1. Antennas and Propagation

2. Lecture Learning Outcomes
Understand the radiation pattern of an antenna and calculate parameters for different antenna types.
Understand the basis of signal propagation.

3. Lecture Learning Outcomes
Understand the concepts associated with LoS transmissions.
Been able to calculate noise parameters, antenna gain and transmission losses for different types of antennas in LoS transmissions.

4. Class Contents Antennas Radiation Patterns Antenna Types & Gains
Propagation Modes
Ground Wave
Sky Wave
Line of Sight
Line of Sight Transmission
Attenuation
Free Space Loss
Noise
Atmospheric Absorption
Multipath
Refraction
Fading in the Mobile Environment
Multipath Propagation

5. Antennas
An antenna is an electrical conductor or system of conductors used either for radiating electromagnetic energy into space or for collecting electromagnetic energy from space.
Radiation Patterns
is a graphical representation of the radiation properties of an antenna as a function of space coordinates.
Radiation patterns are almost always depicted as 2-dimensional cross section of the three-dimensional pattern

6. The Isotropic Antenna
An Isotropic Antenna radiates power in all directions
equally. (Omnidirectional Antenna)

7. Beam Width (Half-Power Width)
Is the angle within which the power radiated by the antenna
is at least half of what is in the most preferred radiation
position.
Directional Antenna: Power radiated in the direction of B is greater than that radiated in the direction of A

8. Antenna Types & Gains Dipoles Half-Wave Dipole (Hertz Antenna)
Quarter Wave Dipole (Marconi Antenna)
Half-Wave
Dipole
Marconi
Antenna
Dipole Radiation Pattern

9. Parabolic Reflective Antenna
(a) Parabola Properties
(b) Parabolic Antenna: principle of operation
(c) Radiation Pattern

10. Typical beam width for parabolic antennas at 12 GHz
Antenna Diameter (m)
Beam Width (degrees)
0.5
3.5
0.75
2.33
1.0
1.75
1.5
1.166
2.0
0.875
2.5
0.7
5.0
0.35

11. Antenna Gain Is a measure of directionality of an antenna
It is defined the power output in a particular direction compared to that produced in any direction by a perfect omnidirectional antenna (isotropic antenna).

12. Effective Area of typical antennas
Type of Antenna
Effective Area Ae (m2)
Power Gain
(Relative to Isotropic)
Isotropic 1
Infinitesimal Dipole or loop
1.5
Half-Wave Dipole
1.64
Parabolic (face area A)

13. Propagation Modes Ground Wave Propagation Sky Wave Propagation
Line of Sight

14. Ground Wave Frequency Below 2 MHz
Slowed down wave front due to EM current induced into
the earth. (downwards tilt)
Suffer from difraction and scattering from the atmosphere
Classical Example: AM radio

15. Sky Wave Frequency between 2 and 30 MHz
Transmitted signal is refracted by the ionosphere and reflected
By the earth.
Bouncing allows signal to be picked up thousands of kilometres
from the transmitter.
Classical Example: Amateur radio, CB radio and international
broadcast (BBC & Voice of America)

16. Line of Sight Above 30 MHz, ground wave and sky wave do not operate
There is no reflection from the ionosphere (allowing satellite
communications not beyond the horizon and back).
For Ground Based communications, the antennas need to be
in LOS with each other.

17. Optical and radio LOS Optical LOS with no intervening obstacles
K is and adjustment factor
used to compensate for the
refraction

18. Optical and radio LOS h is measured in metres
Maximum distance between two antennas (radio LOS) with K=4/3
h is measured in metres
d is measured in kilometres
K depends on weather conditions
Perfect
Standard Atmosphere
Ideal
Without mist
Average
Sub-standard Light Mist
Hard
Surface Ducts, ground mist
Bad
Wet Mist over water
Typical
Mild Climate (Non tropical), air mix day and night
Dry, Mountainous without mist
Plains, some mist
Tropical Coast
Coast K
1,33
1,33  1
1  0,66
0,66  0,5
0,5  0,4

19. Line of Sight Transmission
Sources of Impairment
Attenuation & Attenuation Distortion
Noise
Atmospheric Absorption
Multipath
Refraction

20. Attenuation & Attenuation Distortion
Defined as the loss of strength of the signal over the communications
channel. It is a complex function of the distance and the make of the
atmosphere.
Attenuation Distortion
Occurs when the frequency components of the received signal
have different relative strengths than the frequency components
of the transmitted signal.

21. Factors encountered when dealing with attenuation
Strength on the received signal (solved using amplifiers or repeaters in the communications path).
SNR considerations (must be high enough to avoid errors in the transmission) – solved using amplifiers of repeaters.
Attenuation increase with frequency (known as attenuation distortion) – solved using equalizing techniques across a band of frequencies.

