In this paper, a novel miniaturized nested split-ring resonator (SRR) structure is proposed. The nested SRR structure incorporates multiple split-ring resonators in a compact nested structure, and has more split gaps than the conventional SRR structure. Compared with conventional SRR, this nested SRR has better performance on miniaturization and high-Q value. To verify good characteristics of the proposed resonator structure, a novel resonator-embedded band-pass filter (BPF), which is constructed by four nested resonators, is designed. This novel BPF is very compact and has good in- and out-band performances. The proposed nested SRR unit cell has size of 0.04λg x 0.04λg(λg is the signal wavelength at the 2.4 GHz central frequency of the pass-band). Its stop-bands are extended 0.5~2 GHz at lower band and 2.7~5.4 GHz at upper band with a rejection level of higher than 20 dB, and its 1-dB pass-band is 2.2~2.55 GHz with 1.8 dB optimized insertion loss. The measured and simulated results are well complied with each other.
In order to eliminate the negative influence of the rotational phase component (RPC) of target prominent scattering centres on the performance of Doppler centroid tracking (DCT) method, a coherent phase compensation method is proposed. The coherence of echo pulses sampled directly in intermediate frequency (IF) is firstly analyzed and proved. Based on the coherence property, the proposed approach improves the translational phase component (TPC) estimation accuracy of DCT. Compared to the modified Doppler centroid tracking (MDCT) algorithm, the proposed method achieves better phase compensation performance with simpler operations. Both the theoretical analysis and experimental results based on the real ISAR data prove the effectiveness and efficiency of the presented strategy.
A new method for broadening the impedance and the axial-ratio (AR) bandwidths of circular polarized microstrip antennas (CPMAs) is proposed. It has improved the bandwidths of a reference antenna greatly without enlarging the antenna size or deteriorating circular polarized radiation characteristics by placing four sequentially rotated parasitic split-ring resonators (SRRs) around the patch of the reference antenna and embedding four defeated ground structure (DGS) elements on the ground plane. Improvements of 51.3% and 49.8% in the impedance and the axial-ratio bandwidths of the antenna are achieved in simulation, respectively. The simulated -10dB impedance and 3dB axial-ratio bandwidths of the antenna have been improved from 101.1 MHz (4.12%) to 153.0 MHz (6.26%) and from 25.1 MHz (1.02%) to 37.6 MHz (1.54%).
A compact printed antenna for WWAN tablet computer application is proposed in this article. The designed antenna occupies a small area of 35×12 mm2, which is small enough to be incorporated in a tablet computer, and is placed close to the edge of the shielding wall with a distance of 10 mm. The antenna has a simple structure of comprising a long coupling strip and a feeding strip to capacitively excite the long coupling strip. In this scheme, a chip inductor (L = 25 nH) is loaded on one branch of the feeding strip, which can form a parallel resonant structure to enhance the bandwidth of the lower band. As a result, two wide operating bands to cover GSM850/900 and GSM1800/1900/UMTS2100 operation are obtained with desired 3:1 VSWR. The proposed antenna is an all-printing structure with low production cost, which is especially suited for the thin-profile tablet computers.
A profile reconstruction method using a surface inverse currents technique implemented on GPU is presented. The method makes use of the internal fields radiated by an equivalent currents distribution retrieved from scattered field information that is collected from multiple incident fields. Its main advantage over other inverse source-based techniques is the use of surface formulation for the inverse problem, which reduces the problem dimensionality thus decreasing the computational cost. In addition, the GPU implementation drastically reduces the calculation time, enabling the development of real time and accurate geometry reconstruction at a low cost.
In this paper we explore electromagnetic behavior of arbitrarily oriented biaxially anisotropic media; specifically with respect to reflection and transmission. The reflection and transmission of electromagnetic waves incident upon half-space and two-layer interfaces are investigated. The waves may be incident from either the isotropic region or the biaxial region. The biaxial medium considered may be aligned with the principal coordinate system or may be arbitrarily oriented. Critical angle and Brewster angle effects are also analyzed.
