I'm using an "IOT" radio module designed with a 50 ohm single ended antenna output. The working frequency is about 868 MHz, the maximum transmit power is 14dBm. The module antenna output is connected to a 50 ohm PCB transmission line and some RF switches and ends in a SMA female connector. The connector is meant for attaching an external 50 ohm antenna. In the path is also place for PI matching network.
I know how to correctly match a path and SMA including attached antenna (PCB or external) with a VNA - many explanations can be found online for this task.
In my current case the antenna is not yet known, but I want to make sure that any antenna would see 50 ohm on the SMA connector.
How can I match just the RF path + SMA connector to 50ohm instead of matching the RF path, SMA connector, and attached antenna?
thanks for your answer. I see your point that everything should be 50ohm. But my "own" antenna is not pure 50 ohm and needs some tuning.
Let me show you my situation in more detail: I use a custom L pcb antenna attached to a std. 50 ohm rf connector (mmcx in my case). The unmatched or single network matched bandwidth of the L-monopole is not enough to cover 791 to 960 MHz, needed for LTE Bands 8, 20 and 868 MHz SRD. This is why I added four individual matching networks using rf switches (see image) that switch according to the used frequency. My custom antenna is obviously not 50ohm but most likely no to far of since it's a monopole.
So I think my actual question is: How to determinate how much the match alters the 50 ohm impedance on the rf connector if one attaches an external antenna that has been tuned to 50 ohm? From my understanding i should measure the transmission line including the match to the rf connector and "hope" that the match for my pcb antenna does allow also the usage of an external antenna.