Antennas and Propagation Review/Recap

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Antennas and PropagationReview/Recap

• Lecture 17

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Overview

• Antenna Functions
• Isotropic Antenna
• Radiation Pattern
• Parabolic Reflective Antenna
• Antenna Gain
• Signal Loss in Satellite Communication
• Noise Types
• Refraction
• Fading
• Diffraction and Scattering
• Fast and Slow Fading
• Flat and Selective Fading
• Diversity Techniques

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Review Question Antenna Functionality

• Q- What two functions are performed by an
  antenna?

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Antenna Definition

• An antenna is defined as usually a metallic
  device (as a rod or wire) for radiating or
  receiving radio waves.
• The IEEE Standard Definitions of Antenna defines
  the antenna or aerial as a means for radiating
  or receiving radio waves. In other words the
  antenna is the transitional structure between
  free-space and a guiding device, as shown in
  Figure

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Why Antennas of Different Shapes

• In addition to receiving or transmitting energy,
  an antenna in an advanced wireless system is
  usually required to optimize or accentuate the
  radiation energy in some directions and suppress
  it in others.
• Thus the antenna must also serve as a directional
  device in addition to a probing device.
• It must then take various forms to meet the
  particular need at hand, and it may be a piece of
  conducting wire, an aperture, a patch, an
  assembly of elements (array), a reflector, a
  lens, and so forth.
• For wireless communication systems, the antenna
  is one of the most critical components. A good
  design of the antenna can relax system
  requirements and improve overall system
  performance.
• The antenna serves to a communication system the
  same purpose that eyes and eyeglasses serve to a
  human

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Basic Antenna Functions

• As Antenna resides between cable/waveguide and
  the medium air, the main function of antenna is
  to match impedance of the medium with the
  cable/waveguide impedance. Hence antenna is
  impedance transforming device.
• The second and most important function of antenna
  is to radiate the energy in the desired direction
  and suppress in the unwanted direction. This
  basically is the radiation pattern of the
  antenna. This radiation pattern is different for
  different types of antennas.

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The Role of Antennas

• Antennas serve four primary functions
• Spatial filter
• directionally-dependent sensitivity
• Polarization filter
• polarization-dependent sensitivity
• Impedance transformer
• transition between free space and transmission
  line
• Propagation mode adapter
• from free-space fields to guided waves
• (e.g., transmission line, waveguide)

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Spatial filter

• Antennas have the property of being more
  sensitive in one direction than in another which
  provides the ability to spatially filter signals
  from its environment.

Radiation pattern of directive antenna.
Directive antenna.
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Polarization filter
Antennas have the property of being more
sensitive to one polarization than another which
provides the ability to filter signals based on
its polarization.
In this example, h is the antennas effective
height whose units are expressed in meters.
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Impedance transformer

• Intrinsic impedance of free-space, E/H
• Characteristic impedance of transmission line,
  V/I
• A typical value for Z0 is 50 ?.
• Clearly there is an impedance mismatch that must
  be addressed by the antenna.

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Propagation Mode Adapter

• In free space the waves spherically expand
  following Huygens principle each point of an
  advancing wave front is in fact the center of a
  fresh disturbance and the source of a new train
  of waves.
• Within the sensor, the waves are guided within a
  transmission line or waveguide that restricts
  propagation to one axis.

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Propagation Mode Adapter

• During both transmission and receive operations
  the antenna must provide the transition between
  these two propagation modes.

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Antenna purpose

• Transformation of a guided EM wave in
  transmission line (waveguide) into a freely
  propagating EM wave in space (or vice versa) with
  specified directional characteristics
• Transformation from time-function in
  one-dimensional space into time-function in three
  dimensional space
• The specific form of the radiated wave is defined
  by the antenna structure and the environment

Space wave
Guided wave
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Antenna functions

• Transmission line
• Power transport medium - must avoid power
  reflections, otherwise use matching devices
• Radiator
• Must radiate efficiently must be of a size
  comparable with the half-wavelength
• Resonator
• Unavoidable - for broadband applications
  resonances must be attenuated

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Review Question Antenna Functionality
Q- What two functions are performed by an
antenna?

