radio wave propagation

1. Radio Wave Propagation

2. Propagation of Radio Waves
• Radio waves can propagate through air,
water, various solid objects, vacuum and
etc. The ability of radio waves to
propagate through various materials
depends on the wavelength and the
frequency of the radio waves.

3. Modes of Radio Wave
Propagation
• ground wave
• sky wave
• and space wave.

4. Sky Wave Propagation
• This mode of propagation occurs when the signal is
transmitted by the transmitting antenna (Tx) is reflected by
the ionosphere layer (sky) and received by the receiving
antenna (Rx) is known as sky wave propagation.

5. Characteristics
• Frequency Range: In the case of sky wave propagation, the
permitted frequency range ranges from 3 MHz to 30 MHz. Basically,
the ionosphere reflects electromagnetic radiation between 3 and 30
MHz. However, despite reflection, signals with frequencies greater
than 30 MHz are penetrated. Therefore, only this particular
frequency range is acceptable for sky wave propagation.
• When the transmitting antenna sends an electromagnetic wave at
an angle (equal to or greater than the critical angle), the earth’s
atmosphere’s ionisation causes it to be reflected back toward the
planet’s surface. As a result, the receiving antenna is able to receive
the signals that are reflected.
• For electromagnetic waves to reflect through the air layer, the field
must be sufficiently strong. This is because it’s likely that the lower
part of the ionosphere won’t reflect a high-frequency wave.

6. Skip Distance in Sky Wave
Propagation
• Skip distance is a crucial aspect of ionospheric wave propagation.
The minimal distance on the earth’s surface between the point at
which a signal is transmitted and the point at which a signal
reflected from the ionosphere is received is known as the skip
distance.
• Here,
• fc denotes critical frequency, h is the height where the reflection
takes place and fmul is maximum usable frequency.

7. Critical Frequency for Sky Wave
Propagation
• The maximum frequency at which the ionosphere’s entire
internal reflection occurs is known as the critical frequency.
According to the following formula, the crucial frequency for
sky wave propagation is
Where fc is the critical frequency and Nmax is the electron density.
Frequency and wavelength have an inverse relationship; the higher the
frequency, the shorter the wavelength. Additionally, a signal with a
lower wavelength travels a greater distance.

8. Applications of Sky Wave
Propagation
• Short-wave (SW) radio services use skywave propagation. Radio
transmission over vast distances is conducted on medium and
high frequencies.
• Skywave propagation can be utilised for extraordinarily long-
distance communication because it employs a high frequency that
experiences several internal reflections between the earth and
ionosphere.
• Skywave propagation is used for satellite communication since it
depends on the upper atmospheric conditions.
• Radar systems and mobile communication services are also
based on sky wave propagation.

9. Advantages & Disadvantages
of sky wave propagation
Advantages
• It is the most straightforward
mode of transmission and offers
constant support for electronic
communications system
because it makes use of the
reflective feature of the
ionosphere that is present above
the planet at higher frequencies.
• Large-distance propagation is
supported. The operating
frequency range is very broad.
• Less attenuation is caused by
atmospheric factors.
Disadvantages
• Ionospheric proximity varies
depending on whether it is day or
night. Sky waves can therefore cover
greater or lesser distances. Before a
transmitter signal reaches a receiver,
it makes several hops. If there are
greater gaps between the transmitter
and receiver antennas, the signal
intensity is significantly reduced.
• Large-sized antennas are required
for long-distance propagation.
• There are differences in signal
transmission between day and night
due to the ionosphere’s existence
during night and day, respectively.

10. Space Wave Propagation
• Space wave propagation is the transmission of radio waves
directly from the transmitter to the receiver through the
troposphere region of the atmosphere. It is a type of line of
sight communication.

11. Characteristics
• It allows for transmission of the waves using a high frequency.
These waves can travel in the troposphere region which is almost
20km above ground level. Thus most of the space wave propagation
occurs in the troposphere layers. They are also known as
tropospheric communication. Since these waves propagate like any
other electromagnetic wave in free space, they are called space
waves.
• Frequency Range: Space waves propagate in the frequency range
of 30 MHz to 300 MHz, which is considered as ultra high frequency
(UHF) bands. Due to their high frequency, they have less
wavelength thus they cannot be transmitted to long distances
restricting them to the line of sight characteristics. Their high
frequency allows these waves to carry more energy.

12. Factors Affecting Space Wave
Propagation
• Height of the receiving and transmitting antennas. For
improved range, the antennas should be high but making
too high antennas have its own set of limitations.
• The curvature of the Earth is also an important factor
governing space wave propagation.
• The distance between the antennas determines the type
of space wave propagation.
• The presence of obstacles in the path of the waves
results in the loss of energy of the waves.

