Faraday rotation

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Brief introduction abuot Faraday rotation.

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Faraday rotation

  1. 1. Created By:- AndroidWallet.blogspot.in 1
  2. 2. Radio energy emitted in space exhibits both electric and magnetic fields. A changing magnetic field produces an electric field and a changing electric field produces a magnetic field. Direction of wave propagation: E x H E H 2 AndroidWallet.blogspot.in
  3. 3. Orientation of a waves in a particular direction. Polarization is the alignment of the electric field vector of the plane wave relative to the direction of propagation. Linear polarization (vertical, horizontal) Circular polarization (right-hand, left-hand) Elliptical polarization E H E Horizontal polarization H Vertical polarization Right-handed circular polarization Left-handed elliptical polarization 3 AndroidWallet.blogspot.in
  4. 4.  On 432MHz and below, we all use linear polarization for EME.  A big problem with VHF/UHF EME is that the transmitted polarization is usually rotated before it reaches the receiving station, so there can be very large losses in signal strength.  EME signals are always close to the noise, with rapid fading, so even a 1dB loss is noticeable. 4 AndroidWallet.blogspot.in
  5. 5. •To keep the signal losses below 1dB, the polarization error must be less than about ±(20-30°). • The good news is that the signal loss within the ±20° region is very small. 5 AndroidWallet.blogspot.in
  6. 6.  mission of ,1994.  Radio waves passing through the Earth's ionosphere are likewise subject to the Faraday effect.  Ionosphere consists of a plasma containing free electrons which contribute to Faraday rotation.  The rotation of the plane of polarization of a plane-polarized light passing through a transparent isotropic medium or magnetic field undergoes Faraday rotation.  Faraday rotation is proportional to the square of the radar wavelength to the total Electron Content of the ionosphere. 6 AndroidWallet.blogspot.in
  7. 7. E E H H H E 7 AndroidWallet.blogspot.in
  8. 8. 8 AndroidWallet.blogspot.in
  9. 9. Satellite Communication galaxy sun ionosphere troposphere 9 AndroidWallet.blogspot.in
  10. 10.  A periodic change in the amount of irradiation from the sun that is experienced on Earth.  It has a period of about 10.7 years.  It is one component of solar variation, the other being a periodic fluctuations.  Solar variation causes changes in space weather and to some degree weather on Earth. 10 AndroidWallet.blogspot.in
  11. 11. *The effects of the ionosphere correlate with sun spot activity . *Possible effects include:fading,which can be significant (20dB or more). This tells why radio stations adjust their power o/p at sunset & sunrise. 11 AndroidWallet.blogspot.in
  12. 12.  The cycle is observed by counting the frequency and placement ofsunspots visible on the Sun. 12 AndroidWallet.blogspot.in
  13. 13.  Ionospheric effects are significant for frequencies up to about 10 GHz & particularly significant for non-geostationory satellites operating below 3 GHz.  The total electron content(TEC) accumulated through the ionospheric transmission path result in roation of the linear polarisation of the carrier & time dealy .The delay is known as Group dealy, while the rotation of the linear polarisation of the carrier is known as FARADAY ROTATION. 13 AndroidWallet.blogspot.in
  14. 14.  Faraday Rotation, The electrons in the ionosphere along with the Earth's magnetic field cause a rotation in the plane . which creates a cross-polarized component with linear polarization and a loss of circular polarization. 14 AndroidWallet.blogspot.in
  15. 15. • When no faraday rotation is present• The received power is proportional to E 2 O • A faraday rotation of some degrees will result in the copolarized component of the received signal being reduced to Eco = E cos__ • Recived power=Eco 2 15 AndroidWallet.blogspot.in
  16. 16. The polarization loss (PL) isPL = 20log(Eco/E) = 20log(cos__) 16 AndroidWallet.blogspot.in
  17. 17.  faraday rotation controlled varies by one order of magnitude between day and night as solar illumination exerts a major control on the level of ionospheric activity.  Faraday rotation can be minimized by employing circular polarization, and in fact, some satellite communication systems use circular polarization to avoid the problem. 17 AndroidWallet.blogspot.in
  18. 18.  Today Haselgrove's equations are widely used in scientific investigations involving radio propagation .  Therefore have found much applicability in exploration and utilization of the Earth's ionosphere. 18 AndroidWallet.blogspot.in
  19. 19.  11/12/2013 19 AndroidWallet.blogspot.in 19

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