• Ans- Two functions of an antenna are
• For transmission of a signal, radio frequency
  electrical energy from the transmitter is
  converted into electromagnetic energy by the
  antenna and radiated into the surrounding
  environment (atmosphere, space, water)
• For reception of a signal, electromagnetic energy
  impinging on the antenna is converted into
  radio-frequency electrical energy and fed into
  the receiver.

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Isotropic Antenna

• Q- What is an isotropic antenna?

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Isotropic Antenna

• Isotropic antenna or isotropic radiator is a
  hypothetical (not physically realizable) concept,
  used as a useful reference to describe real
  antennas.
• Isotropic antenna radiates equally in all
  directions.
• Its radiation pattern is represented by a sphere
  whose center coincides with the location of the
  isotropic radiator.

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Reference Antenna for Gain

• Gain is Measured Specific to a Reference Antenna
• isotropic antenna often used - gain over
  isotropic
• Isotropic antenna radiates power ideally in all
  directions
• Gain measured in dBi
• Test antennas field strength relative to
  reference isotropic antenna at same power,
  distance, and angle
• -Isotropic antenna cannot be practically realized
• e.g.
• A lamp is similar to an isotropic antenna

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Isotropic
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An Isotropic Source Gain

• Every real antenna radiates more energy in some
  directions than in others (i.e. has directional
  properties)
• Idealized example of directional antenna the
  radiated energy is concentrated in the yellow
  region (cone).
• Directive antenna gain the power flux density is
  increased by (roughly) the inverse ratio of the
  yellow area and the total surface of the
  isotropic sphere
• Gain in the field intensity may also be
  considered - it is equal to the square root of
  the power gain.

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Antenna Gain Measurement
Antenna Gain (P/Po) SS0
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Isotropic Antenna

• Q- What is an isotropic antenna?
• Ans- An isotropic antenna is a point in space
  that radiates power in all directions equally.

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Review Radiation Pattern

• Q- What information is available from a
  radiation pattern?

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Radiation Pattern

• In the field of antenna design the term radiation
  pattern (or antenna pattern or far-field pattern)
  refers to the directional (angular) dependence of
  the strength of the radio waves from the antenna
  or other source.
• Particularly in the fields of fiber optics,
  lasers, and integrated optics, the term radiation
  pattern may also be used as a synonym for the
  near-field pattern or Fresnel pattern. This
  refers to the positional dependence of the
  electromagnetic field in the near-field, or
  Fresnel region of the source. The near-field
  pattern is most commonly defined over a plane
  placed in front of the source, or over a
  cylindrical or spherical surface enclosing it.
• The far-field pattern of an antenna may be
  determined experimentally at an antenna range, or
  alternatively, the near-field pattern may be
  found using a near-field scanner, and the
  radiation pattern deduced from it by computation.
  The far-field radiation pattern can also be
  calculated from the antenna shape by computer
  programs such as NEC. Other software, like HFSS
  can also compute the near field.

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Antenna Radiation Pattern

• Radiation pattern
• Graphical representation of radiation properties
  of an antenna
• Depicted as two-dimensional cross section
• The radiation pattern of an antenna is a plot of
  the far-field radiation from the antenna. More
  specifically, it is a plot of the power radiated
  from an antenna per unit solid angle, or its
  radiation intensity U watts per unit solid
  angle. This is arrived at by simply multiplying
  the power density at a given distance by the
  square of the distance r, where the power density
  S watts per square metre is given by the
  magnitude of the time-averaged Poynting vector
• Ur²S

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Radiation pattern

• The radiation pattern of antenna is a
  representation (pictorial or mathematical) of the
  distribution of the power out-flowing (radiated)
  from the antenna (in the case of transmitting
  antenna), or inflowing (received) to the antenna
  (in the case of receiving antenna) as a function
  of direction angles from the antenna
• Antenna radiation pattern (antenna pattern)
• is defined for large distances from the antenna,
  where the spatial (angular) distribution of the
  radiated power does not depend on the distance
  from the radiation source
• is independent on the power flow direction it is
  the same when the antenna is used to transmit and
  when it is used to receive radio waves
• is usually different for different frequencies
  and different polarizations of radio wave
  radiated/ received

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Power Pattern Vs. Field pattern

