response on terminal circuit can be obtained. Numerical simulations have been taken into account to verify the the accuracy and efficiency of this field-to-circuit hybrid method by comparing with the traditional FDTD method.

A novel optically-switched antenna is proposed, in which a photodiode is embedded into an antenna radiator. In order to avoid the high loss problem in series structures for the integration of photodiodes and patch antenna, a photodiode parallel structure with sensitive radio frequency response is selected for the design. The status of the antenna while at work can be effectively adjusted by illumination. Its reflection coefficient and radiation gain vary with the exposure of photodiode to light illumination and non-illumination state. The simulation and experiment of this design at 1.52 GHz produce an obvious effect on light control with a maximum 6.6 dB gain variation on omnidirectional pattern. It is thus deemed suitable for speed measurement and occlusion detection in remote wireless sensor networks and other applications.

In order to overcome the problem of high voltage loss rate caused by the increase of current harmonics due to dead-time effect and the decrease of average potential output of inverter in the control process of the interior permanent magnet synchronous motor (IPMSM) for electric vehicles, a dead-time compensation control method based on an extended Kalman filter (EKF) and a neural network bandpass filter (NNBPF) is proposed. Firstly, from the mechanism of dead-time effect, the problems and causes of dead-time effect are analyzed. Secondly, the extended Kalman filter combining feedback and prediction function is used to filter the d- and q-axis currents of the motor, so as to solve the problem that zero current polarity is difficult to judge in the traditional dead-time compensation process. Thirdly, the high-order harmonics due to dead-time effect in the d- and q-axis currents are extracted by using the neural network band-pass filter, and the dead-zone compensation is carried out after the amplitude phase adjustment. Finally, the effectiveness of the proposed dead zone compensation method is proved by comparing no dead-time compensation with the dead-time compensation strategy proposed in this paper. The experimental results show that the proposed dead-time compensation method can effectively suppress the current harmonics, reduce the current distortion, reduce the voltage loss rate to 0.04%, improve the voltage utilization ratio, and effectively improve the operating performance and endurance of electric vehicles.

In practice, the amplitude and phase excitations of array elements undergo random errors that lead to unexpected variations in the array radiation patterns. In this paper, the technique of the clustered array elements with discretized amplitude excitations is used to minimize the effect of random amplitude excitation errors and restore the desired array patterns. The most important feature of the proposed technique is its implementation in the design stage which may instantly count for any errors in the amplitude excitations. The cost function of the used optimizer is constrained to prevent any undesirable increase in the sidelobe levels due to unexpected excitation errors. Moreover, the error occurrences on the element amplitude excitations are considered to be either randomly over the whole array aperture or regionally (i.e., error affecting only a part of the array elements that located in a particular quadrant of the array aperture). Simulation results fully verify the effectiveness of the proposed technique.

The (6k±1)th harmonics exist in the extended electromotive force estimates due to the influence of the inverter nonlinearities and the flux spatial harmonics in the process of sensorless control of permanent magnet synchronous motor (PMSM), which give rise to the (6k)th harmonic in the rotor position estimate. A method of rotor position observation based on the time delay signal cancellation-frequency locked loop (DSC-FLL) is proposed to improve the sensorless control system of PMSM. The equivalent back EMF information is obtained by using the sliding mode observer, and the harmonic component in the specified back EMF observation value is filtered by using the delay signal elimination operator in the two-phase static coordinate system. The frequency locking loop is designed to track the rotor position information online, so as to improve the observation accuracy of the rotor position information. The model of sensorless control system of PMSM based on DSC-FLL is established, and compared with the model of sensorless control system of PMSM based on arctangent function. The results show that after adopting the method of rotor position observation based on DSC-FLL, the high harmonic in back EMF is suppressed, the error of rotor position fluctuation observation reduced, and the error of rotation speed observation reduced. The observation accuracy of rotor position information is significantly improved.

