Radiowave propagation over rectangular plateau

The solution to the problem of radiowave propagation over a perfectly conducting cliff-edge has previously been reported in closed form. This solution is now extended to deal with a radiowave propagation over a perfectly conducting, finite-length plateau of rectangular cross-section.<>     

Application of a perfectly matched layer in problems of simulation of electromagnetic ultralong wave propagation in the spherical earth-ionosphere waveguide channel

A method based on the use of a perfectly matched layer is proposed for creating a nonreflecting boundary involved in the simulation of ultralong electromagnetic wave propagation in the spherical Earthionosphere waveguide channel. It is shown that this channel provides for the attenuation of electromagnetic waves propagating in a perfectly matched layer along a radio path. A system of differential equations describing the propagation of electromagnetic waves in this region is presented.     

Analysis of the numerical error caused by the stair-steppedapproximation of a conducting boundary in FDTD simulations ofelectromagnetic phenomena

A rigorous analysis of the numerical error associated with the use of stair-stepped (saw-toothed) approximation of a conducting boundary for finite-difference time-domain (FDTD) simulations is presented. First, a dispersion analysis in two dimensions is performed to obtain the numerical reflection coefficient for a plane wave scattered by a perfectly conducting wall, tilted with respect to the axes of the finite-difference grid, under both transverse electric and transverse magnetic polarizations. The characteristic equation for surface waves that can be supported by such saw-tooth conducting surfaces is derived. This equation leads to expressions that show the dependence of the propagation constant along the boundary and the attenuation constant perpendicular to it on cell size and wavelength. Numerical simulations that demonstrate the effects predicted by the dispersion analysis are presented     

A heuristic UTD slope diffraction coefficient for rough lossywedges

Heuristic wedge diffraction coefficients for computing propagation path loss over finitely conducting earth are extended to include slope diffraction, with the assumption that propagation of energy through the wedge is negligible. The slope diffraction terms for the lossy wedge are obtained in an analogous manner as for the perfectly conducting case, except that special care must be taken with the factor multiplying the incident field for grazing incidence. Results given show that the slope diffraction term produces continuous results that behave reasonably when compared with results for perfectly conducting wedges     

A dual-polarization rain profiling algorithm

A new attenuation correction algorithm based on profiles of reflectivity, differential reflectivity, and differential propagation phase shift is presented. A solution for specific attenuation retrieval in rain medium is proposed, which solves the integral equations for reflectivity and differential reflectivity with cumulative differential propagation phase shift constraint. The conventional rain profiling algorithms that connect reflectivity and specific attenuation can retrieve specific attenuation values along the radar path assuming a constant intercept parameter of the normalized drop size distribution. However, in convective storms, the drop size distribution parameters can have significant variation along the path. This paper presents a dual-polarization rain profiling algorithm for horizontal looking radars incorporating reflectivity as well as differential reflectivity profiles. The dual-polarization rain profiling algorithm has been evaluated with X-band radar observations simulated from drop size distribution derived from high-resolution S-band measurements collected by the Colorado Statue University CHILL radar. The analysis shows that the retrieved specific attenuation, differential attenuation, reflectivity, and differential reflectivity from the dual-polarization rain profiling algorithm provide significant improvement over the current algorithms.     

Slant path rain attenuation predictions for Ku and Ka band frequencies from rain cell size distribution over a tropical region in southern India

Rain cell size distribution that provides an insight into the modelling of effective slant path length and also imperative for site diversity studies are carried out for a tropical inland location, Tirupati (13.6°N, 76.3°E), India. Rain cell size distribution obtained from 5 years (2013–2015 and 2017–2018) of Parsivel disdrometer measurements is observed to follow the power law. Reduction factor that accounts for the inhomogeneity of the rain along the propagation path for the region of study is modified in terms of the rain cell size distribution of the area. Slant path rain attenuation, a major propagation impediment at Ku and Ka-band links, is then studied using the results from the regional rain characteristics by modifying the CCIR 564-4 report. The attenuation results are compared with Garcia-Lopez, Excell, Bryant, and Ramachandran models while considering the ITU-R P. 618-13 as the standard model.     

Guided Waves Propagating Along the Magnetostatic Field at a Plane Boundary of a Semi-Infinite Magnetoionic Medium

The characteristics of the surface waves supported by a plane boundary of a semi-infiite region of gyrotropic plasma are investigated for the case in which the direction of the magnetostatic field is parallel to both the interface and the propagation direction. Two cases are considered, one for which the plasma is terminated by a perfectly conducting screen, and the other for which it is terminated by a semi-infinite region of free space. Surface waves are found to be propagated for all frequencies below both the plasma and the gyromagnetic frequency in the first case, and below both the plasma and 1/ /spl radic/2 times the upper hybrid resonant frequency in the second case. The characteristics of the surface waves are discussed, and numerical results of the phase velocity and the propagation coefficient of the surface waves along the interface, as well as their attenuation rates normal to the interface, are given.     

