A couple of days ago I watched a video from Phil’s Lab on YouTube and learned something. In the video he goes into detail about impedance matching for RF-traces in KiCAD. As an example he discusses the design of the GPS part of his flight controller. He explains that not only the wires you are using for the antenna have to be impedance matched (usually 50 Ohms), but also the traces from the GPS chip to the antenna socket.
The trace width, dielectric constant of the base material and distance of the trace to ground are important factors that I have not considerd in my design. Although my module works just fine, I can not estimate how big impact is for not considering.
For an optimal implementation he uses a 4-layer board with 0.3 mm trace width for the trace from he u-blox chip to the socket. The calculation is done with the KiCAD calculator and material properties from the manufacturers homepage. A 4-layer board is definitifly not in the reach for home manufactoring, so if one wants to do a proper design of my module or something similar the PCB has to be manufactured by one of the many affordable services.