In the forward modeling of the transient electromagnetic (TEM) method, a frequency-domain solution is usually obtained first, and the solution in the time domain is then calculated by a frequency-time transformation. At present, the three main fast frequency-time transformation methods are the Guptasarma algorithm, the sine and cosine numerical filtering algorithms, and the Gaver-Stehfest (G-S) algorithm. In recent years, with the increasing demand for fine detection at shallow depths, the small-loop TEM method has undergone rapid development. It is therefore important to evaluate whether the traditional forward modeling approaches can be directly applied to the small-loop method. In this paper, the principles of the three forward modeling methods and their limitations when being applied to the small-loop TEM method are discussed. Through a comparison with the analytical solution for a uniform half-space, we demonstrate that the accuracy of forward numerical calculation is affected by loop size and earth resistivity. When the Guptasarma, G-S, and cosine numerical filtering algorithms are used for small-loop TEM forward calculation, the overall calculation error becomes non-negligible, whereas the sine numerical filtering algorithm retains a high calculation accuracy. By studying the response of the frequency-domain solution, we analyze the cause of the error in the forward calculation. Generally, the sine numerical filtering algorithm is the most suitable method for fast and high-precision small-loop TEM forward modeling. The results obtained here should provide a foundation for high-precision forward modeling and inversion of the small-loop TEM method.

A pattern reconfigurable patch antenna with dual band characteristic is investigated in this paper. Two substrates with an air layer of 2 mm is used to design the antenna. Two radiators are respectively printed on the top surfaces of the two substrates. The first radiator, which is the circular patch, is printed on the top surface of the upper substrate. Eight rectangular slots are also introduced to obtain directional radiation pattern with reconfigurable characteristic in low band by changing the current distribution, and no metal layer is printed on the bottom surface of the upper substrate. The second radiator, which is composed of a cross branch and four arc-shaped branches, is printed on the top surface of the lower substrate to provide weak coupling effect with the circular patch. A round ground plane and four symmetrical rectangular slots are printed on the bottom surface of the lower substrate to generate additional resonance point in high band with the characteristic of pattern reconfiguration. A total of 12 PIN diodes are installed in the rectangular slots to verify the accuracy of dual-band and pattern reconfigurable features. The measured result exhibits that the designed antenna has dual band characteristic, in which the low band f₁ is from 2.43 to 2.50 GHz with an average gain of 3.2 dBi and an average radiation efficiency of 73.5%, and the high band f₂ is from 4.83 to 5.03 GHz with an average gain of 5.24 dBi and an average radiation efficiency of 73.9%. Moreover, the measured radiation patterns show that the patterns can be reconfigured at 90-degree intervals simultaneously in two bands.

Bearingless switched reluctance motor can be used in aerospace and flywheel energy storage industry. Taking a 6/4/4 hybrid excitation double stator bearingless switched reluctance motor as an example, the motor adopts an E-block structure on the outer stator and is excited by permanent magnet and current. The loss calculation and thermal analysis of the motor is carried out by using finite element method. The result shows temperature distributions of the motor under natural air-cooling condition. The temperature change under different operating status is analyzed. Finally, the temperature change and transient temperature curve of each part of the motor are obtained through simulation, and the motor can run stably.

Conformal low profile antenna array has been widely used towards reduced radar cross section and good radiation characteristics. Being conformal, it has a number of advantages over planar antenna structure. This paper presents the radiation and scattering characteristics of a planar and conformal patch array with conventional and hybrid HIS-based ground plane on a low loss dielectric substrate. The use of a hybrid HIS layer instead of conventional metallic ground plane contributes to achieving wideband RCS reduction over 8 GHz-50 GHz, without degrading the radiation performance in terms of antenna gain, return loss and VSWR. The measurement results of the fabricated antennas are found in good agreement with the simulated ones. The radiation mode RCS of the conformal patch array has been analytically estimated and shown to be controlled in the operating frequency range. Such a low profile low RCS antenna array can be used as a subarray of phased arrays in fire control radars.

