Chapter 14: Electromagnetic Wave Propagation - Review Notes

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

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Reviewer in Electronic Communications System by Wayne Tomasi

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Communications Engineering Coaching Materials

Series of Communications Engineering Exams: ECE Pre-Board

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