# Chapter 14: Electromagnetic Wave Propagation – Tomasi Review

(Last Updated On: March 17, 2020) This is the summary notes of the important terms and concepts in Chapter 14 of the book "Electronic Communications System" by Wayne Tomasi. The notes are properly synchronized and concise for much better understanding of the book. Make sure to familiarize this review notes to increase the chance of passing the ECE Board Exam.

 CHAPTER 14 ELECTROMAGNETIC WAVE PROPAGATION

 Items Definitions Terms 1 Propagation of electromagnetic waves often called radio-frequency (RF) propagation or simply radio propagation. Free-space 2 Electrical energy that has escaped into free space. Electromagnetic wave 3 The orientation of the electric field vector in respect to the surface of the Earth. Polarization 4 Polarization remains constant Linear Polarization 5 Forms of Linear polarization Horizontal Polarization and Vertical Polarization 6 Polarization vector rotates 360◦ as the wave moves one wave-length through the space and the field strength is equal at all angles of polarization. Circular Polarization 7 Field strength varies with changes in polarization. Elliptical Polarization 8 Used to show the relative direction of electromagnetic wave propagation. Rays 9 Formed when two points of equal phase on rays propagated from the same source are joined together. Wavefront 10 A single location from which rays propagate equally in all directions. Point source 11 Invisible force field produced by a magnet, such as a conductor when current is flowing through. Magnetic Field 12 Strength of a magnetic field (H) produced around a conductor is expressed mathematically as: H = 1/2πd 13 Invisible force fields produced by a difference in voltage potential between two conductors. Electric fields 14 Electric filed strength (E) is expressed mathematically as: E = q/4πЄd2 15 Dielectric constant of the material separating the two conductors. Permittivity 16 The permittivity of air or free space is approximately. 8.85 x 10-12 F/m 17 The rate at which energy passes through a given surface area in free space. Power density 18 Intensity of the electric and magnetic fields of an electromagnetic wave propagating in free space. Field intensity 19 Mathematically power density is expressed as: P = €H W/m2 20 The characteristic impedance of a lossless transmission medium is equal to the square root of the ratio of its magnetic permeability to its electric permittivity. Zs = (μo/Єo)1/2 21 Point source that radiates power at a constant rate uniformly in all directions. Isotropic radiator 22 Power density is inversely proportional to the square of the distance from the source. Inverse Square Law 23 Propagation medium. Isotropic medium 24 Waves propagate through free space; they spread out, resulting in a reduction in power density. Attenuation 25 Reduction of Power. Absorption Loss 26 Reduction in power density with distance is equivalent to a power loss. Wave attenuation 27 Spherical spreading of the wave. Space attenuation 28 One with uniform properties throughout. Homogeneous medium 29 Absorption coefficient varies considerably with location, thus creating a difficult problem for radio systems engineers. Inhomogeneous medium 30 Optical properties of Radio Waves. Refraction, Reflection, Diffraction and Interference 31 Bending of the radio wave path. Refraction 32 Square root of the dielectric constant and is expressed in: Refractive index; n = (k) 33 (k) Equivalent dielectric constant relative to free space (vacuum). K = (1- 81N/f2)1/2 34 Boundary between two media with different densities. Plane 35 Imaginary line drawn perpendicular to the interface at the point of incidence. Normal 36 Angle formed between the incident wave and the normal. Angle of Incidence 37 Angle formed between the refracted wave and the normal. Angle of Refraction 38 Ratio of velocity of propagation of a light ray in free space to the velocity of propagation of a light ray in a given material. Refractive Index 39 Perpendicular to the direction of propagation (parallel to the waveform) Density gradient 40 To cast or turn back. Reflect 41 Ratio of the reflected to the incident voltage intensities. Reflection Coefficient 42 Portion of the total incident power that is not reflected. Power transmission Coefficient 43 Fraction of power that penetrates medium 2. Absorption coefficient 44 Incident wave front strikes an irregular surface, it is randomly scattered in many directions. Diffuse reflection 45 Reflection from a perfectly smooth surface. Specular (mirror like) Reflection 46 Surfaces that fall between smooth and irregular. Semirough surfaces 47 Semirough surface will reflect as if it were a smooth surface whenever the cosine of the angle of incidence is greater than λ/8d, where d is the depth of the surface irregularity and λ is the wavelength of the incident wave. Rayleigh criterion Cos θi > λ/8d 48 Modulation or redistribution of energy within a wavefront when it passes near the edge of an opaque object. Diffraction 49 Diffraction occurs around the edge of the obstacle, which allows secondary waves to “sneak” around the corner of the obstacle. Shadow zone 50 States that the total voltage intensity at a given point in space is the sum of the individual wave vectors. Linear Superposition 51 Electromagnetic waves travelling within Earth’s atmosphere. Terrestrial waves 52 Communications between two or more points on Earth. Terrestrial radio Communications 53 Used for high-frequency applications. Sky waves 54 Earth –guided electromagnetic wave that travels over the surface of earth. Surface wave 55 Relative Conductivity of Earth Surfaces:  56 Disadvantages of surface waves. 1. Ground waves require a relatively transmission power. 2. Ground waves are limited to very low, low and medium frequencies. 3. Requiring large antennas. 4. Ground losses vary considerably with surface material and composition. 57 Advantages of ground wave propagation. 1. Given enough transmit power, round waves can be used to communicate between any two locations in the world. 2. Ground waves are relatively unaffected by changing atmospheric conditions. 58 Travel essentially in a straight line between transmit and receive antennas. Direct waves 59 Space wave propagation with direct waves. Line-of-Sight (LOS) Transmission 60 The curvature of Earth presents a horizon to space wave propagation. Radio Horizon 61 Occurs when the density of the lower atmosphere is such that electromagnetic waves are trapped between it and Earth’s surface. Duct propagation 62 Lowest layer of the ionosphere and is located approximately between 30 miles and 60 miles (50 km to 100 km) above Earth’s surface. D Layer 63 Located approximately between 60 miles and 85 miles (100 km to 140 km) above Earth’s surface. E Layer 64 The upper portion of the E layer. Sporadic E layer 65 Made up of two layers, F 1 and F 2 layers. F Layer 66 Highest frequency that can be propagated directly upward and still be returned to Earth by the ionosphere. Critical frequency 67 Maximum vertical angle at which it can be propagated and still be refracted back by the ionosphere. Critical Angle 68 A measurement technique used to determine the critical frequency. Ionospheric Sounding 69 Height above the Earth’s surface from which a refracted wave appears to have been reflected. Virtual Height 70 Highest frequency that can be used for sky wave propagation between two specific points on Earth’s surface. Maximum Usable Frequency (MUF) 71 Secant law. MUF = critical frequency/cosθi 72 Operating at a frequency of 85% of the MUF provides more reliable communications. Optimum Working Frequency (OWF) 73 Minimum distance from a transmit antenna that a sky wave at a given frequency will be returned to Earth. Skip distance 74 The area between where the surface waves are completely dissipated and the point where the first sky wave returns to Earth. Quiet, or skip, zone 75 Formed by the ionosphere is raised, allowing sky waves to travel higher before being returned to Earth. Ceiling 76 Define as the loss incurred by an electromagnetic waves as it propagates in a straight line through a vacuum with no absorption or reflection of energy from nearby objects. Free-space path loss 77 Occurs simply because of the inverse square law. Spreading loss 78 Variation in signal loss. Fading 79 To accommodate temporary fading, an additional loss is added to the normal path loss Fade margin Fm = 30 logD + 10log (6ABf) – 10log (1-R) – 70