Mohammad N. Abdallah

Electromagnetic Macro Modeling of Propagation in Mobile Wireless Communication: Theory and Experiment

The objective of this paper is to illustrate that an electromagnetic macro modeling can properly predict the path loss exponent in a mobile cellular wireless communication [1]. Specifically, we illustrate that the path loss exponent in a cellular wireless communication is three preceded by a slow fading region and followed by the fringe region where the path loss exponent is four. Theoretically this will be illustrated through the analysis of radiation from a vertical electric dipole situated over a horizontal imperfect ground plane as first considered by Sommerfeld in 1909 [2,3]. To start with, the exact analysis of radiation from the dipole is made using the Sommerfeld formulation. The semi-infinite integrals encountered in this formulation are evaluated using a modified saddle point method for field points moderate to far distances away from the source point to predict the appropriate path loss exponents. The reflection coefficient method can also be derived by applying a saddle point method to the semi-infinite integrals and it is shown not to provide the correct path loss exponent. The various approximations used to evaluate the Sommerfeld integrals are described for different regions [3]. It is also important to note that Sommerfelds original 1909 paper had no error in sign [1]. However, Sommerfeld overlooked the properties associated with the pole. Both accurate numerical analyses along with experimental data are provided to illustrate the above statements. Both Okumuras experimental data [4,5] and experimental data taken from different base stations in urban environments [6-8] at two different frequencies will validate the theory. Experimental data reveal that a macro modeling of the environment using an appropriate electromagnetic analysis can accurately predict the path loss exponent for the propagation of radio waves in a cellular wireless communication scenario.

Further Validation of an Electromagnetic Macro Model for Analysis of Propagation Path Loss in Cellular Networks Using Measured Driving-Test Data

Received signal level measurements are frequently used to check the performance and the quality of service (QOS) inside the coverage area in cellular networks. These expensive, time-consuming measurements are carried out using actual driving tests to assess the coverage area of a base station for a given cell, and to thus evaluate the quality of service. In a driving-test measurement system, a receiving antenna is placed on top of a vehicle. The vehicle is then driven along radial and circular lines around the base station, to measure the received power and thus assess the quality of service. These driving-test measurements are also used to tune the empirical models in the radio-planning tools that have to be employed for various types of environments. This model tuning is a lengthy procedure. In this paper, it is shown that an electromagnetic macro modeling of the environment can provide simulation results comparable to the data one would obtain in an actual driving-test measurement for a cellular environment. The input parameters for the electromagnetic macro model can be generated using only the physical parameters of the environment, such as the height of the transmitting and receiving antennas over the ground, their tilts towards the ground, and the electrical parameters of the ground. Such analysis can provide realistic plots for the received power as functions of the separation distance between the receiving and the transmitting base-station antennas. The novelty of the electromagnetic-analysis technique proposed in this paper lies in its ability to match the macro-model-based simulation results and the driving-test measurements without any statistical or empirical curve fitting or an ad hoc choice of a reference distance. In addition, a new concept, called the proper route, is introduced to enhance the analysis of the measured data. A Method-of-Moments-based integral-equation-solver code has been used to simulate the effects of the macro parameters of the environment on the propagation-path loss of the signals emanating from a base-station antenna. The perfect match between the simulation results and the driving-test data was illustrated by monitoring the signal levels from some cellular base stations in western India and Sri Lanka, and then comparing the observed results with the simulated results. The goal here is to illustrate that these numerical simulation tools can accurately predict the propagation path loss in a cellular environment without tweaking some non-physical models based on statistical modeling or heuristic assumptions.

Application of the Schelkunoff Formulation to the Sommerfeld Problem of a Vertical Electric Dipole Radiating Over an Imperfect Ground

The objective of this presentation is to illustrate the accuracy of the Schelkunoff formulation over the Sommerfeld solution for a vertical electric dipole radiating over an imperfect ground. In an earlier paper, the alternate form of the Sommerfeld Greens function developed by Schelkunoff was presented (Schelkunoff, 1943 and Dyab, 2013). Here we demonstrate the application of this new methodology for two classes of problems. First, the problem of predicting the propagation path loss in a wireless communication environment is illustrated. The second application problem described in this paper deals with the verification of experimental data related to propagation over an Aluminum sheet at THz frequencies. It is seen that the main contribution of the reflected field is due to a specular image point as expected for a metal and the presence of surface waves in the total reflected field is absent, even though the permittivity of the metal is negative at these frequencies. Both theoretical predictions and experimental data demonstrate that there is little contribution to the reflected field due to a surface wave. Also, a clear definition is made to characterize surface waves as there is confusion as to what a surface wave really is.

On the relation between Surface Plasmons and Sommerfeld's Surface Electromagnetic Waves

The term “Surface Plasmons, SP” was first coined in the middle of the twentieth century to study the interaction of plasma oscillations with the electrons on the surface of metal foils. Surface Plasmons have a wide variety of applications such as in Terahertz spectroscopy. In the literature, Surface Plasmons are frequently related to Surface Electromagnetic Waves, SEW, which were first studied by Zenneck and independently by Sommerfeld in the early 1900s. However, Zenneck and Sommerfeld surface waves are rarely examined critically in the current literature on SP. Looking for a solid understanding for the relation between SP and SEW, it was necessary to study Sommerfelds work thoroughly. The revisiting of Sommerfelds work on Surface waves led to some important conclusions which are communicated in this paper.

