Ground-wave Field Research Articles

Electromagnetic ground-wave propagation over the earth’s surface in the transition range

In this paper, the weighted average method is proposed for treating the ground-wave field of a vertical electric dipole over the earth’s surface in the transition range. Analysis and computations in HF/LF ranges are carried out specifically. In order to improve the computation accuracy, the weighted average method is proposed for evaluating the field component in the transition range. It is seen that the computation accuracy for the field component of the ground wave will be improved by using the weighted average method. The proposed method can be extended to the cases of the earth-ionosphere waveguide structure and the multi-layered cases.

Measurements of Vertically Polarized Electromagnetic Surface Waves Over a Calm Sea in HF Band. Comparison to Planar Earth Theories

Radio communication over Earth along mixed-paths in the HF band is a relevant subject today. In this paper, we present measurements of electric field propagating over sea water in HF Band compared to K.A. Norton, R.W.P. King and G. Millington's theories, thanks to a reliable measurement setup. The transmitting antennas are located on the coast while the receiver antenna is installed on a boat steering a constant course. The electric field measurements are carried out with a loop antenna and we measured the field strength attenuation versus distance between the transmitter and the boat along a sea water path. In order to take into account the media change (the coast and the sea water), Millington's solution has been added to King's and Norton's theories with the planar Earth model. The measurements performed at three frequencies (10 MHz, 20 MHz and 30 MHz) and the calculations are in a good agreement. At 10 MHz, the smoothly attenuation is shown and is very well correlated with the theory. The EM field decrease as 1/d² has been clearly observed at 20 MHz and 30 MHz. Keywords— HF band measurements, surface-wave propagation, ground-wave field, vertical electric dipole, planar Earth model.

LF Ground-Wave Propagation Over Irregular Terrain

Traditional methods used to predict the ground-wave field strength at low frequency are not applicable for terrains with serious irregularities because of the analytical approximations. In this paper, the two dimensional finite-difference time-domain (FDTD) algorithm is applied to calculate the field strength of the low frequency (LF) ground wave propagating over irregular terrains. The propagation characteristics are studied as functions of the mountain's gradient, height, and width, respectively. We also focus on studying the cases with multiple mountains in the path. Moreover, the error of the traditional integral equation method is analyzed by comparisons. The results show that when the mountain's gradient and height are high, additional oscillations in the field strength will appear in front of and in the mountain region due to the wave reflection and scattering. At last, measurements of the Loran-C signals are taken along a real path between Pucheng and Tongchuan in Shaanxi province, China. It is found that most of the measured and FDTD results have good agreements while some still have big errors owing to the model approximation. The FDTD method gets better precision than the integral equation method in the irregular terrain.

Electromagnetic ground-wave field of vertical antennas for communication at 1 to 30 MHz

Radio communication over the spherical surface of the Earth and sea makes use of vertical antennas in the frequency range from 1 to 30 MHz. For distances that extend beyond the approximation of a planar Earth, use must be made of the ground-wave. Following a description of antennas used on shipboard, their radiated fields are analyzed in the planar- and spherical-Earth regions. The latter involves new formulas for the field of vertical dipoles over the spherical surface of the sea.

The ancient and modern history of EM ground-wave propagation

Radio-wave transmission over the surface of the Earth is a subject of enquiry going back to the beginning of the century. In this review, an attempt is made to describe the ground-wave mechanism that is omni-present. We first call attention to the early analytical contributions of Zenneck and Sommerfeld, based on a flat-Earth model. The subsequent controversies, particularly with regard to the role of the Zenneck surface wave, are outlined. Further developments by other pioneers, such as van der Pol, Fock, Bremmer, Norton, and Millington, are reviewed, and an attempt is made to put these in a modern context. We also show that the trapped surface wave can be a significant contribution to the total ground-wave field, when the Earth boundary is sufficiently inductive. Mixed-path theory and confirming model tests by Ray King are described briefly, along with calculated propagation curves for twoand three-section paths. The bibliography includes references to related topics, such as tropospheric refraction and topographic influences.

A Coverage Prediction Model for Radio Beacon Differential Satellite Navigation Systems

Coastal radio beacon stations are now widely used to transmit corrections for differential satellite navigation systems (DSNS). The paper describes a computer model developed for predicting the stations' coverage areas: the regions in which all the key parameters of the signal, field strength, signal-to-noise ratio, and signal-to-interference ratio meet the minimum values specified for an internationally acceptable service. Each parameter is examined, and the factors that control it are elucidated. Groundwave and skywave field strengths of signals and atmospheric noise intensity are derived from International Telecommunication Union (ITU) data. The fading of the radio beacon signal at night as a result of skywave propagation is taken into account. The model also predicts the levels of interference from cochannel and adjacent-channel beacons received via groundwave and skywave propagation, which commonly limits coverage in Europe. The paper presents coverage prediction diagrams for Europe and the Middle East produced using the model.

