This paper presents an effective modeling methodology for Ultra-wideband (UWB) antennas. The methodology is based on augmenting an existing narrow-band model with a macro-model while simultaneously perturbing component values of the narrow-band model. The narrow-band model is an empirical-based circuit and the macro-model described by rational functions is determined using data fitting approaches. The perturbation of component values of the narrow-band model is achieved by adjustments in SPICE. This method is demonstrated on the example of a 2.5 cm dipole antenna and a circular disc monopole antenna for UWB systems. Simulation results show that this methodology is effective over a wide bandwidth and suitable for modeling most UWB antennas.
This paper's aim is to classify cylindrical targets from their ultrawide-band radar returns. To calculate the radar returns, image technique formulation is used to obtain the Electric Field Integral Equations (EFIEs). Then, the EFIEs are solved numerically by Method of Moment (MoM). Because of wide frequency range of the ultrawide-band radar signal, the database to be used for target classification becomes very large. To deal with this problem and to provide robustness, wavelet transform is utilized. Application of wavelet transform significantly reduces the size of the database. The coefficients obtained by wavelet transform are used as the inputs of the artificial neural networks (ANNs). Then, the actual performances of the networks are investigated by Receiver Operating Characteristic (ROC) analysis.
Two different types of Vivaldi antenna arrays have been designed for UWB see through wall applications. The first is a 16×1 antipodal Vivaldi antenna covering 8-12GHz, and the second is an 8×1 tapered slot antenna for 2-4GHz frequency range. The array elements are optimized to have a compact size and almost constant gain with frequency. Wilkinson power dividers were designed and fabricated to compose the feed network for the Vivaldi antenna arrays. Measured results of the manufactured antipodal and tapered slot Vivaldi antenna arrays are in excellent agreement with the simulated ones, with a gain of more than 13dBi and 12dBi respectively within their respective operating band. The first array is geared towards see through dry wall with high resolution, while the second is designed at lower frequencies to allow see through concrete wall applications. Full arrays were manufactured and connected to multi-throw switches and have been utilized as part of synthetic aperture radar.
This paper presents a computational approach to the two-dimensional time domain inverse scattering problem of a dielectric cylinder based on the finite difference time domain (FDTD) method and the particle swarm optimization (PSO) to determine the shape, location and permittivity of a dielectric cylinder. A pulse is incident upon a homogeneous dielectric cylinder with unknown shape and dielectric constant in free space andthe scattered fieldis recorded outside. By using the scattered field, the shape and permittivity of the dielectric cylinder are reconstructed. The subgridding technique is implemented in the FDTD code for modeling the shape of the cylinder more closely. In order to describe an unknown cylinder with arbitrary shape more effectively, the shape function is expandedb y closedcubicspline function insteadof frequently used trigonometric series. The inverse problem is resolved by an optimization approach, and the global searching scheme PSO is then employedto search the parameter space. Numerical results demonstrate that, even when the initial guess is far away from the exact one, good reconstruction can be obtained. In addition, the effects of Gaussian noise on the reconstruction results are investigated. Numerical results show that even the measured scattered E fields are contaminated with some Gaussian noise, PSO can still yield good reconstructed quality.
The sum and difference multiple channels were usually applied to the monopulse system only in a receiver. But this paper presents a technique of multiple beam modulation transmitted by the sum and difference multiple channels. The modulated field is designed as three chip signal vectors whose sum and whose differences are controlled by the gains of antennas,and the angle between the sum vector and the differential vector depends on the phase error between the channels so that the different microwave signals can be transmitted in the different directions. A receiver with single-antenna can extract azimuth and elevation with respect to the transmitter. Simulation results show that the proposed modulation system has been successfully designed to integrate digital communication with direction-finding in the way of the reverse monopulse.
A theoretical analysis of the lateral shift for an electromagnetic beam reflected from an uniaxial anisotropic slab coated with perfect conductor is presented. The analytic expression for the lateral shift is derived by using the stationary-phase approach, and the conditions for negative and positive lateral shifts are discussed. It is shown that the lateral shift depends not only on the slabthic kness and the incident angle, but also on the constitutive parameters of the uniaxial medium. Enhancement and suppression of lateral shift are observed and are attributed to the interference between the reflected waves from the two interfaces of the slab. By tuning the thickness of the slaband material parameters, large negative and positive shifts can be attained. In particular, when total reflection occurs at the upper interface, the lateral shift will saturate with increasing slabthic kness.
A new full-wave Parabolic --- Integral Equation Method (PE-IEM) for the simulation of wave propagation in realistic, highly complex indoor communication environments is proposed, together with an extensive validation via measurements. The method is based on a wide-angle parabolic equation, further enhanced by an integral equation correction and is capable of providing good approximations of the electromagnetic fields and the received power, incorp orating all fundamental propagation mechanisms in a single simulation. For a rigorous validation, it has been applied in a complex twelve-room office space and compared with measurements at the two different frequencies of 1 GHz and 2.5 GHz. The accuracy of the approximation is within reasonably expected margins, while the method retains all the advantages of full wave methods and it also has moderate requirements of computational resources.
