Where is the far field located relative to the emitter?

Where is the far field located relative to the emitter?

• A. The region very close to the antenna where reactive fields dominate.
• B. The region very distant where fields become static.
• C. The region at a distance of a few wavelengths where the fields radiate.
• D. The region inside the conductor.

Answer: (C)

The far field is where the emitter’s energy shows up as radiating waves rather than stored energy near the source. In this region, the electric and magnetic fields are outward-propagating, in phase, and the field strength falls roughly as 1/r, with the wavefronts appearing nearly planar. This typically occurs at distances of a few wavelengths from the antenna, where the radiated fields dominate and the angular pattern is stable. The other descriptions describe near-field behavior (where reactive energy dominates) or non-radiating conditions (static fields far away) or simply something unrelated like being inside a conductor. So the region a few wavelengths away is where the fields are radiating, which is why that choice is correct.

The far field is where the emitter’s energy shows up as radiating waves rather than stored energy near the source. In this region, the electric and magnetic fields are outward-propagating, in phase, and the field strength falls roughly as 1/r, with the wavefronts appearing nearly planar. This typically occurs at distances of a few wavelengths from the antenna, where the radiated fields dominate and the angular pattern is stable. The other descriptions describe near-field behavior (where reactive energy dominates) or non-radiating conditions (static fields far away) or simply something unrelated like being inside a conductor. So the region a few wavelengths away is where the fields are radiating, which is why that choice is correct.