The Antenna Near Field and Far Field Distance conversion calculator determines the boundaries between the reactive near field, radiating near field (Fresnel region), and far field regions based on antenna size and operating frequency. Understanding these distances is essential for antenna measurements, placement, and performance evaluation in RF design.
Formulas
λ = c / f
Reactive Near Field Distance (R_nf) = 0.62 * √(D³ / λ)
Radiating Near Field (Fresnel Region) = D² / (2 * λ)
Far Field Distance (R_ff) = 2 * D² / λ
Formula Explanation
- λ is the wavelength, found by dividing the speed of light (c) by frequency (f).
- D is the largest dimension of the antenna.
- The reactive near field is the region very close to the antenna, dominated by stored energy.
- The radiating near field or Fresnel region extends beyond the reactive zone where the radiation pattern is distance-dependent.
- The far field begins where the radiation pattern stabilizes and power density follows the inverse-square law.
Uses of this calculator
- Determining safe measurement distances for antenna testing.
- Evaluating antenna placement in RF chambers and open-field ranges.
- Classifying near and far field regions for compliance and performance analysis.
- Planning antenna setups in communication, radar, and EMC testing.
What is the far field distance for a 1-meter antenna operating at 3 GHz?
Input: D = 1 m, f = 3 GHz
Output:
- λ = 3e8 / 3e9 = 0.1 m
- Reactive Near Field = 0.62 * √(1³ / 0.1) = 0.62 * 3.16 = 1.96 m
- Radiating Near Field = 1² / (2 * 0.1) = 5 m
- Far Field = 2 * 1² / 0.1 = 20 m
- The far field starts at approximately 20 meters from the antenna.