Elevated vertical monopole antennas: effects of changes in radiator height and radial length

Computer analysis and field tests indicate that an elevated vertical monopole with elevated horizontal radials can provide ground-wave field intensities which are comparable to those generated by a conventional ground-mounted monopole with 120 buried radials. Computer modeling was used to investigate the effects of changes in monopole height and radial length on the transmitted field intensity. The tower height was varied in 45-degree increments from 45 degrees to 225 degrees as was the length of the four elevated horizontal radials. Born the direct and isolated feed methods were utilized, and elevation heights of 5 m and 10 m were modeled. The results show that 90 degrees radials generally give the strongest field strength, irrespective of the radiator height or the feed method. Isolated feed was usually somewhat better than direct feed, and an elevation height of 10 m was slightly superior to a height of 5 m in most cases. Taller towers always produced higher maximum values of electric field strength. Conventional antenna systems with various heights and radial lengths were also modeled to serve as a baseline reference. >

Compensation-theorem analyses of ground wave propagation over irregular, inhomogeneous terrains

Work during the last 40 years on various aspects of ground wave propagation is surveyed, including dipole propagation over flat homogeneous and inhomogeneous terrains, smooth homogeneous earth, and irregular homogeneous and inhomogeneous terrains. The Ott-Volterra integral equation for TM p ground wave field over irregular homogeneous paths is discussed and an occasional troublesome behavior of the modified Sommerfeld attenuation function explained. Several representations of spatially distributed transmitter current are presented. A Compensation-theorem Volterra for the ground wave over inhomogeneous terrain is derived, in the parabolic wave equation approximation. A recent Compensation-theorem integral equation for general terrain satisfying the hyperbolic wave equation is reviewed. Computations for several very rough terrains indicate the ‘parabolic’ integral equations may often be more accurate.

AM broadcast antennas with elevated radial ground systems

Results are presented of computer modeling studies indicating that an elevated vertical monopole antenna with four elevated horizontal radials produces more ground-wave field strength than does a conventional ground-mounted monopole with 120 buried radials. For the analysis, the length of the radials and the height of the monopole were set equal to 0.25 of the free-space wavelength, and the frequency of operation was fixed at 1.0 MHz. Three different sets of ground constants were used, simulating averaging, very good, and very bad soil electrical parameters in accordance with the Numerical Electrical Code (NEC-GS). >

Location Statistics of AM Broadcast Groundwave Signal Amplitudes

A location-dependent statistical distribution model for AM broadcast groundwave signal amplitudes is presented. The distribution is in the fonm of a probability density function (pdf) whose expected value is the predicted feld strength based on propagation formulas, and whose variance can be empirically derived from analysis of actual groundwave field strength measurements. The results are useful for aessing the percentage of locations at which a selected signal strength will be exceeded given the predicted signal strength and typical variance of the pdf.

A Computer Program System for Predicting AND Plotting Mediumwave Broadcast Groundwave Field Strength Contours

A computer program system and associated data bases have been developed to automate the calculation and plotting of groundwave field strength contours for mediumwave broadcast stations in the United States. The programs use the propagation curves and M3 soil-conductivity map in the FCC Rules, and produce contours suitable for engineering exhibits filled with the FCC. The programs and data bases, together with new soil conductivity data bases for Canada and Mexico, were recently implemented on the FCC computer.

Seasonal Effects on Ground-Wave propagation in Cold Regions

Abstract The ground-wave is the most important mode of propagation of radio waves in Connection with glaciology. In cold regions, special conditions are often prevalent, involving propagation over non-homogeneous earth, presence of stratified media, and low values of conductivity and dielectric constant in the upper strata. A radio wave which propagates along the Earth's surface is, however, also influenced by atmospheric refraction. As the frequency is increased, the roughness of the Earth's surface must also be taken into account. Thus seasonal variations are to be expected due to changes in the electrical and topographical properties of the ground as well as the propagation conditions in the atmosphere. It is, however, difficult to separate these various effects, a fact which reduces the possibility of using ground-wave propagation as a loot for obtaining information on the properties of the ground. Though the propagation of the ground-wave has been dealt with both theoretically and experimentally for almost a century, some of the most valuable information of major importance in cold regions has been obtained during the last ten years. New theoretical papers on propagation over stratified media offer an explanation of the amplitude and phase variations of the ground-wave field, which have been measured, as well as suggesting new methods to be tested as possible aids in solving glaciological problems. In many practical eases of ground-wave propagation in arctic regions, the formula for the ground-wave field strength can be written in a very simple way. Such a propagation model for frequencies above 30 MHz is presented in which account is taken of the Earth's curvature, the terrain irregularities, and the effect of the tropospheric refraction. This model also includes the recovery effect which occurs in propagation over mixed paths. At the higher frequencies the effect of depolarization becomes very important and sometimes overshadows field-strength variations due to the influence of the electrical properties. Finally some problems will be discussed which remain to be solved or have been given very little attention up to now.