In this paper an improved particle swarm optimization algorithm (IPSO) for electromagnetic applications is proposed. In order to overcome the drawbacks of standard PSO, some improved mechanisms for velocity updating, the exceeding boundary control, global best perturbation and the simplified quadratic interpolation (SQI) operator are adopted. To show the effectiveness of the proposed algorithm, a selected set of numerical examples, concerned with linear as well as planar array, is presented. Simulation results show that the refined pinpointing search ability and the global search ability of the proposed algorithm are significantly improved when compared to the particle swarm optimization (PSO) and Genetic Algorithm (GA).
This work is aimed at presenting a methodology that exploits the scattered electromagnetic radiation collected on a measurement region outside the area under investigation to locate and characterize multiple unknown profiles. In many practical cases, an accurate quantitative imaging of the scenario under test is required and it can be reached by using a high resolution representation of the dielectric profile of the scatterers. Towards this aim, an enhanced iterative multi-resolution procedure that exploits a morphological processing for detecting and focusing on different non-connected regions-of-interest is developed. A suitable set of representative numerical results is presented for demonstrating that the proposed approach is able to efficiently detect the objects located in the test domain and to enhance the accuracy in reconstructing multiple scatterers.
To investigate the effect of microwave emitted by mobile phones on the rat central nervous system (CNS), in vitro cultured cortical neuronal cells and in vivo rat's brain were exposed to the electromagnetic waves emitted by a microwave transmitter that mimics the working frequency of mobile phones. Trypan blue staining and terminal deoxynucleotidy transferase-mediated dUTP nick-end labeling (TUNEL) were used to determine the survival state of neuronal cells while immunohistochemistry method was used to determine the expression level of Bcl-2 and Bax. Our results show that microwave lead to significant cell death in culture and more in vivo brain neuronal cells were stained positive for TUNEL, Bax and Bcl-2 in rats with cranial defect after exposure than that for control groups (with intact cranium, or had no microwave exposure) (P < 0.01). However, no significant differences were observed in the ratio of Bax/Bcl-2 among the groups studied. Therefore, microwave emitted from mobile phones is harmful to both in vitro cultured cortical cells and in vivo brain neuronal cells from rat with cranial defect. The integrity of cranium is important in protecting the CNS against apoptotic injuries inflicted by the microwaves from mobile phones.
In this paper, propagation model considers the region as a perfect conductor, covered by the two layer dielectrics, and air above. Propagation of the electromagnetic field in the presence of a four-layered region is examined in detail when a vertical electric dipole and observation point are located in the air. Similar to the three-layered case, analytical results are found for the electromagnetic field, which includes four wave modes: a direct wave,an ideal reflected wave, trapped surface waves, and lateral waves. The wave number of the trapped surface wave, which is contributed by the sums of residues of the poles, is between the wave numbers k0 in the air and k2 in the lower dielectric layer. The lateral wave is evaluated by the integrations along the branch cut. Analysis and computations shows that the trapped surface wave play a major role in communication at large distance when both the source point and observation point are on or close to the boundary between the air and the upper dielectric layer.
The propagation properties of surface plasmon polaritons (SPP) modes and surface magnetoplasmon polaritons (SMP) modes in a semiconductor slit waveguide are analyzed by the effective dielectric constant approach, and the interaction of the external magnetic field with the dispersion properties and field distributions of SMP modes in the Voigt configuration are emphasized in our analysis. Both the symmetric structure and the asymmetric structure are discussed in details. In contrast to the SPP modes which have one propagation band below the plasmon frequency only, the SMP modes have both the low-frequency propagation band below the plasmon frequency and the high-frequency propagation band above the plasmon frequency. When the external magnetic field increases, the two bands of the SMP modes will separate further in frequency, and the even symmetric distribution of the fundamental mode, which usually associates with the SPP mode, will be destroyed. These results can provide some guidance for the design of the tunable semiconductor waveguide in the terahertz regime.
An efficient, electrically small prolate spheroidal antenna coated with confocal double-negative (DNG) metamaterials (MTMs) shell is presented. The radiation power of this antenna-DNG shell system excited by a delta voltage across an infinitesimally narrow gap around the antenna center is obtained using the method of separation of the spheroidal scalar wave functions. Our results show that this electrically small dipole-DNG shell system has very high radiation efficiency comparing with the normal electrically small antenna due to the inductive effect of the MTMs shell that cancel with the capacitive effect of the electrically small antenna. It is found that the spheroidal shell can achieve more compact structure and higher radiated power ratio than the corresponding spherical shell. This dipole-DNG shell systems with different sizes are analyzed and discussed.
