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An experimental investigation to characterize the transient and spectral behavior of the ultrawideband (UWB) on-body radio propagation channel for body-centric wireless communications is presented. The measurements were performed considering over thirty on-body links in the front of human body in the anechoic chamber, and in indoor environment. Two different pairs of planar antennas have been used, namely, CPW-fed planar inverted cone antennas (PICA), and miniaturized CPW-fed tapered slot antennas (TSA). A path loss model is extracted from measured data, and a statistical study is performed on the time delay parameters. The goodness of different statistical models in fitting the root mean square (RMS) delay has been evaluated. Results demonstrate that the TSA, due to its more directive radiation behavior is less affected from the reflections from body parts and surrounding environment. The antenna shows significant size reduction and improved time delay behavior, and hence is an ideal candidate for UWB body area networks (BAN). [ABSTRACT FROM AUTHOR]

This paper presents a systematic measurement campaign of diversity reception techniques for use in multiple-antenna wearable systems operating at 868 MHz. The experiments were performed using six time-synchronized bodyworn receivers and considered mobile off-body communications in an anechoic chamber, open office area and a hallway. The cross-correlation coefficient between the signal fading measured by bodyworn receivers was dependent upon the local environment and typically below 0.7. All received signal envelopes were combined in post-processing to study the potential benefits of implementing receiver diversity based upon selection combination, equal-gain and maximal-ratio combining. It is shown that, in an open office area, the 5.7 dB diversity gain obtained using a dual-branch bodyworn maximal-ratio diversity system may be further improved to 11.1 dB if a six-branch system was used. Firstand second-order theoretical equations for diversity reception techniques operating in Nakagami fading conditions were used to model the postdetection combined envelopes. Maximum likelihood estimates of the Nakagami-m parameter suggest that the fading conditions encountered in this study were generally less severe than Rayleigh. The paper also describes an algorithm that may be used to simulate the measured output of an M-branch diversity combiner operating in independent and identically-distributed Nakagami fading environments. [ABSTRACT FROM AUTHOR]

The theory of propagating waves near a surface is reviewed with an eye to gain insight into the mechanisms involved, and to provide analytical-based models, for power-efficient on-body propagation. The Zenneck wave, and in particular the Norton wave, are appraised as candidate mechanisms for the propagation. For flush-mounted ("band aid") antennas, desired for on-body sensors, the Norton wave is the only direct propagation mechanism between the sensors. The Norton wave fits very well to simulation results presented here, and comparisons are also made with available published physical experiments, although these measurements typically feature the optical paths of elevated, or non-flush, antennas. [ABSTRACT FROM AUTHOR]

Large bandwidth microwave signals propagating in dispersive media can result in pulses decaying according to a nonexponential law. In particular, large bandwidth signals in the microwave band, propagating in media that can be described by the Debye model (for example fresh water), decays as the square root of the inverse of the propagation distance, instead of exponentially. Although it is a direct consequence of well-known theory of propagation in dispersive media, this result is a bit surprising and its experimental evidence has required a careful set-up. [ABSTRACT FROM AUTHOR]

In a dispersive medium, the appearance of the steady-state part of the signal is preceded by oscillations known as precursors. These early oscillations are the product of the interrelated effects of phase dispersion and frequency dependent attenuation. Inside water, the attenuation rate of the Brillouin precursor is sub-exponential, following the inverse square-root of the distance traveled. Based on that, a near-optimal pulse that could achieve this attenuation rate, and, hence, would lend itself to underwater detection and communication applications, was recently proposed. The "optimality" of this pulse is shown to be related to the temporal support of the pulse and its spectral characteristics, rather than its shape. A family of alternative pulses is found to have the low attenuation feature of the "optimal" pulse, as they eventually evolve into the Brillouin precursor itself shortly after they enter water. In addition, this work considers the practical case when such a pulse would be generated in air, would impinge onto an air-water interface and then propagate inside water. It is shown how the presence of the interface affects the attenuation rate of the pulse inside water and a simple way to recover its low attenuation rate is suggested. The finite-difference time-domain technique is employed in all the simulations. [ABSTRACT FROM AUTHOR]