• The power pattern is the measured (calculated)
  and plotted received power P(?, ?) at a
  constant (large) distance from the antenna
• The amplitude field pattern is the measured
  (calculated) and plotted electric (magnetic)
  field intensity, E(?, ?) or H(?, ?) at a
  constant (large) distance from the antenna

• The power pattern and the field patterns are
  inter-relatedP(?, ?) (1/?)E(?, ?)2
  ?H(?, ?)2
• P power
• E electrical field component vector
• H magnetic field component vector
• ? 377 ohm (free-space, plane wave impedance)

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Normalized pattern

• Usually, the pattern describes the normalized
  field (power) values with respect to the maximum
  value.
• Note The power pattern and the amplitude field
  pattern are the same when computed and when
  plotted in dB.

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3-D pattern

• Antenna radiation pattern is 3-dimensional
• The 3-D plot of antenna pattern assumes both
  angles ? and ? varying, which is difficult to
  produce and to interpret

3-D pattern
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2-D pattern

• Usually the antenna pattern is presented as a 2-D
  plot, with only one of the direction angles, ? or
  ? varies
• It is an intersection of the 3-D one with a
  given plane
• usually it is a ? const plane or a ? const
  plane that contains the patterns maximum

Two 2-D patterns
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Example a short dipole on z-axis
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Principal Patterns

• Principal patterns are the 2-D patterns of
  linearly polarized antennas, measured in 2 planes
• the E-plane a plane parallel to the E vector and
  containing the direction of maximum radiation,
  and
• the H-plane a plane parallel to the H vector,
  orthogonal to the E-plane, and containing the
  direction of maximum radiation

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Example
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Antenna Mask (Example 1)

• Typical relative directivity- mask of receiving
  antenna (Yagi ant., TV dcm waves)

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Antenna Mask (Example 2)
0dB
Phi
-3dB

• Reference pattern for co-polar and cross-polar
  components for satellite transmitting antennas in
  Regions 1 and 3 (Broadcasting 12 GHz)

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Review Radiation Pattern

• Q- What information is available from a
  radiation pattern?
• Radiation Patterns in Polar and Cartesian
  Coordinates Showing Various Types of Lobes
• Ans- A radiation pattern is a graphical
  representation of the radiation properties of an
  antenna as a function of space coordinates.

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Parabolic Reflective Antenna

• Q- What is the advantage of a parabolic
  reflective antenna?

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Two Main Purposes of Antenna

• Impedance matching matches impedance of
  transmission line to the intrinsic impedance of
  free space to prevent wanted reflection back to
  source.
• Antenna must be designed to direct the radiation
  in the desired direction.
• So a parabolic antenna
• is a high gain reflector antenna. It is used for
  television, radio and data communications. It may
  also be used for radar on the UHF and SHF
  sections of the electromagnetic spectrum.

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Reflector Antenna

• Reflector antenna such as parabolic antenna are
  composed of primary radiator and a reflective
  mirror.

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Parabolic Reflector Antenna

• Any electromagnetic wave incident upon the
  paraboloid surface will be directed to the focal
  point.
• Primary antenna is used at the focal point of the
  parabolic reflector antenna instead of isotropic
  antenna. The isotropic antenna would radiate and
  receive radiation from all directions resulting
  in spillover.
• Primary antenna should be designed to
  illuminate just the reflector uniformly.

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Loss
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Characteristics

• Aperture
• r radius of the diameter
• Larger dish has more gain than smaller
• Clear line of sight is important

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Calculations

• Physical area
• D Diameter
• Effective area
• illumination efficiency
• Wavelength
• Gain
• 3db beamwidth

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Half Power Beamwidth
The half power graph showing the angle between
the half power point on either side of maximum
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Radiation Pattern for Parabolic Antenna
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Advantage of a Parabolic Antenna

