I am developing an embedded system that performs GPS and Wifi operation with separate modules for each and two SMA connectors to connect the respective antennas. Once it is being installed, is there a way I can identify whether the antennas are connected properly or the cable I am using is broken? As I am writing the diagnostic software, it would be great if I could include this case so as to identify wrong installations.
For GPS receivers in particular, many of them use an "active" antenna that has a built-in preamp, and requires typically 3.3V or 5.0V at a few 10s of mA of DC power fed down the coax. Some GPS receiver modules actually monitor the amount of current being drawn by the antenna and can alert you if it is either too low (cable open) or too high (cable shorted).
Other GPS modules don't monitor the current themselves, but they do have a separate power input specifically for antenna power, to which you can add your own monitor circuit.
Unfortunately, WiFi antennas are usually passive, so the same technique can't be used there.
I am sure somebody with more knowledge about antennas will have a more elegant solution, but you could put these antennas on a sub-board if this is your own design, and then see if the sub board is plugged in (ie. simply closing two pins on the connector to the sub-board). This will add more parts and cost though.