A high-frequency field prediction model, useful to evaluate the radio wave propagation in realistic tunnels having rectangular cross-section, is presented. The model is based on a hybrid implicit/explicit finite-difference numerical scheme adopted to solve the vector parabolic equation (VPE) governing the electromagnetic field propagation in straight and curved tunnels. To model the materials forming the tunnel walls, mixed Dirichlet-Von Neumann boundary conditions are employed. In this way, all the relevant field propagation processes are properly taken into account. To show the feasibility of the proposed numerical method, results concerning the spatial distribution of the electromagnetic field and the power flux in straight and curved rectangular tunnels are provided. An analysis concerning the convergence properties of the proposed numerical scheme is also reported. [ABSTRACT FROM AUTHOR]

An extensive review of the statistical characterization of 60-GHz indoor radio channels is provided from a large number of published measurement and modeling results. First, the most prominent driver applications for 60 GHz are considered in order to identify those environment types that need to be characterized most urgently. Large-scale fading is addressed yielding path-loss parameter values for a generic 60-GHz indoor channel model as well as for the office environment in particular. In addition, the small-scale channel behavior is reviewed including the modeling of time-of-arrival and angle-of-arrival details and statistical parameters related to delay spread, angular spread and Doppler spread. Finally, some research directions for future channel characterization are given. [ABSTRACT FROM AUTHOR]

In order to get the information about multipath propagation, this communication presents two estimation methods for slowly varying fading coefficients. With known numbers of the far-field sources and multipaths from each far-field source, the fading coefficients in multipath propagation can be well estimated. The methods not only have low complexity but also have high performance, and the fading coefficients can be resolved directly without a searching procedure. Afterwards, we make an extension to further improve the estimation accuracy of both direction of arrival (DOA) and fading coefficients after obtaining their estimations. The Cramer-Rao bound (CRB) for this problem is also deduced. Simulation results demonstrate the effectiveness and efficiency of the proposed methods. [ABSTRACT FROM AUTHOR]

We investigate analytically the fully polarimetric electromagnetic wave propagation through a 3-D layered structure. In the framework of the first-order limit of the perturbation theory, a transmission model for a layered structure with an arbitrary number of rough interfaces is developed and an elegant closed-form solution is obtained. The final expressions, in terms of generalized reflection/transmission coefficients, provide parametrically a direct characterization of the scattering properties of the layered structure in terms of the structure's (geometric and electromagnetic) parameters. In addition, we point out the complementary character of the obtained scattering solution with respect to the existing one. Finally, we demonstrate that our solution satisfied the reciprocity principle. [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]

A fundamental step in ultrawideband (UWB) communication system design involves the characterization of the indoor propagation channel. In this paper, we show that the UWB propagation channel parameters can be accurately predicted by employing ray tracing (RT) simulation carried out at various frequencies over the signal bandwidth. It is important to note that the determination of the rays reaching a given location is made only once, as the RT algorithm is independent of frequency. A parallel ray approximation (PRA) is used to significantly improve the computational efficiency of the RT based method. Moreover the accuracy of the approximation is verified through a measurement campaign. [ABSTRACT FROM AUTHOR]

