This paper presents the design of an X-band stepped lens-loaded flat reflector (STLR) using reflectarray unit cell approach. A flat reflector of size 15×15 cm2, loaded with a 10×10 dielectric unit cell array, centre-fed by a horn antenna, is evaluated by simulation and measurement. The simulated performance of the proposed structure is compared with a smooth lens loaded plane reflector (SMLR) and microstrip reflectarray (RA), of equivalent cross section. The results are in good agreement for SMLR, whereas a fair match is observed only in the main lobes of RA. It is worth to note that the reported STLR has a reduced thickness compared to SMLR. Furthermore, a simulation-based study is carried out on the effect of tapering of the dielectric structure in the proposed design, and a similar performance to when stepping is used is noted.
In this study, we propose an asymmetrical input transformer for the input baluns in a differential RF CMOS power amplifier to minimize the loss induced by the input transformer. To reduce the loss caused by the magnetic coupling between the primary and secondary parts of a typical transformer, we modify the interconnection between the input transformer and the differential input of the driver stage. Unlike a typical transformer, the primary and secondary parts of the proposed transformer are directly connected to the input of the driver stage. As a result, the input signal in the primary part can reach one of the inputs of the differential driver stage, thereby reducing the loss caused by magnetic coupling. To verify the functionality of the proposed asymmetrical input transformer, we designed a 4.5-GHz differential CMOS power amplifier for IEEE 802.11n WLAN applications with 64-QAM, 9.6 dB PAPR, and a bandwidth of 20 MHz. The designed power amplifier is fabricated using the 180-nm SOI RF CMOS process. The measured maximum linear output power is 17.59 dBm with a gain of 29.23 dB.
The performance of magnetic bearing is determined by its electromagnetic parameters and mechanical parameters. In order to improve the performance of hybrid magnetic bearing (HMB) to better meet the engineering requirements, which needs to be optimized, a multi-objective optimization method based on genetic particle swarm optimization algorithm (GAPSO) is proposed in this paper to solve the problem that the optimization objectives are not coordinated during the optimization design. By introducing the working principle of HMB, a mathematical model of suspension force is established, and its rationality is verified by the finite-element method. By optimization, the suspension force of the HMB is increased by 18.5%, and the volume is reduced by 22%. The optimization results show that the multi-objective optimization algorithm based on GAPSO can effectively improve the performance of HMB.
A novel, simple and inexpensive microstrip antenna is designed for vehicle communication and specifically for blind spot detection in this work. The proposed antenna is 20.2 mm x 24.1 mm x 1.6 mm in size. Since offset feeding technique is used, manufacturing is simple and cheap. ANSYS Electromagnetics Suite 17.2 simulates the antenna. To suppress mutual coupling, defected ground structure is employed. In addition, the Genetic Algorithm is used to optimize the ground plane width to obtain high gain and omnidirectional characteristics. The simulated results conceive that the `Dedicated Short Range Communication' (DSRC) band band is covered by using the antenna. Moreover, the antenna is fabricated, and the measured results are found to be consistent with the simulated ones.
Statistical characteristics of scattered electromagnetic waves in the turbulent magnetized plasma caused by electron density fluctuations are calculated using complex geometrical optics approximation taking into account both diffraction effects and polarization coefficients. Scintillation level normalized on the variance of the phase fluctuations is analyzed analytically and numerically for small-scale plasma irregularities using the experimental data. New properties of the electromagnetic wave scintillations have been revealed. It is shown that splashes arise in the ionosphere leading to the turbulence and generation of new oscillations (waves and/or Pc pulsations) propagating in space and the terrestrial atmosphere. Turbulence extending in the lower atmospheric layers can influence on the meteorological parameters leading to climate change.
