A generalized coupled-line circuit is introduced to construct a wide-stopband low-pass filter in this paper. This circuit configuration includes two-section coupled lines and a connected transmission-line stub. Due to the symmetry of this proposed structure, closed-form equations for scattering parameters are investigated. The transmission zeros and poles locations for different circuit parameters are discussed, and the corresponding design curves are given. For theoretical verifications, four typical numerical examples are designed, calculated and illustrated. Furthermore, two single-stage low-pass filters (LPF 1 and LPF 2) with the 1-dB cutoff frequencies of 0.72 GHz and 1.45 GHz are fabricated and measured. The implemented LPF2 has 19-dB stopband rejection in the range of 2.05 to 6.36 GHz. Finally, two LPF cells (LPF 1 and LPF 2) and an additional connected transmission line are used to construct a new two-stage low-pass filter (LPF 3) with extended stopband. The measured 16-dB stopband of LPF 3 is up to 7.5 GHz while the 1-dB passband range is from DC to 0.67 GHz. The advantages of this proposed low-pass filter are avoiding any lumped elements and compact layout structure.
To improve the impaired azimuth resolution of the novel Terrain Observation by Progressive Scans (TOPS) mode, a new multi-channel single phase center multiple beam (SPCMB) TOPS mode is proposed in this paper for high-resolution wide-swath (HRWS) imaging. However, the progressive azimuth beam scanning leads to the Doppler spectrum aliasing and both beam center time and Doppler centroid varying with the target's azimuth location. Challenges may arise for processing the SPCMB-TOPS SAR data from these problems. In this paper, an efficient full aperture imaging approach is proposed to process the raw data. The sketch of the proposed imaging approach is described in detail. Simulation results of point targets validate the proposed imaging approach.
A novel bandpass filter design method of achieving different selectivity based on E-shaped dual-mode resonator is presented. The characteristic of the E-shaped dual-mode resonator is investigated. The technique of utilizing capacitive and inductive input-output cross-coupling to generate two adjustable transmission zeros at stopband is explored intensively. Advantages of this type of filter are not only its dual-mode resonator and miniaturization, but also its controllable transmission zeros. The coupling scheme is presented to model the operations of these filters. Four dual-mode microstrip BPFs have been designed, fabricated, and measured. Both the simulated and measured results are presented. The exemplary filters verify the feasibility of the new design method.
In this paper, a numerical method for improving the performance of the beamforming algorithm and the MUSIC algorithm for TOA (Time-of-Arrival) estimation is presented. It has been shown that the conventional beamforming algorithm and the MUSIC algorithm can be used for time delay estimation. Using the beamforming algorithm and the MUSIC algorithm for TOA estimation, the initial estimate for the TOA is obtained. To improve the accuracy of the TOA estimation, we apply the Newton iteration to the initial estimate. The initial estimates obtained from the beamforming algorithm and the MUSIC algorithm are updated to obtain the final estimates which are more accurate than the initial estimates in terms of the RMSE (Root Mean Square Error). To find the TOA which maximizes the beamforming spectrum or the MUSIC spectrum, we find the TOA at which the derivative of the beamforming spectrum with respect to the delay is zero. To find numerically the TOA at which the derivative of the beamforming spectrum or the MUSIC spectrum is zero, the Newton iteration is adopted. In numerical results, the validity of the proposed scheme is illustrated using various examples.
Calculating the EM scattering fields from a three-layer canopy which comprises of many leaves, trunks and the ground needs intensive computational burden, when the area becomes large and obviously lames the application of the traditional serial algorithm. With the development of graphics hardware, the Graphics Processing Unit (GPU) can be used to calculate the electromagnetic (EM) scattering problems parallelly. In this paper, the Compute Unified Device Architecture (CUDA) is combined with the four-path method and the reciprocity theorem to predict the EM scattering properties from scatterers which are sampled by using Monte-Carlo method in a three-layer canopy model. We get a highest speedup of 294 times in comparison with the original serial algorithm on a Core (TM) i5 CPU with a GTS460 GPU as a coprocessor.
We present a three-dimensional finite difference time domain (FDTD) method on graphics processing unit (GPU) for plasmonics applications. For the simulation of plasmonics devices, the Lorentz-Drude (LD) dispersive model is incorporated into Maxwell equations, while the auxiliary differential equation (ADE) technique is applied to the LD model. Our numerical experiments based on typical domain sizes as well as plasmonics environment demonstrate that our implementation of the FDTD method on GPU offers significant speed up as compared to the traditional CPU implementations.
