In this paper, an innovative method for obtaining a pencil beam pattern is presented. Planar arrays of parasitic dipoles are used to modify the pattern of an active dipole above a ground plane, in order to obtain a pencil beam of moderate gain and bandwidth. Only one feed point and one active element provides a very simple feeding network that reduces the complexity of the antenna. The correct configuration of the elements of the parasitic arrays allows to obtain the desired pencil beam pattern. Three designs that use parasitic arrays fed by a λ/2-dipole and synthesize pencil beam patterns are shown: 1) an antenna designed at 1.645 GHz and composed by one layer of 49 parasitic elements; 2) an antenna designed at the same frequency but composed by two layers of 49 parasitic elements; 3) an antenna designed at 5 GHz, composed by one layer of 49 parasitic elements, and taking into account the dielectric substrate and teflon screws.
To solve radiation problems in time domain directly the modal representation of transient electromagnetic fields is considered. Using evolutionary approach the initial nonstationary three-dimensional electrodynamic problem is transformed into the problem for one-dimensional evolutionary equations by the construction of the modal basis for electromagnetic fields with arbitrary time dependence in spherical coordinate system. Elimination of the radial components of electrical and magnetic field from Maxwell equation system permits to form the four-dimensional differential operators. It is proved that the operators are self- adjoint ones. The eigen-functions of the operators form the basis. The completeness of the basis is proved by means of Weyl Theorem about orthogonal detachments of Hilbert space. The expansion coefficients of arbitrary electromagnetic field are found from the set of evolutionary equations. The transient electromagnetic field can be found directly without Fourier transform application by means of one-dimensional FDTD method for the medium with dependence on longitudinal coordinate and time or using Laplace transform and wave splitting for the case of homogeneous stationary medium. The above mentioned methods are compared with the three-dimensional FDTD method for the case of the problem of small loop excitation by transient current.
We present the design and simulation of an ultra-compact polarization beam splitter (PBS) by combining a photonic crystal (PhC) multimode waveguide and an internal PhC section. The PhC multimode waveguide is designed to collect the powers reflected by or transmitted through the internal PhC structure which serves as a polarization sensitive scatterer. Plane wave expansion (PWE) method is used to calculate the band structure and the finite-difference time-domain (FDTD) method is employed to obtain the spectrum response. The simulation results show that the present design can give an ultra-compact PBS with high extinction ratio over a broad bandwidth.
The following paper deals with the problem of computing a safety perimeter, i.e., where the electromagnetic field due to a radiating system exceeds a certain electromagnetic value. The flexibility of the source reconstruction method (SRM) is employed to compute the fields almost everywhere around the antenna. Techniques for fast computing of the fields in the spectral and spatial domains exploiting the characteristics of the SRM are considered in order to avoid expensive integrations over the sources surface. Results for a logperiodic antenna and a base station antenna for cellular phone systems are shown, and compared with the usual far-field approximation.
A new Mean Effective Gain (MEG) expression using SphericalWave Expansions (SWE) is presented in order to evaluate the impact of mobile environments on radiating structures. The proposed approach takes into account the pattern polarization and transforms a continuous functional optimization problem into an approximate discrete formulation. It allows to synthesize efficient antenna radiation patterns in terms of the Mean Effective Gain when it is combined with modern heuristic optimization techniques. In addition, antenna performance limits are evaluated by means of certain bounds. These depend on the modal number which is required to describe accurately far fields and depend ultimately on the antenna size. The method estimates the optimum patterns for two different wireless scenarios that are characterized by the statistical probability density functions of incoming waves and particularized in the case of Gaussian statistics. The numerical evaluation has been performed by means of the Particle Swarm Optimization (PSO) technique, which is slightly modified to include a specific constrain and whose parameters have been computed previously by solving a canonical problem. Finally, representative results in outdoor and mixed wireless scenarios are discussed, pointing out some useful consequences in antenna design.
A perturbation method based on the decoupling of propagation and diffusion phenomenons is proposed in order to calculate losses in microwave structures. Starting from the first problem in which the conducting regions are not described, a perturbation is calculated by solving a second problem restricted to the vicinity of the conductors; iterations between these problems can be performed when the perturbed solution is not sufficiently accurate. The perturbation approach is however more accurate than a method based on a surface impedance model, without introducing the huge calculations that appear when both conducting region and external medium are described in a single problem. 2D examples are presented using the finite element method and the integral equation method.
