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Propagation of electromagnetic waves often called radio-frequency (RF) propagation or

simply radio propagation. Free-space

Electrical energy that has escaped into free space. Electromagnetic wave

The orientation of the electric field vector in respect to the surface of the Earth.

Polarization

Polarization remains constant Linear Polarization

Forms of Linear polarization Horizontal Polarization and Vertical Polarization

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

Field strength varies with changes in polarization. EllipticalPolarization

Used to show the relative direction of electromagnetic wave propagation. Rays

Formed when two points of equal phase on rays propagated from the same source are

joined together. Wavefront

A single location from which rays propagate equally in all directions. Point source

Invisible force field produced by a magnet, such as a conductor when current is flowingthrough.Magnetic Field

Strength of a magnetic field (H) produced around a conductor is expressed mathematically

as:

Invisible force fields produced by a difference in voltage potential between two conductors.

Electric fields

Electric filed strength (E) is expressed mathematically as: 2

Dielectric constant of the material separating the two conductors. Permittivity

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. Power density

Intensity of the electric and magnetic fields of an electromagnetic wave propagating in freespace. Field intensity

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 electric permittivity. Zs = (o0)1/2

Point source that radiates power at a constant rate uniformly in all directions. Isotropic

radiator

Power density is inversely proportional to the square of the distance from the source.

Inverse Square Law

Propagation medium. Isotropic medium

Waves propagate through free space, they spread out, resulting in a reduction in powerdensity. Attenuation

Reduction of Power. Absorption Loss

Reduction in power density with distance is equivalent to a power loss. Wave attenuation

Spherical spreading of the wave. Space attenuation

One with uniform properties throughout. Homogeneous medium

Absorption coefficient varies considerably with location, thus creating a difficult problem

for radio systems engineers. Inhomogeneous medium

Optical properties of Radio Waves. Refraction, Reflection, Diffraction and Interference

Bending of the radio wave path. Refraction

Square root of the dielectric constant and is expressed in:Refractive index; n = (k)

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(k) Equivalent dielectric constant relative to free space (vacuum).

K = (1- 81N/f2)1/2

Boundary between two media with different densities. Plane

Imaginary line drawn perpendicular to the interface at the point of incidence. Normal

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. Refractive Index

Perpendicular to the direction of propagation (parallel to the waveform) Density gradient

To cast or turn back. Reflect

Ratio of the reflected to the incident voltage intensities. Reflection Coefficient

Portion of the total incident power that is not reflected. Power transmission coefficient

Fraction of power that penetrates medium 2. Absorption coefficient

Incident wave front strikes an irregular surface, it is randomly scattered in many directions.

Diffuse reflection

Reflection from a perfectly smooth surface. Specular (mirrorlike) reflectionSurfaces that fall between smooth and irregular. Semirough surfaces

Semirough surface will reflect as if it were a smooth surface whenever the cosine of the

angle of incidence is greater than /8d, where d is the depth of the surface irregularity and

is the wavelength of the incident wave.

Rayleigh criterion

Cos i > /8d

Modulation or redistribution of energy within a wavefront when it passes near the edge of

an opaque object. Diffraction

Diffraction occurs around the edge of the obstacle, which allows secondary waves to

sneak around the corner of the obstacle. Shadow zoneStates that the total voltage intensity at a given point in space is the sum of the individual

wave vectors.

Linear Superposition

Electromagnetic waves travelling within Earths atmosphere.

Terrestial waves

Communications between two or more points on Earth. Terrestial radio communications

Used for high-frequency applications. Sky waves