Superdirective beamforming can highly reduce the aperture size of high-frequency receive array. At the same time, the closely spaced elements of a small aperture array can make it low efficiency and sensitivity to the array uncertainty, which limit its application in practice. Using a parameter called sensitivity factor, we found that array efficiency and robustness against array error could be considered simultaneously. On that basis, we derive a novel superdirective beamforming criterion based on a constrained sensitivity factor for the HF circular receive array. New method is analytical and computationally inexpensive. Through making the directive gain with a given sensitivity factor maximum, we calculate the optimal weights of the array elements. To illustrate the proposed method can increase the acceptance of HF superdirective receive arrays in practice, several numerical results are provided.
Magnetic field shielding at low frequencies is a problem of high importance that is known for a long time. Metamaterials, which are known from fancy applications such as the so-called perfect lens and cloaking, also offer a new way to create efficient magnetic shielding by means of anisotropic metamaterials with low permeability in one direction. Such metamaterials can be constructed by assembling arrays of relatively simple LC circuits. In this paper, we analyze different metamaterials and show how they may be designed. We show that typical resistive losses in the coils and capacitors of the LC circuits reduce the shielding quality. Then, we consider the possibility of active electronic loss compensation and discuss the drawbacks of this concept. After this, we propose a purely passive way that benefits from the inhomogeneity of the magnetic field to be shielded. Finally, we present experimental results, which show the performance of metamaterial shields.
A serial resonant antenna for the large field of view (FOV) magnetic resonance imaging (MRI) is presented. It consists of metallic patches cascaded through lumped capacitors in serial on the top layer of a grounded dielectric substrate. The theoretical analysis show that at the resonant frequency, uniformly distributed current with zero phase delay is produced independent of the antenna length, hence a uniform magnetic field for large FOV MRI can be achieved. Integrated with the L-shaped tunable matching network, the antenna can be tuned easily to operate rigorously at the working frequency of the MRI system. The numerical modeling, physical fabrication and measurement, as well as the phantom imaging are carried out to design, characterize and verify the performance of the proposed antenna for MRI.
In this paper, a novel coplanar waveguide (CPW) fed dual band-notched ultra-wideband (UWB) antenna with circular slotted ground is proposed. In order to achieve two notched bands at 3.3-3.7 GHz for worldwide interoperability for microwave access (WiMAX) and 5.15-5.825 GHz for wireless local area network (WLAN) respectively, a pair of bended dual- L-shape branches are attached to the slotted ground. By optimizing the lengths and positions of the branches, the desired notch-bands of WLAN and WiMAX can be achieved. The prototype of the proposed antenna was fabricated and tested. The simulated and measured results show good agreement over the ultra-wideband. Besides these mechanical features, such as compact in size, easy in fabrication, the proposed antenna also shows good characteristics in its radiation patterns and time-domain behaviors. So it is a nice candidate for modern UWB communication systems.
We carefully investigate the structure of single- and multi frequency imaging functions, that are usually employed in inverse scattering problems. Based on patterns of the singular vectors of the Multi-Static Response (MSR) matrix, we establish a relationship between imaging functions and the Bessel function. This relationship indicates certain properties of imaging functions and the reason behind enhancement in the imaging performance by multiple frequencies. Several numerical simulations with a large amount of noisy data are performed in order to support our investigation.
A novel single-cavity dual mode substrate integrated waveguide (SIW) filter with mixed source-load coupling (MSLC) is presented. By using an interdigital slot-line (ISL) to introduce mixed coupling between source and load, the proposed filter with only one cavity could have three transmission zeros which can be controlled flexibly. Under the circumstances, the filter exhibits better frequency selectivity in comparison with conventional dual mode SIW filters. An experimental filter with a center frequency of 10 GHz and a 3 dB fractional bandwidth of 6.0% is designed, fabricated, and measured to validate the proposed structure. Measured results are provided to show good performance and in agreement with the simulated ones.