A wideband directional measurement campaign was managed inside an arched highway tunnel to analyze the radio propagation channel inside such tunnel for future cellular systems in terms of coverage, delay spread and dominant scatterers. Measurements were performed in 3 rounds with different transmitter positions. Using a wideband channel sounder equipped with a cylindrical dual polarized array at the receiver, the spatio-temporal characteristics of the received propagation paths could be estimated by means of a super-resolution estimation algorithm. The extracted paths using this super-resolution algorithm constitute 88% of the total received power. It was also observed that the line-of-sight component (53%) plus single-bounce scattering (26%) comprise up to 79% of the total received power. In other words, more than 90% (i.e. 79% in 88%) of the extracted paths consists of the line-of-sight component and single-bounce scatterings. The strong contribution from single-bounce scattering paths causes the path gain exponent along the tunnel to be larger than -2 which is the value for free space. This validates that there is wave guiding effect in the tunnel and coverage is extended relative to open space. The rms delay spreads are generally less than 20 ns and increase when influenced by scattering objects such as jetfans. The dominant scatterers are identified and classified into 6 classes based on the structure of the tunnel and existing objects such as ground, wall, light-frame, ceiling, jetfan and cleaner-parking. It was observed that scattering from ground was dominant among all classified scatterers in all scenarios. [ABSTRACT FROM AUTHOR]

We examine two spurious numerical artifacts of the complex envelope (CE) alternating-direction-implicitfinite-difference time-domain (ADI-FDTD) method, viz, spurious charges and anomalous wave propagation (modes with positive phase velocity and negative group velocity). These artifacts are also present in the conventional ADI-FDTD; however, the spurious charges in CE-ADI-FDTD have a fundamental distinction from those of ADI-FDTD: they are static in ADI-FDTD and implicitly time-harmonic in CE-ADI-FDTD. Spurious charges are particularly detrimental to CE-ADI-FDTD simulations because they produce secondary radiation. We also show that spurious charges can be reduced by a fixed-point iterative correction in CE-ADI-FDTD. [ABSTRACT FROM AUTHOR]

In this paper, a 4 × 4 indoor multiple-input multiple-output (MIMO) measurement campaign at a frequency of 2.45 GHz is presented. The main contribution of this work is the analysis of the impact of radio-wave polarization in MIMO systems operating at a typical indoor scenario through the calculation—from the measurements carried out-of a great deal of parameters such as the mean path loss, the cross polarization discrimination (XPD), and the RMS delay spread, which are all essential to estimate the performance of real MIMO systems. In this sense, some path loss models—which have been adjusted according to the measurements-are given, taking into account polarization, attenuation through walls, and the effect of T-junctions existing in the considered indoor scenario. Moreover, additional parameters such as the K-factor and statistical distribution, as well as spatial parameters, are discussed. [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]

A model is presented that extends the applicability of the propagation data collected during a long measurements campaign in a particular site and for a particular radiolink, to a generic link in a generic site. In fact, the objective of the model is to create a set of attenuation time series to be used in the design of advanced TLC systems. The model assumes that the marked differences of the rain statistics observed in various locations are, in first approximation, mainly due to the different frequency of occurrence of the various rainy events rather than to their shape. Starting from this assumption the model selects, from a large database of rain attenuation events collected in a particular site, a subset that, after an appropriate frequency and elevation scaling, can be used to represent time series of attenuation recorded in other experimental conditions (as for both site and link). The model has been applied to the attenuation data collected at Spino d'Adda (Milan, Italy) during the ITALSAT propagation campaign in order to simulate attenuation time series in several different links and sites. The model demonstrated good performance both in link conditions and climates, similar and different from the Spino d'Adda ones. [ABSTRACT FROM AUTHOR]

We study the proximity effects of metallic environments on the performance of high frequency (HF) radio frequency identification (RFID) reader antenna operating at 13.56 MHz. The performance of a typical HF REID reader loop antenna in the proximity of various metal plate configurations is experimentally investigated in terms of resonant frequency, field intensity, and field distribution. The study shows that the presence of the metal plates shifts up the resonant frequency of the antenna and weakens its field intensity. The proximity effects are strongly dependent on the size of the metal plate, distance between the plate and the antenna as well as the orientation of the plate. Such effects greatly degrade the reading range and restrict the co-existence of HF RFID systems. A solution to alleviate the effects is to re-tune or co-design the reader antenna in proximity with the metallic objects based on the information from the study. As an example, a loop antenna is co-designed with a metal plate to configure a metal-backed loop antenna, and optimized for an RFID smart shelf system to restrain the interference and enhance the detection accuracy. [ABSTRACT FROM AUTHOR]

