UNIVERSITY OF THE EAST

College of Engineering

ECE Department

ECN 411 – 1 CPT

Assignment No. 1

RADIOWAVE PROPAGATION

Date Submitted: 07 / 23 / 2013

Submitted by:

Fajardo, Shiela Monique A.

20101115224

4 - ECE

________________________

Engr. Francis P. Gubangco

Instructor

GRADEEEEE

A. RADIOWAVE PROPAGATION

Figure 1.1 – Normal modes of wave propagation

Radio wave propagation is the study of the transfer of energy at radio frequencies from

one point, a transmitter, to another, a receiver. Radio waves are part of the broad

electromagnetic spectrum that extends from the very low frequencies which are

produced by electric power facilities up to the extremely high frequencies of cosmic

rays. Between these two extremes are bands of frequencies that are found in every day

uses: audio frequencies used in systems for the reproduction of audible sounds, radio

frequencies, infrared light and ultraviolet light and x-rays.

Once a radio signal has been radiated by the antenna, it will travel or propagate through

space and will ultimately reach the receiving antenna. The energy level of the signal

decreases rapidly as the distance from the transmitting antenna is increased. Further,

the electromagnetic signal can take one or more of several different paths to the

receiving antenna. The path that a radio signal takes depends upon many factors

including the frequency of the signal, atmospheric conditions and the time of the day.

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1. SURFACE OR GROUND WAVE PROPAGATION

Figure 1.2 – Ground or Surface wave radiation from an antenna

A surface wave, also called ground wave, is an Earth-guided wave that travels over the

surface of the Earth. The surface wave leaves the antenna and will actually follow the

curvature of the Earth and can, therefore, travel at distances beyond the horizon. As a

surface wave travels through the Earth, it is accompanied by charges induced in the

Earth.

Ground wave propagation is strongest at the low- and medium-frequency ranges.

Ground waves are the main signal path for radio signals in the 30kHz to 3MHz range.

The signals can propagate for hundreds and sometimes thousands of miles at these low

frequencies. Amplitude modulation broadcast signals are propagated primarily by

ground waves.

At the higher frequencies beyond 3MHz, the Earth begins to attenuate the radio signals.

Objects on Earth and terrain features become the same order of magnitude in size as

the wavelength of the signal and will absorb and otherwise affect the signal. The ground

wave propagation of signals above 3MHz is insignificant except within several miles of

the antenna.

Ground wave radio propagation is used to provide relatively local radio communications

coverage, especially by radio broadcast stations that require covering a particular

locality, ship-to-ship and ship-to-shore communications, radio navigation and marine

mobile communication.

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2. IONOSPHERIC WAVE PROPAGATION

Figure 1.3 – Ionospheric wave propagation

The ionosphere is a continually changing area of the atmosphere. Extending from

altitudes of around 60 kilometers to more than 400 kilometers it contains ions and free

electrons. The free electrons affect the ways in which radio waves propagate in this

region and they have a significant effect on HF radio communications.

Ionospheric wave propagation refers to the phenomenon in which certain radio waves

can propagate in the space between the ground and the boundary of the ionosphere.

Because the ionosphere contains charged particles, it can behave as a conductor. The

earth operates as a ground plane, and the resulting cavity behaves as a large

waveguide.

Extremely low frequency (ELF) and very low frequency (VLF) (300 Hz – 30 kHz) signals

can propagate efficiently in this waveguide. For instance, lightning strikes launch a

signal called radio atmospherics, which can travel many thousands of miles, because

they are confined between the Earth and the ionosphere. The round-the-world nature of

the waveguide produces resonances, like a cavity, which are at ~7 Hz.

The ionosphere can be categorized into a number of regions corresponding to peaks in

the electron density. These regions are named the D, E, and F regions. In view of the

fact that the radiation from the Sun is absorbed as it penetrates the atmosphere,

different forms of radiation give rise to the ionization in the different regions as outlined

in the summary table below:

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Table 1.1 Summary of forms of radiation causing ionization in the ionosphere

REGION PRIMARY IONISING RADIATION FORMS

C Cosmic

D Lyman alpha, Hard X-Rays

E Soft X-Rays and some Extreme Ultra-Violet

F1 Extreme Ultra-violet, and some Ultra-Violet

F2 Ultra-Violet

The ionosphere is a continually changing area. It is obviously affected by radiation from

the Sun, and this changes as a result aspects including of the time of day, the

geographical area of the world, and the state of the Sun. As a result radio

communications using the ionosphere change from one day to the next and even one

hour to the next. Predicting how what radio communications will be possible and radio

signals may propagate is of great interest to a variety of radio communications users

ranging from broadcasters to radio amateurs and two way radio communications

systems users to those with maritime mobile radio communications systems and many

more.

3. DIRECT WAVE OR LINE-OF-SIGHT (LOS) PROPAGATION

Figure 1.4 – Direct wave or Line-of-sight (LOS) propagation

A direct wave travels in a straight line directly from the transmitting antenna to the

receiving antenna. It is often referred to as line-of-sight communications. Direct or space

waves are not refracted nor do they follow the curvature of the Earth.

Because of their straight line nature, direct waves will at some point be blocked because

of the curvature of the Earth. The signals will travel horizontally from the antenna until

they reach the horizon at which the point is blocked. If the signal to be received beyond

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the horizon then the antenna must be high enough to intercept the straight-line radio

waves.

