Ultra-High Frequency (UHF) RFID
860–960 MHz · RAIN RFID · EPC Gen2
What is UHF RFID?
Ultra-High Frequency (UHF) RFID operates in the 860–960 MHz band and is the dominant RFID technology for retail, supply chain, logistics, and asset tracking. Unlike LF and HF which use near-field inductive coupling, UHF uses far-field electromagnetic backscatter – enabling read ranges up to 12 metres with passive tags and the ability to read hundreds of tags per second.
UHF RFID is standardised as EPC Gen2 (GS1 EPC UHF Gen2 Air Interface Protocol) and ISO 18000-63. The industry alliance RAIN RFID promotes UHF as a connectivity platform. When someone says "RFID tag" without qualification, they almost always mean a UHF passive tag.
How it works
UHF RFID uses far-field backscatter communication. The reader transmits a continuous-wave RF signal. A tag in the reader's field harvests energy from this signal through its antenna, powering the chip. To communicate, the tag switches its antenna impedance between two states – this modulates the signal reflected back to the reader (backscatter). The reader detects these tiny modulations to decode the tag's data.
The EPC Gen2 protocol manages the inventory process. The reader sends a Query command, and tags respond in randomly chosen time slots. If two tags collide (respond in the same slot), the reader adjusts the number of slots and tries again. This slotted Aloha anti-collision algorithm can singulate hundreds of tags per second.
Each tag has four memory banks: Reserved (kill and access passwords), EPC (the identifier, typically 96 bits), TID (chip manufacturer and model, read-only), and User (optional additional data). The EPC bank is where the SGTIN or other encoding scheme is written.
Regional frequencies
Unlike HF (which is 13.56 MHz worldwide), UHF frequencies vary by region due to different radio spectrum regulations:
| Region | Frequency band | Max power (EIRP) | Notes |
|---|---|---|---|
| North America | 902–928 MHz | 4 W | FCC Part 15. Frequency hopping (FHSS) across 50 channels. |
| Europe | 865.6–867.6 MHz | 2 W | ETSI EN 302 208. Listen-before-talk (LBT) protocol. Narrower band than US. |
| China | 920–925 MHz | 2 W | MIIT regulations. Overlaps with parts of US and Japan bands. |
| Japan | 916–921 MHz | 1 W | Previously 952–954 MHz (now largely phased out). |
| Australia/NZ | 920–926 MHz | 4 W | ACMA regulations. Similar to US band. |
| India | 865–867 MHz | 4 W | Similar to European frequencies but higher power. |
Modern UHF tags are designed to work across the entire 860–960 MHz range, so a single tag model typically works worldwide. However, reader power settings and frequency hopping patterns must be configured for the local regulations.
Read range
UHF passive tag read range depends on tag design, reader power, antenna gain, and the tagged item:
| Scenario | Typical range |
|---|---|
| Handheld reader, label on apparel | 2–5 m |
| Fixed reader with directional antenna, label in free air | 8–12 m |
| On-metal tag on steel asset | 1–5 m |
| Tag on water bottle / liquid container | 0.5–2 m |
| Windshield tag through glass | 5–10 m |
| Battery-assisted passive (BAP) tag | 15–30 m |
Range is governed by the Friis transmission equation – power drops with the square of distance. In practice, the tag's chip sensitivity (how little power it needs to wake up) is the main determinant. Modern chips like the Impinj M700 series have sensitivity below -23 dBm, extending range significantly over older designs.
Advantages
- Long range: Up to 12 m passive, 30 m+ with battery assist. Enables doorway portals, overhead readers, and warehouse-scale inventory.
- High speed: Reads hundreds of tags per second. A handheld reader can count an entire retail store (10,000+ items) in under 30 minutes.
- Low tag cost: Wet inlays cost under $0.05 at volume, making item-level tagging economically viable.
- Standardised: EPC Gen2 / ISO 18000-63 ensures interoperability between tag and reader manufacturers.
- Rich data model: The EPC system provides standardised encoding schemes ( SGTIN , SSCC , etc.) for product, asset, and location identification.
- Bulk reading: No line-of-sight required. Read through boxes, on pallets, and in dense tag environments.
Limitations
- Metal and liquid: UHF signals are reflected by metal and absorbed by water. Tags on or near these materials require specialised on-metal designs or spacers.
- Regional frequency variation: Unlike HF, UHF frequencies differ by country. Readers must be configured for local regulations.
- Limited security: Standard EPC Gen2 tags have minimal cryptographic capability. The kill password is only 32 bits. Secure variants (NXP UCODE DNA) exist but are more expensive.
- Not smartphone-readable: Unlike NFC , UHF requires a dedicated reader. No consumer phone has a UHF reader.
- Orientation sensitivity: Linearly polarised antennas may miss tags at certain orientations. Circularly polarised antennas help but reduce range.
- Read accuracy in dense environments: Very dense tag populations (thousands in close proximity) can cause missed reads despite anti-collision.
Common applications
- Retail inventory: Item-level RFID on apparel, footwear, and accessories. Zara, H&M, Nike, Uniqlo, and Decathlon all use UHF RFID for inventory accuracy and omnichannel fulfilment.
- Supply chain: Pallet and case-level tagging for shipping, receiving, and cross-docking. SSCC encoding on logistics units.
- Airline baggage: IATA Resolution 753 mandates baggage tracking. UHF RFID labels on luggage tags enable automated sorting and reconciliation.
- Healthcare: Surgical instrument tracking, pharmaceutical serialisation, blood bag management, and specimen tracking.
- Asset tracking: IT assets, tools, equipment, and returnable containers. Rugged hard tags for outdoor and industrial assets.
- Vehicle identification: Windshield tags for electronic toll collection and parking access.
- Manufacturing: Work-in-progress tracking, quality control, and traceability through the production process.
EPC Gen2 memory structure
| Bank | Contents | Access |
|---|---|---|
| Bank 0 – Reserved | Kill password (32 bits) + Access password (32 bits) | Read/write with access password |
| Bank 1 – EPC | CRC-16 + PC bits + EPC (typically 96 bits) | Read/write (lockable) |
| Bank 2 – TID | Tag manufacturer ID, chip model, unique serial | Read-only (factory programmed) |
| Bank 3 – User | Optional user data (0–512+ bits, chip dependent) | Read/write (lockable) |