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.
Propagation of electromagnetic waves often called
radio-frequency (RF) propagation or simply radio propagation.
Electrical energy that has escaped into free space.
The orientation of the electric field vector in respect to the
surface of the Earth.
Polarization remains constant
Forms of Linear polarization
Horizontal Polarization and Vertical
Polarization vector rotates 360◦ as the wave moves one
wave-length through the space and the field strength is equal at all angles
Field strength varies with changes in polarization.
Used to show the relative direction of electromagnetic wave
Formed when two points of equal phase on rays propagated from
the same source are joined together.
A single location from which rays propagate equally in all
Invisible force field produced by a magnet, such as a
conductor when current is flowing through.
Strength of a magnetic field (H) produced around a conductor
is expressed mathematically as:
H = 1/2πd
Invisible force fields produced by a difference in voltage
potential between two conductors.
Electric filed strength (E) is expressed mathematically as:
E = q/4πЄd2
Dielectric constant of the material separating the two
The permittivity of air or free space is approximately.
8.85 x 10-12 F/m
The rate at which energy passes through a given surface area
in free space.
Intensity of the electric and magnetic fields of an
electromagnetic wave propagating in free space.
Mathematically power density is expressed as:
P = €H W/m2
The characteristic impedance of a lossless transmission medium
is equal to the square root of the ratio of its magnetic permeability to its
Zs = (μo/Єo)1/2
Point source that radiates power at a constant rate uniformly
in all directions.
Power density is inversely proportional to the square of the
distance from the source.
Inverse Square Law
Waves propagate through free space; they spread out, resulting
in a reduction in power density.
Reduction of Power.
Reduction in power density with distance is equivalent to a
Spherical spreading of the wave.
One with uniform properties throughout.
Absorption coefficient varies considerably with location, thus
creating a difficult problem for radio systems engineers.
Optical properties of Radio Waves.
Refraction, Reflection, Diffraction and Interference
Bending of the radio wave path.
Square root of the dielectric constant and is expressed in:
Refractive index; n = (k)
(k) Equivalent dielectric constant relative to free space
K = (1- 81N/f2)1/2
Boundary between two media with different densities.
Imaginary line drawn perpendicular to the interface at the
point of incidence.
Angle formed between the incident wave and the normal.
Angle of Incidence
Angle formed between the refracted wave and the normal.
Angle of Refraction
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.
Perpendicular to the direction of propagation (parallel to the
To cast or turn back.
Ratio of the reflected to the incident voltage intensities.
Portion of the total incident power that is not reflected.
Power transmission Coefficient
Fraction of power that penetrates medium 2.
Incident wave front strikes an irregular surface, it is
randomly scattered in many directions.
Reflection from a perfectly smooth surface.
Specular (mirror like) Reflection
Surfaces that fall between smooth and irregular.
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
Modulation or redistribution of energy within a wavefront when
it passes near the edge of an opaque object.
Diffraction occurs around the edge of the obstacle, which
allows secondary waves to “sneak” around the corner of the obstacle.
States that the total voltage intensity at a given point in
space is the sum of the individual wave vectors.
Electromagnetic waves travelling within Earth’s atmosphere.
Communications between two or more points on Earth.
Terrestrial radio Communications
Used for high-frequency applications.
Earth –guided electromagnetic wave that travels over the
surface of earth.
Relative Conductivity of Earth Surfaces:
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.
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.
Travel essentially in a straight line between transmit and
Space wave propagation with direct waves.
Line-of-Sight (LOS) Transmission
The curvature of Earth presents a horizon to space wave
Occurs when the density of the lower atmosphere is such that
electromagnetic waves are trapped between it and Earth’s surface.
Lowest layer of the ionosphere and is located approximately
between 30 miles and 60 miles (50 km to 100 km) above Earth’s surface.
Located approximately between 60 miles and 85 miles (100 km to
140 km) above Earth’s surface.
The upper portion of the E layer.
Sporadic E layer
Made up of two layers, F 1 and F 2 layers.
Highest frequency that can be propagated directly upward and
still be returned to Earth by the ionosphere.
Maximum vertical angle at which it can be propagated and still
be refracted back by the ionosphere.
A measurement technique used to determine the critical
Height above the Earth’s surface from which a refracted wave appears
to have been reflected.
Highest frequency that can be used for sky wave propagation
between two specific points on Earth’s surface.
Maximum Usable Frequency (MUF)
MUF = critical frequency/cosθi
Operating at a frequency of 85% of the MUF provides more
Optimum Working Frequency (OWF)
Minimum distance from a transmit antenna that a sky wave at a
given frequency will be returned to Earth.
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
Formed by the ionosphere is raised, allowing sky waves to
travel higher before being returned to Earth.
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
Occurs simply because of the inverse square law.
Variation in signal loss.
To accommodate temporary fading, an additional loss is added
to the normal path loss
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