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Antenna properties:

  • Height x Diameter = 3.3 inches x 1.4 inches
  • Test Frequency: 900 MHz (Wavelength = 33 cm or 13 inches)

I see some conflicting formulas to calculate the near field distance for an antenna w.r.t. the frequency of interest.

Method 1: (multiple sources)

Reactive Field <= 0.63 x sqrt(Height^3/Wavelength) ===> 2.6 cm or 1.02 inches

Method 2:

Reactive Field <= Wavelength ===> 33 cm or 13 inches

Which one applies here accurately.

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In literature, there is a difference between the reactive near field (containing bounded energy) and radiating near field. This might explain why you have two formulas.

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