This document summarizes key concepts about antennas and wireless signal propagation. It discusses different types of antennas like dipole antennas and parabolic reflective antennas. It also describes the main modes of wireless signal propagation including ground-wave propagation, sky-wave propagation, and line-of-sight propagation. Additionally, it outlines several factors that can impair wireless signals during propagation, such as attenuation, noise, multipath, and atmospheric absorption.

1. GOLLIS UNIVERSITY
Department of Telecommunication Engineering
WIRELESS
COMMUNICATION
CHAPTER-2
ANTENNAS AND PROPAGATION
Lecturer
Khadar A. Muse

2. Introduction
₭ An antenna is an electrical conductor or system of conductors.
used either for radiating electromagnetic energy or for collecting
electromagnetic energy
₭ An antenna is a transducer that converts radio frequency to
electromagnetic waves that are radiated into space
◦Transmission - radiates electromagnetic energy into space
◦Reception - collects electromagnetic energy from space.
₭ In two-way communication, the same antenna can be used for
transmission and reception

3. Radiation Patterns
•An antenna will radiate power in all directions.
• Graphical representation of radiation properties of an antenna.
• The radiation pattern provides a convenient means of determining
the beam width of an antenna, which is a common measure of the
directivity of an antenna.
• Depicted as two-dimensional cross section

5. Types of Antennas
₭ Dipole antennas
₭Parabolic Reflective Antenna
₭Isotropic antenna

6. Dipole Antenna
Dipoles Two of the simplest and most basic antennas are the
half-wave dipole, or Hertz, antenna (Figure 5.2a) and the
quarter-wave vertical, or Marconi, antenna (Figure 5.2b).
The half-wave dipole consists of two straight collinear
conductors of equal length, separated by a small gap.
The length of the antenna is one-half the wavelength of the
signal that can be transmitted most efficiently.
A vertical quarter wave antenna is the type commonly used for
automobile radios and portable radios.
A half-wave dipole has a uniform or omnidirectional radiation
pattern.

8. Parabolic Reflective Antenna
Parabolic Reflective Antenna An important type of antenna
is the parabolic reflective antenna, which is used in terrestrial
microwave and satellite applications.
A parabola is the locus of all points equidistant from a fixed
line and a fixed point not on the line.
The fixed point is called the focus and the fixed line is called
the directory (Figure 5.4a).

10. Isotropic antenna
The simplest pattern is produced by an idealized antenna
known as the isotropic antenna.
An isotropic antenna is a point in space that radiates power in
all directions equally. The actual radiation pattern for the
isotropic antenna is a sphere with the antenna at the center.

11. Antenna Gain
Antenna gain
◦Power output, in a particular direction, compared to that produced in any direction
by a perfect omnidirectional antenna (isotropic antenna)
Effective area
◦Related to physical size and shape of antenna
•Relationship between antenna gain and effective area
• G = antenna gain
• Ae = effective area
• f = carrier frequency
• c = speed of light (» 3 x 108
m/s)
• λ = carrier wavelength
2
2
2
44
c
AfA
G ee π
λ
π
==

12. Propagation Modes
₭ Ground-wave propagation
₭ Sky-wave propagation
₭ Line-of-sight propagation

13. Ground Wave Propagation
Follows contour of the earth.
Ground waves must have vertical polarization to be propagated from
an antenna. Horizontally polarized waves are absorbed or shorted by
the earth.
Can Propagate considerable distances. The signals can propagate for
hundreds and sometimes thousands of miles at these low frequencies.
Ground wave propagation is strongest at the low- and medium-
frequency ranges. That is, ground waves are the main signal path for
radio signals in the 30-kHz to 3-MHz range.

14. The best-known example of ground wave communication is AM
radio.
AM broadcast signals are propagated primarily by ground waves
during the day and by sky waves at night.
The best propagation of ground waves occurs over salt water
because the water is an excellent conductor.

