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
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
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
Impedance matching: matches impedance of
transmission line to the intrinsic impedance of
free space to prevent wanted reflection back to
Two main purposes of Antenna
Antenna must be designed to direct the
radiation in the desired direction.
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.
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.
The type of system you are installing will help
determine the type of antenna used. Generally
speaking, there are two ‘types’ of antennae:
- 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
- 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
- Isotropic antenna
• Log periodic dipole array
- BW is smaller than LPDA
- typical gain 12 – 14 dBi
Reflector Driven element (dipole)
• Yagi antenna
main lobeside lobe
- very wide BW, with constant SWR
- typical gain 10 dBi
An antennas polarization is relative to the E-field of antenna.
– If the E-field is horizontal, than the antenna is Horizontally
– If the E-field is vertical, than the antenna is Vertically Polarized.
No matter what polarity you choose, all antennas in the same RF
network must be polarized identically regardless of the antenna
The electric field is vertical to the ground (In the maximum
The electric field is parallel to the ground (In the maximum gain
Polarization Requirements for various frequencies
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