Figure 4-13. Block diagram of a directional coupler.
How Couplers Work
To understand how couplers function, I will use the analogy of wine tasting. Before you buy an expensive bottle of wine, you want to taste a sample. The sample does not have to be very big to know whether you are going to enjoy the whole bottle. This is how couplers work; only instead of sampling wine, they sample the RF signal.
Visually, a signal enters the coupler at point A (see Figure 4-13) and generally makes its way to point C and along its merry way somewhere else in the system. Except, as it goes from A to C, a tiny fraction of the signal ...