A finite element-boundary integral-domain decomposition method is presented for analyzing electromagnetic scattering problems involving multiple three-dimensional cavities. Specifically, the edge-based finite element method is applied inside each cavity to derive a linear system of equations associated with unknown fields. The boundary integral equation is then applied on the apertures of all the cavities to truncate the computational domain and to connect the matrix subsystem generated from each cavity. With the help of an iterative domain decomposition method, the coupling system of equations is reduced to a small one which only includes the unknowns on the apertures. To further reduce computational burdens, the multilevel fast multipole algorithm is adopted to solve the reduced system. The numerical results for the near and far fields of several selected multi-cavity problems are presented to demonstrate the validity and capability of the proposed method.
In this article the influence of both dispersion and losses on waveguides with metamaterials is investigated. The analysis is focused on surface waveguides (planar interfaces and grounded slabs) containing either double-negative (DNG) or chiral metamaterials. The main goal is to show how the combined effect of material dispersion and losses with the structural dispersion affect the solutions of the modal equations. It is shown that this interplay is essential to obtain a correct modal analysis of these waveguides. Namely, the overall behavior can qualitatively change - so that it is not possible to state that the corresponding lossy case - even when a very small amount of losses is introduced - can be interpreted as a small perturbation of the lossless case.
A new L-shaped chiral structure working in microwave and optical frequency bands has been designed and simulated. The circular dichroism, ellipticity angle, polarization azimuth rotation angle, and effective parameters of this structure, including relative permittivity, relative permeability, chiral parameter and refractive index, are retrieved from simulated transmission and reflection spectra. The results show that the exceptionally strong optical activity is found for the L-shaped chiral structure. Because of the large chiral parameter of this structure, negative refractive index of one circularly polarized wave can be obtained without simultaneously negative permittivity and negative permeability.
A novel strategy for topside ionosphere sounder based on spaceborne Multiple-Input Multiple-Output (MIMO) radar is proposed, which takes advantage of frequency division and code division (FDCD) as a substitution for swept-frequency regime employed by the current ionosphere explorers, e.g., TOPside Automated Sounder (TOPAS). The azimuth resolution can be improved by 153 times compared with TOPAS by means of frequency division, producing two-dimensional electron density images. The signal-to-noise ratio (SNR) can be enhanced and complete orthogonality among channels at different frequencies can be achieved by code division, which uses Complete Complementary Sequence (CC-S) as phase coding waveform. The simulation results show that root mean square (RMS) of normalized electron density measurements error of novel ionosphere sounder is as low as 1.7%.
In this paper, we present a RF directional modulation technique using a switched antenna array for physical layer secure communication. The main idea is that a switching scheme of the switched antenna array is designed according to a spreading sequence for the purpose of spreading spectrum of the transmit signal. The transmit signal is associated with the spreading sequence and the direction of the desired receiver because of information data modulated both in the baseband and the antenna level. In this way, the desired receiver with a single antenna can demodulate the receive signal as traditional spread-spectrum signal, while eavesdroppers can not extract any useful information from the receive signal even if eavesdroppers know the spreading sequence of the RF directional modulation signal. Simulation results show that the proposed technique offers a more secure transmission method for wireless communication comparison with traditional spread-spectrum signal.
E®ective complex permittivity measurements of materials are important in microwave engineering and microwave chemistry. Artificial neural network (ANN) computational module has been used in microwave technology and becomes a useful tool recently. A neural network can be trained to learn the behavior of an effective permittivity of material under microwave irradiation in a test system, and it can provide a fast and accurate result for the permittivity measurement of material. Thus, an on-line measurement has been realized. This paper presents a simple and convenient reconstruction algorithm for determining the dielectric properties of materials. First, a measurement system is designed, and the reflection coefficient is calculated by employing full-wave simulations. Second, an artificial nerve network has been applied, and adequate simulated materials are utilized to train the networks. Last, the trained network is employed to reconstruct the effective permittivity of several organic solvents using the measured scattering parameters, and the reconstructed results for several organic solvents agree well with reference data and the relative errors between them are less than 5%.
