The antenna is the device responsible of converting the electric signal confined ‘’guided’’ in the cables to a radiating waves.
Isotropic Antenna
•An isotropic antenna is a completely non‐directional antenna that radiates equally in all directions. Since all practical antennas exhibit some degree of directivity, the isotropic antenna exists only as a mathematical concept .•All the antenna specs will be measured relative to the isotropic antenna (Reference antenna)
Antenna specs
1-Gain
-Defined as the ratio between the power of the max direction of the antenna to the power obtained by an isotropic antenna in the same direction.
-Virtual gain (antenna is a passive element).
-Define for both vertical and horizontal plans.
2-BeamWidth
-Defined as the angel between the max direction to the direction where the power is reduced to the half in the max direction.
-Represent the directivity of the antenna.
-Define for both vertical and horizontal plans.
-Defined as the angle between the direction of the maximum radiation to the direction of the horizontal axes
-Define for the horizontal plane only.
-Can be achieved electrically (remotely) or mechanically.
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4-Diveristy-Defined as the redundancy in receiving and/or transmitting the signal.
-The purpose is to overcome fading/attenuation that may be experienced in the signal path.
-Typical gain value is (36)db.
•First side loops suppression ratio
•Front to back loop ratio.
•Side loops is important for GSM to achieve near field coverage; while the effect for the back loop is bad as it’s adding an interference.
•The mechanical tilt affecting both the main loop only; while the electrical tilt affecting the front and back loops.
•Input Current amplitude.
•Input current phase.
•Geographical shape of the radiating element.
•UMTS antenna pattern (N-array dipole)
A half-wave dipole antenna may also be used as a gain reference for practical antennas.
