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Antenna chapter 1


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antenna and propagation

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Antenna chapter 1

  2. 2. Introduction  The electric charges are the sources of the electromagnetic (EM) fields. When these sources are time varying, the EM waves propagates away from the source and the radiation takes place.  In general, the radiation can be considered as a process of transmitting energy.  The radiation of the electromagnetic wave into the space is effectively achieved by using a conducting or dielectric structure called antennas or radiators.  A metallic device used for radiating or receiving radio waves is called antenna.  According to IEEE, antenna is defined as a means for radiating or receiving radio waves. Thus antenna is regarded as a transition between the free space and transmission line.  The antenna is a matching device between free space and the transmission line.
  3. 3. Impedance matching: matches impedance of transmission line to the intrinsic impedance of free space to prevent wanted reflection back to source. Two main purposes of Antenna Antenna must be designed to direct the radiation in the desired direction.
  4. 4. Antenna - How it Works The antenna converts radio frequency electrical energy fed to it (via the transmission line) to an electromagnetic wave propagated into space. Antenna is a transducer which converts electrical energy into EM wave and vice versa.
  5. 5. Antenna Fundamentals  Antenna can be used as transmitting antenna or receiving antenna. It has directional properties. It is the important component of a wireless communication system.  Different antennas are used in different systems. But all the antennas possess basic fundamental properties which are same for all. -radiation pattern -radiation intensity - gain -directivity -power gain -antenna efficiency -effective aperture - radiation resistance, - beamwidth - bandwidth, etc. - Polarization
  6. 6. The type of system you are installing will help determine the type of antenna used. Generally speaking, there are two ‘types’ of antennae: 1. Directional - this type of antenna has a narrow beamwidth; with the power being more directional, greater distances are usually achieved but area coverage is sacrificed - Yagi, Panel, Sector and Parabolic antennas 2. Omni-Directional - this type of antenna has a wide beamwidth and radiates 3600; with the power being more spread out, shorter distances are achieved but greater coverage attained - Isotropic antenna
  7. 7. dBd and dBi isotropic radiator half-wave dipole 2.15dB eg: 0dBd = 2.15dBi
  8. 8. Yagi Uda
  9. 9. Parabolic
  10. 10. Sectoral
  11. 11. • Log periodic dipole array (LPDA) DipolesTransmission line - BW is smaller than LPDA - typical gain 12 – 14 dBi Reflector Driven element (dipole) Directors • Yagi antenna Directional Radiation Pattern main lobe main lobeside lobe back lobe - very wide BW, with constant SWR - typical gain 10 dBi
  12. 12. Antenna Radiation pattern Directional Antenna Radiation Pattern Horizontal plane Vertical plane
  13. 13. Typical Radiation Pattern for a Yagi
  14. 14. 0 90 180 270 0 -3 -6 -10 -15 -20 -30 dB 0 90 180 270 0 -3 -6 -10 -15 -20 -30 dB Typical Radiation Pattern for a Sector
  15. 15. Pattern
  16. 16. Upper Side Lobe Suppression (dB) Side lobes
  17. 17. 120° (eg) Peak Peak - 10dB Peak - 10dB 10dB Beamwidth 60° (eg) Peak Peak - 3dB Peak - 3dB 3dB Beamwidth Beamwidth
  18. 18. An antennas polarization is relative to the E-field of antenna. – If the E-field is horizontal, than the antenna is Horizontally Polarized. – If the E-field is vertical, than the antenna is Vertically Polarized. Polarization No matter what polarity you choose, all antennas in the same RF network must be polarized identically regardless of the antenna type.
  19. 19. Polarization Vertical Horizontal Vertical Polarization: The electric field is vertical to the ground (In the maximum gain direction) Horizontal Polarization: The electric field is parallel to the ground (In the maximum gain direction)
  20. 20. Polarization Requirements for various frequencies
  21. 21. Polarization may deliberately be used to: – Increase isolation from unwanted signal sources (Cross Polarization Discrimination (x-pol) typically 25 dB) – Reduce interference – Help define a specific coverage area Horizontal Vertical