Near-Field Antenna

Hardware

Antenna designed for short-range inductive coupling, used in UHF RFID for encoding stations and point-of-sale applications.

Near-Field Antenna

A RFID antenna." data-category="Hardware">near-field antenna is an RFID reader antenna designed for short-range inductive coupling rather than far-field radiative propagation. While most UHF RFID antennas operate in the far field to maximise read range, near-field antennas intentionally limit the read zone to a few centimetres, providing precise, isolated tag communication.

How Near-Field UHF Works

At UHF frequencies (860-960 MHz), the near-field region extends only about 5 cm from the antenna surface. A near-field antenna is typically a small loop or segmented loop that creates a strong magnetic field within this region while rapidly attenuating beyond it. Tags within the near-field couple magnetically with the antenna, similar to HF RFID (ISO 14443, ISO 15693), but using the EPC Gen2 protocol.

This approach combines the advantages of both worlds: the mature, low-cost UHF tag ecosystem with the precise spatial control of near-field operation.

Comparison with Far-Field Antennas

Attribute Near-Field UHF Far-Field UHF
Read range 0 - 10 cm 0.5 - 12 m
Isolation Excellent -- reads only the target tag Poor -- reads all tags in beam
Orientation sensitivity Low High
Antenna gain < 3 dBi 6 - 12 dBi
Typical size 5 - 20 cm 15 - 40 cm

Applications

Near-field antennas solve problems where precise tag isolation is essential:

  • Printer-encoders -- the internal antenna must encode only the current label on the roll, not adjacent labels 2-3 cm away. Near-field antennas provide the spatial selectivity required.
  • Point-of-sale -- encoding and reading individual items at checkout without cross-reading items in the customer's bag or adjacent lanes.
  • Pharmaceutical commissioning -- encoding individual drug packages on a high-speed line where packages are closely spaced.
  • Smart shelf slots -- reading a specific shelf position without cross-reading adjacent positions.

Design Considerations

Near-field antenna design is more constrained than far-field. The loop geometry must produce a uniform magnetic field across the intended read zone while maintaining sharp roll-off beyond it. Designers specify the "keep-out zone" -- the distance beyond the intended read zone where stray reads must be below a threshold (typically -30 dB from peak).

See also: Coupling | Printer-Encoder | Antenna Gain

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常见问题

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