The systematic design of size-confined, polarization-independent metamaterial absorbers that operate in the microwave regime is presented in this paper. The novel unit cell is additionally implemented to create efficient multi-band and broadband structures by exploiting the scalability property of metamaterials. Numerical simulations along with experimental results from fabricated prototypes verify the highly absorptive performance of the devices, so developed. Moreover, a detailed qualitative and quantitative analysis is provided in order to attain a more intuitive and sound physical interpretation of the underlying absorption mechanism. The assets of the proposed concept, applied to the design of different patterns, appear to be potentially instructive for various EMI/EMC configurations.
In this work, the multiple filtering phenomenon in a photonic crystal made of single-negative (SNG) materials is investigated. We consider a finite photonic crystal (AB)N immersed in air, in which A, B are epsilon-negative (ENG) and mu-negative (MNG) materials, respectively, and N is the stack number. It is found that such a photonic crystal can function as a multichannel transmission filter with a channel number equal to N-1. The required condition is that the thickness of MNG layer must be larger than that of ENG layer when magnetic plasma frequency is greater than electric plasma frequency. The channel frequencies can be red-shifted as the thickness of MNG layer decreases. The channel positions can be tuned by the incidence angle for both TE and TM polarizations. That is, the peak frequency is blue-shifted when the angle of incidence increases. Additionally, the influence of the static permeability of ENG medium and permittivity of MNG medium is also illustrated. The proposed structure can thus be used to design as a tunable multichannel filter which is of technical use in signal processing.
In this paper, a new time domain fast dipole method (TDFDM) is proposed for solving time-domain magnetic field integral equations. The proposed scheme is the extension of the frequency domain fast dipole method (FDM) to the time domain. The principle is based on the Taylor series expansion of far fields. The computational complexity of TD-FDM scales as O(Ns3/2Nt) as opposed to O(Ns2Nt ) for marching-on in-time (MOT) method. Here, Ns is the number of spatial basis functions and Nt is the number of the time steps. Numerical results about the electromagnetic scattering from perfect electric conductor (PEC) objects are given to demonstrate the validity and efficiency of the proposed scheme.
One of the difficulties for frequency stepped chirp radar (FSCR) is to resolve the range-Doppler coupling due to relative motion between the radar and the target. Motion compensation is usually adopted to solve the problem in realizing synthetic high range resolution profile (HRRP) for a moving target. For missile-borne FSCR, the range migration of target echo during a coherent processing interval, which is resulted from the high speed motion of missile, is serious and will affect target detection and synthetic high range resolution profile. Therefore, range migration correction and motion compensation are very important for missile-borne FSCR signal processing. In the paper, with the background of terminal guidance anti-ship FSCR seeker, the range alignment is accomplished in frequency domain during the process of real-time digital pulse compression. Then an effective velocity estimation algorithm based on the waveform entropy of the Doppler amplitude spectrum of target echoes is addressed and the velocity estimation accuracy is derived. Finally, the simulation indicates that the new method can estimate the radial velocity accurately and reconstruct the distorted HRRP successfully. In addition, the method has good anti-noise performance and works in the scenario of multi-target with different velocities as well.
Improved quasi-static expressions are derived for the time-harmonic electromagnetic (EM) field components excited by a vertical electric dipole (VED) lying on the surface of a flat and homogeneous lossy half-space. An analytical procedure is developed that allows to evaluate the complete integral representations for the fields, once the non-oscillating part of the integrand in the expression of the magnetic vector potential is replaced with its quadratic approximation for small values of the free-space wavenumber. The advantage of the proposed second-order quasi-static approximations resides in the possibility of relaxing the assumption of highly conducting half-space. This makes it possible to overcome the limitations implied by the previously published zeroth-order formulation, whose validity is restricted to extremely low frequencies for poorly conducting media. Numerical results are presented to illustrate the reduction of relative percent error arising from using the improved quasi-static field expressions.
The novel multibeam ScanSAR takes advantage of the displaced phase center multiple azimuth beam (DPCMAB) imaging scheme and intra-pulse beam steering in elevation in ScanSAR to achieve the high-resolution ultra-wide-swath imaging capacity. This letter proposes an innovative two-dimensional (2D) digital beamforming (DBF) space-time preprocessing approach for multibeam ScanSAR. According to echo proprieties of such imaging scheme, both azimuth ambiguity and range ambiguity problems should be resolve before a conventional ScanSAR imaging processor. After range compressing in each receive channel, a 2D DBF processor is carried out in the range-Doppler domain. The azimuth DBF operation is adopted to resolve the azimuth nonuniform sampling problem in multichannel SAR systems, while the DBF preprocessing in elevation is carried out to separate echoes from different subswaths corresponding to different sub-pulses. Imaging results on simulated distributed targets validate the proposed 2D DBF preprocessing approach.
