Items

Definitions

Terms

1

Propagation of electromagnetic waves often called
radiofrequency (RF) propagation or simply radio propagation.

Freespace

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
wavelength 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 1012 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 = โฌH 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 โsneakโ 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 Earthโs atmosphere.

Terrestrial waves

52

Communications between two or more points on Earth.

Terrestrial radio
Communications

53

Used for highfrequency applications.

Sky waves

54

Earth โguided 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.

LineofSight (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 Earthโs 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 Earthโs surface.

D Layer

63

Located approximately between 60 miles and 85 miles (100 km to
140 km) above Earthโs 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 Earthโs 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 Earthโs 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.

Freespace 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) โ 10log (1R) โ
70
