High Gain Antennas - Leica mojoRTK How-To Manual

High Gain Antennas

The first thing to note about antennas with higher gain is that they do not
produce higher transmit powers, instead they transmit the same power
into a more directed field. However, when receiving, high gain antennas do
produce more power when the signal is received from its higher gain
direction, and lower power when receiving signals from other directions.
Figure 3 shows the basic concept of the difference between antenna gain
and antenna directivity. In the diagram, the darker the signal the stronger it
is. The low gain antenna spreads the transmitted signal over a greater area
and is therefore weaker than the signal from the high gain antenna which
transmits the same signal into a smaller area.
You can often obtain the gain pattern of an antenna from the
manufacturer or the supplier. The gain patter specification provides a plot
of gain versus direction. These plots can be difficult to read but generally
provide a general guide as to which directions they don't work well at.
Figure 3 – Directivity of antennas with different antenna gains
NOTE: although the high gain antenna pushes a stronger signal further out it may cause problems when trying to
receive the signal when you are too close to the antenna and it is mounted high up a tower. Also note that the
diagram may exaggerate the reduction in transmission area and was drawn only to explain the concept.
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