Higher order symmetrical moments play an important role in wave propagation and scattering in random media, however it remains to be solved under strong fluctuations. In this paper, a modified Gaussian solution method is proposed for analytically solving the n-nth moment. After propagating through a random medium in the fully saturated regime, the higher order symmetrical moment of the received wave is the sum of products of the second moments, i.e., the Gaussian solution. In strong scattering regimes, the higher order symmetrical moment can be considered as a sum of the Gaussian solution and a non-Gaussian correction term, where the key issue is how to solve the derived equation of the correction term. Two methods are proposed, i.e., Green's function method and the Rytov approximation approach. Green's function method leads to a rigorous solution form, but it is complicated due to an integral equation. The approach using the Rytov approximation is found to be reasonable, as the correction is relatively small. [ABSTRACT FROM AUTHOR]

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]

The multiresolution frequency domain parflow (MR-FDPF) approach is applied to radio wave propagation in indoor environments. This method allows for a better understanding of indoor propagation and hence greatly assists the development of WiFi-like network planning tools. The efficiency of such wireless design tools is strongly impacted by the quality of the coverage predictions which have to be estimated with a limited computational load. The usual approaches are based either on an empirical modeling relying on measurement campaigns or on geometrical optics leading to ray-tracing. While the former approach suffers from a lack of accuracy, the later one needs to balance accuracy with computational load requirements. The new approach proposed herein is based on a finite difference formalism, i.e., the transmission line matrix (TLM). Once the problem is developed in the frequency domain, the linear system thus obtained is solved in two steps: a pre-processing step which consists of an adaptive MR (multigrid) pre-conditioning and a propagation step. The first step computes a MR data structure represented as a binary tree. In the second step the coverage of a point source is obtained by up-and-down propagating through the binary tree. This approach provides an exact solution for the linear system whilst significantly reducing the computational complexity when compared with the time do- main approach. [ABSTRACT FROM AUTHOR]

A modified pseudocovariance matrix is described which can improve the performance of Kim et al.'s (‘Fast DOA estimation algorithm using pseudocovariance matrix’ IEEE Trans. Antennas Propagat., vol. 53, no. 4, pp. 1346–1351, Apr. 2005) algorithm to realize the fast direction finding with single snapshot in coherent or uncorrelated case. By adding the backwards formulation of pseudocovariance matrix, the rank of pseudocovariance matrix is enhanced. Then a set of pseudocovariance matrices are constructed by circularly shifting the matrix. By weighted averaging, a modified pseudocovariance matrix is reconstructed whose noise is reduced. The proposed matrix has less array element loss than that of the original matrix. Moreover, this algorithm can be applied in the lower signal-noise-ratio (SNR) through noise preprocessing. The new matrix has expanded the application of high-resolution direction finding to nonuniform linear array (NLA), since traditional methods usually assume the array is uniform linear when handling coherent sources. Simulations are conducted to compare the performance of the modified method and the original method. The results illustrate that the high performance of DOA estimate could be obtained rapidly. [ABSTRACT FROM AUTHOR]

The results of signal strength measurements and ray tracing model calculations of indoor propagation at 900 and 1800 MHz are presented. Corridors are being illuminated by ceiling mounted 2 dB gain omni antennas. The objectives of these experiments are to study behavior of the received signal strength at 900 and 1800 MHz in comparison of cell coverage, signal attenuation and variation through the line of sight (LOS) and non line of sight (NLOS) orientation of halls. It is shown that large fluctuations occur between average signal levels in LOS and NLOS case of propagation. It is also obtained that ray tracing model neglecting diffraction effects work better for LOS then NLOS, and requires detailed database information for better prediction. [ABSTRACT FROM AUTHOR]

