The use of wireless devices has become very common in many companies and homes in recent years. Bluetooth =99 connected computer peripherals, cell phones, wireless LAN links and cordless phones all depend upon antennas to make a connection. Often the antenna is inside the device and is invisible, but if an external antenna is used, perhaps to increase the range of the connection, it needs a cable to connect it to the device. Both antennas and their feeder cables are prone to damage. This is particularly true if any part of the system is located outdoors. Fault finding these systems can be more difficult than say testing a DC system like an electric door bell. This is because the loss of the cable varies with frequency. It may be perfectly connected when tested with an ohmmeter, but still show a high loss when transmitting power at a frequency of Gigahertz or two, like some of the systems mentioned above. Measurement of the match of the antenna and the cable loss are part of the answer. This article explains what is involved, and how they are measured with a dual directional coupler. For details see:
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15 years ago
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rectional_coupler.pdf