Faraday rotation
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Radio waves propagating through space exhibit electric and magnetic fields that are oriented perpendicular to each other and the direction of propagation. Polarization describes the orientation of these oscillating fields and can be linear, circular, or elliptical. For Earth-Moon-Earth (EME) communications, linear polarization is typically used below 432MHz to minimize signal losses from polarization rotation caused by propagation through the ionosphere, which can exceed 1dB for rotations greater than 20-30 degrees. Faraday rotation, proportional to electron density and wavelength squared, further contributes to polarization rotation as radio waves pass through the ionosphere.
Faraday rotation
- 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. 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. 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. •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. 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
- 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. *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. The cycle is observed by counting the frequency and placement ofsunspots visible on the Sun. 12 AndroidWallet.blogspot.in
- 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. 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. • 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. The polarization loss (PL) isPL = 20log(Eco/E) = 20log(cos__) 16 AndroidWallet.blogspot.in
- 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. 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