Cobham Antenna Systems

Antenna Primary Specification
SIDELOBES
In antenna engineering, side lobes are the
lobes of the radiation pattern that are not the
main beam. An antenna radiation pattern is
more commonly called a beam pattern. The
power density in the side lobes is generally
much less than that in the main beam.
Sidelobe levels are measured in dBs relative to
the peak of the main beam.
It is possible to control sidelobe levels, if
necessary, depending on the application.
Azimuth cut
Sidelobes
8
POLARISATION
All electromagnetic radiation is polarised. The
figures below show the electric (E) vector
in a propagating wave for various types of
polarisation.
The polarisation of an antenna describes the
orientation of its electrical field or E-Plane.
The polarisation of antenna can be linear or
circular.
Linear Polarisation is usually vertical or
horizontal. Dual polar antennas can produce
both vertical and horizontal polarisations via
separate ports. A further extension of this are
dual slant antennas; these are essentially the
same as dual vertical and horizontal antennas
but with the polarisations rotated by 45°.
Circular polarisation is produced when the
E-plane of the antenna spins. Depending on
the direction of spin the polarisation is right
or left.
Elevation cut
CROSS POLAR
Antennas are never perfectly polarised. Cross
polar is a measure of how much energy is
in the plane perpendicular to the E-plane or
opposite hand of circular polarisation. It is
typically quoted relative to the peak gain of the
antenna.
Vertical
Horizontal
Circular, right or left