13. Components of Space Wave
Propagation
• Direct Waves- These waves are propagated directly between the
transmitting and the receiving antenna.
• Reflected Waves- Some waves reach the receiver after getting
reflected by the ground.
• Tropospheric Waves- These types of waves traverse through the
troposphere of the Earth to reach the receiver.

14. Application of Space Wave
Propagation
• Line of sight communication
• Television broadcast
• Radar communication including both general
communication by radio waves or transmission at
specific channels and frequencies
• Microwave linking or the transmission of radio waves in
the microwave frequencies to transmit videos, audios,
etc.

15. Advantages and Disadvantages of
Space Wave Propagation
Advantages
• Absorption of the space
waves is almost
negligible due to them
being propagated at
very high frequencies.
• It is a simple method of
communication.
Disadvantages
• Due to their straight path of
propagation, the radius of the
Earth becomes a limitation to
their range.
• There is a requirement for
big-sized antennas for an
improved range of
communication.

16. Ground Wave propagation
• This mode of propagation occurs when the transmitting waves
travel along the earth’s surface and are received at the
receiving antenna is known as the Ground wave propagation.
The range of the Ground wave Propagation depends on the
frequency of the transmitted wave, the power of the transmitter,
and the properties of the earth’s surface and the earth’s
atmosphere.

17. Characteristics
• Ground wave propagation requires a lower-power transmitter than
other methods of radio wave propagation.
• It is used for medium-range communication such as 100km to
1000km.
• Frequenct Range: mostly the frequency used for the ground wave
propagation lies between 3khz to 3Mhz. Ground waves are efficient
for frequencies between 50 kHz and 250 kHz and travel over the
earth’s surface.
• Signals from AM (amplitude modulation) broadcasts (540 kHz–1650
kHz) are predominantly carried via ground waves during the day and
sky waves at night.

18. Factors Affecting Ground Wave
Propagation
• Nature of Ground: In ground wave propagation, variables including
ground conductivity, terrain, and dielectric constant affect the signal
attenuation. For low-frequency ground wave propagation, surface
conductivity and ground penetration are crucial factors.
• Signal transmission is somewhat impacted by ground strata down to
a distance of up to 100m at a lower frequency range of ground wave
propagation. Low-frequency ground waves have a deep ground
penetration and have an impact on surface conductivity.
• The ideal terrain for ground wave propagation is that which has
strong conductivity. Soil type and moisture content are significant
factors. The best options include fertile agricultural or marshy land
and salty seawater. The worst areas are by far are urban areas and
dry, sandy terrain.

19. contd...
• Polarization: Antennas with vertical polarization are more appropriate for
ground wave propagation than those that have horizontal polarisation.
Medium and long-wave radio stations typically use self-radiating vertical
transmitting antennas due to the vertical polarisation requirement.
• Weather: The losses suffered in ground wave propagation are significantly
influenced by the weather. Ground wave propagation is not ideal for signal
transmission routes that are dry or sandy. The propagation of ground waves
might benefit from the amount of moisture in the atmosphere.
• Signal Strength: In ground wave propagation, the signal frequency affects
the signal attenuation. The losses in wave propagation increase with
frequency, and this effect restricts ground wave propagation over 3MHz.
Additionally, the signal frequency affects the maximum ground wave
propagation range. The density of the layer’s ionisation and the incidence
angle at which the waves reach the surface are additional parameters
influencing the ground wave’s propagation maximum range.

20. Applications of Ground Wave
Propagation
• Ground wave propagation is typically used, particularly
by radio broadcast stations needing to cover a specific
location, to offer local radio communications coverage.
• As they reach a substantial depth in the sea, ground
waves can be employed for one-way communication
from the military to submerged submarines.
• Ground waves can be used to broadcast via AM, FM,
and television.
• On these frequencies throughout the day, ground wave
propagation of radio signals is appropriate for relatively
short distance propagation.

21. Advantages & Disadvantages of
Ground Wave Propagation
Advantages
• Only atmospheric noise causes
interference because it operates at
lower frequencies. Additionally, there
is less EM wave absorption at lower
frequencies. Therefore, it can travel
farther. However, as the distance
from the transmitter grows, the path
loss increases. Therefore, the
distance between Tx and Rx ought
to be ideal.
• To avoid an electric field (E)
component short circuit, they are
vertically polarised.
Disadvantages
• The transmitter (Tx) and receiver (Rx)
antennas should not be too far apart;
otherwise, ground and air
absorptions would cause a
significant reduction in the received
signal intensity. As a result, the two
stations cannot establish
communication. Repeaters must
frequently be used between Tx and
Rx for this. The system’s overall cost
goes up as a result.
• Electric field components short circuit
with the ground if there is a change
in the polarisation of the ground
wave

22. Comparison

23. Ground -Sky- Space