This work is intended to investigate the accuracy of modelling simple cylindrical vegetation structures for microwave remote sensing applications. Plane wave scattering by dielectric cylinders of finite length and circular cross section is examined. Cylinders with a radius that varies linearly along the cylinder length hereafter referred to as tapered cylinders are also considered. Exact expressions for the scattering cross section do not exist for those objects. Numerical methods can provide accurate results, but they are computationally intensive and therefore less suitable when calculations on a large number of scatterers of different sizes and orientations are necessary. In this paper the scattering cross section of finite cylinders is computed by physical optics methods, which are faster and often employed in microwave vegetation models. Tapered cylinders are modelled by a number of coaxial finite cylinders stacked on top of each other. To check the validity of the results, the problems are also solved numerically by the moment method. For cases often encountered in vegetation studies, the results of the application of the approximate analytical methods are then compared with the corresponding numerical solution. For both constant-radius and tapered cylindrical structures, a good agreement with the numerical solution is found in the region of the main scattering lobe, which is the one of interest when considering complex media such as vegetation canopies. However, the accuracy of the approximate solutions decreases as the angle of the incident wave approaches the end-on angle.
When one uses integral equations to determine the input admittance of dipole antennas, one must choose between two kernels, the exact and the approximate kernel, and also between (at least) two types of feed, the delta-function generator and the frill generator. For dipole antennas of infinite length, we investigateanalytically and numericallythe similarities and differences between the various admittance values. Particular emphasis is placed on the fact, discussed in detail in recent publications, that certain combinations lead to non- solvable integral equations.
The Sommerfeld integrals for the electromagnetic field due to a delta-function current in a horizontal electric dipole located on the planar boundary between air and a homogeneous dielectric are examined in detail. Similar to the case of the vertical dipole, the tangential electric fields consist of a delta-function pulse travelling in the air with the velocity c, the oppositely directed delta-function pulse travelling in the dielectric with the velocity c/ε1/2 for the component Eρ and the velocity cε1/2 for the component Eφ, and the final static electric fields due to the charge left on the dipole. The appearance of the vertical magnetic field is similar to that of the tangential electric field. It is pointed out that the amplitude of the pulsed field along the boundary is 1/&rho2, which is characteristic of the surface-wave or lateral pulse.
Scattering characteristic of target in rain is studied in this paper, which calculates scattering matrix of rain area and that of cylinder target in rain, taking the effect from rain into account by substituting rain media for random media with equivalent complex permittivity. SCR (ratio of scattering signal induced by target in rain to clutter from rain) is computed, and the relation between SCR and polarization status of transmitting and receiving antennas is deduced. By optimizing the SCR, optimal polarization status of transmitting and receiving antennas are found. And, the results found in this paper are serviceable for communication system design [2, 4].
In this paper, a novel reconfigurable two-layer microstrip antenna fed using a coplanar waveguide through a slot/loop combination is investigated. The slot/loop combination allows for easy reconfigurability of the frequency band of operation by incorporating switches in the feed network. Furthermore, broad impedance bandwidths were obtained by using two substrate layers consisting of a high-εr substrate that contains the feed network and a low-εr substrate that contains two patches, one patch on either side of the substrate. The two substrates are not separated by a ground plane. Impedance bandwidths of about 23% were obtained for two selectable frequency bands using two switches. The two frequency bands obtained for the parameters chosen in this paper are 8.73-10.95 GHz and 7.68-9.73 GHz.
The Electromagnetic (EM) fields of a concentric, mismatched-material, elliptical system are studied when excited by an interior or exterior electric surface current. The interior or exterior surface current is assumed to be proportional to a single, angular Mathieu mode. It is shown that despite the fact that the system is concentric, that a single Mathieu mode surface current excites EM Mathieu-mode fields of all orders. A derivation of the EM fields due a single mode electric surface in an infinite, homogeneous media is given, as well as the matrix formulation from which the EM fields of the mismatched-material, elliptical system may be determined. Validation of numerical results and comparison with other research work is given for both interior and exterior single-mode, current sources. Detailed numerical examples of the EM fields that result for a single-mode, exterior source excitation are given for the first time. Discussion of the EM mode coupling that results by single-mode excitation on a mismatched elliptical system is given.
A single-level compression algorithm is described for the plane wave response matrix, which defines the current excited on the surface of a scatterer by a spectrum of incident plane waves. The reported method is based on the physical principle that it is often possible to organize plane waves originating from a given angular region to form incident beams which excite localized currents on the surface of an electrically large target. The properties of the method are illustrated for several scattering problems in two dimensions.
The application of polarization diversity reception at the mobile terminal in micro cells at 2 GHz is presented in this paper. Ray-tracing tool is used to study effects of electric field polarization on the received power in outdoor environments. The performance of diversity schemes with vertical/horizontal polarization and +45°/âˆ’45° slanted polarization are compared in different line-of-sight (LOS) and nonline- of-sight (NLOS) environments. Based on the evaluation of cross polarization discrimination (XPD) parameters, it is clarified that different environments will affect XPD values in micro cells. Then, the vertical/horizontal polarization diversity and +45°/âˆ’45° slanted polarization diversity are chosen to compare with space diversity. Several different combining techniques of polarization and space diversity schemes are also compared in different environments. It is found that dual-polarized antennas for mobile terminal are a promising alternative for two spaced antennas.
The problem of studying modal characteristics of metallic waveguides filled with lossless inhomogeneous and/or anisotropic media, is one of studying properties of the propagation constant of the guiding structure. It is shown that modal behavior in the neighborhood of critical frequencies such as cutoff frequencies and frequencies marking the onset of complex wave mode intervals, can be modeled through approximation of the propagation constant by a root of an algebraic equation. The particular form of the algebraic function approximating the propagation constant is discussed in the neighborhood of a singularity. A numerical example is included to stress the viability of the technique.
The photon, that is the messenger of the electromagnetic force, is considered with a zero restmass. Yet, just as there is no energy with a zero value, so we talk about a "Zero Point Energy", for the equivalence between mass and energy (datum point of the Theory of Relativity and foundation of modern Physics), there should exist also a "Zero Point Mass". That is, no particle, with energy, though extremely small, as the energy of the quantum of light, the Planck's grain, can have a zero mass. In other words, just for the equivalence Mass-Energy (E = mc2), to any particle with energy should correspond a mass equal to the energy carried, divided the square of the speed of light. Of course when we consider particles like the photon this value will be extremely small, however it should be ≠ 0. Thus, a lot of the behaviours of the photon, in which it shows a clear sort of mechanic action (see photoelectric effect, Compton effect, or the Raman effect), so far ascribed to a mere energetic effect, may probably be considered as real "mass effects".
Three mathematical models based on approximate surface integral equations for electromagnetic analysis of scalar wave scattering from thin extended target are considered. Such models include different systems of the second kind singular integral equations determined on the target median. The effective algorithm for direct (without preliminary regularization) numerical solution of the systems is based on the special quadrature formulae for singular integrals. Verification of the mathematical models and their comparison is performed in the case of penetrable cylindrical shell in homogeneous non-magnetic medium.
The multilevel fast multipole algorithm (MLFMA) is used in computing acoustic and electromagnetic fields with integral equation The multilevel fast multipole algorithm (MLFMA) is used in computing acoustic and electromagnetic fields with integral equation methods. The traditional MLFMA, however, suffers from a low-frequency breakdown that effectively limits the minimum division cube side length to approximately one wavelength. To overcome this low-frequency breakdown and get a broadband MLFMA, we propose an efficient and relatively straightforward implementation of the field translations based on the spectral representation of the Green's function. As an alternative we also consider the so called uniform MLFMA, which has a lower computational cost but limited accuracy. We consider the essential implementation details and finally provide numerical examples to demonstrate the error controllability of the translations.
In this paper, two new interconnect structures called Multi-Segmented S-G-S (Signal-Ground-Signal) and S-O-S (Signal- Open-Signal) interconnects are proposed and compared with the conventional S-S-S interconnects. In these interconnect structures a multi-segmented grounded or opened line is inserted between two adjacent signal lines. The grounded (opened) lines have been grounded (opened) not only in their terminals, but also in some places along their length. The performances of these interconnects are studied via some examples.
A surface with periodic corrugations of sufficiently small periodicity is shown to be electromagnetically equivalent to an inhomogeneous transition region (slab). Explicit expressions for the inhomogeneous transition region are found for one-dimensional corrugations and for two-dimensional corrugations a local elliptic problem has to be solved in order to find the equivalent electromagnetic properties. The homogenized surface can be characterized by its surface impedance dyadic or its reflection dyadic. A few numerical examples illustrate the theory.