Seasonal Effects on Ground-Wave propagation in Cold Regions

AbstractThe ground-wave is the most important mode of propagation of radio waves in Connection with glaciology. In cold regions, special conditions are often prevalent, involving propagation over non-homogeneous earth, presence of stratified media, and low values of conductivity and dielectric constant in the upper strata.A radio wave which propagates along the Earth's surface is, however, also influenced by atmospheric refraction. As the frequency is increased, the roughness of the Earth's surface must also be taken into account. Thus seasonal variations are to be expected due to changes in the electrical and topographical properties of the ground as well as the propagation conditions in the atmosphere. It is, however, difficult to separate these various effects, a fact which reduces the possibility of using ground-wave propagation as a loot for obtaining information on the properties of the ground.Though the propagation of the ground-wave has been dealt with both theoretically and experimentally for almost a century, some of the most valuable information of major importance in cold regions has been obtained during the last ten years. New theoretical papers on propagation over stratified media offer an explanation of the amplitude and phase variations of the ground-wave field, which have been measured, as well as suggesting new methods to be tested as possible aids in solving glaciological problems.In many practical eases of ground-wave propagation in arctic regions, the formula for the ground-wave field strength can be written in a very simple way. Such a propagation model for frequencies above 30 MHz is presented in which account is taken of the Earth's curvature, the terrain irregularities, and the effect of the tropospheric refraction. This model also includes the recovery effect which occurs in propagation over mixed paths. At the higher frequencies the effect of depolarization becomes very important and sometimes overshadows field-strength variations due to the influence of the electrical properties. Finally some problems will be discussed which remain to be solved or have been given very little attention up to now.

Height‐gain experimental data for groundwave propagation: 2, Heterogeneous paths

Analytical as well as experimental height‐gain studies for mixed‐path groundwave propagation are virtually nonexistent. Therefore, it was shown how the theoretical height‐gain for a homogeneous path relates to heterogeneous‐path experimental measurements versus height and distance. The results show that the magnitude of a groundwave field which crosses an abrupt boundary rapidly acquires the characteristic properties of the second medium, and the field over a heterogeneous surface attenuates at essentially the same rate as the field on the surface. The groundwave which has crossed an abrupt boundary can be predicted for small heights above the surface by simply multiplying the well‐established mixed‐path theory for antennas located on the surface by appropriate homogeneous‐path height‐gain factors corresponding to the local surface impedance, provided the field is predominantly a surface wave.

Terrain Influences on Effective Ground Conductivity

Measurements of the ground wave field intensity were made along radial paths from a low-frequency transmitter in Rapid City, S. Dak. Ground wave attenuation curves for different conductivities are compared with the measured data. Millington's mixed path theory for path segments with different conductivities is then applied to obtain a ground conductivity map. Effects of topological features such as hills, ridges, and rivers, and variations in ground moisture and temperature are discussed. Hills and ridges are described along each radial path for the purpose of indicating the influence of terrain irregularities. The conductivity variations have an impact on radio station coverage which is described for a low-frequency range station.

Design and Performance Measurements on a New Anti-Fade Antenna for Radio Station WOAI

A new anti-fade type radiator for Station WOAI is described. Vertical radiation patterns are presented on the basis of computations from predicted current distributions. Measurements on a model antenna generally confirm the performance predicted by the computations. Skywave measurements using pulse techniques were made on the full scale antenna to determine the optimum tuning and the suppression of skywave signals. These measurements show skywave signals transmitted by both the E and F layers of the ionosphere. Final performance data are presented, including current distribution measurements, the vertical radiation pattern and groundwave field intensity measurements.

The effect of the ground constants, and of an earth system, on the performance of a vertical medium-wave aerial

The compensation theorem is used to determine the effect of finite ground conductivity, and of an earth system, on the performance of a vertical aerial, such as is used for medium-frequency broadcasting.The characteristics affected are the input impedance, the ground-wave field strength for a given aerial current and the vertical radiation pattern. The first two of these together determine the efficiency, which is the most important consideration in the design of earth systems. When the effective height of the aerial exceeds 0.1λ, little can be gained by the use of an earth system exceeding 0.2λ in radius when the ground is highly conducting and 0.3 or 0.4λ when it is poorly conducting. The effect of the earth system on the vertical radiation pattern is shown to be unimportant practically, but results are given for one case in order to compare with experimental radiation patterns. The agreement is quite good.

Calculation of Ground-Wave Field Strength over a Composite Land and Sea Path

A brief discussion of the problem is given, together with a description of the three proposed methods of solution. The results of a practical experiment are shown, and curves calculated by the three methods are compared with the observed results. It is shown that the BBC method gives field strengths much nearer to the observed values than the P. P. Eckersley method, and that the method proposed by Millington, while somewhat more laborious to use, also gives results which agree well with observed values. The difference between the three methods is small at low frequencies and when the effect of the discontinuity is not large.

Correction [to "The calculation of ground-wave field intensity over a finitely conducting spherical earth," by K.A. Norton, ibid., Dec 1941

Correction [to "The calculation of ground-wave field intensity over a finitely conducting spherical earth," by K.A. Norton, ibid., Dec 1941

The Calculation of Ground-Wave Field Intensity over a Finitely Conducting Spherical Earth

Equations and curves are presented which simplify the calculation of ground-wave field intensity over a finitely conducting spherical earth for transmitting and receiving antennas of arbitrary heights and polarization.