The fundamental limits of the gain and efficiency of an antenna are explored. These are very important quantities for e.g., superdirective arrays. The antenna is in this paper confined in a sphere and all of the currents are assumed to run in a material with a given conductivity. It is shown that one can find the current distribution in the sphere that optimizes the gain, given the frequency and the radius of the sphere. The results indicate the distribution of antenna elements in an antenna array in order to maximize gain, or efficiency. The analysis is based on the expansion of the electromagnetic fields in terms of vector spherical harmonics. Explicit expressions for the limits of gain and efficiency, and the corresponding current densities, are derived for different types of antennas.
Based on Time-Domain Reflectometry (TDR) technique, a novel method which could locate faults on the coaxial cable distribution network by using Support Vector Machine (SVM) is proposed in this paper. This approach allows the faulty network to be reconstructed by estimating the lengths of branches. A State-transition Matrix model is employed to simulate the TDR response at any port and evaluate the transfer function between two points. SVM is used to solve the inversion problem through training datasets created by the State-transition matrix model. Compared to the existing reflectometry methods, our proposed method can tackle multiple faults in the complex cable networks. Numerical and experimental results pointing out the performance of the SVM model in locating faults are reported.
A three-dimensional (3-D) source localization algorithm of joint elevation, azimuth angles and range estimation for the mixed near-field (NF) and far-field (FF) sources is presented in this paper. We first estimate the elevation angles of all mixed sources by using the generalized ESPRIT method. With the elevation angle estimates, the range parameters of all mixed sources are obtained, and then both the NF and FF sources are distinguished. Finally, with the elevation angle and range estimates, the azimuth angles of all mixed sources are acquired based on the conventional high-resolution MUSIC method. The proposed algorithm avoids parameter match operation, and requires neither a multidimensional search nor high-order statistics (HOS). Simulation and experiment results show the performance of the proposed algorithm in this paper.
This paper presents an evaluation of measurement uncertainty for complex-valued quantities in microwave applications, mainly focusing on the non-linear transformation of measurement uncertainty from rectangular coordinate to polar coordinate. Based on the law of propagation of uncertainty in matrix form, general expressions of the covariance matrix for the magnitude and phase uncertainties in polar coordinate have been derived, and several different application scenarios have been analyzed and evaluated with numerical simulations. This is followed by some recommendations on the coordinate transformations in practical microwave measurements.
In this research, a compact printed antenna design operating on ultra-wideband (UWB) and three extra wireless communication bands is proposed. An ellipse-shaped monopole is utilized to realize UWB application (3.1-10.6 GHz). The modified ground employs three folded Capacitive Loaded Line Resonators (CLLRs) to obtain triple relatively lower communication bands, including parts of global System for Mobile Communications (GSM) band at the centre frequency of 1.78 GHz, Wideband Code Division Multiple Access (WCDMA) band at the centre frequency of 2.15 GHz, and Wireless Local Area Networks (WLAN) band at the centre frequency of 2.4 GHz. The CLLRs are designed with quarter-wavelength to control the corresponding frequencies independently. Good agreement is achieved between the simulation and measurement to verify our presented design. The basic, dual-, triple-band UWB antennas are also simulated and good results are obtained. Small group delay variations across UWB frequencies are obtained for the presented antenna and reference antennas, with some level of distortion observed.
The emerging field of compressed sensing provides sparse reconstruction, which has demonstrated promising results in the areas of signal processing and pattern recognition. In this paper, a new approach for synthetic aperture radar (SAR) target classification is proposed based on Bayesian compressive sensing (BCS) with scattering centers features. Scattering centers features are extracted as a l1-norm sparse problem on the basis of the SAR observation physical model, which can improve discrimination ability compared with original SAR image. Using an overcomplete dictionary constructed of training samples, BCS is utilized to design targets classifier. For target classification performance evaluation, the proposed method is compared with several state-of-art methods through experiments on Moving and Stationary Target Acquisition and Recognition (MSTAR) public release database. Experimental results illustrate the effectiveness and robustness of the proposed approach.
In recent years, particle probability hypothesis density (PHD) filtering has become an active research topic for multiple targets tracking in dense clutter scenarios. However, it is highly required to improve the real-time performance of particle PHD filtering because it is a kind of Monte Carlo approach and the computational complexity is very high. One of major difficulties to improve the real-time performance of particle PHD filtering lies in that, resampling, which is usually a sequential process, is crucial to the fully-parallel implementation of particle PHD filter. To overcome this difficulty, this paper presents a novel threshold-based resampling scheme for the particle PHD filter, in which the particle weights are all set below a proper threshold. This specific threshold is determined using a distinguishing feature of the particle PHD filters: The weight sum of all particles in weight update is equal to the total target number in the current iteration. This proposed resampling scheme allows the use of fully-pipelined architecture in the hardware design of particle PHD filter. Theoretical analysis indicates that the particle PHD filter employing the proposed resampling technique can reduce the time complexity by 33% around in a typical multi-target tracking (MTT) scenario compared with that employing the traditional systematic resampling technique, while simulation results show that it can maintain the almost same performance of estimation accuracy.
This paper presents the design and analysis of an inside-out axial-flux permanent-magnet (AFPM) synchronous machine optimized by genetic algorithm (GA) based sizing equation, finite element analysis (FEA) and finite volume analysis (FVA). The preliminary design is a 2-pole-pair slotted TORUS AFPM machine. The designed motor comprises sinusoidal back-EMF waveforms, maximum power density and the best heat removal. The GA is used to optimize the dimensions of the machine in order to achieve the highest power density. Electromagnetic field analysis of the candidate machines from GA with various dimensions is then put through FEA in order to obtain various motor characteristics. Based on the results from GA and FEA, new candidates are introduced and then put through FVA for thermal behavior evaluation of the designed motors. Techniques like modifying the winding configuration and skewing the permanent magnets are also investigated to attain the most sinusoidal back-EMF waveform and reduced cogging torque. The performance of the designed 1 kW, 3-phase, 50 Hz, 4-pole AFPM synchronous machine is tested in simulation using FEA software. It is found that the simulation results fully agree with the designed technical specifications. It is also found from FVA results that the motor temperature reaches at highest temperature to 90°C at the rated speed and full load under steady state condition.
In the ground moving target indication with synthetic aperture radar (SAR) community, algorithms used to estimate the velocity of a detected moving target are important because they are relative to the topics about refocusing and azimuth displacement correction. The velocity is regarded as a vector with two components, one in azimuth and one in range direction, and new algorithms aiming at estimating the two components are proposed and verified. The range velocity estimator transforms a detected patch containing a moving target to range Doppler domain by using the 1-D fast Fourier Transform in each range bin to achieve its range Doppler locus. The slope of the range Doppler locus is computed by using the Radon Transform on the range Doppler plane and the range velocity component is worked out according to radar system parameters and the slope value. Two estimators are proposed to compute the azimuth velocity component. One is based on symmetric defocusing in Doppler domain, the other is based on phase gradient in wave-number domain. Experiments confirm the effectiveness of the estimators by using simulated and field data.
Permanent magnet (PM) array affects flux field distribution of electromagnetic linear machine significantly. A novel dual Hal-bach array is proposed in this paper to enhance flux density in the air gap, and thus to improve output performance of linear machines. Magnetic field in the three-dimensional (3D) space of a tubular linear machine with dual Halbach array is formulated based on Laplace's and Poisson's equations. Numerical result from finite element method is employed to simulate and observe the flux distribution in the machine. A research prototype and a testbed are developed, and experiments are conducted to validate the analytical models. The study is useful for analysis and design optimization of electromagnetic linear machines.
We numerically analyze the optical response and nonlinear susceptibilities of fishnet metamaterials with the holes infiltrated by a third-order nonlinear dielectric. Through full-wave simulations and by employing a nonlinear parameter retrieval method, we confirm and quantify the enhanced nonlinearities, showing bulk third-order nonlinear susceptibilities that are up to two orders of magnitude larger than the nonlinear dielectric. We also use the retrieved parameters to calculate the material figure of merits and the conversion efficiencies, showing material figure of merits up to two orders of magnitude larger and conversion efficiencies up to four orders of magnitude larger than the nonlinear dielectric alone. Though these results are calculated using one-unit-cell thick structures, the large magnitude of the enhancement still makes these structures attractive, allowing reasonable conversion efficiencies supported by even subwavelength slabs.
A functional microstrip circuit module for annular slot antenna is proposed. This module consists of an annular microstrip line component, two PIN diodes and a DC bias circuit. Reconfigurable circular polarizations can be simply controlled by this functional module. Axial ratio is adjustable by changing the clip angle of the notch made by the annular microstrip line component. Simulated and experimental results have shown good impedance bandwidth for return loss and antenna gains in circularly polarized states.
Battlefield surveillance is a common application of synthetic aperture radar (SAR), in which minefield detection is a challenging task. In this paper, a novel minefield detection approach is proposed via the morphological diversities between targets and background. Firstly, SAR image speckle is suppressed effectively by total variation, and targets edges are preserved well. Secondly, a nonlinear transform is introduced to map the special distributed targets, e.g. landmines, into spot targets. Lastly, the modification of morphological component analysis is adopted to improve the signal-to-clutter ratio and separate the spot targets from image. The performance of the proposed approach is validated by using the data acquired over an airship mounted SAR system.
In this paper, we examine the imaging ability of a planar superlens in both the transverse and vertical dimension. By studying the field patterns of the image from different objects (points and scattering surfaces with subwavelength details) in front of a planar superlens, we show the relation between the transverse and vertical resolutions. We mainly discuss why we cannot get high subwavelength resolution for three dimensions at the same time, and there is a trade-off between the transverse and vertical resolution capabilities which is fundamental in nature for a planar superlens.
One miniaturized multilayer dual-band bandpass filter (BPF) is developed using standard low temperature co-fired ceramic (LTCC) technology. The filter makes use of four double-folded substrate integrated waveguide (SIW) resonators. Two sets of coupling paths between the source and load are implemented to generate dual-band responses. Utilizing this method, the two passbands can operate at independent frequencies and the bandwidth can be easily controlled. High isolation is obtained between two passbands, and two pairs of transmission zeros close to the passband edges are generated by source-load coupling, resulting in high skirt-selectivity. Good agreement between the simulated and measured results of the filter sample is obtained, with its high electrical performance validated.
In this paper, we present a novel fast method to solve Poisson's equation in an arbitrary two dimensional region with Neumann boundary condition, which are frequently encountered in solving electrostatic boundary problems. The basic idea is to solve the original Poisson's equation by a two-step procedure. In the first stage, we expand the electric field of interest by a set of tree basis functions and solve it with a fast tree solver in O(N) operations. The field such obtained, however, fails to expand the exact field because the tree basis is not curl-free. Despite of this, we can retrieve the correct electric field by purging the divergence-free field. Next, for the second stage, we find the potential distribution rapidly with a same fast solution of O(N) complexity. As a result, the proposed method dramatically reduces solution time compared with traditional FEM with iterative method. In addition, it is the first time that the loop-tree decomposition technique has been introduced to develop fast Poisson solvers. Numerical examples including electrostatic simulations are presented to demonstrate the efficiency of the proposed method.
In passive millimeter-wave imaging systems used indoors, the radiometric temperature contrast is barely enough for coarse object detection, being usually insufficient for recognition due to the absence of cold sky. The image contrast results from a combination of emissivity and reflectivity which are dependent on the dielectric constant of objects, the angle of incidence, and the polarization direction. To improve the capability of target recognition, we proposed the linear polarization sum imaging method which is based on the combination of the different polarization images for increasing the intensity contrast between the target area and the background area. In order to capture the linear polarization sum images of a metal sphere, a metal and a ceramic cup, we designed W-band quasi-optical imaging system which can generate the polarization dependent images by manually changing the linear polarization direction of its radiometer receiver from 0 to π /2 by the step size of π/8. The theoretical and experimental results of the linear polarization sum imaging show that it is capable for achieving good image quality enough to recognize the target.