• The advantage of a parabolic antenna is that it
  can be used as primary mirror for all the
  frequencies in the project, provided the surface
  is within the tolerance limit only the feed
  antenna and the receiver need to be changed when
  the observing frequency is changed.
• An advantage of such a design is the small
  irradiation loss, which allows for an optimum
  antenna gain.
• It is an advantage of such an arrangement that
  the exciter system and/or the exciter 3
  are/is protectively located within the parabola
  or the parabolic reflector.
• Parabolic antenna is the most efficient type of a
  directional antenna - large front/back ratio,
  sharp radiation angle and small side lobes. It
  fits well for noisy locations where other
  antennas factually do not work.
• The antenna's Gain is adequate to the area of the
  reflector. The reflector can be
  central-focused(the focus is in the center of the
  dish) or offset (the focus is off the axis of the
  dish).
• In general, they serve for connection of end
  users (so-called last mile) to a wireless
  network. However, in areas with lower intensity
  of Wi-Fi networks, they can be successfully used
  also for back-bone links. In fact, this frequency
  is used for connections up to maximum 10 km

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Parabolic Reflective Antenna

• Q- What is the advantage of a parabolic
  reflective antenna?
• A parabolic antenna creates, in theory, a
  parallel beam without dispersion. In practice,
  there will be some beam spread. Nevertheless, it
  produces a highly focused, directional beam.

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Antenna Gain

• Q- What factors determine antenna gain?

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Antenna Gain
Change in coverage by focusing the area of RF
propagation

• Antenna Gain (Directivity)
• Power output, in a particular direction, compared
  to that produced in any direction by a perfect
  omnidirectional antenna usual reference is an
  isotropic antenna (dBi) but sometimes a simple ½
  ? antenna is a more practical reference good
  sales trick to use an isotropic reference when a
  dipole is inferred resulting in a 1.64 power
  gain
• Antenna gain doesnt increase power only
  concentrates effective radiation pattern
• Effective area (related to antenna aperture)
  Expressed in terms of effective area
• Related to physical size and shape of antenna
  related to the operational wavelength of the
  antenna

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Passive Gain

• Focusing isotropic energy in a specific pattern
• Created by the design of the antenna
• Uses the magnify glass concept

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Passive Gain

• Antennas use passive gain
• Total amount of energy emitted by antenna doesnt
  increase only the distribution of energy around
  the antenna
• Antenna is designed to focus more energy in a
  specific direction
• Passive gain is always a function of the antenna
  (i.e. independent of the components leading up to
  the antenna

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Passive Gain

• Advantage
• Does not require external power
• Disadvantage
• As the gain increases, its coverage becomes more
  focused
• Highest-gain antennas cant be used for mobile
  users because of their tight beam

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Active Gain

• Providing an external power source
• Amplifier
• High gain transmitters
• Active gain involves an amplifier

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Antenna Gain

• 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)
• ? carrier wavelength

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Antenna gain

• Antenna gain is increased by focusing the antenna
• The antenna does not create energy, so a higher
  gain in one direction must mean a lower gain in
  another.
• Note antenna gain is based on the maximum gain,
  not the average over a region. This maximum may
  only be achieved only if the antenna is carefully
  aimed.

This antenna is narrower and results in 3dB
higher gain than the dipole, hence, 3dBD or
5.14dBi
This antenna is narrower and results in 9dB
higher gain than the dipole, hence, 9dBD or
11.14dBi
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Antenna gain
Instead of the energy going in all horizontal
directions, a reflector can be placed so it only
goes in one direction gt another 3dB of gain,
3dBD or 5.14dBi
Further focusing on a sector results in more
gain. A uniform 3 sector antenna system would
give 4.77 dB more. A 10 degree range 15dB
more. The actual gain is a bit higher since the
peak is higher than the average over the range.

• Mobile phone base stations claim a gain of 18dBi
  with three sector antenna system.
• 4.77dB from 3 sectors 13.33 dBi
• An 11dBi antenna has a very narrow range.

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Antenna Gain

• The power gain G, or simply the gain, of an
  antenna is the ratio of its radiation intensity
  to that of an isotropic antenna radiating the
  same total power as accepted by the real antenna.
  When antenna manufacturers specify simply the
  gain of an antenna they are usually referring to
  the maximum value of G.