This paper presents an effective Polar Format Algorithm (PFA) for spotlight bistatic synthetic aperture radar (SAR) with arbitrary geometry configuration. Nonuniform interpolation and resampling are adopted when converting raw data from polar coordinates to Cartesian coordinates according to the characteristics of raw data samples in spatial frequency space. Thus, the proposed algorithm avoids both rotation transformation and the calculation of azimuth compensation factor and thereby avoids the corresponding approximate error appeared in the conventional PFA. Meanwhile, the proposed algorithm inherits the character of decomposing 2-D interpolation to two 1-D interpolations from conventional PFA algorithm applied in monostatic SAR imaging. Therefore, the processing flow, computation efficiency and performance of the proposed algorithm are the same as those of conventional PFA for monostatic spotlight SAR. Point target simulations are provided to validate the proposed algorithm.
We apply the linear embedding via Green's operators (LEGO) method to the scattering by large finite dielectric bodies which contain metallic or penetrable inclusions. After modelling the body by means of LEGO bricks, we formulate the problem via an integral equation for the total incident currents over the boundaries of the bricks. This equation is turned into a weak form by means of the Method of Moments (MoM) and sub-domain basis functions. Then, to handle possibly large MoM matrices, we employ an order-reduction strategy based on: i) compression of the off-diagonal sub-blocks of the system matrix by the adaptive cross approximation algorithm and ii) subsequent compression of the whole matrix by using a basis of orthonormal entire-domain functions generated through the Arnoldi iteration algorithm. The latter leads to a comparatively small upper Hessenberg matrix easily inverted by direct solvers. We validate our approach and discuss the properties of the Arnoldi basis functions through selected numerical examples.
Guided-wave propagation in chiral H-guides is analyzed, using a building-block approach. In a first stage, a 2D chiral parallel-plate waveguide is studied using a frequency dispersion model for the optically active medium, where the constitutive chiral parameter is assumed to be dependent on the gyrotropic parameter. In the second stage, the mode matching technique and the transverse resonance method are used to characterize the 3D structure. A full parametric study is presented for a fixed frequency. The operational and dispersion diagrams for the chiral H-guide are presented. By replacing the common isotropic slab with a chiral slab, chirality provides an extra degree of freedom in the design of new devices.
This paper presents an approach to the design of a novel dual-band power divider with variable power dividing ratio. To achieve dual-band operation, a novel dual-band quarter-wave length transformer based on coupled-lines is proposed, which is used to replace the quarter-wave length transformer in Wilkinson power divider. The proposed dual-band power divider features a simple compact planar structure with wide bandwidth performance for small frequency ratio. Closed-form design equations with one degree of design freedom are derived using even- and odd-mode analysis and transmission line theory. For verification purpose, power dividers operating at 2.4/3.8 GHz with dividing ratios of 2:1 and 1:1 are designed, simulated and measured. The simulated and measured results are in good agreement.
In this paper, a novel double-printed trapezoidal patch dipole antenna suitable for UWB applications with band-notched characteristic is presented and investigated. The band -notched characteristic is achieved by inserting T-shape slots on the trapezoidal radiating patches. The impedance characteristic, radiation patterns and the transfer function are studied. Experimental results show that the proposed antenna covers the entire UWB band (3.1-10.6 GHz) while it has a notched band for the IEEE 802.11a frequency band (5.15-5.825 GHz). Measured group delay, transmission characteristics and Time domain characteristics indicate that the proposed antenna satisfies the requirement of the current wireless communications systems.
This paper presents SPICE models to analyze the radiated and conducted susceptibilities of multiconductor shielded cables in the time and frequency domains. These models, which can be used directly in the time and frequency domains, take into account the presence of both the transfer impedance and admittance, and allow the transient analysis when the termination is nonlinear or time-varying. The radiated and conducted susceptibilities are studied by using an incident plane-wave electromagnetic field and an injection current on the cable shield as the source, respectively. Results obtained by these models are in good agreement with those obtained by other methods.
We propose a hybrid finite-difference frequency-domain method to study the perpendicular crossing waveguide, dielectric and microwave, TE and TM modes, by exploiting built-in structural symmetries in these waveguide devices. In the plus (+) symmetry model, the complete solution is obtained by solving two rectangular-shaped quarter structures each with two transparent boundaries and two symmetry boundaries. For the cross (x) symmetry model, solutions of four triangular-shaped quarter structures are needed but each with only one transparent boundary. Numerical results are verified by comparison between these two models and with the power conservation test. We show the total and the fundamental-mode, coupling coefficients of the reflected, cross and through power in the crossing waveguide as functions of the normalized frequency.
A novel DOA finding method for conformal array applications is proposed. By using sub-array divided and interpolation technique, ESPRIT-based algorithms can be used on conformal arrays for 1-D and 2-D DOA estimation. In this paper, the circular array mounted on a metallic cylindrical platform is divided to several sub-arrays, and each sub-array is transformed to virtual uniform linear array or virtual uniform planar array through interpolation technique. 1-D and 2-D direction of arrivals can be estimated accurately and quickly by using LS-ESPRIT and 2-D DFT-ESPRIT algorithms, respectively. This method can be applied not only to cylindrical conformal array but also to any other arbitrary curved conformal arrays. Validity of this method is proved by simulation results.