This paper presents the resonant properties of a new Asymmetric Single Split Resonator (ASSR) structure for metamaterial applications. The compact uniplanar structure is an asymmetric single split ring resonator with two non-concentric rings. The prototype is fabricated on a substrate of dielectric constant 4.4, loss tangent 0.025, and thickness 1.6 mm and analyzed based on reflection and transmission coefficients and unit cell simulations. The fabricated unit cell of miniaturized ASSR has a footprint area of 0.163ƛ₀ x 0.163ƛ₀ where ƛ₀ is the measured free-space wavelength corresponding to 1.63 GHz. The negative permeability meta-particle is best suited for high-performance multiband bandstop filters, sensors, and RFID applications in advanced communication systems. The paper presents the electric and magnetic responses of ASSR with its constitutive parameters for different field orientations in normal incidence.

In this paper, the performance analysis of a reconfigurable intelligent surface (RIS) assisted underwater optical communication (UWOC) system with a decode-and-forward (DF) relaying protocol is presented. The radio frequency (RF)-RIS link is subjected to Rayleigh fading while the optical UWOC link experiences mixture Exponential-Gamma distributions subject to heterodyne detection and intensity modulation with direct detection (IMDD). In order to obtain a traceable closed-form expression, the statistical distribution of the RF-RIS link is derived in terms of Meijer-G function. Thus, the exact closed-form expressions for system end-to-end outage probability and average bit error rate (ABER) for different modulation schemes are then derived. To gain further insight about the derived analytical expressions, asymptotic expressions for the system are derived at high signal-to-noise ratio (SNR) through which the diversity gain is obtained. The findings show the significant impact of the number of RIS elements, detection technique, and the UWOC optical turbulence on the system performance. Finally, Monte-Carlo simulation is used to justify the accuracy of the derived analytical results.

According to the orthogonality of each sub-carrier in the multi-carrier phase-coded (MCPC) signal, this paper focuses on anti-interrupted sampling repeater jamming (ISRJ) and creatively proposes a novel radar signal based on time-frequency random coded (TFRC) method, namely TFRC-MCPC signal. Based on the perspective of waveform design, the TFRC-MCPC signal adopts a chaotic sequence with good pseudo-random to code each chip in time-domain and each subcarrier in frequency-domain. The TFRC method increases the pseudo-randomness of radar waveform pulses and reduces the correlation between radar echo and ISRJ, thereby effectively suppressing the interference of false targets. The TFRC-MCPC method and common filter design methods do not conflict with each other and can be used in combination. The simulation experiment results show that under the typical parameters described in the paper, compared with the traditional MCPC signal and LFM signal, the signal-jamming ratio (SJR) improvement factor of the TFRC-MCPC signal is optimized by 1-2dB after pulse compression, which verifies its feasibility and effectiveness.

A new metasurface (MS) structure for wideband low radar cross section (RCS) and its performance as an antenna has been analyzed and proposed in this paper. The MS has been designed with two different AMC unit cells, and the novel AMCs scatter the incident waves diffusively. The parameters and dimensions of the AMCs are optimized to get the best performance of the antenna. Furthermore, the unit cell structure of metasurface is designed and positioned to improve the directivity of the antenna. The reflected electromagnetic waves scatter in a manner of 180⁰ out of phase with the incident waves, and the antenna's scattering and radiation performance has also been examined. Full-wave simulations and measurements confirm that the proposed antenna achieves 10 dB RCS reduction over a wide bandwidth of 3-12 GHz (61.2%). A monostatic peak RCS reduction of 45 dB is accomplished at 5 GHz, 7 GHz, and 11.5 GHz. Besides, the radiation characteristics of the antenna are appropriate in the boresight direction, and the antenna exhibits good performance in $E$-, $H$-planes and ensures adequate directivity.

