I am designing a PCB in which there are 3 SIM800 GSM modules sharing a (commercial) external antenna. The external antenna is connected to the PCB via an antenna connector, and from that connector, the antenna signal is “shared” via PCB traces running to the GSM_ANT port of the GSM modules (please see photo)
The reason I prefer this design is that it is both cheap and convenient. But without in-depth knowledge on antenna design and EMI, my question is Could this be a bad design? Or should there be scenarios that this design does not work reliably?
Just to provide more info, the PCB will be housed inside a steel enclosure, and its main PSU is an AC-DC adapter (good brand) which is already sealed for EMI. The adapter is also inside the steel enclosure. The steel enclosure will be deployed in a residential area where there are no large machineries around.
Following some of your answers, I update the question as follows: Below is the old design, which uses 3 separate antenna connectors for the 3 GSM modules. However, these 3 antenna cables are combined (soldered) into one (with seal) outside the PCB and go to the external antenna.
The 3 GSM modules are supposed to be sending signal one at a time.
This old design has been tested and worked (though I suspect that signal strength are just around 8/10 of what it should be - good enough for the application though)