This phase difference can impact a lot of different fields. In reality, the waves do not remain coherent for an infinite interval, and after the coherence time the phase difference drifts.
More generally, if the phase difference of two waves remains the same during this "coherence time,” they are coherent during that time. Looking at it this way, the signals are said to have a “coherence time.” If the phase difference of the two waves is the same, they are coherent. Within a small time segment, the signals depicted are close to being coherent. But if you look at a small time segment (a few cycles), they are close to being coherent.ģ. In the broad spectrum of the graph, the signals aren’t coherent. As with everything, real life is somewhere in the middle. The figures above represent the ideal and the worst case. The relative difference is always fluctuating. The relative difference between any two matching points is exactly the same. The two sine waves depicted are not coherent.įigure 1 is coherent. The two sine waves depicted are coherent.Ģ. Instead think of a signal that looks sinusoidal in any small piece, but the phase is slowly drifting (Fig. Also, the two frequencies aren’t always exactly the same. However, no real wave is perfectly sinusoidal. When the two waves are always shifted by the same amount (Fig. With two perfect sine waves of the same frequency, the relative phase never changes. Keep these questions in mind as we break them down and find the answers you’re looking for! How stable is the phase between the two waves (electrical, light, etc.)?.Let’s get into the good stuff… These Two Questions Will Lead to Many Answers!Ī better way to look at the problem of phase coherence might be to ask yourself two simple questions: What do these definitions really mean?”ĭon’t worry! I hate definitions, too. These are both great definitions, although I have a feeling you may be thinking to yourself:
In physics, two wave sources are perfectly coherent if they have a constant phase difference and the same frequency.Often, it is interpreted as signals/systems operating at the same frequency with a consistent phase relationship. In many ways, the term “phase-coherent” is not strictly defined.We saved you the time (and suffering) and found two of our favorite definitions: Turns out the internet is flooded with several different, and sometimes confusing, definitions. There’s lots to learn…let’s get to it! Two Definitions of Phase Coherence (Out of Many) Finally, you will learn if and why phase coherence is affecting your various designs and applications. We will then break down these definitions into a simple way of fully understanding this topic. In this post, you will learn some basic definitions of phase coherence. Great question! Phase coherence can be an ambiguous topic, yet one that’s important for RF, electrical, and design engineers to understand.
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