A combined method of the non-uniform fast fourier transform (NUFFT) migration and the least-square based matching pursuit decomposition (MPD) algorithms is proposed to obtain better discrimination and interpretation for subsurface from ground penetrating radar (GPR) signals. By using the modified NUFFT migration algorithm, a fast and high resolution GPR reconstruction can be obtained with an additional reduction in storage and computation requirements. By incorporating the MPD algorithm into a migration method, denoised reconstructions are obtained to enhance objects detection, including the identification of objects' geometries and the estimation of their sizes and locations. Several examples from synthetic data and field data are demonstrated to establish the effectiveness of the synergic effect by comparing it with the conventional migration methods.
A theoretical analysis of the properties of the defect modes in a one-dimensional defective photonic crystal (PC) is given. Two defective PCs stacked in symmetric and asymmetric geometries are considered. The defect modes are investigated by the calculated wavelength-dependent transmittance for both TE and TM waves. It is found that there exists a single defect mode within the photonic band gap (PBG) in the asymmetric PC. There are, however, two defect modes within the PBG in the symmetric one. The dependences of defect modes on the angle of incidence are illustrated. Additionally, the effect of defect thickness on the number of defect modes is also examined.
Confocal Microwave Imaging (CMI) for the early detection of breast cancer is based on several assumptions regarding the dielectric properties of normal and malignant breast tissue. One of these assumptions is that the breast is primarily dielectrically homogeneous, and that the propagation, attenuation and phase characteristics of normal breast tissue allows for the constructive addition of the UWB returns from dielectric scatterers within the breast. However, recent studies by Lazebnik et al. have highlighted a very signi cant dielectric contrast between normal adipose and broglandular tissue within the breast. This dielectric heterogeneity presents a considerably more challenging imaging scenario, where constructive addition of the UWB returns, and therefore tumor detection, is much more di cult. In a dielectrically homogeneous breast, each additional beamformed backscattered signal adds coherently with existing signals, resulting in an improved image of any dielectric scatterers present. However, in a dielectrically heterogeneous breast, signals with a longer propagation distance are more likely to encounter heterogeneity and therefore are more prone to incoherent addition, reducing the overall quality of the breast image. In this paper, a novel beamforming algorithm is described, which gives extra weighting to signals with shorter propagation distances to create an improved image of the breast. The beamformer is shown to provide improved images of more dielectrically heterogeneous breasts than the traditional delay and sum beamformer from which it is derived.
The novel characteristics of wave transmission and reflection in one-dimensional semi-infinite chiral photonics have been investigated theoretically. Waves in each region have been formulated for both normal and oblique incidences. At a given incident angle, the transmission or reflection is found to be easily adjusted to be equal to 1 for the chiral photonics using chiral nihility media. The wave tunneling and rejection properties in chiral nihility photonics, as well as their parametric dependences on periodicity, chiral nihility and incident angles, have been explicitly presented theoretically and verified numerically.
A novel fractal antenna-array type is proposed. The design is based on the Sierpinski rectangular carpet concept. However, the generator is a circular ring area, filled with radiating elements, so the higher stages of the fractal development produce large arrays of circular rings which, besides the high directivity, have the advantage of the almost uniform azimuthal radiation pattern, attribute that many applications require. The introduced arrays can operate as direct radiating multi-beam phased arrays and meet the requirements of satellite communications links: high End of Coverage (EOC) directivity, low Side Lobe Level (SLL) and high Career to Interference ratio (C/I). These operational indices were further optimized by a synthesized multi-objective and multi-dimensional Genetic Algorithm (GA) which, additionally, gave arrays no more than 120 elements.
Here we report a prism made of stacked quasi-selfcomplementary extraordinary transmission surfaces which allows simultaneously left- and right-handed propagation within the V-band for vertical and horizontal polarizations, respectively and righthanded propagation within the W-band for both polarizations. The numerical dispersion diagram of the infinite structure and effective indexes of refraction retrieved from S-parameters under normal incidence together with the finite integration time domain simulations predict single negative and double positive birefringence. The unusual type of birefringence single negative and regular double positive birefringence are afterwards demonstrated experimentally at the millimeter-waves (V- and W-bands) by the wedge experiment which lets us check, using a straightforward geometrical method, the refraction of each component. The effective index of refraction is retrieved via the Snell's law and compared to those obtained through the dispersion diagram and the retrieval method from S-parameters computed with the commercial software CST Microwave StudioTMTM.