The design of a novel ultrawideband printed-circuit antenna is presented. By using a stepped-patch in combination with multiple resonating elements, a bandwidth of more than 150% is obtained. The performance is demonstrated through measurements and calculations with a commercially available field solver. A phase center analysis shows very small variations over the entire available bandwidth. [ABSTRACT FROM AUTHOR]

Planar grating diffraction analysis based on Legendre expansion of electromagnetic fields is reported. In contrast to conventional RCWA in which the solution is obtained using state variables representation of the coupled wave amplitudes; here, the solution is expanded in terms of Legendre polynomials. This approach, without facing the problem of numerical instability and inevitable round off errors, yields well-behaved algebraic equations for deriving diffraction efficiencies, and can be employed for analysis of different types of gratings. Thanks to the recursive properties of Legendre polynomials, for longitudinally inhomogeneous gratings, wherein differential equations with non-constant coefficients are encountered, it can also be used to analyze the whole structure at one stroke. Although this is the only case for which the presented approach is efficient from both aspects of stability and computation load, the presented approach is applied to different test cases, and justified by comparison of the results to those obtained using previously reported methods. The method is general, and can handle many different cases like thick gratings, non-Bragg incidence, and cases in which higher diffracted orders or evanescent orders corresponding to real eigenvalues, have to be included in the solution of the Maxwell's equations. In deriving the formulation, a rigorous approach is followed. [ABSTRACT FROM AUTHOR]

Complex coordinate transformations are introduced for the analysis of time-harmonic electromagnetic wave propagation in perfectly matched double negative layers. The layer is perfectly matched to free space in the sense that any incident plane wave is transmitted through the free space-material interface without reflection, irrespective of the frequency and angle of incidence of the plane wave. The material constitutive parameters are obtained by mapping spatial coordinates into a manifold in complex space. The layer turns out to be anisotropic in general, and the special case where the medium is isotropic can be deduced from the coordinate transformations. The left-handedness, as well as the reversal in phase velocity appear naturally as a result of the mapping of the spatial coordinates into complex space. The consequences of this analysis are demonstrated by some examples. [ABSTRACT FROM AUTHOR]

Antennas based on the Soret and folded zone plates are analyzed using the body-of-revolution finite-difference time-domain method. Parametric studies of the focusing performance of these antennas are performed by varying the number of zones, the focal length, and the diameter of the zone plate. The results of the studies provide insight into the factors that influence the performance of these zone plate antennas and are used to generate accurate design graphs. The full analysis is validated by comparison with previously measured data for an integrated-circuit zone plate antenna. [ABSTRACT FROM AUTHOR]

Open-sleeve dipoles are versatile antennas primarily because they have several design parameters that can be varied to achieve a wide range of VSWR performance and operating bandwidth. By properly adjusting their parameters, it is possible to create versions of these antennas that have either a broadband or a dual-band response. In this paper, a new variation of the conventional open-sleeve dipole antenna is introduced, which we call an end-loaded planar open-sleeve dipole (ELPOSD). This configuration provides a degree of miniaturization while retaining a comparable bandwidth in terms of the VSWR response to that of conventional open-sleeve dipoles. Several designs are presented for the conventional and end-loaded configurations that demonstrate the VSWR and miniaturization capabilities of this class of antennas. Measured results have been compared with simulations and found to be in good agreement for an end-loaded planar open-sleeve monopole. [ABSTRACT FROM AUTHOR]

A circular Fresnel zone plate antenna was simulated using a finite difference time domain software to study the effect of changing the reference phase from the standard 0° to any value between 0° and 180% Several prototypes were built to validate the simulations using four different focal-length-to-diameter (F/D) ratios. It was found that a significant improvement in the level of the first sidelobe, up to about 9 dB according to the simulations, could be achieved without sacrificing gain or cross-polarization levels. [ABSTRACT FROM AUTHOR]