This paper presents new balanced single- and dual-band bandpass filters (BPFs), both of which are constructed using two ring resonators. For each BPF, opencircuited stubs are added to one of the two resonators so that the transmitted common-mode (CM) signals can be attenuated, and source-load coupling is established so that two transmission zeros are generated near the edges of each desired differential-mode (DM) passband to sharpen the passband selectivity. The measurement agrees well with the simulation. For the single-band BPF, the measured minimum DM insertion loss is 1.4 dB in the DM passband, in which the CM suppression is larger than 41.6 dB. For the dual-band BPF, the minimum DM insertion losses are 1 and 1.35 dB in the first and second passbands, respectively, in which the CM rejections are larger than 29 and 22 dB.
Chipless ultra-wideband (UWB) has been proposed as a low-cost alternative for radiofrequency identification (RFID). In this paper, a comprehensible theoretical introduction to time-domain operation of a UWB RFID tag is described, and a circuit model is proposed. For commercial applications low-cost RFID readers are demanded. To this end, this paper addresses the measurement of time-coded UWB chipless tags for RFID in time domain. Two different setups to detect time-coded tags are presented, one based on a commercial UWB impulse radar (IR) and the other based on a vector network analyzer (VNA). The experimental results show the feasibility of using an IRUWB radar as a UWB RFID reader, achieving very good read ranges.
Coaxial magnetic gear (CMG) is a non-contact device for torque transmission and speed variation which exhibits promising potential in several industrial applications, such as electric vehicles, wind power generation and vessel propulsion. CMG works lying on the modulating-effect aroused by the ferromagnetic segments. This paper investigates the optimum design for improving the modulating-effect. Firstly, the operating principle and the modulating-effect is analyzed by using 1-D field model, which demonstrates that the modulatingeffect is essential for the torque transmission capacity of CMGs, and the shape of the ferromagnetic segments have impact on the modulatingeffect. Secondly, the fitted model of the relationship between the maximum pull-out torque and the shape factors including radial height, outer-edge width-angle and inner-edge width-angle is built up by using surface response methodology. Moreover, FEM is engaged to evaluate its accuracy. Thirdly, the optimum shape of the ferromagnetic segment is obtained by using genetical algorithm.
The paper discusses the radiation of compressed high power short RF pulses using two different types of antennas: (i) A simple monopole antenna and (ii) a novel array design, where each of the elements is constructed by combining a compressor and a radiator. The studies on the monopole antenna demonstrate the possibility of a high power short RF pulse's efficient radiation even using simple antennas. The studies on the novel array design demonstrate that a reduced size array with lower pulse distortion and power decay can be constructed by assembling the array from elements each of which integrates a compressor and a radiator. This design idea can be used with any type of antenna array; in this work it is applied to a phased array.
Proper design of efficient microwave energy compressors requires precise understanding of the physics pertinent to energy accumulation and exhaust processes in resonant waveguide cavities. In this paper, practically for the first time these highly non-monotonic transient processes are studied in detail using a rigorous time-domain approach. Additionally, influence of the geometrical design and excitation parameters on the compressor's performance is quantified in detail.
This paper presents both simulation and experimental study to detect and locate breast tumors along with their classification as malignant and/or benign in three dimensional (3D) breast model. The contrast between the dielectric properties of these two tumor types is the main key. These dielectric properties are mainly controlled by the water and blood content of tumors. For simulation, electromagnetic simulator software is used. The experiment is conducted using commercial Ultrawide-Band (UWB) transceivers, Neural Network (NN) based Pattern Recognition (PR) software for imaging and homogenous breast phantom. The 3D homogeneous breast phantom and tumors are fabricated using pure petroleum jelly and a mixture of wheat flour and water respectively. The simulation and experimental setups are performed by transmitting the UWB signals from one side of the breast model and receiving from opposite side diagonally. Using discrete cosine transform (DCT) of received signals, we have trained and tested the developed experimental Neural Network model. In 3D breast model, the achieved detection accuracy of tumor existence is around 100%, while the locating accuracy in terms of (x,y,z) position of a tumor within the breast reached approximately 89.2% and 86.6% in simulation and experimental works respectively. For classification, the permittivity and conductivity detection accuracy are 98.0% and 99.1% in simulation, and 98.6% and 99.5% in experimental works respectively. Tumor detection and type specification 3D may lead to successful clinical implementation followed by saving of precious human lives in the near future.
An efficient hybrid method, based on time-domain integral equation (TDIE) and time-domain physical optics (TDPO), is proposed for studying on transient electromagnetic responses of some wire and surface structures illuminated by an electromagnetic pulse (EMP), respectively. Two groups of triangular-type basis functions are used to expand the currents on both of them. The derived hybrid TDIE-TDPO equations are solved by marching-on-in-time (MOT) scheme. In comparison with the full TDIE-based MOT method, computational complexity of our developed method is reduced significantly, and at the same time, with high accuracy maintained. Numerical results of EMP responses of some typical wire and surface structures are presented to demonstrate its versatility, accuracy and efficiency, with proximity effects between them captured and discussed.
