To stabilize impedance in near-field coupling, which measure is recommended?

• A. Increase spacing between the antenna and feed line.
• B. Decrease spacing between the antenna and feed line.
• C. Remove shielding.
• D. Use a larger conductor.

Answer: (A)

In near-field coupling, the antenna and nearby conductors (like the feed line) form a tightly coupled system. Close spacing introduces mutual capacitance and mutual inductance that detune the antenna and make its input impedance vary with position, frequency, and surrounding objects. Increasing the distance between the antenna and the feed line reduces this unwanted coupling, lowering the reactive loading and making the input impedance more stable and predictable.

Removing shielding would increase coupling and worsen stability, while simply using a larger conductor mostly affects resistance and losses rather than the near-field interaction that drives impedance variation.