15. Sky Wave Propagation
Signal reflected from ionized layer of atmosphere back down to
earth.
Signal can travel a number of hops, back and forth between
ionosphere and earth’s surface.
With this propagation mode, a signal can be picked up thousands of
kilometers from the transmitter.
Reflection effect caused by refraction. This bending of the signal is
caused by refraction in a region of the upper atmosphere known as
the ionosphere.

16. Ultraviolet radiation from the sun causes the upper atmosphere
to ionize, i.e., to become electrically charged. The atoms take on
or lose electrons, becoming positive or negative ions.
If a receiver lies in that area between the place where the ground
wave is fully attenuated and the point of first reflection from the
earth, no signal will be received. This area is called the skip zone.
Examples
• Amateur radio
• CB radio

20. Line-of-Sight Propagation
•The third method of radio signal propagation is by direct waves, or
space waves.
•A direct wave travels in a straight line directly from the transmitting
antenna to the receiving antenna. Direct wave radio signaling is often
referred to as line-of-sight communication.
•Direct or space waves are not refracted, nor do they follow the
curvature of the earth.
•Above 30 MHz, neither ground wave nor sky wave propagation
modes operate, nor must communication be by line of sight.

21. Line-of-sight communication is characteristic of most radio signals
with a frequency above approximately 30 MHz, particularly VHF,
UHF, and microwave signals.
Transmission distances at those frequencies are extremely limited,
and it is obvious why very high transmitting antennas must be used
for FM and TV broadcasts.
The antennas for transmitters and receivers operating at the very
high frequencies are typically located on top of tall buildings or on
mountains, which greatly increases the range of transmission and
reception.

24. Attenuation and attenuation distortion
Free space loss
Noise
Atmospheric absorption
 Multipath
 Refraction
the most significant impairments are

25. Attenuation
The strength of a signal falls off with distance over any transmission
medium.
Attenuation introduces three factors for the transmission engineer.
1.A received signal must have sufficient strength so that the electronic
circuitry in the receiver can detect and interpret the signal.
2.The signal must maintain a level sufficiently higher than noise to be
received without error.
3.Attenuation is greater at higher frequencies, causing distortion.

26. Free Space Loss
 For any type of wireless communication the signal disperses
with distance.
For satellite communication this is the primary mode of
signal loss.

27. Noise
 For any data transmission event, the received signal will consist
of the transmitted signal, modified by the various distortions
imposed by the transmission system, plus additional unwanted
signals that are inserted somewhere between transmission and
reception.
Noise may be divided into four categories:
Thermal noise
 Intermodulation noise
 Crosstalk
 Impulse noise

28. Atmospheric Absorption
An additional loss between the transmitting and receiving
antennas is atmospheric absorption.
Water vapor and oxygen contribute most to attenuation.
 Rain and fog (suspended water droplets) cause scattering of
radio waves that results in attenuation. This can be a major
cause of signal loss

29. Multipath
 For wireless facilities where there is a relatively free choice of
where antennas are to be located, they can be placed so that if
there are no nearby interfering obstacles, there is a direct line-of-
sight path from transmitter to receiver.
The signal can be reflected by such obstacles so that multiple
copies of the signal with varying delays can be received.

31. Refraction
Radio waves are refracted (or bent) when they propagate through
the atmosphere.
The refraction is caused by changes in the speed of the signal
with altitude or by other spatial changes in the atmospheric
conditions.
Normally, the speed of the signal increases with altitude, causing
radio waves to bend downward.

32. Types of Fading
Reading Assignment
•Fast fading
•Slow fading
•Flat fading
•Selective fading
•Rayleigh fading
•Rician fading

33. Forward Error Correction
•Transmitter adds error-correcting code to data block
• Code is a function of the data bits
•Receiver calculates error-correcting code from incoming data
bits
• If calculated code matches incoming code, no error occurred
• If error-correcting codes don’t match, receiver attempts to
determine bits in error and correct

34. THE END