This paper presents a Quad-Rectangular Shaped Microstrip Antenna (QRSMA) fed by a single microstrip line feed. QRSMA having different frequency bands is designed to be applied to L(1-2GHz), S(2-4GHz) and C(4-8GHz) bands applications. QRSMA is loaded with a single square patch and 4 rectangular patches. The patches are loaded using a flame retardant substrate (Fr-4). The patches are connected with 1 mm width of copper (Cu) stripline. Thus the proposed design of patches and width is responsible for desired multiband operations. The antenna resonates at frequencies f1=1.074, f2=3.119, f3=4.089, f4=5.683 and f5=6.514 GHz. Thus, the antenna is useful in the L, S and C band applications. Compared to other antenna designs, the proposed antenna exhibits multiband performance, size reduction and is economical. It also realizes tunability of frequencies having stable radiation pattern with compact electrical size. The paper analyses the simulated and experimental results. Various cases of QRSMA performances are also compared in this paper.
In this study, the misalignment of bistatic clutter spectral centers is considered, and an efficient adaptive main-lobe clutter compensation approach is presented for mitigating the bistatic geometry-induced clutter dispersion. In order to reduce computational load, an improved orthogonal matching pursuit (OMP) is introduced into the space-time clutter spectrum estimation. This method can accurately extract the required parameters for compensating the clutter spectral centers misalignment via sparse reconstruction with the desired Doppler cells. Simulation results are presented to demonstrate the effectiveness and efficiency of the proposed method.
In this paper, off-grid DOA estimation based on sparse representation and Rife algorithm is presented to improve performance when the sparse signal directions are not on the predefined angular grids. The algorithm is divided into two steps. Firstly, the real-valued sparse representation of array covariance vector (RV-SRACV) algorithm is used to do off-grid DOA estimation, and it does not need to estimate the noise power. Secondly, Rife algorithm is used to correct the DOA estimation, and after that the DOA can be accurately estimated. The effectiveness and superior performance of the proposed algorithm are demonstrated in the simulation results.
The least square method has been widely applied in many fields. However, while the approach is used for antenna array pattern synthesis, it is not excellent. In this paper, the least square is used to synthesize antenna array pattern and its performance is reviewed. Then contraposing to the shortcoming of the least square method, a new steerable least square(SLS) method is put forward. For an antenna array whose manifold matrix has been determined, the projection matrix equation can be derived from array manifold matrix easily. In order to get premium solution of array element excitation, a novel projection matrix equation with adjustable matrices is adopted. The results of simulations show that the pattern synthesized by the traditional least square method fits the targeted pattern badly and is worse in the key performance indicators of main-lobe width, peak level of side-lobe and null beam level than the targeted pattern; however, the pattern synthesized by the new SLS method fits the targeted pattern well in zero point and local peak distribution and is better in the key performance indicators of main-lobe width, peak level of side-lobe and null beam level than the targeted pattern.
A new low cost method for implementing an Instantaneous Frequency Measurement (IFM) system is presented in this paper. The proposed method is based on dividing the incoming RF signal into four signals and filtering each one by an appropriate band-pass filter. The frequency is then estimated from the power level of the filtered signals. A closed form for the Standard Deviation (STD) and the bias of the frequency estimator is derived. A design example for an IFM system with a working frequency band of 2 to 4 GHz is presented with simulated and measured results. The design is implemented on a commercial FR-4(DE104) substrate using printed circuit board technology. Experiments in a laboratory show a maximum error of about 15 MHz in estimating the frequency value.
The use of transverse circular representation in circular cylinder coordinate system provides an alternative approach to the solution for vector Helmholtz partial differential equations (VH-PDE) of electromagnetics. After separation, VH-PDE for electric (magnetic) field splits into a set of three ordinary differential (Bessel) equations for two opposite transverse circular polarizations (TCP) and the axial component. The approach is suitable for solving the problem of cylindrical waveguides and cavities starting from the transverse fields. The coupling between TCP fields via the axial component affects nonreciprocal propagation in waveguides. The procedure is illustrated on a dielectric waveguide. It may be extended to the media with circular eigen polarizations including those displaying magnetooptical Faraday effect or optical activity.
