Side-by-side comparison
| Parameter | Near Field | Far Field Antenna |
|---|---|---|
| Distance boundary | r < 0.62√(D³/λ) (reactive near field) | r > 2D²/λ (Fraunhofer far field) |
| Field components | Dominant reactive E or H (not both equal) | E and H in phase, ratio E/H = 377 Ω |
| Wave impedance | Varies widely; can be >> or << 377 Ω | Fixed at η₀ = 377 Ω in free space |
| Power flow | Mostly reactive (oscillates back and forth) | Real, outward-directed Poynting vector |
| Field decay rate | 1/r² and 1/r³ terms dominate | 1/r term dominates |
| Radiation pattern validity | Pattern not stable; changes with distance | Pattern stable; used for gain/directivity spec |
| Typical application | NFC (13.56 MHz), wireless charging (Qi, 6.78 MHz) | Wi-Fi (2.4/5 GHz), GSM (900/1800 MHz) links |
| Measurement challenge | Probe loading distorts field | Requires anechoic chamber or far-field range |
| Intermediate zone | Radiating near field (Fresnel): 0.62√(D³/λ) to 2D²/λ | Not applicable — far field starts at 2D²/λ |
Key differences
Near field splits into two sub-regions: the reactive near field (r < 0.62√(D³/λ)) where energy oscillates without propagating, and the radiating near field (Fresnel region) up to 2D²/λ. In the far field (r > 2D²/λ), the 1/r field term dominates, E and H are in phase at 377 Ω, and the radiation pattern is fixed. NFC and Qi wireless charging intentionally operate in the reactive near field; all antenna datasheets quote gain and beamwidth from far-field measurements only.
When to use Near Field
Use near-field analysis for NFC card readers (13.56 MHz), Qi wireless charging coils (6.78 MHz), and coupled resonator designs where reactive energy transfer is the mechanism.
When to use Far Field Antenna
Use far-field analysis for designing and measuring link budgets in Wi-Fi (2.4 GHz/5 GHz), cellular base-station antennas, and any system where radiated power and gain matter.
Recommendation
For antenna design projects and exams, choose far-field formulas for all gain and directivity calculations — they are the only ones that make physical sense beyond 2D²/λ. Near-field is the right choice only when your operating distance is explicitly within that reactive zone.
Exam tip: GATE and university papers test the far-field distance formula 2D²/λ; always know how to derive it and apply it numerically for a given aperture size and frequency.
Interview tip: Interviewers at RF-focused companies like Qualcomm or L&T expect you to explain why antenna gain is always specified in the far field and what happens to wave impedance as you move from near to far field.