Compressed sensing (CS) is utilized in antenna measurements. The antenna data are compressed using the CS method, and the performances of different sparse and recovery algorithms of CS are used to solve antenna measurements. Experiments are conducted on various types of antennas. The results show that efficiency can be greatly improved by reducing the number of measurement points. The best reconstruction performance is exhibited by the Discrete Wavelet Transform (DWT) algorithm combined with the Compressive Sampling Matching Pursuit (COSAMP) algorithm.
In this paper, an analytical calculation of the magnetic field in a consequent-pole bearingless permanent magnet (PM) type motor with rotor eccentricity is proposed. The analytical method is based on the resolution of Laplace's and Poisson's equations. Due to the presence of consequent-pole, the general solution of the first-order for the vector potential distribution in the air-gap is presented considering the first harmonic. Here, the magnetic field distributions by the analytical method are compared with those obtained from finite element (FE) analyses. Then, the corresponding performances are quantitatively assessed by the ﬁnite-element method.
The output power of a magnetic coupling resonance wireless power transfer (MCR-WPT) system attains the maximum value at two frequencies splitting in an over-coupled region. To achieve suitable transfer characteristics, impedance compensation methods have been used in MCR-WPT domain. In securingthe constant output power and transfer efficiency in a constant frequency mode, a topology of the MCR-WPT system with two transmitting coils is employed. First, the circuit model is designed while evaluating the transmission characteristics. Second, when the two transmitting coils are placed into the transmitting loop, the main transmitter and sub-transmitter loops are created by sharing the same transmitter. The use of two transmitting coils to achieve a magnetic field superposition is investigated. Constant output power and transfer efficiency are then investigated in a constant frequency mode.Finally, the experimental equipment is designed. Experimental results confirm the effectiveness and robustness of the topology. Such a topology can be optimized for the transfer performance by itself and can achieve constant output power and transfer efficiency.If the distance between the two transmitting coils is appropriate and the receiving coil moves between the two transmitting coils, the fluctuation of the output power and transfer efficiency of the MCR-WPT system is less than 5%.
A practical coplanar waveguide (CPW) fed ultra-wideband (UWB) antenna with reconfigurable dual band-notched characteristics is proposed in this paper. A cup-shaped branch is added to the grounding plate and a step impedance resonator (SIR) added to the microstrip line, which realize notch characteristics in 5.1~5.9 GHz and 7~7.8 GHz bands and realize double notch function with good radiation direction characteristics. The antenna bandwidth is extended by using CPW feeding, ranging from 3 GHz to 16 GHz with the relative bandwidth of 137%. The notch band reconfigurability is realized by integrating three switches into the cup-shaped branch and SIR. In addition, the proposed antenna has a compact size of 24 mm × 32 mm × 1.5 mm and can provide omnidirectional radiation pattern, which is suitable for UWB communication applications.
In this paper, a W-band single-pole four-throw (SP4T) switch for multichannel high power transceiver chipset design is proposed based on a standard commercial 100 nm GaAs power pseudomorphic high electron mobility transistor (pHEMT) technology. The process used in this work is optimized for use in power amplifier (PA) design, resulting in larger drain electrode capacitance. In order to reduce the effect of large drain capacitance for switch design, a proper series capacitor is adopted. This capacitor can not only reduce the parasitic capacitance of the turn-off state transistor but also resonate with the parasitic inductance of the turn-on state transistor to improve the isolation. As known, the short stub is adopted to compensate the remaining parasitic capacitance. For verification, a prototype is fabricated and measured. The measured results are in good agreement with the simulated ones, and it shows that the fabricated SP4T switch achieves a bandwidth of 75 GHz-96 GHz, with an insertion loss and isolation about 4.8 dB and 28 dB, respectively. The fabricated switch also realizes a Pin1 dB about 22 dBm.
