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RFID UHF Signal Propagation Analysis for Improved Antenna Performance

Explore UHF RFID system components and signal propagation for optimal performance and compliance with regulatory standards. Learn about antenna configurations, system losses, and factors affecting signal quality. Discover how to mitigate interference and enhance RFID reader performance in real-world applications.

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RFID UHF Signal Propagation Analysis for Improved Antenna Performance

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  1. UHF Gen2 RFIDPropagation View Prof. Roland Kueng

  2. 0 0 1 2 3 4 5 6 7 8 9 5 Starting Motivation Wanted: Smart Wireless Electronic Barcode which allows to create and operate an Internet-of-Things Needs: Ultra low cost Tags with a Global Standard behind to tag all goods and items Future: Upgrade Tag with Sensors

  3. RFID Systems up to Edgeware RFID Reader System Decoupling Line to RFID - Application Enterprise Application Integration

  4. European Regulatory Requirements

  5. Example: Dock Door Application Reader related risks • Mutual interference among readers • Co-channel interference • Adjacent channel interferences • Intersystem interferences

  6. RFID Reader

  7. UHF Reader Block Diagram power amp TX antenna modulation switch RADIATING ANTENNA RX antenna signal processor synthesizer I Q D A direct conversionreceiver • Air Interface Options: • 2 Separated Antennas • 1 Antenna and Circulator • 1 Antenna and Directional Coupler

  8. Details Reader Architecture Signal Processing - Sample Level on FPGA - Symbol Level on DSP - Air Protocol on DSP • RISC Processor • MAC • Reader Protocol • Interfaces • UHF Frontend • Direct Conversion Receiver • Carrier Suppression • Multi Antenna

  9. FPGA ADC DAC DSP Synthesizer DC-RX Xscale TX Amp Supply Circulator Ethernet USB RS232 4 Antenna Ports Modern Reader Example

  10. RFID Tag

  11. UHF Passive Tag Block Diagram RADIATING ANTENNA DC power control & signal sub carrier with processing data from reader unit memory backscatter modulator sub carrier with data from tag

  12. Tag Zoo

  13. RFID Antenna and Propagation

  14. Best what Radiation can do • The fundamental formula (d>> ) : • Pr = received power • Pt = transmitted power • Gt = transmit antenna gain • Gr = receive antenna gain •  = wavelength • d = distance • n = propagation exponent • L = system loss factor • do = breakpoint distance for n>2 G = 4·Ae/2 Pt ·Gt = EIRP (limited by regulations*) 2/(4)2d2 Free space attenuation, n = 2 *Regulations: ETSI EN 320 208 US FCC Part 15

  15. Path Loss 49 dB @ 8 m Path Loss 49 dB @ 8 m PassiveUHF RFID: Limited by Tag Power Consumption * EPC Class 1 Gen 2 -13…-17 dBm - 16 dBm received at tag * S/N= 35 dB + 33 dBm (2 W) - 71 dBm (0.1 nW) Gain = 7 dB • 22 dBm (6 μW)backscatter signal Receiver Noise: -99 dBm (F = 25 dB, B = 100 kHz) Reality: Additionally orientation losses, system losses, fading, n > 2 ... Additional noise sources, amplitude phase, TX to RX coupling

  16. Fading - Problem for Passive Solutions Simple 2-Ray Model

  17. UHF Signal Propagation Material Orientation • Test fixture with 73 Gen2 tags, equally spaced in air medium • Target read time: < 1 second

  18. UHF Signal Propagation Multi-path reflections from metal (reinforcing in floors/ dock levellers and other objects), cause nulls and peaks that get worse with distance from the antenna.

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