This paper presents a dynamic modelling of a series of induction motors (IM) squirrel cage with different shapes of rotor deep bars taking into account the skin effect. The approach is divided into two parts. The first part consists in modelling the skin effect in a rectangular rotor deep-bar with three methods (conventional analytical method, nite element method and analysis method of circuit). These are compared (estimate of the relative error), and subsequently, generalized to more complex forms (trapezoidal, inverted, direct trapezoidal and double cage), done by using the two last methods which take into account the geometrical non-linearity of the slots. The second part consists in a dynamic modelling with variable parameters that take into account the skin effect, simulated for a series of motors with the same power (with different geometric shapes of rotor bars), to see their influence on the starting characteristics of these IM, and the results are compared and discussed.
In this paper, the inverse scattering of a conducting cylinder is given by modified fireworks algorithm. Initially, the direct scattering is formulated as an integral equation, which contains the target shape function. The scattering integral equation is then solved by the moment method. To achieve image reconstruction, the target shape function is expanded as a Fourier series. The inverse scattering is transformed into a nonlinear optimization problem. The variables are Fourier series coefficients of the target shape function. The objective function is defined by comparing the scattered electric fields of guessed and true shapes. This nonlinear optimization problem is then optimized by our modified fireworks algorithm. The fireworks algorithm is a novel swarm intelligence algorithm for global optimization. It is inspired by practical fireworks explosion. In this paper, it is suitably modified so that it can treat the inverse scattering problem with fast convergence. Numerical results show that the inverse scattering based on our modified fireworks algorithm can accurately reconstruct the target shape with fast convergence.
The article presents a research of the effect of different types of short circuits (SC) on the performance of the gas turbine and ultra-high-speed microgenerator (MG) in a wide frequency range (from 200 000 rpm to 1,000,000 rpm) at a power from 10 W to 1 kW. The studies are carried out on a specific two-pole 100 W, 500,000 rpm microgenerator with permanent magnets with a toroidal winding. The research is carried out by finite element method using Ansys Maxwell software. Numerical study by the finite element method is performed at the rated operation mode and various types of short circuits: single-phase, two-phase, three-phase circuits coil inside MG. By the results of these studies, we estimate a negative impact of different types of faults on the parameters of MG and the mechanical characteristics of the gas turbine. Also we consider various options MG with SC for various types of bearings. Then, using the full-sized 100 W sample we carried out experimental studies of the MG operation in nominal operation mode at the 500,000 rpm. That allows to verify the developed computer model and confirm the results of our practice research. The obtained results can be used in the aerospace industry for design the high reliability complexes such as new energy systems for satellite power supply, unmanned aerial vehicles and microturbines. In addition, it can be used to design the ultra-high-voltage electric machines with a high fault tolerance for the compressor plants, air supply systems of hydrogen fuel cells, new medical tools and machine tools.
New generation wireless communications are expected to provide new services over the existing variety of wireless applications in the coming years. In this perspective, advances in utilization of computational electromagnetics (EM) and millimeter-waves (mmW) frequency bands make them as candidates for ultra-high-resolution and ultra-high-speed wireless communications. With the deployment of mmW wireless technologies, brinks of potential mmW induced biological and health effects should be evaluated carefully. The EM exposure is usually measured in terms of absorbed power from any user operating wireless devices. The exposure varies with the part of the body and location of the source that is exposed to the radio frequency waves. The purpose of this study is to observe EM exposure in terms of Specific Absorption Rate (SAR) and temperature elevations at mmWs from the designed Antipodal Linear Tapered Slot Antenna (ALTSA) at 60 GHz on different body parts utilizing EM computations and experiments with Infrared Thermal Camera.
