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Extremely low-frequency (ELF: below 30 Hz) wave penetration theory in the layered oceanic lithosphere is essential for studying submarine communications. In this article, we investigate the mode theory of ELF wave propagation in a layered oceanic lithosphere waveguide. Based on the real situation of the oceanic lithosphere approximated by the stratified prototype, in which a low-conductivity layer lies between two overlying and underlying high-conductivity regions, a theoretically sound physical model of oceanic lithosphere waveguide is built. The modal equations for transverse magnetic (TM) and transverse electric (TE) polarized guided modes are delivered using surface impedance boundary conditions. By evaluating the reflection coefficients of the upper and lower waveguide boundaries, formulas for the modal equation’s roots are derived. Analytical expressions for propagable mode parameters, such as the phase velocity, attenuation rate, excitation factor, and the field strength for different components, are obtained, and the cutoff frequency for high-order modes is given. Computations show that the field component curves exhibit typical peaks and nulls associated with multiple-mode propagation in the waveguide region, with each mode traveling at different phase velocities and attenuation rates. Moreover, it is found that all the high-order modes are evanescent below the cutoff frequency. [ABSTRACT FROM AUTHOR]

Parabolic equation (PE) methods have been widely applied to the modeling of wireless propagation in tunnel environments. However, the relevant literature does not include concrete guidelines for the choice of the parameters of these methods and the tradeoffs involved. This paper provides a comprehensive analysis of the two sources of error that arise when PE methods are employed for the modeling of radio-wave propagation scenarios: the well-known numerical dispersion error stemming from the finite-difference solvers for PE and the approximation error stemming from the use of PE for the solution of wave propagation problems that are subject to Maxwell’s equations. The analysis is performed for four methods, three of which have been already used in PE-based propagation studies, namely, the Crank–Nicolson (CN) scheme, the alternative-direction-implicit (ADI) method, and its locally one-dimensional (LOD-ADI) version. The fourth method is the Mitchell-Fairweather (MF)-ADI scheme that has been recently shown to be a promising alternative technique for tunnel propagation modeling. The proposed method leads to robust criteria for the choice of spatial discretization in realistic propagation scenarios, as shown via numerical examples. [ABSTRACT FROM PUBLISHER]

A novel hybrid model is presented to study the radio wave propagation through frequency selective structures (FSS) used to control propagation in an outdoor to indoor building environment. This hybrid model is based on combining ray-tracing with a commercial tool, Computer Simulation Technology (CST) Microwave Studio. Numerical results of the hybrid model have been compared with those of a full wave rigorous solver for FSS small in wavelength terms. Good agreement has been achieved with substantially increased computation efficiency, which validates the recommended hybrid method for this class of applications. [ABSTRACT FROM AUTHOR]

Analysis of radio propagation over varying, clutter-covered terrain was carried out aiming at prediction of power received by a terminal immersed in clutter, with the transmitter placed above clutter. The need for such prediction arises, for example, in planning and assessing coverage and interference in radio communications. Following a general formulation of the problem, particular solutions were found when the terrain has constant curvature. Asymptotic evaluation yielded compact expressions both for parabolic valleys and ridges. In both cases, ray-optical term dominated for short ranges, while a single mode dominated at large ranges. Strong focusing was found to occur in valleys, while ridges produced strong blockage beyond the "horizon". The resulting procedure for predicting pathloss over varying terrain is therefore to apply the formulae using the terrain curvature extracted from terrain files. In comparison to measured power across a valley, mean errors of less than 1 dB were found, a marked improvement over standard terrain-unaware models that produce a mean error of 30 dB. [ABSTRACT FROM AUTHOR]

