ANTENNA PATTERN DIAGRAM
Most of the antenna manufacturers show the pattern diagram of the antennas in their product catalogues.
However some people do have problems in understanding the information that is being shown.
Let┬┤s see a generic antenna pattern diagram and make some conclusions:
It is obtained by rotating the antenna from 0 to 360 degrees whilst its output signal level is measured in relation to the signal level of the transmitter.
The black trace shows the behaviour of the antenna at a glance:
The maximum value is obtained when the antenna is pointing directly to the transmitter ( zero degrees).
At both sides of this direction the power received decreases.
The shape of this measurement is the mentioned black lobe.
The A/B ratio is an indication of the front-to-back ratio: it measures how the incoming signal is rejected from its rear.
The smaller is A and the greater is B, the better is this parameter.
The blue angle is where the antenna is radiating most of its energy.
It is measured between two points where the radiated power decreases to half its value (-3 dB).
This angle is the parameter known as the antenna beamwidth, which at the same time is a measurement of the directivity of the antenna.
The smaller this angle the greater the directivity.