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Antenna gain and effective areas
Type of antenna Effective area Power gain
Isotropic ?2/4? 1
Infinitesimal dipole or loop 1.5?2/4? 1.5
Half-wave dipole 1.64?2/4? 1.64
Horn, mouth area A 0.81A 10A/ ?2
Parabolic, face area A 0.56A 7A/ ?2
turnstile 1.15?2/4? 1.15
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Antenna Gain

• Q- What factors determine antenna gain?
• Ans- Effective area and wavelength

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Satellite Communication

• Q- What is the primary cause of signal loss in
  satellite communications?

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Basics How do Satellites Work

• Two Stations on Earth want to communicate through
  radio broadcast but are too far away to use
  conventional means.
• The two stations can use a satellite as a relay
  station for their communication
• One Earth Station sends a transmission to the
  satellite. This is called a Uplink.
• The satellite Transponder converts the signal and
  sends it down to the second earth station. This
  is called a Downlink.

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Basics Advantages of Satellites

• The advantages of satellite communication over
  terrestrial communication are
• The coverage area of a satellite greatly exceeds
  that of a terrestrial system.
• Transmission cost of a satellite is independent
  of the distance from the center of the coverage
  area.
• Satellite to Satellite communication is very
  precise.
• Higher Bandwidths are available for use.

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Basics Disadvantages of Satellites

• The disadvantages of satellite communication
• Launching satellites into orbit is costly.
• Satellite bandwidth is gradually becoming used
  up.
• There is a larger propagation delay in satellite
  communication than in terrestrial communication.

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Basics Factors in Satellite Communication

• Elevation Angle The angle of the horizontal of
  the earth surface to the center line of the
  satellite transmission beam.
• This effects the satellites coverage area.
  Ideally, you want a elevation angle of 0 degrees,
  so the transmission beam reaches the horizon
  visible to the satellite in all directions.
• However, because of environmental factors like
  objects blocking the transmission, atmospheric
  attenuation, and the earth electrical background
  noise, there is a minimum elevation angle of
  earth stations.

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Basics Factors in satellite communication .

• Coverage Angle A measure of the portion of the
  earth surface visible to a satellite taking the
  minimum elevation angle into account.
• R/(Rh) sin(p/2 - ß - ?)/sin(? p/2)
• cos(ß ?)/cos(?)
• R 6370 km (earths radius)
• h satellite orbit height
• ß coverage angle
• ? minimum elevation angle

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Basics Factors in satellite communication.

• Other impairments to satellite communication
• The distance between an earth station and a
  satellite (free space loss).
• Satellite Footprint The satellite
  transmissions strength is strongest in the
  center of the transmission, and decreases farther
  from the center as free space loss increases.
• Atmospheric Attenuation caused by air and water
  can impair the transmission. It is particularly
  bad during rain and fog.

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Atmospheric Losses

• Different types of atmospheric losses can disturb
  radio wave transmission in satellite systems
• Atmospheric absorption
• Atmospheric attenuation
• Traveling ionospheric disturbances

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Atmospheric Absorption

• Energy absorption by atmospheric gases, which
  varies with the frequency of the radio waves.
• Two absorption peaks are observed (for 90º
  elevation angle)
• 22.3 GHz from resonance absorption in water
  vapour (H2O)
• 60 GHz from resonance absorption in oxygen (O2)
• For other elevation angles
• AA AA90 cosec ?

Source Satellite Communications, Dennis Roddy,
McGraw-Hill
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Atmospheric Attenuation

• Rain is the main cause of atmospheric attenuation
  (hail, ice and snow have little effect on
  attenuation because of their low water content).
• Total attenuation from rain can be determined by
• A ?L dB
• where ? dB/km is called the specific
  attenuation, and can be calculated from specific
  attenuation coefficients in tabular form that can
  be found in a number of publications
• where L km is the effective path length of the
  signal through the rain note that this differs
  from the geometric path length due to
  fluctuations in the rain density.

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Traveling Ionospheric Disturbances

• Traveling ionospheric disturbances are clouds of
  electrons in the ionosphere that provoke radio
  signal fluctuations which can only be determined
  on a statistical basis.
• The disturbances of major concern are
• Scintillation
• Polarisation rotation.
• Scintillations are variations in the amplitude,
  phase, polarisation, or angle of arrival of radio
  waves, caused by irregularities in the ionosphere
  which change over time.
• The main effect of scintillations is fading of
  the signal.

