This document discusses various topics related to antennas and propagation. It describes what antennas are, their characteristics, and different types of antennas like dipole, parabolic, and arrays. It also covers radiation patterns, antenna gain, and different propagation modes like ground wave, sky wave, and line-of-sight. Key factors affecting line-of-sight transmission are discussed, including attenuation, free space loss, noise from thermal, intermodulation, crosstalk and impulse sources, and atmospheric absorption and multipath effects. Common antenna types and their uses as well as concepts like radiation patterns, antenna gain, and propagation modes are summarized.

1. Antenna and Propagation
By
Waheed ur Rehman
wahrehman@gmail.com

2. Antenna
• Electrical conductor for conduction
electromagnetic energy
• Electric energy < -- > electromagnetic
energy
• Antenna characteristics are essentially the
same whether an antenna is sending or
receiving electromagnetic energy.

3. Radiation pattern
• A common way to characterize the
performance of an antenna
• Graphical representation of the radiation
properties of an antenna
• The simplest pattern is produced by an
idealized antenna known as isotropic
antenna (sphere with an antenna in
center)

4. Radiation pattern

5. Isotropic Antenna
• Isotropic Antenna is a point in space that
radiate power in all directions equally
• Its not a practical antenna just used as a
reference.

6. Antenna Types
• Isotropic radiator
• Monopole
• Loop
• dipole
• Rhombic
• Dielectric Rod
• Yagi
• Horn
• Parabolic dish
• Patch
• Dielectric lens
• arrays

7. Dipole Antenna
• Lamda / 2 half wave dipole
• Lamda / 4 Quarter-wave dipole

8. Parabolic Antenna
• Used for terrestrial and satellite
communication
• Signals reflected back to focus

9. Antenna Types

10. Antenna Types

11. Antenna types

12. Antenna Gain
• Measure of directivity of an antenna
• Defined as power output in a particular direction,
compared to that produced in any direction by a
perfect radiator (isotropic)
• Its only possible on the expense of radiation in
other directions
• If an antenna has a gain of 3dB that means that
antenna improves upon isotropic antenna in that
direction by 3dB.

13. Antenna Gain
• Antenna gain is not related to more output
power but with directionality
• Effective area of an antenna is related to
that of the physical size of the antenna
and its shape
G = 4 х pi х Ae/lamda ^2
Ae is different from antenna to antenna

14. Propagation Modes
• A radiated signal from antenna travels
along one of three routes
– Ground wave
– Sky wave
– LOS
• We will only be concerned with LOS

15. Ground Wave Propagation
• More or less follow the earth curvature
• Propagate considerable distance well over the visual
horizon
• Frequency upto 2MHz
• One factor is that electromagnetic wave induces a
current in the earth’s surface (causes a bend towards the
earth)
• Another factor is diffraction
• Electromagnetic waves in this frequency range are
scattered in such a way that they don’t penetrate the
upper atmosphere.
• AM radio

16. Ground Wave Propagation

17. Ground Wave Propagation

18. Sky Wave Propagation
• Signal from the earth-based antenna is
reflected from the ionized layer of the
upper atmosphere back down to the earth
• Seems like reflection but actually
refraction.
• 2 – 30 MHz
• BBC , VoA

19. Sky Wave Propagation

20. Sky Wave Propagation

21. LOS Propagation
• Above 30MHz
• Not reflected by ionosphere (satellite
comm)
• For ground-based LOS communication
both Tx and Rx antennas must be within
effective LOS of each others
• Optical Vs Radio LOS

22. LOS Propagation
• Optical LOS
– d = 3.57 √h
– d= distance b/w antenna and horizon
– h= height of antenna in meters
• Effective / Radio LOS
– d=3.57√Kh
– K = adjustment factor to account for refraction,
typically K=4/3
• Max distance between two antennas
– 3.57 (√Kh1 + √Kh2)
– h1, h2 are height of antennas

23. LOS Transmission
• Signal received is not similar to signal
transmitted
• Significant impairments are
– Attenuation and attenuation distortion
– Free space loss
– Noise
– Atmospheric Absorption
– Multipath
– Refraction

24. Attenuation
• Strength of the signal falls with the
distance
• Expressed in decibels dB
• For unguided medium attenuation is a
complex function of distance and makeup
of the atmosphere

25. Attenuation
• Attenuation involves these factors
– Receive signal must be sufficiently strong to
be detected and interpreted
– Signal level must be sufficiently higher than
noise
– Attenuation is greater at higher frequencies,
causing distortion.
Amplifiers
Repeaters
can be used
Amplifiers that
amplify higher
frequency more
Than lower
frequency

26. Free Space Loss
• Signal disperses with distance
• Signal spreads larger over distances
• This type of attenuation is called free
space loss
• In ideal free space propagation
– Pr = Pt Gt Gr (lamda/4 х pi х d) 2
• For microwave systems
• Ls = 32.45 +20log d(km) + 20 log f (MHz)

27. Noise
• Unwanted signal created from the source
other than the transmitter
• Four categories
– Thermal noise
– Intermodulation noise
– Cross talk
– Impulsive noise

28. Noise
Thermal Noise
• Due to thermal agitation of electrons
• Always present and cannot be eliminated
• Uniformly distributed across the frequency spectrum
hence referred to as white noise
• Independent of frequency
• Thermal noise in watts present in a bandwidth of B Hertz
can be expressed as
N = kTB where k = boltzmann’s constt
1.38 х 10-23 J/K
T is Temp, in Kelvin
• Or in decibels-watt
– N = 10 log k + 10log T + 10 log B

29. Noise
Intermodulation Noise
• When signal with different frequencies
share the same medium, results in I.N.
• It produces signal at frequency that is the
sum, difference or multiple of two other
frequencies.
• E.g. f1 , f2 would result in f1+f2

30. Noise
Crosstalk
• Unwanted coupling between signal paths.
• The effect of one wire over the other in
twisted pair
• Can also occur when unwanted signals
are picked up by microwave antenna

31. Noise
Impulse Noise
• Irregular , continuous pulses
• Unpredictable therefore not possible to engineer
a transmission system to cope with it
• Generated from external electromagnetic
disturbance like lightning and faults and flaws in
the communication system
• A sharp spike of energy of 0.01 s duration can
destroy 560 bits of data being transmitted at
56kbps