What are the different RFID frequency bands?

LF (125 to 134.2 kHz): uses inductive coupling (near field), range 0.1 to 0.5 m, penetrates water and metal well. Applications: animal identification (ISO 11784/85), access control, automotive immobilizers. HF (13.56 MHz): also inductive coupling, range 0.1 to 1 m. ISO 14443 (proximity cards, NFC) and ISO 15693 (vicinity cards). Applications: contactless payment (NFC), library books, pharmaceutical tracking. UHF (860 to 960 MHz): electromagnetic backscatter coupling (far field), range 1 to 15 m. Regional frequency allocations: 902 to 928 MHz (Americas), 865 to 868 MHz (Europe), 920 to 925 MHz (China). EPC Gen2 (ISO 18000-6C) is the dominant standard. Applications: supply chain, retail inventory, warehouse management. Microwave (2.45/5.8 GHz): longest range for active tags (100+ m), smallest antennas. Applications: vehicle tolling (E-ZPass), real-time location systems.

What determines RFID read range?

The forward link range (reader to tag) is determined by the Friis equation: r_max = (lambda / (4*pi)) * sqrt(P_reader * G_reader * G_tag * tau / P_tag_sensitivity), where tau is the tag's power transfer efficiency. For UHF at 915 MHz: lambda = 0.328 m, reader EIRP = 36 dBm (4 W), tag antenna gain = 2 dBi, tag sensitivity = minus 20 dBm (10 microwatts), this gives approximately 10 meters. The return link (tag to reader) range is determined by: r_max = (lambda / (4*pi)) * fourth_root(P_reader * G_reader^2 * G_tag^2 * RCS_delta / (P_reader_sensitivity * (4*pi))), where RCS_delta is the differential radar cross section of the tag. Regulatory limits (FCC: 36 dBm EIRP in 902 to 928 MHz) cap the maximum reader power. Practical factors reducing range: tag orientation (polarization mismatch), multipath, tag detuning from nearby materials (especially metal and liquids), and reader antenna gain.

Identification Technology

RFID

Q: How does passive RFID work?

A passive RFID tag has no battery. The reader transmits a continuous wave (CW) RF signal at the operating frequency (e.g., 915 MHz for UHF). The tag's antenna captures this energy and rectifies it using a charge pump circuit to power the tag's integrated circuit. The IC reads its stored Electronic Product Code (EPC) from memory and communicates back to the reader by modulating the backscattered signal. The tag toggles its antenna impedance between matched (absorb) and mismatched (reflect) states, creating amplitude or phase modulation on the reflected signal. This backscatter modulation carries the tag data at rates of 40 to 640 kbps. The read range depends on the reader's EIRP, tag sensitivity, and path loss: for a 36 dBm EIRP reader and tag sensitivity of minus 20 dBm, the forward link range is approximately 10 meters. The return link is typically shorter due to the weak backscattered signal, though modern readers with minus 80 dBm sensitivity can read tags at 10 to 15 meters.

/ahr-eff-eye-dee/ — Radio Frequency Identification

Uses EM fields to identify and track tags. Passive: no battery, powered by reader field, backscatter modulation, range 1-15 m (UHF). Active: battery-powered, 30-100 m. Bands: LF (125 kHz, animals), HF (13.56 MHz, NFC/payments), UHF (860-960 MHz, supply chain), microwave (2.45 GHz, tolling). EPC Gen2/ISO 18000-6C: 640 kbps, 96-bit EPC, anti-collision for 1000+ tags/s. 30+ billion tags/year.

UHF range: 1-15 m

Tags/yr: 30B+

Standard: EPC Gen2

Understanding RFID

RFID technology has transformed supply chain management, retail operations, and asset tracking by enabling automatic, contactless identification of objects at a distance. Unlike barcodes that require line-of-sight and individual scanning, RFID tags can be read through packaging materials, at distances of up to 15 meters, and hundreds of tags can be inventoried simultaneously. This makes RFID the enabling technology for automated warehousing, real-time inventory visibility, and item-level tracking.

The RF engineering challenge of RFID lies in maximizing read range while operating within regulatory power limits and maintaining reliable communication with tags that have minimal power (passive) or limited battery life (active). Tag antenna design is critical: a dipole-based tag on cardboard achieves 10+ meter range, while the same tag on a metal surface may have zero range unless a spacer or specialized antenna design compensates for the metal's effect on impedance and radiation pattern.

RFID Frequency Band Comparison

Band	Frequency	Range	Coupling	Application
LF	125-134 kHz	0.1-0.5 m	Inductive	Animal ID, access
HF	13.56 MHz	0.1-1 m	Inductive	NFC, payments
UHF	860-960 MHz	1-15 m	Backscatter	Supply chain, retail
μWave	2.45 GHz	1-100 m	Backscatter	Tolling, RTLS
Active UHF	433 MHz	30-100 m	Active TX	Container tracking

Common Questions

Frequently Asked Questions

How does passive RFID work?

Reader transmits CW RF (e.g., 915 MHz). Tag antenna harvests energy via charge pump to power IC. IC reads stored EPC from memory. Communicates by modulating backscatter: toggles antenna impedance matched/mismatched. 40-640 kbps data rate. Range: 10 m with 36 dBm EIRP, -20 dBm tag sensitivity. Return link limited by weak backscatter signal.

What frequency bands?

LF (125 kHz): inductive, 0.1-0.5 m, penetrates water/metal, animal ID. HF (13.56 MHz): inductive, 0.1-1 m, NFC/payments. UHF (860-960 MHz): backscatter, 1-15 m, supply chain. Regional: 902-928 MHz (US), 865-868 MHz (EU). Microwave (2.45 GHz): smallest antennas, tolling. Active 433 MHz: battery, 30-100 m, containers.

What determines range?

Forward link: r = (λ/4π)√(EIRP×G_tag×τ/P_sens). Reader EIRP (FCC: 36 dBm max). Tag sensitivity (-20 dBm typical). Tag antenna gain/efficiency. Return: r&sup4; dependence on reader sensitivity. Practical factors: tag orientation, multipath, material effects (metal, liquid detune antenna). Near-metal tags need spacer or specialized antenna design.

Related Terms

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