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Satellite Communication

• Q- What is the primary cause of signal loss in
  satellite communications?
• Ans- Free space loss.

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Impairments

• Q- Name and briefly define four types of noise.

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Transmission Impairments

• Signal received may differ from signal
  transmitted causing
• Analog - degradation of signal quality
• Digital - bit errors
• Most significant impairments are
• Attenuation and attenuation distortion
• Delay distortion
• Noise

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Noise

• Signal strength falls off with distance over any
  transmission medium
• Varies with frequency

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Categories of Noise
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Categories of Noise

• Impulse Noise
• caused by external electromagnetic interferences
• noncontinuous, consisting of irregular pulses or
  spikes
• short duration and high amplitude
• minor annoyance for analog signals but a major
  source of error in digital data

• Crosstalk
• a signal from one line is picked up by another
• can occur by electrical coupling between nearby
  twisted pairs or when microwave antennas pick up
  unwanted signals

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Noise

• Thermal noise due to thermal agitation of
  electrons.
• Present in all electronic devices and
  transmission media.
• As a function of temperature.
• Uniformly distributed across the frequency
  spectrum, hence often referred as white noise.
• Cannot be eliminated places an upper bound on
  the communication system performance.
• Can cause erroneous to the transmitted digital
  data bits.

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Noise Noise on Digital Data
Error in bits
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Thermal Noise

• The noise power density (amount of thermal noise
  to be found in a bandwidth of 1Hz in any device
  or conductor) is

N0 noise power density in watts per 1 Hz of
bandwidth k Boltzmann's constant 1.3803 ?
10-23 J/K T temperature, in kelvins (absolute
temperature) 0oC 273 Kelvin
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Thermal Noise

• Noise is assumed to be independent of frequency
• Thermal noise present in a bandwidth of B Hertz
  (in watts)
• or, in decibel-watts (dBW),

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Noise Terminology

• Intermodulation noise occurs if signals with
  different frequencies share the same medium
• Interference caused by a signal produced at a
  frequency that is the sum or difference of
  original frequencies
• Crosstalk unwanted coupling between signal
  paths
• Impulse noise irregular pulses or noise spikes
• Short duration and of relatively high amplitude
• Caused by external electromagnetic disturbances,
  or faults and flaws in the communications system

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Impairments

• Q- Name and briefly define four types of noise.
• Ans- Thermal noise is due to thermal agitation
  of electrons. Intermodulation noise produces
  signals at a frequency that is the sum or
  difference of the two original frequencies or
  multiples of those frequencies. Crosstalk is the
  unwanted coupling between signal paths. Impulse
  noise is noncontinuous, consisting of irregular
  pulses or noise spikes of short duration and of
  relatively high amplitude.

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Refraction?

• Q- What is refraction?

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Law of refraction

• A refracted ray lies in the plane of incidence
  and has an angle ?2 of refraction that is
  related to the angle of incidence ?1 by

the symbols n1   and n2    are dimensionless
constant, called the index of refraction
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Refraction
Refraction occurs when an RF signal changes speed
and is bent while moving between media of
different densities.
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Refraction
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Refraction?

• Q- What is refraction?
• Ans- Refraction is the bending of a radio beam
  caused by changes in the speed of propagation at
  a point of change in the medium

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Fading

• Q- What is fading?

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Fading in a Mobile Environment

• The term fading refers to the time variation of
  received signal power caused by changes in the
  transmission medium or paths.
• Atmospheric condition, such as rainfall
• The relative location of various obstacles
  changes over time

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Types of Fading

• Fast fading
• Slow fading
• Flat fading
• Selective fading
• Rayleigh fading
• Rician fading

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Fading in the Mobile Environment

• Fading time variation of received signal power
  due to changes in the transmission medium or
  path(s)
• Kinds of fading
• Fast fading
• Slow fading
• Flat fading ? independent from frequency
• Selective fading ? frequency-dependent
• Rayleigh fading ? no dominant path
• Rician fading ? Line Of Sight (LOS) is dominating
  presence of indirect multipath signals

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Fading

• Q- What is fading?
• Ans- The term fading refers to the time
  variation of received signal power caused by
  changes in the transmission medium or path(s).