Green’s Function Using Schelkunoff Integrals for Horizontal Electric Dipoles Over an Imperfect Ground Plane

Recently, Schelkunoff integrals have been used to formulate a Greens function for analysis of radiation from a vertical electric dipole over an imperfect ground plane. Schelkunoff integrals were proved to be more suitable for numerical computation for large radial distances than the Sommerfeld integrals which are used conventionally to deal with antennas over an imperfect ground. This is because Schelkunoff integrals have no convergence problem on the tail of the contour of integration, especially when the fields are calculated near the boundary separating the media and for large source-receiver separations. In this paper, the Schelkunoff integrals are utilized to derive a Greens function for the case of a horizontal electric dipole radiating over an imperfect ground plane (a two-media problem where the lower medium is lossy). A detailed comparison between the presented expressions and the conventional ones based on Sommerfeld integrals is illustrated both numerically and analytically.

Predicting the starting distance of the far field

The far field of an antenna is generally considered to be the region where the outgoing wavefront is planar and the antenna radiation pattern has a polar variation and is independent of the distance from the antenna. Hence, to generate a locally plane wave in the far field the radial component of the electric field must be negligible compared to the transverse component. Also, the ratio of the electric and the magnetic far fields should equal the intrinsic impedance of the medium. These two requirements must hold in all angular directions from the antenna. The radial and the transverse components of the fields are space dependent so to determine the starting distance of the far field we need to examine the simultaneous satisfaction of these two properties for all θ and φ angular directions, where θ is the angle measured from z-axis and φ is the angle measured from the x-axis. The objective of this paper can be summarized in three points: First, this paper intends to illustrate that 2D2/λ formula, where D is the maximum dimension of the antenna and λ is the operating wavelength, is not universally valid, it is only valid for antennas where D ≫ λ. Second, this paper intends to compute a more specific constraint so instead of D ≫ λ we compute a threshold for D after which the 2D2/λ formula applies. Third, this paper intends to properly interpret D in the formula 2D2/λ when the antenna is operating over an imperfect ground plane. In this paper, we do not use 2D2/λ for antennas operating over an imperfect ground instead we use a formula which depends on the transmitting and receiving antennas heights over the air-Earth interface.

Where Does the Far Field of an Antenna Start? [Stand on Standards]

The far field of an antenna is generally considered to be the region where the outgoing wavefront is planar and the antenna radiation pattern has a polar variation and is independent of the distance from the antenna. Hence, to generate a local plane wave in the far field, the radial component of the electric field must be negligible compared to the transverse component. Also, the ratio of the electric and the magnetic far fields should equal the intrinsic impedance of the medium. These two requirements-that the radial component of the field should be negligible when compared with the transverse component and the ratio of the electric and the magnetic fields equal the intrinsic impedance of the medium-must hold in all angular directions from the antenna. So to determine the starting distance for the far field, we need to examine the simultaneous satisfaction of these two properties for all θ and φ angular directions, where θ is the angle measured from the z-axis and φ is the angle measured from the x-axis. It is widely stated in the antenna literature that the far field of an antenna operating in free space, where all the aforementioned properties must hold, starts from a distance of 2D2/Λ, where D is the maximum dimension of the antenna and Λ is the operating wavelength.

Further validation of an electromagnetic macro model for analysis of propagation path loss in cellular networks using measured drive test data

Received signal level measurements are frequently used to check the performance and the Quality of Service (QOS) coverage area in cellular networks. These expensive time consuming measurements are carried out using an actual drive tests to assess the coverage area of a base station for a given cell and thus evaluate the QOS. In this paper, the novelty of the proposed electromagnetic analysis technique lies in its ability to match the macro model based simulation and measurement results without any statistical or empirical curve fitting or an adhoc choice of a reference distance. Furthermore, a new concept called proper route has been introduced to enhance the quality of measured data. The input parameters for the electromagnetic macro model can be generated using only the physical parameters of the environment like the height of the transmitting and receiving antennas over the ground, their tilts toward the ground, and the electrical parameters of the ground. A method of moments-based integral equation solver code called AWAS has been used to simulate the effects of the macro parameters of the environment. Measurements were carried out for cellular networks in western India and Srilanka.

Smart non-uniform antenna arrays deployed above an imperfect ground lane at multiple frequencies

In this paper, it is illustrated how to carry out adaptive processing simultaneously at multiple frequencies using the same antenna array consisting of dissimilar antenna elements nonuniformly spaced and deployed above an imperfect ground plane. First, an electromagnetic transformation technique is described which can compensate for all non-ideal effects of an antenna array deployed in a real environment, such as mutual coupling between the elements, the presence of an imperfect ground, etc. Then, a direct data domain least squares method is used to extract the signal-of-interest (SOI) in the presence of jammer and clutter simultaneously at multiple frequencies, using a single snap shot of the data. The interferers/jammers can come from multiple directions, frequencies and can even be non-coherent.

An expose of Zenneck waves and surface plasmon polaritons

In this paper, the distinction between Zenneck waves and surface plasmon polaritons is illustrated. Both are evanescent waves. The surface plasmon needs to be excited by an electron beam which can be effectively generated by a source of electrons or a quasiparticle like an evanescent wave which can tunnel through the medium and thus excite the electrons. This electron wave produces its own electromagnetic wave. Hence, the surface plasmon propagates at the interface between a metal and a dielectric at petahertz frequencies when the conditions are right. The Zenneck waves are produced at the zero of the reflection coefficient of an incident TM wave on an air-dielectric interface whereas the surface wwaves related to the surface plasmons are produced when the reflection coefficient is infinite. For the Zenneck wave, the evanescent transverse field components do not change appreciably with frequency as the Brewster phenomenon occurring at the zero of the TM reflection coefficient is independent of frequency, whereas for a surface plasmon, with an increase of the frequency, the surface wave is more closely coupled to the surface.