Antenna characterization in presence of obstacles requires removing multipath effects in order to retrieve the nondistorted antenna radiation pattern. In this contribution a new approach based on the Sources Reconstruction Method is proposed. The idea is to characterize the Antenna-Under-Test (AUT) and the region where the scatterers are located through a set of equivalent currents. Finally, the reconstructed equivalent currents on the contour enclosing the AUT can be used to recover the AUT radiation pattern, removing most of the distortion effect due to the presence of the scatterers.
In complex electromagnetic (EM) environment, EM field distribution inside a metallic enclosure is determined by the external EM radiation and emissions from internal contents. In the design of an electronic system, we usually need to estimate the EM field level in a concerned region inside the enclosure under various EM environments. In this paper, we use artificial neural network (ANN), rather than full wave analysis, combined with the numbered measurements to predict the EM field in the concerned region inside a metallic enclosure. To verify this method, a rectangular metallic enclosure with a printed circuit board (PCB) is illuminated by external incident wave. The measured electric fields inside the enclosure combined with ANN model based on back propagation (BP) training algorithm are used to estimate the values of electric field. The calculation is fast and predictions reveal good agreement with the measurements that validate this method.
An effective series RLC model for the electromagnetic response of weakly absorbing dielectric sphere near the first magnetic dipole resonance was developed, and the effective magnetic properties of Mie resonance-based dielectric metamaterials were obtained in terms of this model. In comparison with traditional effective medium theory such as extended Maxwell-Garnett (EMG) theory based on Mie model, this approach is more intuitive and can give an analytical dependence of the magnetic properties of the composite on the electromagnetic and geometric parameters of the constituting dielectric particles.
When developing a wireless communication system, a designer should consider the associated radiated power density, electromagnetic compatibility (EMC), and specific absorption rate (SAR). In this paper, high-impedance surfaces (HISs) are designed as an EM protection screen to reduce the interaction between an antenna and the user behind the screen. The effects of an HIS screen with a finite number of cells placed near a monopole antenna for the application of the 2.4 GHz WLAN band were thoroughly investigated. The screen is first-ever proposed not only to reduce the backward radiation from the antenna, but also to shift the impedance-matching band of the antenna and to adjust the corresponding bandwidth. As a result, the SAR behind the screen is noticeably lowered, and the out-of-band spurious emission from the antenna can be reduced. Two typical kinds of HIS structures, mushroom-shaped and Jerusalem Cross HISs (abbreviated as MSHIS and JCHIS, respectively), were investigated by numerical simulations and measurements. Three different measurement techniques were proposed for predicting the operating frequency band of an HIS. Some HIS-added antenna prototypes were constructed and studied. It was found that the MSHIS and JCHIS can adjust the impedance-matching band of the antenna, do not affect the radiation performance in the forward direction, and can significantly reduce the backward radiated power. In addition, the measured maximum SAR has been significantly reduced from 0.976 W/kg for the monopole antenna without an HIS to 0.037 and 0.038 W/kg, respectively, for the antenna with an MSHIS and a JCHIS.
In this paper, the anisotropic conductivity effect of Quasi-Isotropic Carbon Fiber laminates on new type of conformal load-bearing antenna structure (CLAS), with slots being cut through a carbon fibre reinforced polymer (CFRP) laminate, is presented. The conductivity of a quasi-isotropic IM7/977-3 CFRP laminate is measured using the waveguide technique. The results show that orientation of the surface ply relative to the polarization of the E-field has a major influence on the reflectivity. This difference can be attributed to the fact that carbon fibres oriented parallel to the E-field plies behave as good conductors while off-axis plies as lossy dielectric layers with a finite conductivity. This anisotropic behavior of the ply layers is shown to have a distinctive influence on the operation of both microstrip patch and slot antennas.