A new half-hemispherical dielectric resonator antenna (h-HDRA) is proposed and a two-element h-HDRA configuration is employed to design a broadband monopole-type radiator. Two half sections of a hemispherical DRA are employed to enhance the impedance bandwidth by introducing an additional resonant mode. Since the new geometry of an h-HDRA is studied here for the first time, it is characterized using simulation and experimental studies. Two closely spaced resonant modes, which in a two-element h-HDRA generate monopole-type radiation are investigated. Results for both the single and two-element h-HDRAs are presented. As much as 35% impedance bandwidth (S11 < -10 dB) with more than 5 dBi peak gain, 99.08% efficiency and monopole-type radiation pattern has been demonstrated using a prototype occupying a compact volume measuring 0.48λ0 by 0.2λ0 approximately, λ0 being the wave length corresponding to the center of the impedance bandwidth. [ABSTRACT FROM AUTHOR]

The article presents the authors of the papers published in the IEEE Transactions on Antennas and Propagation journal which were awarded with the 2006 H. A. Wheeler Applications Prize Paper Award. The first study named as the best applications were written by Keyoor Gosalia, Mark S. Humayun and Gianluca Lazzi. Furthermore, the second paper was authored by Benôit Fourestié, Jean-Charles Bolomey, Thierry Sarrebourse, Zwi Altman and Joe Wiart.

In a progressive propagation prediction model, significant time is saved by interrupting the process when specific application related constraints have been met. Such limitations have to do with the statistics of intermediate results as well as their spatial arrangement in the area of interest. We propose a time-efficient method to control the topological distribution of intermediate predictions. The proposed criterion allows different priorities to be set in different regions of the study area. In addition, we put forward two progressive strategies capable of adjusting the ray-tracing engine to the desired prioritization. The advantages of the proposed strategies compared with existing approaches are well demonstrated. [ABSTRACT FROM AUTHOR]

This paper presents a ray-tube tracing method to simulate waves propagating in curved road tunnels from base stations for mobile communications. Ray tubes are traced by including multiple reflections in the curved tunnels and diffractions from wedges of the tunnel structures, together with the direct path. To verify this ray-tube tracing approach, field measurements of 900 MHz signals in two curved road tunnels from GSM base stations were performed for comparisons with the ray-tube tracing simulations. By tracing ray tubes reflected and diffracted from the curved structures of the tunnels, the effects of the curvature on wave propagations in large guiding structures can be evaluated. Good agreement between simulations and measurements has been obtained. A parametric study of the influence of the tunnel geometry and the signal frequency on the path loss is also presented by applying this ray-tube tracing method. Curved tunnels for different radii of curvature in the tunnel cross-section and horizontal plane and also lengths of the curved part are compared, together with rectangular tunnels. Simulations of the field distribution over the cross-section of the curved tunnel away from the transmitting antenna are demonstrated as well. The ray-tube tracing program can be applied to determine the deployment of the base-station antennas for improving signal coverage in tunnels, which may have curved structures. [ABSTRACT FROM AUTHOR]

We study models for propagation in circular tunnels. The excitation is a fundamental electric current source. We produce expressions for the fields in terms of a Fourier transform over the axial variable. We perform an asymptotic analysis of the complex wavenumbers for use as initial estimates in a complex root finder. We then produce the modes in the lossy structure by contour integration techniques. We include numerical results for the field intensity as a function of axial distance for several frequencies and constitutive parameters of interest. We comment in particular concerning the modal content and the specific form of the field both near to and far from the antenna source. [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]