An investigation on the effects of terrain roughness on near-ground radiowave propagation is featured. In spite of the fact that a variety of analytical and numerical routines have been proposed by many workers for the general treatment of the scattering properties of rough surfaces, much disagreement remains in the solution of the problem for near-grazing scenarios. In striving to analytically describe the near-grazing propagation of signals from 2D and 3D radiators, an existing volumetric polarization current- based perturbation approach is exploited in this work to formulate closed-form expressions for the coherent rough surface reflection coefficients. Although the perturbation approach was originally intended for analyzing the scattering coefficients of a ground with scale of roughness much smaller than the wavelength, it is shown through Monte Carlo simulations that the effective reflection coefficients reported herein are applicable for near-ground path-loss prediction even when the surface variation (rms height) is on the order of a wavelength or more. [ABSTRACT FROM AUTHOR]

We have characterized the effect of human presence on path gain and time dispersion over ultrawideband (UWB) channels within the passenger cabin of a typical midsize airliner. We measured a few hundred channel frequency responses over the range 3.1-6.1 GHz between various locations within a Boeing 737-200 aircraft, with and without volunteers occupying the passenger seats. The links were deployed in a point-to-multipoint configuration with the transmitting antenna along the centre-line of the forward part of the cabin at either the ceiling or headrest level and the receiving antenna at the headrest or armrest level at selected locations throughout the rest of the cabin. As the density of occupancy increased from empty to full, path gain dropped by no more than a few dB on the ceiling-to-headrest paths but dropped by up to 10 dB on the ceiling-to-armrest and headrest-to-armrest paths. The gain reduction reached its maximum at the mid-point of the cabin and decreased thereafter. In all cases, increasing the density of occupancy caused the distance dependence of the rms delay spread to decrease greatly, the decay rate of the scattered components in the power delay profile (PDP) to almost double and the number of significant paths to drop by almost half. The results suggest that human presence substantially affects both path gain and time dispersion within the aircraft and should therefore be considered when assessing the performance of in-cabin wireless systems. [ABSTRACT FROM AUTHOR]

Differentially-driven Yagi-Uda antennas have been developed for millimeter-wave applications. The antennas are built on both sides of a Teflon substrate (εγ = 2.2). A key design aspect is the use of a folded dipole feed which increases the input impedance from 18Ω (standard dipole case) to 150 Ω and is compatible with coplanar strip lines. A 7-element design results in a gain of 8-10 dB at 22-26 GHz and a cross-polarization level of < -22 dB. The differentially-fed Yagi-Uda antenna with folded dipole results in high radiation efficiency (> 90% at 22-26 GHz) and is suitable for mm-wave point-to-point links communication systems. [ABSTRACT FROM AUTHOR]

Conformal scanning arrays are important for scanning ranges beyond ±90 degrees and the retrodirective array (RDA) is known as a promising candidate for this application. We discuss the optimization of a previously realized conformal sparse RDA by means of the genetic algorithm, and the RDA numerical model that is used in this approach. In particular, we improve the numerical model of the RDA by identifying practical factors that previous model failed to account for. The impact of each practical factor on the RDA monostatic pattern is visualized, and the improved model provides much better prediction of the monostatic pattern. [ABSTRACT FROM AUTHOR]

A convolutional perfectly matched layer (CPML) is developed for three-dimensional unconditionally stable, locally one dimensional (LOD)-finite-difference time-domain (FDTD) method. The formulation of the LOD-FDTD CPML is derived and numerical results are demonstrated at different positions for different Courant Friedrich Levy numbers in the simulation domain. The method is validated numerically with FDTD-CPML. [ABSTRACT FROM AUTHOR]

Optimizations are proposed for the original frequency domain analytic field propagator (AFP) to source plane waves in a 1D/2D/3D total-field scattered-field (TF/SF) FDTD formulation. The proposed technique essentially produces no field leakage error (limited by -300 dB machine precision error) with finite sampling points dictated by temporal aliasing constraints. By taking advantage of the inherent 1D nature of a plane wave, the memory requirements for the original AFP are reduced significantly. The proposed optimized solution (O-AFP) greatly reduces the computational complexity by calculating a number of spatial fields of O(N) rather than O(N2), which then makes the technique practical enough to include fully 3D simulations. [ABSTRACT FROM AUTHOR]