22. Free Space Loss
Is the ratio of power radiated by the transmitter antenna
to the power received by the receiver antenna.
PT=transmitted power (W)
PR=received power (W)
d = distance
= wavelength (same
units as distance
Isotropic
Antenna :
It is usually expressed in dB
f is expressed in Hz
d is expressed in m

23. Free Space Loss – Other Antennas
For non-isotropic antennas, the gain of the antenna, with respect
to isotropic, should be taken into consideration:
Expressed in dB:
PT(dB) and PR(dB) must be expressed in the same dB unit: dBW or dBm
The gains inside the logarithm should be expressed in adimensional
Quantities. If expressed in dB, they should be in dBi

24. Free Space Loss – Other Antennas
Free space loss can also be expressed in terms of
effective area:

25. Noise Noise are unwanted signals that combine and distort
the signal intended for transmission and reception in
a communications system.
Thermal Noise
Intermodulation Noise
Crosstalk
Impulsive Noise

26. Thermal Noise Due to thermal agitation of electrons
It is present in all electronic devices and transmission
media.
It is a function of the temperature
The amount of thermal noise is defined as noise power density
in watts per 1 Hz of bandwidth.
K is the Boltzmann’s constant: x10-23 J/K
T is the absolute temperature in Kelvins

27. Thermal Noise At room temperature (250 C), the noise power density is:
For any given bandwidth B, the noise present in the band is:
in dBW

28. Intermodulation Noise
Produced when there is nonlinearities in the transmitter, receiver or transmission system, when 2 or more different frequencies share the medium.
The effect is the production of new signals at frequencies that are the sum or difference of the original frequency and multiples of those frequencies.

29. Cross Talk Defined as unwanted coupling between signal paths.
Can occur when unwanted signals are picked up by microwave antennas or by electrical coupling between twisted pair (in guided media transmissions)
Can be identified when in the telephone line, another conversation can be heard.
Typically is in the same order of magnitude or less than the Thermal Noise

30. Impulsive Noise
Non-continuous noise consisting of irregular pulse or noise spikes of short duration and relatively high amplitude.
Causes include external electromagnetic disturbances (lightning) and faults and flaws in the communication system.
It is a minor concern in analogue signals, but is a major concern when dealing with digital data transmissions

31. Impulsive Noise
Example
In a voice communication, impulsive noise will generate clicks and crackles of short duration, however, the conversation will still be intelligible.
In a digital transmission, a small spark of energy
(10 ms in duration) would wash out 560 bits of data
being transmitted at 56 kbps.

32. Ratio of Signal Energy per bit to Noise Power Density
The short name for this equivalent is the Eb/N0 expression
The advantage of Eb/N0 over SNR is that the latter depends on the bandwidth

33. Ratio of Signal Energy per bit to Noise Power Density
A signal containing a binary data transmitted at a data rate of R, is
subjected to thermal noise N0
The Energy per bit in such a signal is:
S = signal power
Tb = time needed to
transmitt 1 bit:
Tb = 1/R
k = Boltzman Constant
(1.3803x1023 J/K)
T = Temp in Kelvin
The expression Eb/No can be written:

34. Ratio of Signal Energy per bit to Noise Power Density
Example:
Suppose a signal encoding technique requires that Eb/N0 = 8.4 dB
for a bit error rate of If the effective noise temperature is 290K
(room temperature) and the data rate is 2.4 Kbps, what received
signal level is required to overcome thermal noise
Solution:

35. Achievable Spectral Density
The parameter N0 is the noise power density in watts/hertz.
The noise in a signal with a bandwidth B is:
Substituting in the Eb/N0 expression
Considering that the Shannon’s capacity formula (in bps)

36. Achievable Spectral Density
Equating the channel capacity C with the data rate R, and using the Eb/N0 expression:
This expression is a formula that relates the achievable
spectral efficiency C/B to Eb/No

37. Atmospheric Absorption
Additional loss between the transmitting and receiving antenna.
The main contributors are the water vapour and oxygen present in the atmosphere.
Water Vapour generates attenuation peaks at frequencies close to 22 GHz
Absorption due to oxygen has a peak in the vicinity of 60 GHz
Rain and Fog cause scattering of radio waves that results in attenuation

38. Multipath
Occurs in environments where there is no direct LOS between the transmitting and receiving antenna due to the presence of intervening obstacles.
Obstacles can reflect the signal creating multiple copies that arrive at delayed times to the receiver. This copies acts as noise to the received signal.

39. Refraction
Is the bend that suffer radio waves when propagating through the atmosphere
It is caused by changes of speed of the signal with altitude or by other spatial changes in atmospheric conditions.
Normally the speed of the signal increases with altitude, causing the radio waves to bend downwards.

40. Fading in the Mobile Environment
Fading refers to the time variation of the received signal power caused by changes in the transmission medium or path(s).
The most important fading mechanism is multipath propagation.

41. Multipath propagation
Reflection
(surface > wavelength)
Diffraction
(edge of body > wavelength)
Scattering
(obstacle = wavelength)

42. Effects of multipath propagation
Copies of the signal arriving at different phases.
If copies add destructively, SNR declines
Signal interpretation then becomes difficult.
Intersymbol interference (ISI)