Radio Wave Propagation

1. RADIO WAVE
PROPAGATION

2. Revisit the concept of transverse electromagnetic (TEM) wave
1
Learn the different wave parameters and properties of the TEM wave
2
Enumerate the radio frequency spectrum
4
Understand the optical properties of the TEM wave
3
LEARNING TARGETS
Discuss the different modes of radio wave propagation
5

3. • This wave is composed of two
components, the magnetic field (H)
and the electric field (E).
• Each field varies sinusoidally in time at
a fixed point in space.
• The EM wave is transvers-e in nature
and hence its direction of propagation
is perpendicular to its two
components.
TRANSVERSE ELECTRO MAGNETIC WAVE

4. WAVE VELOCITY
The velocity of the TEM waves depends on the medium where
it travels. It travels fastest at free space at approximately
3x10^8 m/s.

5. The number of cycles an electromagnetic wave completes in
one second, expressed in Hz
FREQUENCY
WAVELENGTH
The distance that the radio wave travels in the time of one cycle,
expressed in m

6. POLARIZATION
This refers to the physical orientation of the E field
on space

7. TYPES OF POLARIZATION
LINEAR POLARIZTION
E field has a particular direction is space either vertical or horizontal.

8. TYPES OF POLARIZATION
CIRCULAR POLARIZTION
E field is rotation about the axis of the direction of propagation.

9. TYPES OF POLARIZATION
ELLIPTICAL POLARIZATION
Similar to the circular polarization except that E and H are unequal.

10. TYPES OF POLARIZATION
RANDOM POLARIZATION
Polarization with no fixed pattern.

11. For free space: 120π or approximately 377 ohms
The definite ratio between the electric field intensity and magnetic field
intensity.
INTRINSIC CHARACTERISTIC IMPEDANCE

12. Power Density
Inverse Square Law
TRANSVERSE ELECTROMAGNATIC WAVE
PARAMETERS
This refers to the rate at which energy flows through a unit area of
surface in space
This states that power density is inversely proportional to the square of
the distance from the source.

13. Electric Field Intensity/Field Strength (E)
TRANSVERSE ELECTROMAGNATIC WAVE
PARAMETERS
The amount of voltage that will be induced by an electromagnetic wave
at a specific location.

14. OPTICAL PROPERTIES OF RADIO WAVES
Occurs when an incident wave strikes the boundary of two media and
some or all of the incident power does not enter the second material
RELFECTION

15. OPTICAL PROPERTIES OF RADIO WAVES
Reflection at irregular and rough surfaces
DIFFUSE REFLECTION

16. OPTICAL PROPERTIES OF RADIO WAVES
Also called mirrorlike reflection, this refers to the reflection at very
smooth surfaces
SPECULAR REFLECTION

17. OPTICAL PROPERTIES OF RADIO WAVES
This states that a semirough surface will reflect as
if it were a smooth surface if the cosine of the angle
of incidence is greater than λ/8
RAYLEIGH CRITERION

18. Diffraction
OPTICAL PROPERTIES OF RADIO WAVES
This refers to the redistribution of energy within a wavefront when it
passes near the edge of an opaque object while allowing secondary
waves to sneak around the corner of an object
Huygens’ Principle
This states that any point on a
wavefront of light may be regarded
as the source of secondary waves.

19. Interference
OPTICAL PROPERTIES OF RADIO WAVES
This occurs when two waves that left one source and
travelled by different paths arrive at a point.

20. RADIO FREQUENCY SPECTRUM

21. MODES OF WAVE PROPAGATION
Propagation of radio waves within
the Earth’s atmosphere between two
or more points in the Earth’s surface
• Ground/Surface wave propagation
• Sky Wave propagation
• Space Wave/LOS propagation

22. MODES OF WAVE PROPAGATION
• A ground wave is an Earth-guided electromagnetic
wave that travels over the surface of the Earth
• It can be used with frequencies up to 2MHz and must
be vertically polarized
GROUND WAVE PROPAGATION

23. MODES OF WAVE PROPAGATION
• Conductivity and permittivity of the surface play an
important role in propagation
GROUND WAVE PROPAGATION

24. MODES OF WAVE PROPAGATION
• As the ground waves move away from the source, it
can experience tilting and eventually disappear.
• Effective on VLF, LF and MF frequency bands and
commonly used in AM radio broadcasting.
GROUND WAVE PROPAGATION

25. • Also called ionospheric
propagation
• The sky wave strikes the
ionosphere and is reflected back
to the ground
• Ultraviolet radiation from the
sun is the primary cause of
ionization
• Employed on the HF band
MODES OF WAVE PROPAGATION
SKY WAVE PROPAGATION

26. MODES OF WAVE PROPAGATION
SKY WAVE PROPAGATION
Ionospheric Propagation Parameters
Critical Frequency
• The highest frequency that will be returned down to
the earth when beamed vertically upward
• Measured by the process of ionospheric sounding

27. Maximum Usable Frequency (MUF)
• The highest frequency that will be returned down to
the earth at a given distance when beamed at a
specific angle other than the normal
• Follows the secant - law.
MODES OF WAVE PROPAGATION
SKY WAVE PROPAGATION
Ionospheric Propagation Parameters

28. Optimum Working Frequency (OWF)
• The frequency that gives the most consistent
communication.
• It is chosen to avoid irregularities of the ionosphere.
• It is chosen to be 15% lower than the MUF
MODES OF WAVE PROPAGATION
SKY WAVE PROPAGATION
Ionospheric Propagation Parameters

29. Skip Zone and Skip Distance
• Skip zone is the area that is between the outer limit of
the ground wave range and the inner edge of the
energy of return from the ionosphere
• Skip distance is the distance between the originating
site and the beginning of the atmospheric return
MODES OF WAVE PROPAGATION
SKY WAVE PROPAGATION
Ionospheric Propagation Parameters

30. MODES OF WAVE PROPAGATION
SPACE WAVE PROPAGATION
• Also called the Line - Of - Sight (LOS) Propagation
• Employed on VHF and UHF

31. Radio Horizon
• This refers to the boundary line beyond which direct
rays of the radio waves cannot be propagated over
the earth’s surface.
• This is usually 4/3 times greater than the optical
horizon
MODES OF WAVE PROPAGATION
SPACE WAVE PROPAGATION