Line-of-sight communications by direct wave is a characteristic of most radio signals

with a frequency above approximately 30MHz. This is particularly true of VHF, UHF and

microwave signals. Such signals pass through the atmosphere and cannot be bent.

4. GROUND REFLECTED WAVE PROPAGATION

Figure 1.5 – LOS wave and Ground-reflected wave propagation

Ground reflected wave propagation is a case where a part of the signal from the

transmitter is bounced off the ground and reflected back to the receive antenna. It can

cause problems if the phase between the direct wave and the reflected wave are not in

phase. If the direct wave and the reflected waves are received in phase, the result is a

reinforced or stronger signal. Likewise, if they are received out of phase, they tend to

cancel one another, which results in a weak or fading signal.

5. SKY WAVE PROPAGATION

Electromagnetic waves that are directed above the horizon level are called sky waves.

Sky waves are radiated in a direction that produces a relatively large angle with

reference to Earth. Sky waves are radiated towards the sky, where they are either

reflected or refracted back to the Earth by the ionosphere. Because of this sky wave

propagation is sometimes called ionospheric propagation. The ionosphere is the region

of space located approximately 50km to 400km (30mi to 250mi) above the Earth’s

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surface. The ionosphere is the upper portion of the Earth’s atmosphere. It absorbs large

quantities of the sun’s radiant energy, which causes ionization of the air molecules,

creating free electrons. When a radio wave passes through the ionosphere, the electric

field of the wave exerts a force on the free electrons, causing them to vibrate. The

vibrating electrons decrease current, which is equivalent to reducing the dielectric

constant. Reducing the dielectric constant increases the velocity of propagation and

causes electromagnetic waves to bend away from the regions of high electron density

toward regions of low electron density.

Three layers make up the ionosphere: the D, E and F layers. All three layers of the

atmosphere vary in location and in ionization density with the time of day. They fluctuate

in a cyclic pattern throughout the year and according to the 11-year sunspot cycle. The

ionosphere is most dense during times of maximum sunlight (during the daylight hours

and in the summer).

Figure 1.6 – Ionosphere layers: D, E, F1 and F2

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The D layer. The D layer is the lowest layer of the ionosphere, approximately between

30 miles and 60 miles (50km and 100km) above the Earth’s surface. There is little

ionization because is the farthest from the sun. The D layer has very little effect on the

direction of propagation of radio waves. The ions in the D layer can absorb appreciable

amounts of electromagnetic energy. The D layer reflects VLF and LF waves and

absorbs MF and HF waves.

The E layer. The E layer is located approximately between 60 miles and 85 miles

(100km to 140km) above the Earth’s surface. It is sometimes called the Kennelly-

Heaviside layer after the two scientists who discovered it. The E layer has its maximum

density at approximately 70 miles at noon, when the sun is at its highest point. The E

layer totally disappears at night. The E layers aids MF surface wave propagation and

reflects HF waves somewhat during the daytime. The sporadic E layer is the upper

portion of the E layer. It is a thin layer with a very high ionization density. When it

appears, it generally is an unexpected improvement in long-distance radio transmission.

The F layer. The F layer is made up of two layers, The F1 and F2 layers. During daytime,

the F1 layer if located between 85 miles and 155 miles (140km to 250km) above Earth’s

surface; the F2 layer is located 85 miles to 185 miles (140km to 300km) above Earth’s

surface. During the night, the F1 layer combines with the F2 layer to form a single layer.

The F1 absorbs and attenuates some HF waves, although most of the waves pass

through the F2 layer, where they are refracted back to the Earth.

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B. MICROWAVE TERRESTRIAL LINK

Figure 1.7 – Microwave terrestrial link

Terrestrial microwave communication employs Earth-based transmitters and receivers.

The frequencies used are in the low-gigahertz range, which limits all communications to

line-of-sight. You probably have seen terrestrial microwave equipment in the form of

telephone relay towers, which are placed every few miles to relay telephone signals

cross country.

Terrestrial (ground) link is used for long-distance telephone service. It uses a radio

frequency spectrum from 2 to 4GHz, a parabolic dish transmitter, mounted high. It is

used by common carriers as well as private networks. It requires an obstructed line of

sight between source and receiver. The curvature of the Earth requires stations, called

repeaters, for 30 miles.

Terrestrial microwave systems operate in the low gigahertz range, typically at 4-6 GHz

and 21-23 GHz, and costs are highly variable depending on requirements. Long-

distance microwave systems can be quite expensive but might be less costly than

alternatives. A leased telephone circuit, for example, represents a costly monthly

expense. When line-of-sight transmission is possible, a microwave link is a one-time

expense that can offer greater bandwidth than a leased circuit.

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REFERENCES

Tomasi, W. (5th edition). (2004). Electronic Communications Systems. New Jersey:

Pearson Education Inc.

Frenzel, L. (2nd edition). (1995). Communication Electronics. Boston: McGraw-Hill Book

Co.

Wave propagation. Retrieved from

http://www.maisonthenezay.fr/Maintenance_HF/NAB_files/2-01.PDF on July 20, 2013

Surface wave. Retrieved from

http://electriciantraining.tpub.com/14182/css/14182_76.htm on July 20, 2013

Ionospheric wave. Retrieved from

http://apollo.lsc.vsc.edu/classes/met130/notes/chapter1/ion2.html on July 20, 2013

Earth-ionosphere waveguide. Retrieved from

http://en.wikipedia.org/wiki/Earth%E2%80%93ionosphere_waveguide on July 20, 2013

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