Radar cross section (RCS) reduction technology has great significance in stealth and other fields. A PSO-FSP algorithm is proposed based on the particle swarm optimization algorithm and the far-field scattering characteristics of coding metasurface to obtain the optimized coding sequence for RCS reduction. According to the principle of coding metamaterial, a 1 bit cell structure is designed. Therefore, a coding metasurface is constructed by arranging the unit cells based on the optimized coding sequence. Simulation results show that, in the case of vertical incidence, compared with metal plates of the same size, the metasurface can achieve more than 10 dB of RCS reduction within the broadband range from 15 GHz to 35 GHz, and the maximum reduction can reach 36 dB. The proposed coding metasurface has been successfully fabricated and measured, and there is a good agreement between simulated and measured results.
A novel ultra-wideband (UWB) printed monopole antenna with triple band-notched characteristics is proposed in this paper. The antenna bandwidth is extended by grooving on the connecting floor and increasing the impedance transformation line, with antenna bandwidth of 3.0~11 GHz and relative bandwidth of 114%. The overall antenna size is 35 × 30 mm2. The complementary split-ring resonators (CSRRs) are loaded on the UWB antenna patch with microstrip wire feed. A symmetric J gap is loaded on the bottom plate, and the spiral gap is loaded on the feeder. The triple band-notched characteristics at 3.22~3.97 GHz, 4.94~5.84 GHz, and 7.25~7.86 GHz bands are realized. The gain of the designed antenna in the notch frequency segment can be reduced rapidly to -4 dbi, while the gain of other frequency bands is above 2 dBi. Simulated and measured results show that the antenna has stable gain and good radiation characteristics in the UWB frequency range.
This paper presents an exact analytical method to compute the air-gap magnetic field of surface-mounted permanent-magnet (SMPM) motors for evaluating slotting effects accurately. Solution field regions are divided into air-gap domain, permanent magnet (PM) domain, and slot domains. The Laplace's equations or Poisson's equations of the sub-domains are contacted by boundary conditions and then solved by exact analytical method. The actual height of slot and distance between slots are taken into account in the computation. Magnetic field distributions and cogging torque computed with the proposed analytical method are compared with those issued from 2-D finite-element method (FEM), and the comparison results are consistent and show the correctness and effectiveness of the proposed analytical method.
We theoretically propose a novel achromatic optical isolator based on circular dichroism in metamaterials of twisted chains of metallic nanoparticles. The suggested optical isolator consists of an input polarizer, followed by quarter-wave plate, then a circular dichroism material, another quarter-wave plate, and an output polarizer. In contrast to the most commonly used optical isolators, the current scheme does not use magnetic field and does not change the polarization plane.
A novel broadbeam aperture-coupled coplanar parasitic rectangular dielectric resonator antenna is proposed which yields broadbeam in both working planes simultaneously. The antenna consists of a main radiating rectangular dielectric element centered over a wide feed slot and two parasitic rectangular dielectric elements one on each side of the main radiating element with an optimum gap in between. The dielectric height and wide slot both play an important role in enhancing the beamwidth in two principal planes simultaneously. It is validated that inclusion of parasitic elements enhances the broadbeam bandwidth in addition to frequency bandwidth. First three azimuthal modes are excited out of which first two modes TEx111 and TEx112 are desired. The proposed antenna is compared with single element rectangular dielectric resonator antenna. To validate the proposed design, a prototype is fabricated and measured. The simulated and measured operating frequency bands of the proposed antenna respectively are 4.8 to 6.9 GHz and 5 to 6.8 GHz. The measured E- and H-plane beamwidths range from 115° to 144° and from 115° to 124°, respectively, yielding a wider coverage area.
