User's Manual

LE920A4 HW User Guide Antenna(s)
Doc#: 1VV0301261 GPS/GNSS Antenna Requirements
Rev. 4.3 Page 66 of 123 2017-12-07
7.5.2. Linear and Patch GPS/GNSS Antenna
Using this type of antenna introduces at least 3 dB of loss compared to a circularly
polarized (CP) antenna. Having a spherical gain response instead of a hemispherical gain
response can aggravate the multipath behavior and create poor position accuracy.
7.5.3. Front End Design Considerations
Since there is no antenna connector on the module, the antenna must be connected to
the module through the PCB to the antenna pad.
If the antenna is not directly connected at the antenna pad of the module, a PCB line is
required. This line of transmission must meet the following requirements:
Table 23: Antenna Line on PCB Requirements
Characteristic impedance 50 Ohm
Max attenuation 0.3 dB
Avoid coupling with other signals.
Cold End (Ground Plane) of the antenna must be equipotential to the module’s ground
pads.
Furthermore, if the device is developed for the US and/or Canada market, it must comply
with the FCC and/or IC requirements.
This device is to be used only for mobile and fixed application.
7.5.4. GPS/GNSS Antenna – PCB Line Guidelines
• Ensure that the antenna line impedance is 50 Ohm.
• Keep the line on the PCB as short as possible to reduce the loss.
• The antenna line must have uniform characteristics, constant cross section, and
avoid meanders and abrupt curves.
• Keep one layer of the PCB used only for the ground plane; if possible.
• Surround (on the sides, over and under) the antenna line on the PCB with ground.
Avoid having other signal tracks directly facing the antenna line track.
• The ground around the antenna line on the PCB must be strictly connected to the
main ground plane by placing vias at least once per 2mm.
• Place EM-noisy devices as far as possible from the module antenna line.
• Keep the antenna line far away from the module power supply lines.
• If EM-noisy devices are around the PCB hosting the module, such as fast
switching ICs, ensure shielding the antenna line by burying it inside the layers of
PCB and surrounding it with ground planes; or shield it with a metal frame cover.
• If you do not have EM-noisy devices around the PCB of the module, use a Micro
strip line on the surface copper layer for the antenna line. The line attenuation will
be lower than a buried one.