Running two inputs 180° out-of-phase puts the peaks and valleys of the sine wave so that they null each other out when summed (see the middle picture below). This has a tendency to cancel out both inputs, and is quite pronounced in the "far" field, but negligible in the "near" field. Normally phase cancellation is undesirable, but when you know what you want (and in this case, what you don't want) then you do it deliberately.
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Pages in category "Phase"
The following 12 pages are in this category, out of 12 total.