A a new compact ultrawideband (UWB) patch antenna based on the resonance mechanism of a composite right/left-handed (CRLH) transmission line (TL) is proposed. The radiating element of the antenna is made from three left-handed (LH) metamaterial (MTM) unit cells placed along one axis, where each unit cell combines a modified split-ring resonator (SRR) structure with capacitively loaded strips (CLS). An analysis of the eigenfrequencies of these unit cells yields one- and two-dimensional dispersion diagrams, which correspond to one-unit cell antenna and the three unit-cell antenna, respectively. A trident feed and a slotted-partial ground plane are used to match the right-and left-handed (RH and LH) modes of the antenna, respectively. In addition, an analysis of the surface current distribution of the antenna shows that, slots on the metallic area reduce the Q-factor. This recdution in the Q-factor results in a wide bandwidth of 189% at 3.7 GHz, which spans the UWB frequency range between 2.9-9.9 GHz. The total footprint of the antenna at the lowest frequency is 0.2λ0 x 0.2λ0 x 0.015λ0, where λ0 is the free space wavelength. The gain of the antenna ranges between -1 to 5 dB throughout the frequency band.
This paper deals with electromagnetic design and three-dimensional (3-D) magnetic field analysis of a novel configuration brushless DC (BLDC) field assisted machine based on a hybrid analytical and 3-D finite element method (FEM) analysis. Aid of this hybrid design method is improving the accuracy and computation time for complex magnetic structure like to presented machine structure. In this hybrid design methodology obtained primary magnetic and electric characteristics including magnetic flux density, flux linkage and induced Back-EMF profile for studied configuration are verified by 3-D FE computation. Comparison of the calculated magnetic field and terminal voltage characteristics by their requested values and obtained values form analytical analysis respectively illustrates the conformity of design parameters stage. In this study in order to determine the optimum operation, geometry parameter of proposed machine are optimized based on multi objective optimization design and genetic algorithm, and finally 3-D FEM verification coupled by boundary integral equation method (BIEM). Additionally the accuracy of 3-D FE analysis is verified by comparing the calculated results with the experimental measured values.
In this paper, a new technique to realize lumped dual-band impedance transformers for arbitrary frequency-dependent complex loads is proposed. For the complex impedance transforming, closed-form design equations are presented for a series-shunt and a shunt-series type and a concept of combination is also presented. They use the proposed equation of input impedance. This equation can easily and exactly obtain the input impedance of any two-port network using the ABCD matrix. Then, in order to realize dual-band operation, four topologies comprising two types and a design method are presented. This technique is numerically demonstrated by various examples with excellent results and it has advantages of simplicity, intuitiveness and versatility because it is a general solution for complex impedance transforming. The proposed dual-band impedance transforming technique can be utilized for practical matching problems such as microwave amplifiers and other devices.
This paper introduces a theoretical analysis as well as a design example for bandpass filters (BPF) with a distinctive topology. Based on the analysis of simple two-port symmetrical lossless networks with a parallel structure, a method for obtaining normalized BPF prototypes with desired bandwidths was developed. These prototypes can be scaled to any central frequency and symmetrical real termination in the same way as conventional filters. It is also demonstrated that with a slight modification of the basic BPF prototypes, transmission zeros with controllable frequencies can be introduced in both the lower and the upper stopband region. Such modified prototypes are more convenient for the realization of printed filters than the basic BPF prototypes. The proposed filters have almost identical characteristics in the broad vicinity of the passband region either when composed of ideal lumped elements or of transmission lines (TLs). Due to its simplicity, the proposed concept could be applied for the realization of a printed BPF at a large variety of PCB types, substrates and practical design configurations. A microstrip BPF model is realized for the experimental verification of the presented theory. The measured and theoretical results show excellent agreement, confirming the proposed concept and the exactness of the methodology.
