Radio energy emitted in space exhibits both electric and
A changing magnetic field produces an electric field and a
changing electric field produces a magnetic field.
Direction of wave propagation: E x H
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)
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.
•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.
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.
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
Solar variation causes changes in space weather and to some
degree weather on Earth.
effects of the ionosphere correlate with sun spot activity .
*Possible effects include:fading,which can be significant (20dB or more).
at sunset &
The cycle is observed by counting the frequency and placement
ofsunspots visible on the Sun.
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.
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.
• When no faraday
rotation is present• The received
proportional to E 2
• 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
The polarization loss (PL) isPL = 20log(Eco/E)
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.
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.