In the iterative solution of the matrix equation arising from the multilevel fast multipole algorithm (MLFMA), sparse approximate inverse (SAI) preconditioner is widely employed to improve convergence property. In this paper, based on the geometric information of nearby basis functions pairs and finer octree grouping scheme, a new sparse pattern selecting strategy for SAI is proposed to enhance robustness and efficiency. Compared to the conventional selecting strategies, the proposed strategy has only one variable parameter instructing the constructing time and memory usage, which is more user friendly. Numerical results show that the proposed strategy can make use of the non-zero entries of near-field matrix in MLFMA more effectively and elaborately without compromising the numerical accuracy and the natural parallelization of SAI.

This paper presents a novel compact printed antenna exploitable for Dedicated Short-Range Communication at 5.8 GHz. The design of the proposed device is based on the concentric arrangement of two contemporary fed patches operating with different modes. The resulting antenna exhibits a fan-beam pattern, with a wide lobe in one plane and narrow lobe in the plane perpendicular to the former, while retaining exceptionally small dimensions. The actual width of the beam makes the antenna suitable to cover a single road lane, as prescribed by the Intelligent Transportation System framework requirements. Furthermore, it natively operates in Circular Polarization, as prescribed by the ETSI EN 302 663 normative. Experimental validations demonstrate that the proposed antenna presents a Left-Hand gain of 4.1 dB at center frequency, with HPBW_x and HPBW_y equal to 160˚ and 45˚, respectively, showing good agreement with the simulations. This measured performance confirms that the device is adequate to cover a single road-lane, according to the European framework for Dedicated Short-Range Communication for traffic monitoring.

The loss of magnetic bearing in the process of operation will lead to the temperature rise of the bearing and affect its performance. A permanent magnet is used to provide bias magnetic flux for hybrid magnetic bearing, which can reduce the loss and temperature rise of the magnetic bearing. In this paper, the loss of radial 2-DOF hybrid magnetic bearing (HMB) is analyzed. On this basis, the 3D thermal analysis model of HMB is constructed by using ANSYS Workbench finite element software. The loss is introduced into the temperature field as a heat source, and the temperature distribution of magnetic bearing is calculated. Combined with the results of loss and temperature analysis, the structural parameters were optimized by using genetic particle swarm optimization algorithm (GAPSO). The results show that the loss and temperature rise of the optimized magnetic bearing are significantly reduced.

Synthetic aperture interferometric radiometer (SAIR) is a high-resolution passive imager by sparsely arranging a number of small aperture antennas to synthesize a large aperture. However, the SAIR requires as many receivers as antennas needed, which results in high system complexity and hardware cost and limits the application of the SAIR. Aiming to reduce the system complexity of SAIR, a new passive coding imaging method is proposed in this paper. By using a new aperture coded measurement approach, the proposed method can significantly reduce the number of RF chains while keeping the image fidelity. The effectiveness of the proposed imaging method has been varified by simulations. The results reveal that the proposed method can be an efficient alternative for simplifying the architectures of SAIR.

High Impedance Textured Substrate is presented for suppression of Surface Waves in Microstrip Antennas. Surface wave propagation limits the radiation efficiency, bandwidth, gain, alters the main beam radiation pattern and increases side lobe levels as well as the back lobes. A novel technique to suppress the surface waves with periodic arrangement of metallic cylindrical pins embedded in the substrate except the area underneath the radiating microstrip patch is presented here. Two structures with solid as well as hollow cylindrical pins are analysed with Spectral Domain Analysis. The textured pin bed structure creates negative permittivity and high capacitive impedance and thus suppresses the propagation of TM-surface waves. The gain of 11.83 dB with an enhancement of 6dB over normal microstrip patch antenna is achieved. Further an increase of 1.61 dB gain with 12.27% improvement in radiation bandwidth is observed in the antenna structure with hollow cylindrical pins as compared to that of solid cylindrical pins. A uniform gain of more than 11 dB is achieved with a percentage bandwidth of 17.43%.