This paper aims at finding an algorithm featuring good estimation performance and easy hardware implementation for tracking airborne target hidden in blind Doppler. Incorporating the current statistical model which is effective in dealing with the maneuvering motions that most blind Doppler issues are caused, a current statistical model particle filter (CSM-PF) is presented in this paper for tracking airborne targets hidden in blind Doppler. Simulation results demonstrate that the proposed CSM-PF shows similar performance with the interacting multiple model particle filter (IMM-PF) in terms of tracking accuracy and track continuity, but it avoids the difficulty of model selection for maneuvering targets. In addition, when hardware implementation is considered, the proposed CSM-PF has lower processing latency, fewer resource utilization and lower hardware complexity than the IMM-PF.
A new numerical technique is proposed for analyzing arbitrary shaped hollow waveguides. The method is based on mathematically modelling of physical response of a system to excitation over a range of frequencies. The response amplitudes are then used to determine the resonant frequencies. The results of the numerical experiments justifying the method are presented. The method is validated by circular waveguide,rectangular waveguide an equilateral triangular waveguide. We apply the method for multi connected domains and for waveguides with boundary singularities like the Lshaped waveguide. Good agreements between the simulated and the published results have been obtained. The method does not generate spurious eigenfrequencies.
Guarded ground tracks are extensively used in high density routing for mitigation of crosstalk. However, these ground tracks can influence the electrical properties of the interconnect line also. We present a novel analytical model for extraction of line parameters of high-speed interconnect lines guarded by ground tracks. Based on the proposed model, transient response of such interconnect structures is presented. It is seen ground tracks can significantly affect the time-domain response of the interconnect lines. The computed interconnect circuit parameters are compared with finite-difference time-domain simulations. The proposed model can be practically used for time-domain analysis of microstrip lines also. The results obtained would be useful in design of high-speedin terconnections for MCM, RF and MIC related applications.
The retrieval of the surface profile of a reflector antenna is an important task, mainly for radio-astronomical applications. The microwave holography retrieves the reflector profile starting from a set of measured far-field data. The main step of this technique is the computation of the induced currents on the reflector surface. This requires the solution of a linear inverse problem which is strongly illconditioned. We propose a new technique, based on the Singular Value Decomposition, for the solution of this linear inversion problem. This technique supplies a flexible regularization scheme, able to take into account also the noise level of the data. The proposed procedure has been tested on a number of different cases, with field data generated by a commercial software.
Dual-band bandpass filters featuring compact size and flexible frequency choice are demonstrated using resonators based on slotted ground structures. Two resonators based on slotted ground structures form the basis of the filter design. The resonators allow the back-to-back and face-to-face embedding configuration, hence, greatly reduces the physical size of the filters. By changing the sizes of the two resonators independently, the lower and upper resonance frequencies can be adjusted to the desired values. A dual-band broadband bandpass filter was implemented with good compactness and low insertion loss. A good agreement is obtained between the simulation and measurement results.
A detailed study on the influence of an external magnetic field on a symmetrical gyrotropic slab in terms of Goos-Hanchen (GH) phase shifts is presented. The GH phase shifts at both boundaries of the slab are calculated, and the guidance condition is explained by means of them. It is found that the external magnetic field destroys the spatial symmetry of the field distribution, and we use the concepts of `penetration' distance as well as effective thickness to illustrate the phenomenon. In term of the GH phase shifts, the spatial distribution of the time-average Poynting power is also derived. We find that influenced by the external magnetic field, the positive and negative time-average Poynting power along the waveguide direction can exist simultaneously in the gyrotropic medium, depending on the transverse position.
This paper presents a novel band-notched elliptical slot antenna for Ultra Wide-Band (UWB) communication, which is printed on a dielectric substrate of RT/duroid 6006 with relative permittivity (εr) of 6.0, thickness of 1.27 mm, and fed by an elliptical open ended microstrip line connected to the 50Ω main line. This antenna is designed to be used in frequency band of 3.1-10.6 GHz. Bandnotched characteristics of antenna to reject the frequency band of 5.15-5.825 GHz, which is limited by IEEE 802.11a, is realized by parasitic inverted-U strip attached to the elliptical slot plane. Effects of varying the parameters of parasitic inverted-U strip on performance of proposed antenna have been investigated. The antenna with optimal parameters obtained from parametric study is fabricated and measured. It is observed that the simulation and experimental results have good agreements with each other.
The near and far field properties of the large-scale metal plate with slit array are studied by applying the finite-difference timedomain (FDTD) method. The far region scattering properties at different incident angles are also discussed. We find out the enhanced optical transmission (EOT) through the metal plate with suitable placed narrow slit array is excited by the interaction of the surface plasmon polarization (SPP) and the Fabry-Perot resonance (FPR), and the dielectric substrate has significant influence on the transmission properties by affecting the electromagnetic field distribution on the metal-dielectric interface. Furthermore, the scattering field would be reduced and the transmission efficiency could be improved by the phase shift caused by the dielectric substrate. These unusual properties suggest possible applications to light-transparent metal contacts, stealth materials, etc.
To enhance the flexibility of the parallel FDTD for the analysis of the bio-electromagnetic problems, a universal and efficient interpolation technique based on the super-absorbing boundary principle is presented, which can improve the interpolation accuracy and ensure the stability of the parallel FDTD iterative procedure. Using this technique, we calculate the SAR (Specific Absorption Rate) values in the head for two different human-body postures. In the iteration procedure of parallel FDTD, the data are exchanged between adjacent subdomains with the interpolation technique. Thus, the meshes can be created in local coordinates, which makes it convenient to build the human model in the different posture and use position for FDTD computing. The results show that the change of human-body posture only brings about a slight decrease (within 6.8%) in the peak SAR values, whereas the SAR values in the brain, as a critical organ, are sensitive to the change of the body posture, and it increases by 28% at maximum for the 1-g averaged peak SAR.
The electromagnetic resonances of a spherical cavity, with a perfectly conducting wall and filled with a homogeneous isotropic chiral medium, is studied using the spherical vector wavefunctions. The characteristic equation and the expressions for the field components, when chirality reaches its maximum value, are derived. The characteristic equation is obtained by imposing the boundary condition on the wall of the spherical cavity. The characteristic equation is solved numerically and reported for the first five modes. These modes are hybrid modes. They are classes as either hybrid electric (HE) modes or hybrid magnetic (HM) modes. The explicit expressions for the field components of the HE and HM modes are given, and the field distributions of a few modes are shown. The chirality is observed to have significant effects on the resonances and the field distributions of a chiral filled spherical perfectly conducting cavity. The results show interesting properties of the cavity, which could be applied to new applications.
This paper suggests a pilot-free frequency tracking scheme for ultra-wideband orthogonal frequency-division multiplexing (UWBOFDM) receivers. The proposed scheme uses a frequency-domain spreaded data symbols which is provided in the current UWB-OFDM system. Based on this property, we develop an improved frequency synchronization receiver without the use of pilot symbols. The simulation results indicate that the proposed scheme achieves much better performance than the conventional pilot-based schemes.
In this paper, the high-order hierarchical basis functions are used for solving electromagnetic wave scattering problems. The multilevel fast multipole method (MLFMM) is applied to accelerate the matrix-vector product operation and the Schwarz method is employed to speed up the convergence rate of the Krylov subspace iterative methods. The efficiency of the proposed approach is studied on several numerical model problems and the comparison with conventional Kryloviterativ e methods is made. Numerical results demonstrate that the combination of the Schwarz method and the Krylovsubspace iterative method is very effective with MLFMM and can reduce the overall simulation time significantly.
Tunability of fiber Bragg grating (FBG) in transition region is used to implement wavelength-selective optical intensity modulator, which superimposes a secondary low-speed data on the transit high-speed payload optical signal. Theoretical model of the device is developed and verified by measurements in the linear and nonlinear slopes of the FBG. Experiments with strong and relatively weak gratings confirm the wavelength-selectivity and stability of modulation. The fiber-based modulator is employed for optically tagging or labeling individual wavelength channels using baseband and amplitude-shift keying (ASK) modulated signals. The wavelengthselective channel labeling scheme is useful for the control and management of the optical circuits and services in WDM networks.
Ray tracing has been successfully usedin prediction of wave propagation models in recent years. Although this method has its own obvious benefits, it suffers from a big problem: slow performance. In this paper, novel methods are proposed in which the main focus is on reducing the number of ray-facet intersections. First a preprocessing methodis proposed which reduces the number of ray-facet intersection tests dramatically. Later this method is combined with a volume bounding algorithm to make improvements in the speed of ray-tracing simulations, even more.
We consider the inverse problem of determining both the shape and the conductivity of an un-uniform conductivity scatterer buriedin a three-layer structure by the genetic algorithm. An ununiform conductivity scatterer of unknown shape and conductivity buriedin the secondla yer scatters the incident wave from the first layer or the thirdla yer. We measure the scatteredfieldin the first andthird layers. Based on the boundary condition and the measured scattered field, a set of nonlinear integral equations is derived and the imaging problem is reformulatedin to an optimization problem. The genetic algorithm is then employedto findout the global extreme solution of the object function. As a result, the shape andthe conductivity of the scatterer can be obtained. Numerical results are given to demonstrate that even in the presence of noise, good reconstruction has been obtained.