How Far Is It To Be A Far Field Distance?

บทคัดย่อ

A far field test range is a rather convenient and simple means of antenna performance characterization. An essential ingredient for setting up such a test range is the far field distance criterion, the so called Raleigh criterion. It is widely accepted that beyond the Raleigh distance the radiated field behaves as a planewave. This is unfortunately a pitfall in the case of electrically small antennas. Clarification of the true meaning of the far field is therefore inevitable. This involves description of the reality of practical operating condition of the antennas and the nature of the radiation from the antenna.