Using a dual-directional coupler to measure antenna matching

摘要

In modern wireless communications systems, 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 a DC system. 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 one gigahertz or two, like some of the systems mentioned above. Measurement of the match between the antenna and the cable loss is part of the answer. This article explains what is involved in these measurements, and how the key parameters are measured with a dual directional coupler.