ADVANCED COMPUTER NETWORKS

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ADVANCED COMPUTER NETWORKS

• ANTENNAS
• Presented By
• SANKEPALLY VIDYA SAGAR
• SAI NAVEEN SESHAM
• SHASHIKANT LAKUMA

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OVERVIEW

• INTRODUCTION
• TYPES
• PARAMETERS
• MODELS
• CONCLUSION
• QUESTIONS AND ANSWERS

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INTRODUCTION

• The origin of the word antenna relative to
  wireless apparatus is attributed to Guglielmo
  Marconi. Marconi's use of the word antenna
  (Italian for pole) would become a popular term
  for what today is uniformly known as the antenna
  .
• Antennas play a primary role in wireless
  network.
• An antenna is a transducer designed to transmit
  or receive radio waves which are a class of
  electromagnetic waves.
• Antennas convert radio frequency electrical
  currents into electromagnetic waves and vice
  versa.

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PHYSICAL DESIGN

• Physically, an antenna is an arrangement of
  conductors that generate a radiating
  electromagnetic field in response to an applied
  alternating voltage and the associated
  alternating electric current, or can be placed in
  an electromagnetic field so that the field will
  induce an alternating current in the antenna and
  a voltage between its terminals.
• Antennas usually work in air or outer space, it
  can also be operated under water or even through
  soil and rock at certain frequencies for short
  distances

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A building rooftop supporting numerous dish and
sectored mobile telecommunications antennas
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TYPES OF ANTENNAS

• There are two fundamental types of antennas
  
  
• Omni-directional and Directional.
• A omni-directional antenna (such as a vertical
  rod) is an antenna system which radiates power
  uniformly in one plane with a directive pattern
  shape in a perpendicular plane.
• A directional antenna is an antenna which
  radiates greater power in one or more directions
  allowing for increased performance on transmit
  and receive and reduced interference from
  unwanted sources.

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Yagi-Uda Antenna

• By adding additional conducting rods or coils
  (called elements) and varying their length,
  spacing, and orientation ,an antenna with these
  specific desired properties can be created, such
  as a Yagi-Uda Antenna

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CUTAIN ANTENNA
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ANTENNAS

• Rooftop television Antenna.

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ANTENNA PARAMETERS

• Resonant Frequency.
• Gain.
• Radiation Pattern.
• Efficiency.
• Bandwidth.
• Polarization.
• Impedance.

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TRANSMISSION AND RECEPTION

• Antennas used for transmission have a maximum
  power rating, beyond which heating, arcing or
  sparking may occur in the components, which may
  cause them to be damaged or destroyed.
• Antennas designed specifically for reception
  might be optimized for noise rejection
  capabilities.
• All of the antenna parameters are expressed in
  terms of a transmission antenna, but are
  identically applicable to a receiving antenna .

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ANTENNA MODELS

• Isotropic radiator.
• Dipole antenna.
• Random wire antenna.
• Horn antenna.

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ANTENNA MODELS

• The isotropic radiator is a purely theoretical
  antenna that radiates equally in all directions.
• The dipole antenna is simply two wires pointed in
  opposite directions arranged either horizontally
  or vertically, with one end of each wire
  connected to the radio and the other end hanging
  free in space.
• The random wire antenna is simply a very long
  wire with one end connected to the radio and the
  other in free space, arranged in any way most
  convenient for the space available.
• The Horn is used where high gain is needed, the
  wavelength is short and space is not an issue.

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AFFECT ON GROUND

• At frequencies used in antennas, the ground
  behaves mainly as a dielectric.
• The conductivity of ground at these frequencies
  is negligible.
• When an electromagnetic wave arrives at the
  surface of an object, two waves are created one
  enters the dielectric and the other is reflected.
• If the object is a conductor, the transmitted
  wave is negligible and the reflected wave has
  almost the same amplitude as the incident one.
• Most of the electromagnetic waves emitted by an
  antenna to the ground below the antenna at
  moderate (say lt 60) angles of incidence enter
  the earth and are absorbed .
• When the angle of incidence is near 90 (grazing
  incidence) almost all the wave is reflected.