For inverse synthetic aperture radar (ISAR) imaging of multiple targets, range profiles of different targets are sometimes coupled together, resulting in the ineffectiveness of traditional imaging method, while the couplings in range domain may behave differently in time-frequency domain, and the Doppler histories of different targets are potentially separable. Then the time-frequency analysis method can be utilized for signal separation of multiple targets. Notice that the nonuniform motions of targets may make the time-frequency curves changeful, and accordingly, some preprocessing are needed. In this paper, a novel ISAR imaging method based on modified keystone transform (MKT), short-time Fourier transform (STFT), and Hough transform (HT) is proposed. The radar echoes of multiple targets are approximated to a second-order polynomial. The MKT is firstly utilized to correct the range curvatures. Secondly, the signal in each range cell is transformed into time-frequency domain through the STFT. Meanwhile, HT theory and mask matrix are adopted in time-frequency curves' separation of different targets. Thirdly, after inverse STFT, the separated time-frequency curves are respectively back to the range domain, and the range profiles of different targets are successfully separated. Eventually, with further motion compensation and precise imaging, focused ISAR images of different targets are achieved. Simulation results demonstrate the validity of the proposed method.
This paper presents a method to distinguish multiple passive nonlinear targets, which can be applied to detection and selective wave focusing based on the decomposition of the time-reversal operator (DORT). A recent demonstration of DORT applied to harmonic scattering has shown that passive nonlinear targets (scatterers) can be detected in the presence of linear scatterers and separated into discrete eigenvalues. While DORT is effective in detecting multiple nonlinear targets, it could be difficult to discriminate these nonlinear scatters as their harmonic responses would look similar to each other. Our proposed approach to overcoming this difficulty is based on simply embedding a unique resonant notch in the second harmonic band for each nonlinear scatter, so as to make the notch appear in the associated eigenvalue, permitting identification and discrimination of the scatterer. We numerically demonstrate the basic feasibility of the proposed idea by considering various configurations in a two-dimensional model. The results show that a uniquely embedded resonant notch in a nonlinear target consistently appears in the corresponding eigenvalue of the time reversal operator, allowing it to be a reliable identifying feature. Further investigation into this technique holds promise towards smart wireless power transfer, biomedical, and IoT applications.
The so-called ``fast imaging and scattering centers approach'' originally proposed by Bhalla & Ling has revolutionized the generation of inverse synthetic aperture radar (ISAR) images and scattering center models using computational electromagnetics. Until now this approach has been used exclusively with ray-based methods. The main contribution of this paper is an extension of the Bhalla & Ling formulation for the generation of ISAR images and scattering center models with full-wave methods. Moreover, we discuss an approach to reduce the sampling requirements of the original Bhalla & Ling formulation, rendering the formulation applicable to 3-D imaging of real targets.
This article introduces a new class of electromagnetic materials: unimodular media. Unimodular media are magnetoelectric bi-isotropic media for which the determinant of the normalized four-parameter constitutive material matrix is unity. As special cases of such media are perfect electric conductor, perfect magnetic conductor, perfect electromagnetic conductor, simple skewon media, and simple isotropic media with unit refractive index. The essential parameters in the description of unimodular media (strength of impedance, degree of magnetoelectricity, angle of reciprocity) allow for illuminating visualizations of this class of materials.
Recently, consumer drones have encroached upon airports and pose a potential threat to aviation safety. Radar is an effective remote sensing tool to detect and track flying drones. Radar echoes from flying birds are assumed to be clutters when a radar is detecting drones. Yet, few studies have reported how radar echoes from flying birds interfere with the detection of drones,how similar radar cross section (RCS) and flight feature of birds and drones are,and why the flying birds cause trouble when radar identifies signals from the drone. In this study, we collected 3900×256 of Ku-band radar echoes of flying birds and consumer drones. The targets consist of a pigeon, a crane, waterfowl, and a DJI Phantom 3 Vision drone. We compared the maximum detectable range of birds and drones, the time series and the Doppler spectrum of radar echoes from the birds and the drone, considering oncoming and outgoing radar data with respect to radar location. The statistical results indicate that flying birds have similar RCS, same velocity range, similar signal fluctuation, and approximate signal amplitude. Our results of radar automatic target recognition (ATR) illuminate that the identification probability of airborne drones will be lower due to the interference of the radar signal by flying birds. Above all, these facts confirm that flying birds are the main cause of interference when a radar is detecting and identifying airborne drones.