Near ground radio wave propagation is examined in a tropical plantation experimentally at VHF and UHF bands. The propagation loss with forest depth is empirically analyzed using an integrated model combining both the foliage induced effect and the ground effect. Several well-known empirical foliage models are compared and analyzed. It is observed that the fitted ITU-R model taking into account the ground reflection, can provide a close approximation to the path loss in a tropical palm plantation. However, the accuracy of this model becomes poor when lateral wave dominates in the VHF band. A modification to the ITU-R model is then proposed taking into consideration the lateral wave effect. The modified model is verified using measured and found to have higher accuracy for large foliage depth in the VHF band as compared to the existing empirical foliage models. [ABSTRACT FROM AUTHOR]

Abstract-A modified hybrid uniform theory of diffraction-physical optics formulation for the analysis of the multiple diffraction caused by an array of cylinders, assuming spherical-wave incidence, is hereby presented. The solution, validated with numerical data from technical literature, is mathematically less complex and computationally more efficient—particularly for a large number of cylinders—than other existing methods, due to the fact that high-order diffraction terms (slope diffraction) are not considered, without such lack of terms barely entailing any loss in accuracy. Results can be applied in radiowave propagation analysis when multiple diffraction over rounded obstacles has to be considered. [ABSTRACT FROM AUTHOR]

A high-resolution measurement system for the characterization of the delay and angle-of-arrival properties of all significant multipath components on mobile radio channels is presented. The system uses complex impulse response data obtained from a novel 3-D tilted cross switched antenna array as input to an improved version of 3-D Unitary ESPRIT. Results from simulations and measurements show that the approach is capable of accurately characterizing the delay and angle-of-arrival characteristics of the dominant multipath components at moderate urban speeds along a trajectory in mobile propagation environments with high resolution in both azimuth and elevation. [ABSTRACT FROM PUBLISHER]

An experimental study is described on the natural propagation of UHF band radio waves in straight subterranean galleries. An extensive measurement project took place in five underground localities and, based on the experimental data, an empirical model of radio wave transmission was derived. The model was calibrated according to the measurement data and compared with the theoretical waveguide approach to propagation prediction. The presented results can be used for the practical planning of wireless communications in speleology applications and as an experimental basis for further theoretical works. [ABSTRACT FROM AUTHOR]

In this paper, we consider UHF radio wave propagation in vegetated residential environments. The attenuating effects of trees as well as those due to diffraction over the buildings are investigated. A new radio wave propagation prediction model based on the combined method of ray tracing and diffraction (CMRTD) is proposed. A row of trees is modeled as a two-dimensional (2-D) cylinder. It is then represented by an equivalent phase object (EPO); a row of buildings is replaced by an absorbing screen. The position and size of the EPO as well as the amplitude and phase distributions of the input field at the EPO are determined by ray tracing. Next the scattered field is computed by the Kirchhoff diffraction theory. Among the numerical results are those of the scattering from a row of trees with circular or elliptic canopies and the scattering from a row of trees/buildings configuration. The calculations treat both plane- and cylindrical-incident waves. By comparing the results with those obtained from the exact eigenfunction expansion method, we show that the CMRTD is an accurate and efficient method to calculate the scattering from a 2-D cylinder. Moreover, the range of the validity of using the CMRTD to model the scattering from one row of trees is determined. [ABSTRACT FROM AUTHOR]

