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34
ZETA-xxP Series
Hardware Manual
rev
D
GNSS Antenna Gain
Antenna gain is defined as the extra signal power from the antenna as compared to a
theoretical isotropic antenna (equally sensitive in all directions).
It is important to note that GNSS antenna gain is not the same as external LNA gain.
Most antenna vendors will specify these numbers separately, but some combine
them into a single number. It is important to know both numbers when designing and
evaluating the front end of a GNSS receiver.
An antenna with higher gain will generally outperform an antenna with lower gain.
Once the signals are above about -130 dBm for a particular satellite, no improvement
in performance would be gained. However, for those satellites that are below
about -125 dBm, a higher gain antenna would improve the gain and improve the
performance of the GNSS receiver. In the case of really weak signals, a good antenna
could mean the difference between being able to use a particular satellite signal or
not.
As the GNSS antenna ideally should be located away from the ZETA-xxP modem
series then an active antenna will be required to obtain the best system performance.
The active antenna has its own built in low noise amplifier to overcome RF trace or
cable losses after the active antenna. The active antenna has a low noise amplifier
(LNA) with associated gain and noise figure.
GNSS Antenna Connector (ZETA-GEP Models)
GNSS Antenna Polarization
The GNSS signal as broadcast is a right hand circularly polarized signal. The best
antenna to receive the GNSS signal is a right hand circularly (RHCP) polarized patch
antenna.