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• Q- What is the difference between diffraction
  and scattering?

104
Diffraction
Diffraction is a change in the direction and/or
intensity of a wave as it passes by the edge of
an obstacle.
Diffraction occurs because the RF signal slows
down as it encounters the obstacle and causes the
wave front to change directions Diffraction is
often caused by buildings, small hills, and other
larger objects in the path of the propagating RF
signal.
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Diffraction

• Diffraction - occurs at the edge of an
  impenetrable body that is large compared to
  wavelength of radio wave

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Scattering
Scattering happens when an RF signal strikes an
uneven surface causing the signal to be
scattered. The resulting signals are less
significant than the original signal. Scattering
Multiple Reflections
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Scattering

• Scattering occurs when incoming signal hits an
  object whose size in the order of the wavelength
  of the signal or less.
• Irregular objects such as walls with rough
  surfaces,furniture and vehicles and foliage and
  the like scatter rays in all the direction in the
  form of spherical waves.

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Multipath Propagation
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Diffraction and Scattering

• Q- What is the difference between diffraction
  and scattering?
• Ans- Diffraction occurs at the edge of an
  impenetrable body that is large compared to the
  wavelength of the radio wave. The edge in effect
  become a source and waves radiate in different
  directions from the edge, allowing a beam to bend
  around an obstacle. If the size of an obstacle is
  on the order of the wavelength of the signal or
  less, scattering occurs. An incoming signal is
  scattered into several weaker outgoing signals in
  unpredictable directions

110
Summary

• Antenna Functions
• Isotropic Antenna
• Radiation Pattern
• Parabolic Reflective Antenna
• Antenna Gain
• Signal Loss in Satellite Communication
• Noise Types
• Refraction
• Fading
• Diffraction and Scattering

111
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112

• Complimentary Session for Antennas and
  Propagation
• (Lecture 17)

113
Antenna Gain (Q)
Where
Sol
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115
Q

• Q- For each of the antenna types listed in Table
  above , what is the effective area and gain at a
  wavelength of 30 mm? Repeat for a wavelength of 3
  mm. Assume that the actual area for the horn and
  parabolic antennas is m2 .

116
Antenna Gain
Where
117
Ans

• Q- For each of the antenna types listed in Table
  above , what is the effective area and gain at a
  wavelength of 30 mm? Repeat for a wavelength of 3
  mm. Assume that the actual area for the horn and
  parabolic antennas is m2 .

118
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119
Q
Solution
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121
Q
Question
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123
Thermal Noise
Where
Question-
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125
The Expression Eb /N0

• in decibel notation,

Question-
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127

• Q- It is often more convenient to express
  distance in km rather than m and frequency in MHz
  rather than Hz. Rewrite Equation using these
  dimensions.
• Solution- The equations from Text Book are
• Solution-

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129
Q

• Q- Suppose a transmitter produces 50 W of power.
• Express the transmit power in units of dBm and
  dBW.
• If the transmitter's power is applied to a unity
  gain antenna with a 900-MHz carrier frequency,
  what is the received power in dBm at a free space
  distance of 100 m?
• Repeat (b) for a distance of 10 km.
• Repeat (c) but assume a receiver antenna gain of
  2.

130
Q/A

• Q- Suppose a transmitter produces 50 W of power.
• Express the transmit power in units of dBm and
  dBW.
• If the transmitter's power is applied to a unity
  gain antenna with a 900-MHz carrier frequency,
  what is the received power in dBm at a free space
  distance of 100 m?
• Repeat (b) for a distance of 10 km.
• Repeat (c) but assume a receiver antenna gain of
  2.

• .
• b)
• Therefore, received power in dBm 47 71.52
  24.52 dBm

131
Q/A

• Q- Suppose a transmitter produces 50 W of power.
• Express the transmit power in units of dBm and
  dBW.
• If the transmitter's power is applied to a unity
  gain antenna with a 900-MHz carrier frequency,
  what is the received power in dBm at a free space
  distance of 100 m?
• Repeat (b) for a distance of 10 km.
• Repeat (c) but assume a receiver antenna gain of
  2.

• c)
• d)

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133
Free Space Loss
134
Free Space Loss
135
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136
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