This study investigates in detail the left-handed (LH) properties of the two-layer microstrip line, periodically loaded with broadside-coupled split ring resonators (BC-SRRs) and vias. The mechanism of the left-handed microstrip line (LHML), which includes the diamagnetic response, the backward-wave propagation and the proportionality of the guided wavelength on frequency, is discussed in terms of the field and current distributions and the dispersion diagram. To examine the resonance of the BC-SRR, both the full-wave eigenmode analysis and the closed-form formula based on the quasistatic approach are developed. The effects of the BC-SRR shape on the resonant frequency are evaluated. To facilitate the computer-aided-design (CAD) applications of the LHML, the equivalent-circuit model, which comprises the three-conductor coupled microstrip line for the coupling section, the series LC for the BC-SRR, and the shunt inductance for the via, is established. Good agreement among the results of the full-wave simulation, equivalent-circuit model, published data, and measurement supports the usefulness of the proposed modeling methodology and also validates the analytical expressions. The application of the LHML in the microstrip rectangular loop antenna fed by the conductor-backed coplanar waveguide-to-conductor-backed coplanar stripline (CBCPW-to-CBCPS) transition is presented to highlight the unique features of the LHML. Compared with the conventional loop antenna, the LHML-loaded loop antenna achieves a 50% area reduction and the 52° of main beam steering. [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]

We investigate several sampling strategies in performing model-based parameter estimation based on the rational function model. They are: i) uniform-like sampling; ii) random sampling; and iii) sampling based on the Fisher information theory. The sampling strategies are implemented for the calculation of the input impedance of an antenna over a broad frequency range. The model parameters of the rational functions are found by the Cauchy method. The results are evaluated against the optimal sampling solution obtained by a genetic algorithm search. [ABSTRACT FROM AUTHOR]

The cause for the changes in polarization state of microwave signals is searched after physical properties of the channel of propagation and their variations in accordance with atmospheric state. The characteristics of the air, as propagation medium, are determined by the content, concentration and physical properties of the suspended particulates; especially it is noticeable in the surface layer over the areas with high levels of aerosol concentration and humidity (urban, semi-arid, highways, etc.). The interaction between aerial water and solid particulates leads to the appearance of increased amounts of enlarged grains with changed dielectric permittivity ...g, which value depends on the water fraction in the grain, particularly in the centimeter wave range. The formation of less or more dense volumes with various ...g entails displacement of the transmitted signal, while wind exerts control over the distribution of such irregularities in the air. Fairly high correlation (with coefficients IρI > 0.45) between temperature, humidity, concentration of suspended particles and winds, and the power Pr and cross-polarization discrimination (XPD) characteristics (XPD and 5) of microwave signals was observed under moderate weather conditions. During a quiet 24-h cycle the mean level of Pr and XPD changes in ∼ 10% and 30%, correspondently; fastest variations in depolarization degree are obtained close to sunset and after sunrise, when the large gradients of meteorological parameters and maximum instability of air streams take place. Seasonal fluctuations of Pr and XPD are registered, too. [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]

A deterministic model for propagation in outdoor urban environments based on the Fresnel-Kirchhoff integral is presented. Both two-dimensional (2-D) and three-dimensional (3-D) formulations considering reflection and diffraction are given. The theoretical predictions are compared with 2-D and 3-D measurements and good agreement is achieved. The 3-D experiments, conducted in an anechoic chamber with scaled models representing buildings, are described in detail and provide a benchmark for comparisons with other methods. [ABSTRACT FROM AUTHOR]

The problem of near-earth wave propagation in the presence of a dielectric layer such as a vegetation or snow covering is considered in this paper by modeling the propagation environment as a homogeneous two-layer medium (air/dielectric/ground). A number of studies have demonstrated the relevancy of the lateral wave for the case when both the transmitter and receiver are located within a simple half-space dielectric medium [1]-[6]. Unfortunately, for the generalized two-layer model, for configurations in which the transmitter or receiver (or both) is located above the dielectric layer, far-field analytical expressions that include all propagation features do not exist. In this paper, in order to arrive at a computational efficient solution for the two-layer model, a second-order asymptotic evaluation for the electric fields of an arbitrarily oriented, infinitesimal electric dipole-for source and observation points located in the vicinity of the air/dielectric interface-is carried out through the method of steepest descents. The formulations are valid in the far field, with the limitation that the exponentially decaying pole and branch cut contributions have been ignored. It is observed that the Norton wave, though it is highly localized near the air/dielectric interface, is a significant contribution either when the dipole and observation points are both located above the dielectric layer or when one is above and the other is within the layer. [ABSTRACT FROM AUTHOR]

