Measuring Return Loss
Return loss is a measure of reflection characteristics. One way you can use the return loss measurement is to detect problems in the antenna feedline system and the antenna itself. A portion of the incident power will be reflected back to the source from each transmission line fault as well as the antenna. The ratio of the reflected voltages to the incident voltage is called the reflection coefficient. The reflection coefficient is a complex number, meaning it has both magnitude and phase information. In S-parameter terms, Return Loss is referred to as an S11 measurement.
NOTE: Test signals can cause interference. When testing cables attached to antennas, test signals are radiated. Verify that the signal used for the test cannot cause interference to another antenna.