The Weibel instability of intense and collimated MeV fast electron beams in multi-layer structure is investigated. It is found that the electromagnetic instability of fast electron beams can be significantly suppressed by this structure. A strong magnetic field will be created at the interfaces between materials with different resistivities as these fast electrons are injected into this structure. It obstructs the transverse movement of the fast electrons and confines them to propagate along the interfaces. In consequence, the positive feedback loop between magnetic field perturbation and electrons density perturbation is broken, and the Weibel instability is thus weakened. Furthermore, the calculated results for Au/Si multi-layer structure by a hybrid Particle in Cell code have proven this weakening effect on the Weibel instability of intense fast electron beams. Because of the high energy-density delivered by the MeV electrons, these results indicate applications in high-energy physics, such as radiography, fast electron beam focusing, and perhaps fast ignition.
In this paper we focus on multi-objective optimization in electromagnetic problems with given priorities among the targets. The approach proposed in this paper is able to build a proper cost function capable to correctly implementing the design criteria and their priorities avoiding the evaluation of the Pareto front of the solutions, which is a very time consuming task required in the classic a-posteriori methods. The resulting function, named Quantized Lexicographic Weighted Sum (QLWS), can be used as cost function in a very large class of electromagnetic problems. In this paper we demonstrate its usefulness in two common situations in antenna array design: the synthesis of a sparse linear array and a sparse isophoric ring array.
``Curve-fitting'' method is an important method to extract dielectric parameters of substrate materials from planar transmission lines. At gigahertz frequencies, effective conductivity concept is adopted to model the conductor's surface roughness effects in planar transmission lines, and differential extrapolation method is used to remove surface roughness effects. However, such a concept and method lose their accuracy at extremely high frequency such as terahertz waves. This paper details some new limitations in the terahertz regime and proposes corrections in calculating effective conductivity with rough conductor and curve-fitting method for transmission performance characterization in eliminating the effects of surface roughness. The proposed method is validated by simulation data for conductivity with parallel plate waveguide model, and the corrected method presented here can effectively extract dielectric parameters with an error less than 7% .
Metamaterial absorber (MMA), as a kind of new-style artificial absorption material, has been extensively researched and discussed. Currently, however, the research focuses mainly on the development and application of the novel structure MMA, and only little work is aimed at the physical mechanism of the MMA. In order to deeply understand the absorption mechanism, in this paper, the numerical simulation results of an MMA are given. Then, based on the reflection theory modal, the numerical simulation results are well discussed and explained in detail. It is found that the theoretical results agree well with that of the simulation, which suggests that the reflection theory modal is effective for analyzing the absorption mechanism of the MMA. The main contributions of this paper are to quantitatively discuss and explain the absorption mechanism of the MMA by using the reflection theory and thus offer a consultation in design and fabrication of the advanced MMA for engineers.
In the paper, the electromagnetic scattering (EM) from a one-dimensional (1-D) perfectly electric conducting (PEC) randomly rough sea surface with large windspeed is investigated by the iterative physical optics (IPO) algorithm. In this method the multiple coupling interactions among points on sea surface are considered. To improve computational efficiency, the local coupling technique is adopted to accelerate the iterative process. In numerical results, the EM scattering by 1-D sea surface for different polarizations is calculated and compared with that by the conventional method of moments (MOM), as well as the computing time and memory requirements. In addition, the influence of some parameters on the scattering of sea surface are investigated and discussed in detail, such as the threshold of coupling distance, iteration numbers, and windspeed.
A wide slot antenna with a Y shape tuning element for wireless applications (GSM 1800, WiMAX, PCS and ITM-2000) is presented. The proposed antenna is fabricated on an FR-4 substrate (tan(δ)=0.02, εr=4.3) with the thickness of 1.6 mm. On the top layer of the substrate, a 50 ohm microstrip line is fabricated which is terminated in Y shape tuning element. On ground plane, an irregular wide slot and triangular notch are etched. In addition, for performance improvement two triangular shaped parasitic slots are embedded on the ground plane. The proposed antenna is energized by the microstrip line. It exhibited the bandwidth of 127.55% from 1.15 GHz to 5.2 GHz for |S11| < -10 dB. Surface current distribution and radiation pattern at resonating frequencies 1.15, 1.25, 1.9 and 4.2 GHz are analyzed. Impact of parameters on S11 characteristic is also studied to know the behavior of the antenna.