In this paper, accurate analytical expressions for the impedance of vertical electric and magnetic dipoles which are located over the half-space materials of arbitrary permittivity and permeability are developed. In this regard, the impedance variations are expressed in integral forms. For metamaterial half-space, a proper expression for approximating the Fresnel reflection coefficient is proposed. Using this approximate expression, the impedance integrals are analytically solved, and exact formulas for impedance variations are obtained. The results for the metamaterial half-spaces are compared with the case of natural materials (positive permittivity and permeability), and key differences are explained. The in uences of sign changing in permeability of the half-space material on the impedance of vertical dipole are studied, and the results are validated by comparison with those of numerical solution of integrals. It is shown that for elevated dipoles over materials with high and/or low conductivities, the results of both methods are in complete agreement. For vertical dipoles above low loss materials, the results are somewhat identical. However, a better agreement could be obtained using higher order approximations for the integrand.
A new formalism for electromagnetic and mechanical momenta in a metamaterial is developed by means of the technique of wave-packet integrals. The medium has huge mass density and can therefore be regarded as almost stationary upon incident electromagnetic waves. A clear identification of momentum density and momentum flow, including their electromagnetic and mechanical parts, is obtained by employing this formalism in a lossless dispersive metamaterial (including the cases of impedance matching and mismatching with vacuum). It is found that the ratio of the electromagnetic momentum density to the mechanical momentum density depends on the impedance and group velocity of the electromagnetic wave inside the metamaterial. One of the definite results is that both the electromagnetic momentum and the mechanical momentum in the metamaterial are in the same direction as the energy flow, instead of in the direction of the wave vector. The conservation of total momentum is verified. In addition, the law of energy conservation in the process of normal incidence is also verified by using the wave-packet integral of both the electromagnetic energy density and the electromagnetic p
Automated and accurate classification of magnetic resonance (MR) brain images is a hot topic in the field of neuroimaging. Recently many different and innovative methods have been proposed to improve upon this technology. In this study, we presented a hybrid method based on forward neural network (FNN) to classify an MR brain image as normal or abnormal. The method first employed a discrete wavelet transform to extract features from images, and then applied the technique of principle component analysis (PCA) to reduce the size of the features. The reduced features were sent to an FNN, of which the parameters were optimized via an improved artificial bee colony (ABC) algorithm based on both fitness scaling and chaotic theory. We referred to the improved algorithm as scaled chaotic artificial bee colony (SCABC). Moreover, the K-fold stratified cross validation was employed to avoid overfitting. In the experiment, we applied the proposed method on the data set of T2-weighted MRI images consisting of 66 brain images (18 normal and 48 abnormal). The proposed SCABC was compared with traditional training methods such as BP, momentum BP, genetic algorithm, elite genetic algorithm with migration, simulated annealing, and ABC. Each algorithm was run 20 times to reduce randomness. The results show that our SCABC can obtain the least mean MSE and 100% classification accuracy.
This paper proposes a new sparse matrix storage format which allows an efficient implementation of a sparse matrix vector product on a Fermi Graphics Processing Unit (GPU). Unlike previous formats it has both low memory footprint and good throughput. The new format, which we call Sliced ELLR-T has been designed specifically for accelerating the iterative solution of a large sparse and complex-valued system of linear equations arising in computational electromagnetics. Numerical tests have shown that the performance of the new implementation reaches 69 GFLOPS in complex single precision arithmetic. Compared to the optimized six core Central Processing Unit (CPU) (Intel Xeon 5680) this performance implies a speedup by a factor of six. In terms of speed the new format is as fast as the best format published so far and at the same time it does not introduce redundant zero elements which have to be stored to ensure fast memory access. Compared to previously published solutions, significantly larger problems can be handled using low cost commodity GPUs with limited amount of on-board memory.
A 3D shape reconstruction algorithm for multiple PEC objects immersed in air is presented. The Hamilton-Jacobi PDE is solved in the entire computational domain with employing the marching cubes method to retrieve the evolving objects. The method of moment surface integral equation is used as the forward solver. An appropriate form of the deformation velocity, based on the forward and adjoint fields, is implemented to minimize the mismatch between the reference and evolving objects. The inversion algorithm showed good shape reconstruction results even using limited view data or noise corrupted data down to SNR of 5 dB.
This paper presents a software defined radio six-port receiver for a novel broadband mobile communications system. The prototype covers the frequency range from 0.3 GHz to 6 GHz, and operates with up to 100 MHz-wide channels. The multi-band and multi-mode demodulation capabilities of the six-port architecture have been experimentally demonstrated. The six-port receiver has been satisfactorily proved for high data rates (up to 93.75 Mb/s, limited by the available test instruments). An efficient six-port auto-calibration method suitable for large instantaneous bandwidth systems is presented and validated.