Trace Antenna Design; Table 9. Antenna Design Requirements; Figure 22. Reference Schematic Design At The Antenna Interface - ST STM32WL Series User Manual

6.4.4

Trace antenna design

To ensure an efficient transmission through the air, it is necessary to have a proper trace antenna design. So, an
appropriate antenna type and PCB design must be taken into account.
To feed an antenna, transmission lines on PCBs, designed considering their characteristic impedances, are used.
Then, comprehensive functional tests of the RF part are required before mass production of terminal products.
This chapter is intended to give some general guidelines when routing an RF trace antenna design.
Antenna design requirements
The antenna used on the B-WL5M-SUBG1 product is the ANT-SS900 from LPRS.
Frequency range
Nominal impedance
Maximum input power
Antenna gain
All stubby antennas with similar characteristics can be used.
Reference schematic design
The reference schematic is displayed below:
It might be useful to reserve a matching circuit (π structure) for better RF performances. The topology of the π
filter (C19, L1, and C20) must be placed as close as possible to the antenna connector. It is recommended not to
fit C19 and C20 and to place a 0 Ω resistor at the L1 position.
RF track routing guidelines
The characteristic impedance of the RF line between the STM32WL5MOC and the antenna connector must be
controlled to 50 Ω.
The geometry of the RF trace (trace width (W), the spacing between the RF trace and the ground (G) as well as
the height (H) of the RF trace to the reference ground determines its impedance. The layer of the PCB that the
transmission line is routed on and the dielectric constant of the PCB materials are also used to calculate the
impedance of these types of traces. There are many impedance calculators with coplanar waveguide and
microstrip models that are available for making these calculations.
UM3127 - Rev 1
Table 9. Antenna design requirements
Parameter
Figure 22. Reference schematic design at the antenna interface
Hardware layout and configuration
Requirement
824–928 MHz
50 Ω
50 W
2 dBi max
UM3127
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