This paper describes in detail different formulations of the inverse-source problem, whereby equivalent sources and/or fields are to be computed on an arbitrary 3-D closed surface from the knowledge of complex vector electric field data at a specified (exterior) surface. The starting point is the analysis of the formulation in terms of the Equivalence Principle, of the possible choices for the internal fields, and of their practical impact. Love's (zero interior field) equivalence is the only equivalence form that yields currents directly related to the fields on the reconstruction surface; its enforcement results in a pair of coupled integral equations. Formulations resulting in a single integral equation are also analyzed. The first is the single-equation, two-current formulation which is most common in current literature, in which no interior field condition is enforced. The single-current (electric or magnetic) formulation deriving from continuity enforcement of one field is also introduced and analyzed. Single-equation formulations result in a simpler implementation and a lower computational load than the dual-equation formulation, but numerical tests with synthetic data support the benefits of the latter. The spectrum of the involved (discretized) operators clearly shows a relation with the theoretical Degrees of Freedom (DoF) of the measured field for the dual-equation formulation that guarantees extraction of these DoF; this is absent in the single-equation formulation. Examples confirm that single-equation formulations do not yield Love's currents, as observed both with comparison with reference data and via energetic considerations. The presentation is concluded with a test on measured data which shows the stability and usefulness of the dual-equation formulation in a situation of practical relevance.
An advanced aspheric and asymmetric large aperture dielectric lens antenna is proposed firstly here for high resolution at W-band frequency. Large aperture and aspheric lens provides minimum focusing error and high resolution in millimeter wave quasi-optics application. To the best of the authors' knowledge we design first time 500 mm large aperture lens for W-band quasi optics application. Near field radiation pattern, beam size and focal length of the lens are obtained theoretically and experimentally as well. Dielectric rod waveguide antenna is also designed and employed as a source antenna for the lens. The measured and simulated results of the DRW antenna also show very good performance at W-band frequency, and it has 15.3 dB gain with -22.5 dB sidelobe levels at 94 GHz.
Analytical expressions for the average intensity, mean-squared beam width and angular spread of partially coherent standard and elegant Laguerre-Gaussian (LG) beams propagating in turbulent atmosphere are derived. The properties of the average intensity, spreading and directionality of partially coherent standard and elegant LG beams in turbulent atmosphere are studied numerically and comparatively. It is found that the beam parameters and structure constant of turbulence together determine the properties of the beams in turbulent atmosphere. Partially coherent standard and elegant LG beams with smaller coherence length, larger beam orders and longer wavelength are less affected by the turbulence. A partially coherent elegant LG beam is less affected by turbulence than a partially coherent standard LG beam under the same condition. Furthermore, it is found that there exist equivalent partially coherent standard and elegant LG beams, equivalent fully coherent standard and elegant LG beams, equivalent Gaussian Schell-model beams that may have the same directionality as a fully coherent Gaussian beam both in free space and in turbulent atmosphere. Our results will be useful in long distance free-space optical communications.
This paper applies the recently introduced electrical engineering approach to investigate room temperature THz metal shielding, using the accurate classical relaxation-effect frequency dispersion model. It is shown that, with the simplest case of a uniform plane wave at normal incidence to an infinite single planar shield in air, all figure of merit parameters for the shield can be accurately characterized. The errors introduced by adopting the traditional and much simpler classical skin-effect model are also quantified. In addition, errors resulting from adopting well-established approximations have also been investigated and quantified. It is shown that the engineering approach allows analytical expressions to be greatly simplified and predictive equivalent transmission line models to be synthesized, to give a much deeper insight into the behaviour of room temperature THz metal shielding. For example, it is shown that figures of merit and associated errors (resulting from the use of different classical frequency dispersion models) become essentially thickness invariant when the physical thickness of the shield is greater than 3 normal skin depths.
An analytical approach is developed in the present paper to investigate the interaction between two non-magnetic particles migrating in a conductive fluid due to an imposed strong magnetic field (e.g., 10 Tesla). The interaction between the conductive fluid and a single particle migrating along the magnetic lines is influenced by the magnetic field and can be represented by an additional fluid viscosity. Thus the effective fluid viscosity is discussed and the magnetic field effect on the particle migrating velocity is examined. For two particles, two kinds of magnetic forces are induced: namely, the attractive force due to the magnetisation and the repulsive force caused by the conductive fluid flow around the non-magnetic particles. The forces are then evaluated with the consideration of the magnetic field effect on the particle migration and become significant with the increase of the magnetic flux density. The counteracting behavior with a critical particle size of the interparticle magnetic forces is discussed and compared with different magnetic field densities and gradient values.
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