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Antennas Behavior On Ground
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• The vertical component of the current reflects
  without changing sign. The horizontal component
  reverses sign at reflection

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CONCLUSION

• Antennas are used in systems such as radio and
  television broadcasting, point-to-point radio
  communication, wireless LAN, radar, and space
  exploration .
• ANY MOBLIE NETWORK CANT BE IMAGINED WITHOUT
  ANTENNA.

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QUESTIONS

• Q1. Why did you choose titans mysterious radio
  wave for explaining the concept of antennas?
• Q2. The formula mentioned in the conclusion. What
  significance it has and why/where it is used?
• Q3. How do antennas radiate. Could you explain in
  detail?
• Q4.What is the size of antenna and does size of
  the antenna has effects on other factors?
• Q5.How antennas parameters influence the design
  of antennas?

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QUESTION 1

• Q1. The formula mentioned in the conclusion. What
  significance it has and why/where it is used?
• The simple formula, ltPrgt(E02 /?)(?2/8p), for
  the received power of an antenna with a matched
  load in an over-moded cavity actually holds for
  an antenna of any shape and size.
• Where ,? The radiation efficiency,
• E0is the electrical field radiated by the
  antenna
• ?Wave Length.

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QUESTIONS 2

• Q2. How do antennas radiate. Could you explain in
  detail?
• Ans. The radiation of an antenna describes the
  relative strength of the radiated field in
  various directions from the antenna, at a fixed
  or constant distance. The radiation pattern is a
  "reception pattern" as well, since it also
  describes the receiving properties of the
  antenna. The radiation pattern is
  three-dimensional . In order to know how an
  antenna radiates, let us first consider how
  radiation occurs.
• A conducting wire radiates mainly because of
  time-varying current or an acceleration
  (ordeceleration) of charge. If there is no motion
  of charges in a wire, no radiation takes place,
  since no flow of current occurs.
• Radiation will not occur even if charges are
  moving with uniform velocity along a straight
  wire. However, charges moving with uniform
  velocity along a curved or bent wire will produce
  radiation.

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QUESTION 3

• Q3.What is the size of antenna and does size of
  the antenna has effects on other factors?
• Unfortunately, there is an inverserelationship
  between antenna gain and antenna beamwidth.
  Additionally, there is a proportional
  relationship between antenna gain and the antenna
  size.
• Antenna Size Gain 2 / 4.
• The conclusion, therefore, would be that if we
  increase the antenna size by a factor of two in
  one plane, we would decrease the beamwidth in
  that plane by a factor of two and increase the
  antenna gain by 3 dB.

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QUESTION 4

• Q4.How antennas parameters influence the design
  of antennas?
• Ans.YES
• An antenna with a low gain emits radiation in all
  directions equally, whereas a high-gain antenna
  will preferentially radiate in particular
  directions.
• For the ideal isotropic antenna, it would be a
  sphere. For a typical dipole, this would be a
  toroid
• Radiation in an antenna is caused by radiation
  resistance which can only be measured as part of
  total resistance including loss resistance. Loss
  resistance usually results in heat generation
  rather than radiation, and reduces efficiency.
• The bandwidth of an antenna may be increased by
  several techniques, including using thicker
  wires, replacing wires with cages to simulate a
  thicker wire, tapering antenna components (like
  in a feed horn), and combining multiple antennas
  into a single assembly .
• PolarizationIt has nothing in common with
  antenna directionality terms "horizontal",
  "vertical" and "circular". Thus, a simple
  straight wire antenna will have one polarization
  when mounted vertically, and a different
  polarization when mounted horizontally.

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• ANY QUESTIONS
• ???

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• THANK YOU
• Have a gr8 day