The ionospheric GPS signal delay which is a function of TEC plays a major role in the estimation positional accuracy of satellite based navigation systems and detrimental to position estimation especially in strategic applications. Ionospheric TEC is a function of geographical location (Latitude, Longitude), time, season, etc. In this paper, we propose a system theory based Grey Model (GM(1,1)) which uses past and present data for forecasting TEC (GPS signal delay). In this model, data of nine sequential days data from five stations of a GPS Aided Geo Augmented Navigation (GAGAN) system network located at different places representing different latitudes, longitudes and equatorial anomaly regions are used to forecast the 10th day TEC values of each of these stations. The performance of the model is assessed by comparing the statistical parameters such as Standard Deviation (SD) and Mean Square Deviation (MSD). The forecasted results are very encouraging. For all the considered five stations, forecasting is better for post sunset time than day time. Also, the results indicate that SD and MSD values are comparatively more for Trivandrum (near geomagnetic equator) and Ahmedabad (near the crest of the equatorial anomaly region). These results indicate that the proposed model is useful for forecasting of GPS signal delay both for civil aviation and strategic applications.
Numerical dispersion is the main error source of the finite-difference time-domain (FDTD) method. In this paper, an optimized piecewise linear recursive convolution (PLRC) FDTD method with low numerical dispersion is presented first time for electromagnetic-wave propagation in anisotropic magnetized plasma. An optimized difference item which can achieve better approximation to the partial differential operator from transform domain is induced in this algorithm which decreases numerical dispersion. The item can be regarded as adding a correcting coefficient to conventional central difference format. And it is easy for programming and implementation. Numerical examples of electromagnetic pulse wave propagating in plasma demonstrate that the proposed optimized PLRC-FDTD method can not only reduce the numerical dispersion, but also improve precision, saving computational memory and computational time compared with the conventional PLRC-FDTD method. Same accuracy can be achieved when the spatial mesh size for the optimized PLRC-FDTD method is 2 times coarser as that in the conventional PLRC-FDTD method, corresponding to the computation time consumed in the optimized method is only 1/2 as that in the conventional one.
In airborne systems, where low aerodynamic drag is urgently required, an end-fire antenna is suitable to be used. An effort to develop such an antenna, using planar elements, is described in this paper. Here, a new kind of Microstrip Slotted Antenna with end-fire properties is presented. For investigating the end-fire radiation from microstrip antenna, three antenna elements are proposed during the study - 1) Single Patch Single Feed Microstrip Slotted Antenna, 2) Dual Patch Single Feed Microstrip Slotted Antenna and 3) Dual Patch Dual Feed Microstrip Slotted Antenna. All these proposed antennas are designed and simulated in two different EM tools, which are - CST Microwave Studio (MWS) based on time domain solver and ANSYS HFSS based on frequency domain solver. Thereafter, these antenna prototype models have been fabricated and tested. Good agreement is obtained between the simulated and measured results.
Imaging with electromagnetic waves has a wide range of applications from remote sensing of earth to concealed weapon detection, among the others. When data are collected in the far-field (imaging distance in the order of one wavelength or larger), linear electromagnetic imaging techniques mainly suffer a fundamental limit in the resolution called "diffraction limit". To overcome this limit, we propose the use of resonant near-field scatterers incorporated in the holographic imaging techniques. These scatterers convert part of the evanescent spectrum in the vicinity of the object to propagating spectrum that is measured by the antenna in the far-field. Here, we study the improvement in the resolution with decreasing the object-scatterer distance. We also investigate the effect of using multiple scatterers along the range and cross-range directions.
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