1. Modes of
Electromagnetic Wave
Propagation
1

4. Introduction
 Electromagnetic waves in frequency range of few Hz
to about 1011 Hz are called the radio waves .
 These waves are useful for transmission of
information from one place to another without the
help of wires or any other material medium between
the 2 places. The signal to be transmitted is converted
into an electrical signal and then super imposed on a
high frequency oscillating current flowing through a
metallic conductor of suitable shape and size.
 This conductor , called the transmitting antenna
radiates the corresponding radio waves into the
atmosphere. At the receiving station there is another
metallic conductor of suitable shape and size, called
the receiving antenna.

5.  When the radio waves are intercepted by the
receiving antenna , a small varying e.m.f. is
induced in the antenna .
 This e.m.f. I amplified and decoded to obtain the
information contained in the original signal.
 How does a signal Propagate from a transmitter to
a receiver?
Transmitter Receiver

7. Types of wave propagation
 Surface wave propagation
 Space wave propagation
 Sky wave propagation

9. SURFACE WAVE PROPAGATION

10. SURFACE WAVE PROPAGATION
 When the radio waves from transmitting
antenna propagate along the surface of the
earth so as to reach the receiving antenna
the wave propagation is called Ground wave
propagation or Surface wave propagation .
 These radio waves travel close to the surface
of the earth and move along its curved
surface from the transmitter to receiver.
 The radio waves induce currents in the
ground and lose their energy by absorption

11.  Therefore the signals cannot be transmitted
over a large distances s
 Radio wave shaving frequencies 2MHz are
transmitted by ground wave propagation
 For TV signals and FM signals, ground wave
propagation cannot be used . This is suitable
for local broadcasting

13. Space wave
propagation
Space wave propagation
Definition:- When the radio waves from the transmitting
antenna reach the receiving antenna either directly or after
reflection from the ground or after reflection from troposphere,
the wave propagation is called space wave propagation.

14. The Space wave has three components
Direct waves:- The transmitting waves follow path
in a straight line and directly reach the receiver end are
called as Direct waves.
Ground reflected waves:- The transmitting waves follow
path and reach the receiving antenna after reflection from
the ground are called as Ground reflected waves.
Tropospheric waves:- The transmitted waves follow path
and reach the receiving antenna after reflection from the
troposphere are called as Tropospheric waves.

15. In all the above three waves, the radio waves are not
subjected to the absorption by the ground. Hence, space
waves cover a larger distance then the ground waves. But
due to the curvature of the earth, the receiving antenna
must be in the line of sight distance. The maximum
distance over which the signal can reach is called range.
The range is given by d = √2Rh where R is radius of
curvature of the earth and h is the height of transmitting
antenna. For getting a larger range, h must be increased.
It is for this reason that the transmitting antenna are
located on the top of hills or high building.

17. Uses of Space waves:-
Space waves are useful in transmitting FM radio signals(they
have frequency greater then 30 MHz so they can pass through
ionosphere after suffering a small deviation. Hence, they can
not be transmitted using sky waves).
Also TV signals cannot be propagated by ground wave
propagation, owing to them high frequency, these signals are
easily absorbed by the earth so for transmitting of these waves
the space wave propagation in which the receiving antenna
directly intercepts the signals are used. These and many others
whose frequencies range from 80 MHz to 120 MHz can be
transmitted using Space wave propagation.

19. Definition: When the radio waves from the
transmitting antenna reach the receiving
antenna either directly or after reflection in
the ionosphere, wave propagation is called as
sky wave propagation.

20. 1) It can
be used for transmission of signals with
frequencies 3MHz to 30MHz.
2) The ionosphere is chosen for sky wave propagation
due to two reasons;
It has high concentration of ions.
It has a low refractive index.
3) It is highly unreliable as the signal may be lost due to
seasonal variations and unfaurable weather conditions.
4) It can be used for high frequency signal transmission.
5) This E.M. waves travel directly from the transmitter to
the receiver without being influenced by the ground.

21. •TV programmes can be transmitted all over the world
with the help of geostationary satellites(artificial
satellites).The satellite receives the signals from the
transmitting station, amplifies them and then sends to the
receiving stations on earth.
•It is used for telecommunication for sending signals over
large distance.
•For transmitting FM signals and mobile signals, etc.