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mosaic-X5 Integration
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4.4.3
Antenna Input
The antenna input trace shall be routed as a 50-ohm coplanar waveguide with ground, as
in the picture below. It is best to use stitching vias every few mm for good ground
coherence. The width of the trace to set the impedance to 50 ohm can be calculated with
online tools (e.g.
https://chemandy.com/calculators/coplanar-waveguide-with-ground-
). Usually it is best to use the top-layer for the coplanar waveguide and the
second layer for ground.
The antenna trace can be directly routed to the desired type of coax connector, as all
protection circuitry is integrated in mosaic-x5.
4.4.4
Avoiding Self-Interference
The antenna input connection is sensitive to interference from higher harmonics of other
signals on the board. Even clock signals of just a few MHz can produce harmful harmonics
at GNSS frequencies (1155-1300 MHz and 1540-1610 MHz).
It is best to keep the antenna input connection short, to reduce the area in which signals
can be picked up. Stitching vias at the input trace could be arranged as a via fence to
shield it from interference.
Furthermore, it is important to avoid digital signals in the MHz-
range (SDIO, RMII, MDIO,…)
from running close to the antenna input.
If an external frequency reference is used, it will get close to the antenna input because
of the proximity of the REF_I and ANT pad.
This is not a problem if it doesn’t have many
harmonics. It can however cause issues if the reference signal is originating from a high-
speed buffer or comparator. This can be avoided at circuit level, by filtering the signal with
an RC-filter near the source (see section 3.7.2).
Most self-interference issues relate to radiated interference into a collocated GNSS-
antenna. The following applies when the GNSS antenna is closer than 1 meter from
electronics which are not in a shielded box:
