NINA-B3 series - System integration manual
UBX-17056748 - R13 Design-in Page 33 of 72
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⚠ According to FCC regulations, the transmission line from the module antenna pin to the antenna
or antenna connector on the host PCB is considered part of the approved antenna design.
Therefore, module integrators must either follow exactly one of the antenna reference designs
used for the FCC type approval of the module or certify their own designs.
3.3.1 RF transmission line design (NINA-B3x1 only)
RF transmission lines, such as the ones from the ANT pad up to the related antenna connector or up
to the related internal antenna pad, must be designed so that the characteristic impedance is as close
as possible to 50 . Figure 10 shows the design options and the main parameters to be taken into
account when implementing a transmission line on a PCB:
• Microstrip: track coupled to a single ground plane, separated by dielectric material.
• Coplanar microstrip: track coupled to ground plane and side conductors, separated by dielectric
materials).
• Strip: track sandwiched between two parallel ground planes and separated by dielectric materials.
Figure 10: Transmission line trace design
To properly design a 50 transmission line, the following remarks should be taken into account:
• The designer should provide enough clearance from surrounding traces and ground in the same
layer; in general, a trace to ground clearance of at least two times the trace width should be
considered, and the transmission line should be ‘guarded’ by ground plane area on each side.
• The characteristic impedance can be calculated as a first iteration by using tools provided by the
layout software. It is advisable to ask the PCB manufacturer to provide the final values that are
usually calculated using dedicated software and available stack-ups from production. It could also
be possible to request an impedance coupon on the side of the panel so that the real impedance
of the traces can be measured.
• FR-4 dielectric material, despite its inherent high losses at high frequencies, can be considered in
RF designs providing that:
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