Snell's law applied to finite surfaces

Snell's law of reflection applies to a plane wave incident on an infinite surface. For finite surfaces the size of the surface, the angle of incidence, and the polarization of the incident wave all contribute to deviations from Snell's law. An eigenfunction expansion for the scattering pattern of a perfectly conducting strip and experimental bistatic scattering measurements of rectangular plates are used to verify the deviations. Physical optics calculations also predict these deviations and are used to provide a physical explanation for the deviations     

基于3D FDTD 微型塔电磁模型电流衰减机制

为研究雷电流在高塔中的传输过程和衰减机制,本文基于三维时域有限差分法(3-D FDTD),建立高 度为45cm 的微型塔电磁模型,应用理想导体边界条件求解高斯脉冲电流沿塔体表面的时空分布。结果表明,不同 形状塔体,表面电流衰减特征不同。锥形塔的表面电流衰减具有方向性,自塔顶向塔底传播时,幅值几乎无衰减,方 向相反时,有显著衰减。柱形塔的表面电流自塔顶向塔底以及反向传播时,幅值均有明显衰减。塔体不同高度处电 流的衰减程度随着锥形塔顶角和柱形塔半径的增大、激励源频宽的减小而增大。     

Characteristics of near field of the horizontal vibrator located above a square screen

The 3D vector problem concerned with the diffraction of the horizontal half-wave vibrator field by a perfectly conducting and infinitely thin rectangular screen is solved during observations at a finite distance from the vibrator. The technique for calculating the diffracted field, which is based on the laws of geometric diffraction theory and uniform diffraction coefficients obtained from the rigorous solution to the problem of the diffraction of the field of a Hertzian electric dipole at the edge of a perfectly conducting semiplane, is proposed. Fast-acting programs for calculating and analyzing the amplitudes and phases of the components of diffracted and complete vibrator fields in the entire space of observation angles at the set distance of the observation point from a rectangular screen and along the normal to the screen under changes in the distance between the screen and the observation point are developed. The character of the transformation of the spatial amplitude distribution of three field components depending on removal of observation point from an antenna is studied. It is shown that the distance to the far field zone of the investigated radiating system exceeds two wave lengths.     

Effect of raindrop size distribution and rain rate inhomogeneity on the relationship between attenuation and depolarization

In addition to attenuation, depolarization due to rain is another factor that degrades satellite propagation signals, especially in the higher frequency bands and in places that have high rates of rainfall. A formula to predict cross‐polarization as a function of attenuation has been proposed, and it is derived by a theoretical calculation using frequency, the forward scattering amplitude of raindrops, rainfall rates, the raindrop size distribution (DSD), and various other propagation parameters. In this paper, a formula for predicting cross‐polarization is derived on the basis of the assumption of a gamma‐type DSD up to 100 GHz. These results are compared with conventional exponential‐type DSDs, such as the Marshall‐and‐Palmer DSD. Moreover, for a more realistic propagation situation, we consider the effect on the aforementioned relationship of rainfall rate inhomogeneity along the propagation path. It is shown that, for practical purposes, this inhomogeneity does not have a significant effect on satellite propagation. Copyright © 2017 John Wiley & Sons, Ltd.     

非理想金属感性膜片的等效阻抗

矩形波导中感性膜片的传统分析都局限于理想金属膜片的情况,不能反映其导体损耗特性。本文应用直线法分析非理想导体所构成的薄感性膜片,其等效电抗和等效电阻能同时计算获得。文中给出了几种典型感性膜片等效阻抗的数值结果。作为一应用实例,分析了有耗双膜片通过式谐振腔的传输特性。     

Low-Frequency Behavior of the Propagation Constant Along a Thin Wire in an Arbitrarily Shaped Mine Tunnel

Seidel and Wait have investigated the complex propagation constant (phase and attenuation coefficients) of the fundamental mode of propagation for radio waves along a thin wire or cable, located in an elliptical mine tunnel, and found that the attenuation rate for low frequency is insensitive to the shape of the ellipse if the cable-wall distance and cross-sectional area are kept constant. We consider here tunnels of more general cross section, and obtain a characteristic equation for the propagation constant valid for sufficiently low frequency, by means of a variational formulation of an integral equation. The characteristic equation involves only the electrical parameter of the tunnel walls, the radius of the wire, and the capacitance per unit length that the wire would have if the tunnel walls were perfectly conducting. Agreement with exact calculations for several geometries is found to be excellent below about 100 kHz, and acceptable even up to 1 MHz or more, for typical tunnel parameters. Since the wire capacitance can be shown to depend most importantly on its distance from the wall and on the area of the tunnel, the conclusion of Seidel and Wait can be made more precise and extended to tunnels of arbitrary cross section.     

A new method of estimating microwave attenuation over a slant propagation path based on rain gauge data

A basic problem in estimating the microwave attenuation over a satellite-earth propagation path on the basis of rain gauge data is that, for a given precipitation event, the attenuation and the rainfall records very often do not have consistent detailed correlation. Such inconsistencies can be greatly reduced if the falling speed of the rain drops, i.e., 2 to 9 m/s for drop sizes of 0.05 to 0.7 cm, is taken into account. Adjustments in time and drop size spectrum are needed for data collected from field rain gauges to realize the actual rainfall along the slant path for correlating rain gauge data with measured satellite signals.     