In this paper, a dual-band Multiple Input Multiple Output (MIMO) antenna for fifth-generation (5G) band (3.3-3.6 GHz and 4.8-5.0 GHz) is presented. The proposed MIMO antenna fed by coplanar waveguide (CPW) contains two symmetric antenna elements with two inverted L-shaped stubs. High isolation is successfully acquired by adopting a double-Y-shaped stub and partial ground plane. To obtain compactness, the antenna printed on an FR4 substrate has two triangle corners cut off. To study the performance, the antenna is simulated by Ansoft HFSS 13.0, and then fabricated and tested. The measurement results demonstrate that the antenna has achieved impedance bandwidths (S₁₁ < -10 dB) of 790 MHz (3.08-3.87 GHz) and 880 MHz (4.7-5.58 GHz) with fractional bandwidths of 22.7% and 15.8% respectively, which covers 3.45/4.9 GHz 5G bands. Meanwhile, the measurement results exhibit an enhanced isolation more than 20 dB, a low envelope correlation coefficient (ECC) below 0.001, an average gain better than 2 dB and a stable radiation pattern within operation bands. In addition, the parameters including efficiency, DG, CCL, MEG and TARC are also analysed. The simulated and measured results indicate that the proposed MIMO antenna can be applied to 5G communication system.

The paper aims at studying the shielding effectiveness of a closed cylindrical surface simulated by N dielectric coated conducting strips. The far fields of an electric line source in the presence of the simulated surface and in the absence of the surface were calculated, and the ratio between them represents the shielding effectiveness produced around the surface. The solution of the problem was developed based on full wave analysis. In which all fields are represented in terms of infinite series of Mathieu functions. The addition theorem of Mathieu function was employed to facilitate the application of boundary condition. Computer program was developed based on the resulting formulations to produce numerical values. Numerical results are presented for circular and square cross-sectional cylindrical surfaces. Comparison with the published data for the radiation from slotted circular cylinder showed excellent agreement. Other useful results for shielding effectiveness are furnished.

In coaxial magnetic gear (CMG), magnetic modul ation ring is composed of a modulator and a connecting bridge. The torque performance of the magnetic gear are affected by the different structures of the magnetic modulation ring. In this paper, fifteen different kinds of magnetic modulation rings with different structures are proposed; they consist of three different shapes of modulators and five different locations of connection bridges. By using the two-dimensional finite element method (FEM), the magnetic flux density, magnetic line distribution, static torque, and steady-state torque of the CMG with different structures of magnetic modulation ring are analyzed. The results show that the innermost bridge has the least effect on the torque and torque ripple of the CMG, while the outermost bridge has the opposite effect. The torque capacity of the circular modulator and arc modulator is higher than that of the square modulator, and the circular modulator helps to reduce the inner torque ripple, while the square modulator helps to reduce the outer torque ripple. This paper can provide some references for the design of the magnetic modulation ring.

Magnetic micro-robots are used widely in a narrow space, such as internal inspections and desilting of slender pipelines, minimal- or non-invasive diagnoses and treatments of various human diseases in blood vessels, and micro-manipulations, micro-sensing fields. Magnetic micro-robots are usually driven by several electromagnetic coils. It is essential to understand the magnetic field and magnetic forces acting on micro-robots to drive the magnetic micro-robots more effectively. In this paper, the finite element method is applied to simulate the magnetic field generated by a coil assembly. Moreover, a three-dimensional magnetic force simulation is also performed to reveal the magnetic forces acting on a cylindrical magnetic micro-robot. Experimental measurements validate the simulated results. A Hall sensor is used to measure the magnetic field along the coil assembly's axial and radial direction. The micro-robot is glued to a connecting rod, fixing a force sensor to measure the magnetic forces acting on it. The measured results are in good accordance with the simulated ones, which prove the validity of the simulation. The results from this study show potential to provide a reference to magnetic micro-robot applications.