This paper presents a novel ultra wideband (UWB) channel model in the 3-10 GHz range for body-centric wireless communications. The tests are performed in both indoor anechoic chamber environments, addressing on-body and off-body propagation scenarios. The body channel model is extracted by using a single spatial grid over all the body, and by distinguishing between LOS and NLOS condition. The large number and the uniform placement of the receiver locations attempt a representation of the body propagation links more comprehensive than previously published models. The statistical reliability of the model is investigated by applying jointly the Kolmogorov-Smirnov and the Akaike criteria. The analysis suggested that the Lognormal model fits the channel amplitude distributions with a percentage ≥ 64%. The on-body indoor channel amplitudes are modeled with a stochastic terms of about 4-5 dB higher than previously published models. Finally, a Negative-Binomial and Inverse Gaussian distribution are used to model the expected number of paths and inter-arrival time, respectively. Based on the results presented in this paper, clear recommendations are given with regards to the optimum statistical distribution of an accurate UWB body-centric radio channel modeling.
The aim of this work is to asses the computational performance of a finite element formulation based on nodal elements and the regularized Maxwell equations. We analyze the memory requirements and the condition number of the matrix when the formulation is applied to electromagnetic engineering problems. As a reference, we solve the same problems with the best known finite element formulation based on edge elements and the double curl Maxwell equations. Finally, we compare and discuss the computational efficiency of both approaches.
In this paper, an improved equivalence principle algorithm is proposed to solve the radiation problems of large antenna arrays with periodic structures. This method is a hybridization in which the typical scheme of periodic Green's function is combined with the original equivalence principle algorithm. The repeated elements are changed from the original antenna units into the surfaces enclosing the original ones. The proposed approach is compared with periodic method of moments which is based on the integral equation and the periodic Green's function. Numerical results validate the feasibility of the improved method.
The iterative Fourier technique (IFT) is a high efficiency method that was proposed in recent past for the synthesis of large planar thinned arrays with isotropic radiating elements. However, the selection mechanism of IFT cannot always include the most useful elements in the "turned ON" families, which make the method trap in some local minima. Therefore, in this paper, inspired by invasive weed optimization (IWO) algorithm, a developed version of the iterative Fourier technique (IFT), IWO-IFT, is proposed for thinning large planar arrays. In this new method, the initial weeds are produced by IFT, and are further perturbed by IWO through repeatedly reproduction, dispersion, and exclusion over search space to find better weeds. Numerical results for synthesizing different circular thinned arrays demonstrated the superiority of IWO-IFT over the IFT method.
We have found that a single finite-boundary bowtie aperture (FBBA) antenna with gap separation of 10 nm between its tips is capable of confining the electric field to a 18 nm X 18 nm region (λ/39.4) and enhancing its near-field intensity by 365-fold at 5 nm beneath the gold film enhancing its near-field intensity by 1, 800-fold inside the gap. The FBBA antenna is thus able to provide enhanced trapping potential by virtue of such extraordinarily high (but exponentially decaying) optical near-fields. We have been able to show that 12 nm gold nanoparticles can, in principle, be trapped by the FBBA antenna with 20 nm gap separation; stable trapping is assured where the trapping potential is found to be several times higher than Brownian-motion potential in water. In addition to trapping nanoparticles, this simple but efficient FBBA antenna may find ready application in near-field optical data storage.
A novel type of dual circular polarizer for simultaneously receiving and transmitting right-hand and left-hand circularly polarized waves is developed and tested. It consists of a H-plane T junction of rectangular waveguide, one circular waveguide as an E-plane arm located on top of the junction, and two metallic pins used for matching. The theoretical analysis and design of the three-physical-port and four-mode polarizer were researched by solving Scattering-Matrix of the network and using a full-wave electromagnetic simulation tool. The optimized polarizer has the advantages of a very compact size with a volume smaller than 0.8λ3, low complexity and manufacturing cost. A couple of the polarizer has been manufactured and tested, and the experimental results are basically consistent with the theories.