Low-frequency scattering by rectangular cylinders

An integral equation formulation is used to investigate potential problems associated with low-frequency scattering by both dielectric and perfectly conducting cylinders of rectangular cross section. Induced dipoles and scattering cross sections are obtained for 1) waves withbar{E}orbar{H}parallel to the axis, and 2) directions of propagation perpendicular and parallel to the broad side of the rectangle.     

Dispersion of waves guided along a cylindricalsubstrate-superstrate layered medium

The effects of curvature and of the electrical parameters of thin dielectric layers deposited as superstrates on a perfectly conducting circular cylinder on the modal dispersion of waves guided tangentially along the outer (superstrate) layer of a two-layer geometry are examined. To chart the propagation characteristics of the layer-guided modes relevant to the three-dimensional (dipole-excited) Green's function for this geometry, it is necessary to solve the radial eigenvalue problem for the complex azimuthal propagation constants ν _p(β), p 1, 2, . . ., which also identify poles of the ν-dependent spectral integrand of the Green's function. Here, β is the spectral variable along the axial direction, with the Green's function synthesized as a double spectral integral over ν and β. The pole locations are obtained numerically by solving the dispersion equation using Davidenko's method, and are parameterized in terms of layer radius, dielectric constant, and thickness. The dispersion relation, and hence the propagation constants, are shown to reduce correctly to the corresponding results for the planar geometry in the limit where the superstrate outer radius approaches infinity     

Impedance and radiation pattern of antennas above flat discs

Antenna imaging by a perfectly conducting finite flat disc is investigated analytically and numerically as a function of the radius of the disc. A conical monopole of variable length is considered above the screen and the normalized terminal admittance of the antenna is plotted versus the disc radius. The radiation pattern is also plotted and the current distribution above and below the screen is evaluated. The results provide a quantitative measure of the effectiveness of finite screens in imaging antennas and bring to light the persistent distortion of the pattern caused by the finite size of the screen in contrast to the behavior of the impedance.     

Simultaneous analysis of downlink beacon dynamics and skybrightness temperature. Part II. Extraction of amplitude scintillations

This paper addresses the long-standing problem of separating the tropospheric amplitude scintillations from the dominant trend of atmospheric attenuation in a satellite downlink. Following extensive theoretical and experimental work, it is shown how the use of a radiometer coaxial with the communications beacon receiver constitutes an excellent tool for an optimum separation regardless of the meteorological conditions along the propagation path and avoids the use of the long-traditional high-pass filter approach. The experimental and theoretical work has revealed that the angular resolution of the radiometer together with the dynamics of rain attenuation and tropospheric scintillations determine the success of the extraction. This is because fast fadings require large radiometer antennas in order to resolve the sky temperature fluctuations. The dynamic behavior of rain attenuation has been reanalyzed and adapted for this study with special focus on the Maseng-Bakken (MB) model and the impact of the slant path on attenuation dynamics. The importance of the antenna pattern in the time response of the radiometer is studied in detail and permits to derive the maximum Fourier component observable for a given antenna size. The theoretical work has been verified by means of extensive experimental results obtained using a dual radiometer system and a beacon receiver tracking the ITALSAT 39.5 GHz F40 beacon. Finally, because of its importance and direct relevance to future communication systems benefiting from fade countermeasure strategies, the minimum size of the radiometer antenna for a successful extraction of amplitude scintillations is determined as a function of the elevation angle and carrier frequency     

Numerical investigation of intense rainfall effects on coherent and incoherent slant-path propagation at K-band and above

A model investigation is carried out to analyze the impact of intense rainfall on slant-path microwave propagation, using a rainfall microphysical model. The effects are evaluated both for path attenuation, undergone by coherent radiation, and for multiple scattering phenomena, originating incoherent radiation along the path. Atmospheric spatial inhomogeneity is taken into account. The EM propagation model is formulated by means of the radiative transfer theory. The propagation model is applied both to simplified rain slabs and to vertically and horizontally inhomogeneous raining cloud structures in order to compare the impact of atmospheric models on coherent and incoherent propagation. Beacon frequencies between 20 and 50 GHz, elevation angles between 20/spl deg/ and 40/spl deg/ and surface rain rates from 1 to 100 mm/h are considered. Appropriate sensitivity analysis parameters are defined to present and discuss the numerical results. Our main conclusion is that the impact of the convective rainfall structure can be significant both in determining total attenuation and quantifying the contribution of multiple scattering to the received power. For intense rainfall, the use of a rain slab model can both overestimate coherent attenuation and underestimate incoherent intensity. The analysis of realistic raining clouds structures reveals the significance of modeling the volumetric albedo of precipitating ice, particularly at V-band. Total path attenuation can strongly depend on the pointing direction of the receiving antenna due to the intrinsic variability of the precipitating cloud composition along the slant path. Coupling cloud-resolving models with radiative transfer schemes may be foreseen as a new approach to develop statistical prediction methods at Ka-band and above in a way analogous to that pursued by using weather-radar volume data.