RF signals are very dependent upon timing because they are always in motion. By their
very nature, the signals are made up of electric and magnetic forces that vary over
time. The phase of a signal is a measure of shift in time relative to the start of a cycle.
Phase is normally measured in degrees, where 0 degrees is at the start of a cycle, and
one complete cycle equals 360 degrees. A point that is halfway along the cycle is at the
180-degree mark. Because an oscillating signal is cyclic, you can think of the phase traveling
around a circle again and again.
When two identical signals are produced at exactly the same time, their cycles match
up and they are said to be in phase with each other. If one signal is delayed from the
other, the two signals are said to be out of phase . Figure 1-10 shows examples of both
scenarios.