A Ku-band long linear helical subarray (LLHS) for a high-power cylindrical conformal array antenna has been developed. The LLHS consists of 80 helical antennas can be used to constitute conformal array of cylindrical surface. Through the research on the embedded probe structure, the adjustment of the coupling ability of different types of unit probes and the sealing method of the whole feeding, the problems of large feed reflection, the uneven coupling amount of the unit probe in the rectangular waveguide system are solved, and the LLHS which can be used in the high-power conformal array is realized. The LLHS which is 52.35λ length can obtain 25.2 dB gain, 2.31 dB axis ratio, 90% aperture efficiency, -15.65 dB reflection at 12.5 GHz, and the reflection is lower than -14 dB during 12-13 dB. In addition, it could handle a pulse power of 166 MW under vacuum condition.

Radio frequency (RF) energy harvesting technologies have attracted different efforts from researchers to employ low energy in powering portable electronic devices. In this article, an Ultra-Wide Band (UWB) antenna based on a Vivaldi fractal antenna backed with a Metamaterial (MTM) array is exemplified for RF-energy harvesting in the modern 5G networks. The antenna is connected to a full wave rectifier circuit to obtain a rectified DC current. It is found that the exemplified antenna provides a maximum output voltage of 1.4V and 1.3 V at 3.1 GHz and 4 GHz, respectively, when the incident RF power is around 17 Bm. The measured results and simulations show excellent agreement. The antenna is printed a flexible Kodak photo paper of 0.5 mm thickness with ε_r = 2 and loss tangent of 0.0015. The numerical simulations are conducted using CST MWS and HFSS software packages. The proposed antenna structure is fabricated using an ink jet printing technology based on conductive silver nanoparticle ink. Finally, from the obtained measurements after the comparison to their simulations, the proposed antenna is covers the frequency band from 2.4 GHz up to 20 GHz with a gain of 1.8 dBi at 3.1 GHz and 4 dBi at 4 GHz.

We firstly derived the simplified formulas for calculating attenuation constants of surface wave in double-layer magnetic absorbing sheets (MASs). The fabricated two kinds of magnetic absorbing sheets, having advantages in the low and high frequency range respectively, were used to design a group of 0.5 mm-thick double-layer sheets. Numerical calculation results show that the surface wave attenuation constants of double-layer absorbing sheet with a proper combination of the two MASs can be significantly enhanced in the whole frequency range, compared to those single-layer sheets of the same thickness. Furthermore, the simulations of mono-static RCS reduction of the metal slab coated with double-layer MAS well confirm the calculation analysis. This work demonstrates that it is feasible for double-layer magnetic absorbing sheet to enhance the surface wave attenuation ability and broaden application frequency range.

In this article, a new approach has been demonstrated for the bandwidth enlargement of a substrate integrated waveguide (SIW) cavity-backed antenna. The proposed structure employs bilateral slots, instead of unilateral slots, which is a distinct approach, in contrast to traditional cavity antennas. The proposed antenna embodies SIW cavity with a height less than 0.017λ₀ and thus holds low-profile planar geometry, while retaining lower losses and light weight. The non-resonant slot, at the bottom plate, produces two-hybrid modes (odd TE₂₁₀ and even TE₂₁₀). The quality factor (Q) of these hybrid modes is greatly reduced by loading the resonant slot cut at the top metallic plate of the SIW cavity which leads to achieving a wideband response. A sample is fabricated and investigated at X-band. It is shown that the experimental results are well-matched with the simulated ones. The measured impedance bandwidth of the proposed antenna is 860 MHz (8.6%). Moreover, it renders a maximum gain of 6.56 dBi at 9.78 GHz and 6.75 dBi at 10.35 GHz, within the operating bandwidth. The cross-polarization radiation levels of maximum -26 dB and -28 dB are obtained at the corresponding resonant frequencies, respectively.

