User's Manual

GE910 Hardware User Guide

GE910 Hardware User GuideGE910 Hardware User Guide

GE910 Hardware User Guide

1vv0300962 Rev.9-bis3 2013-05-20

Mod. 0805 2011-07 Rev.2

7.4.1. RF Signal Requirements

Thanks to the internal LNA it amplifies the GNSS signals and provides enough gain for the

receiver to use a passive antenna. A very low noise design is utilized to provide maximum

sensitivity. For better performance the system requires an external BIAS-T and antenna voltage

supply for active antenna.

7.4.2. GNSS Antenna – PCB Line Guidelines

• Ensure that the antenna line impedance is 50ohm.

• Keep the antenna line on the PCB as short as possible to reduce the loss.

• Antenna line must have uniform characteristics, constant cross section, avoid meanders and

abrupt curves.

• Keep one layer of the PCB used only for the Ground plane, if possible.

• Surround (on both the sides, over and under) the antenna line on PCB with Ground, avoid

having other signal tracks facing directly the antenna line of track.

• The ground around the antenna line on PCB has to be strictly connected to the Ground Plane

by placing vias once per 2mm at least.

• Place EM noisy devices as far as possible from antenna line.

• Keep the antenna line far away from power supply lines.

• Keep the antenna line far away from GSM RF lines.

• If you have EM noisy devices around the PCB hosting the module, such as fast switching

ICs, take care of the shielding of the antenna line by burying it inside the layers of PCB and

surround it with Ground planes, or shield it with a metal frame cover.

• If you do not have EM noisy devices around the PCB hosting the module, use a strip-line on

the superficial copper layer for the antenna line. The line attenuation will be lower than a

buried one.

7.4.3. GNSS Antenna Polarization

The GNSS signal as broadcast is a right hand circularly polarized signal. The best antenna to

receive these signals is a right hand circularly (RHCP) polarized antenna.

Remember that IS-GPS-200E specifies the received power level with a linearly polarized

antenna. A linearly polarized antenna will have 3 dB losses as compared to an RHCP antenna

assuming the same antenna gain (specified in dBi and dBic respectively).

An RHCP antenna is better at rejecting multipath than a linearly polarized antenna.

This is because the reflected signal changes polarization to LHCP, which would be rejected by

the RHCP antenna by typically 20 dB or so. If the multipath signal is attenuating the line of

sight signal, then the RHCP antenna would show a higher signal level than a linearly polarized

antenna because the interfering signal is rejected.

However, in the case where the multipath signal is replacing the line of sight signal, such as in

an urban canyon environment, then the number of satellites in view could drop below the needed

number to determine a 3D solution. This is a case where a bad signal may be better than no