For terrestrial radio wave propagation, it has been previously demonstrated that second order effects, such as diffraction, can be estimated through a combination of geometric optics and Kirchhoff style integral relations. In the present paper, it is shown that the approach can also yield accurate estimates when refractive effects, such as atmospheric ducting, are present. [ABSTRACT FROM AUTHOR]

The accuracy of most widely used empirical models are investigated using the spectrally accelerated forward-backward (FBSA) method as a benchmark solution. First, FBSA results are obtained for propagation over large scale terrain profiles and compared with measurements to assess the accuracy of FBSA. Then, accuracy of some International Telecommunication Union (ITU) and Federal Communications Commission (FCC) propagation models are investigated. It has been observed that, for rural areas, the prediction of the most recent ITU recommended propagation model (Rec. 1546) deviates much more than older models do. [ABSTRACT FROM AUTHOR]

A new methodology that facilitates the control of the inherent dispersion error in the case of higher order finite-difference time-domain (FDTD) schemes is presented in this paper. The basic idea is to define suitable algebraic expressions that reflect numerical inaccuracies reliably. Then, finite-difference operators are determined via the minimization of the error estimators at selected frequencies. In order to apply this procedure, an error expansion in terms of cylindrical harmonic functions is performed, which also enables accuracy enhancement for all propagation angles. The design process produces a set of two-dimensional (2-D) FDTD algorithms with optimized frequency response. Contrary to conventional methodologies, the proposed techniques adjust their reliability range according to the requirements of the examined problem and can be, therefore, more efficient in computationally demanding simulations. [ABSTRACT FROM AUTHOR]

Multiantenna systems. such as devices for multiple-input-multiple-output (MIMO) communication can theoretically use array superdirectivity to optimally exploit the propagation channel. In traditional analyses of MIMO systems, such superdirectivity is not observed due to the commonly applied constraint that limits the excitation current magnitudes. However, when an electromagnetically appropriate constraint on the power radiated by the array is applied, the computed capacity can include effects of transmit superdirectivity. A similar result occurs at the receiver for spatially colored noise. This paper formulates the MIMO system capacity under these circumstances and provides a framework for computing this capacity when the level of tolerable superdirectivity (as measured by the superdirectivity Q factor) is constrained. Example computations using the framework illustrate the impact that superdirectivity can have on achievable MIMO system performance. [ABSTRACT FROM AUTHOR]

In this paper, the quasicrystalline model and the differential evolution strategy are applied to analyze the effective electromagnetic properties of composite materials with aligned nonspherical inclusions. The relationship between the effective wave number, volume concentration, direction of wave propagation vector, and aspect ratio of the inclusion particle are numerically studied. It is found that composite materials with small inclusion particles behave like uniaxial material. In addition, we observed general effective anisotropy in composite materials with larger inclusion particles. [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]

This paper presents an extension of the recently developed finite-difference time-domain (FDTD) technique for modeling electromagnetic wave interactions with bianisotropic (BI) media, known as BI-FDTD, to include the more general class of bianisotropic materials. This new FDTD formulation is called BA-FDTD. The theoretical foundation for this method is based on a wave field decomposition technique. The formulations based on the application of this wave field decomposition technique to BA media will be presented. Validations of this new model are demonstrated for the interaction of an electromagnetic wave propagating transversely through a uniaxial BA half-space. [ABSTRACT FROM AUTHOR]

Ray tracing models are known to yield accurate results if a sufficient number of terms (e.g. diffraction mechanisms) are accounted for in the asymptotic formulation. For wireless applications one desires a ray analysis in which the fewest number of terms are retained, to obtain accurate and computationally efficient results. When retaining a subset of scattering mechanisms in a ray solution, validation is desirable via a rigorous numerical model. In the work presented here the multilevel fast-multipole algorithm is used to validate ray-tracing models for complex environments, including forest-like media. [ABSTRACT FROM AUTHOR]