Radiocoverage measurements in urban environments often unveil unexpected power distribution patterns. Architectural features seem to be the cause of this behavior, as demonstrated in this paper. We demonstrate that the elements of a typical building facade, such as windows, exterior doors, balconies' and railings, should be considered as significant ‘sources’ of EM radiation in several current wireless communication systems. We propose a method for modeling the influence of those scatterers in EM wave propagation. In our model, the major structural elements are represented by two sets of orthogonally arranged wedges. The uniform geometrical theory of diffraction is employed to calculate the scattering field. The simulation results show that such ‘urban’ scatterers may create a dominant propagation mode in an urban canyon. Our predictions are additionally verified by experimental measurements, performed at two different sites. Finally, the influence of roadside foliage is investigated and conclusions are drawn on the resultant field. [ABSTRACT FROM AUTHOR]

An experimental tropospheric propagation system was operated for several years on a 50-km link in Ontario. The system provided information on the amplitude and angle-of-arrival of individual signal components under anomalous propagation conditions. Modeling of the observed activity can be attempted using various techniques and the use of ray-tracing and parabolic equation approaches are considered here in the light of the experimental measurements. Emphasis is placed on the latter which is capable of accurately including the effects of the ground in the model. [ABSTRACT FROM AUTHOR]

Impulse response radiowave propagation measurements from an urban area of Denver, CO, are described. The basic transmission loss and delay spread are used to characterize the mobile communications environment. These metrics are quantified using path loss slope and delay spread statistics. By analyzing the results versus carrier frequency, the relative propagation impairments at 430, 1350, 2260, and 5750 MHz are compared. It was found that the path loss slope increased on average by 11 dB/dec and the median delay spread decreased from 0.7 to 03 μs over the decade of frequencies measured. [ABSTRACT FROM AUTHOR]

In order for ray-tracing propagation models to analyze scattering from irregular terrain, some form of preprocessing must be performed to create a linearized terrain profile to approximate the actual profile. This paper describes a preprocessing algorithm that has proven effective in working with large terrain-data files (over 2,000 points) and a 16-ray, geometric theory of diffraction propagation model. The algorithm is based upon Fermat's principle, and it enables a quantitative evaluation of how well the linearized profile created approximates the actual terrain profile in terms of its effect on propagation. The accuracy of the fit can be adjusted to achieve a balance between overall model accuracy and propagation model execution time. [ABSTRACT FROM AUTHOR]

Rain induced attenuation at 19.4 GHz over a terrestrial path link of 2.29 km was measured for the period of one year (i.e. from January to December 2001) at Amritsar (31° 36' N 74° 52' E). An empirical model for predicting rain-induced attenuation on terrestrial line of sight microwave link has been proposed in this paper. Experimentally measured results have been compared with those obtained using international radio communication union (ITU-R). It has been observed that our results differ from those predicted using ITU-R model. [ABSTRACT FROM AUTHOR]

We measured the spatial properties of the three-dimensional (3-D) double-directional. radio channel in urban macroceil environments separately at both ends of the link. In this paper, we study propagation conditions pertaining to reception and transmission at the mobile terminal, measured using a wideband channel sounder and a dual-polarized spherical antenna array. We were able to refine the results of the measurements conducted at the base station, and extend the study to full double-directional 3-D channels. Individual propagation paths could be identified precisely, in some cases even considerable scattering from lampposts was observed. Our results show that over-rooftop-dominated propagation often occurs via building roofs with LOS to the base station antenna, acting as strong secondary signal sources. Based on measurements along continuous routes we demonstrate that the dominant propagation mechanisms can vary considerably when the mobile moves in the environment. We also present typical directional properties of the 3-D radio channel at the mobile terminal in urban macroceil environments characterized by street canyons, showing how the angular distribution of energy is correlated with the excess delay. [ABSTRACT FROM AUTHOR]

Presents information on a study which proposed a ray-tracing method using a ray tube tree for a microcellular wave propagation prediction model. Types of ray tubes; Theory and formulation; Validation of the proposed ray-tracing method; Conclusions.

Presents a discussion concerning the need for three-dimensional (3-D) urban radiowave propagation models. Summary of the asymptotic path-integral technique and its previous applications; Limitations and advantages of the asymptotic path-integral technique; Discussion of the results.