To obtain three-dimensional (3-D) high-precision and real-time through-wall location under ambiguous wall parameters, an approach based on the extreme learning machine (ELM) which is a neural network is proposed. The wall's ambiguity and propagation effects are both included in the hidden layer feedforward network, and then the through-wall location problem is converted to a regression problem. The relationship between the scattered signals and the target properties are determined after the training process. Then the target properties are estimated using the ELM approach. Numerical results demonstrate good performance in terms of effectiveness, generalization, and robustness, especially for the kernel extreme learning machine (KELM) approach. Noiseless and noisy measurements are performed to further demonstrate that the approach can provide good performance in terms of stability and reliability. The location time, including the training time and the test time, is also discussed, and the results show that the KELM approach is very suitable for real-time location problems. Compared to the machine learning approach, the KELM approach is better not only in the aspect of accuracy but also in location time.

The design of a wideband antenna using truncated corners partial ground plane loaded with L-shaped stubs and inverted T-shaped slots has been presented in this manuscript. The different concepts and structures related to antenna designing have been employed to attain the optimized model of antenna. L-shaped stubs and inverted T-shaped slots incised in the structure of antenna improve the impedance matching and bandwidth of proposed antenna. The fed 50Ω microstrip line has been applied to the proposed structure for attaining distinct performance parameters like reflection coefficient, gain and radiation pattern. The distinct structures of proposed antenna have been juxtaposed, and it is found that the structure with L-shaped stubs and inverted T-shaped slots shows improved antenna performance parameters. The designed antenna exhibits the bandwidth of 133.04% (3.14-15.62 GHz) and 16.96% (18.56-2.0 GHz) with improved reflection coefficient and gain. The proposed antenna has also been fabricated and tested for validation of simulated and measured results, and found in good agreement with each other. The design of proposed antenna is carved on a low cost thick substrate with compact electrical size of 0.566λ x 0.452λ x 0.0301λ mm³ at 5.45 GHz frequency and can be used for different wireless applications in the frequency range 3.14-15.62 GHz and 18.56-22.0 GHz.

An elliptical array, composed of 10 uniform elliptical apertures as the radiating elements, is presented. Assume that each aperture in an electric conducting plane spreads on the elliptic orbit and is fed by the uniform plane wave in order to obtain a low SLL array pattern with high directivity, the elliptic orbit eccentricity and the angular position of each array element are stimulated. The applied parameters are determined by an elaborate optimization procedure. The utilized procedure, comprising the geometric computational technique (GCT), and angular positions excitation (APE) is stated in detail, respectively to determine a satisfactory eccentricity and the angular position of each element.

In this manuscript, the thermal effect on a lumped element balanced dual-band band-stop filter (BSF) has been discussed in detail for the first time. The response of a novel filter should maintain consistency over a wide range of temperature. Although any microwave filter in general is designed for room temperature condition, the filter is employed for applications where the operating temperature constantly changes. Therefore, it is necessary to check the reliability of the filter response within a specific temperature range based on its application. Modern simulation software helps to make an initial assumption about the filter performance at different thermal conditions before its lab testing or actual application. Here, a quantitative analysis has been provided to show how change in temperature contributes to the change in each component value of a lumped element filter. This analysis is followed by a simulation to show that a balanced lumped element filter exhibits lower loss than its single-ended counterpart. Also, as the temperature varies, the balanced design demonstrates less deviation in the loss value than a two-port design. Next, a balanced dual-band BSF prototype with center frequencies 1.151GHz and 1.366GHz (25℃)is characterized with a 4-port network analyzer under different temperature conditions. The experimental results exhibit a good match with the simulation results. For a variation of 80℃ in temperature, the maximum deviation obtained for the filter center frequency, absolute bandwidth (ABW) and insertion loss (Sdd21) are 5MHz, 2.8MHz and 2dB, respectively.