dual-frequency antenna design for rfid application
DESCRIPTION
Dual-frequency Antenna Design for RFID Application. Kin Seong Leong Auto-ID Laboratory, School of Electrical and Electronic Engineering, The University of Adelaide. Introduction. Radio Frequency Identification (RFID) Enable supply chain automation. Item level tagging - PowerPoint PPT PresentationTRANSCRIPT
Dual-frequency Antenna Design for RFID Application
Kin Seong LeongAuto-ID Laboratory, School of Electrical and
Electronic Engineering, The University of Adelaide
Introduction
• Radio Frequency Identification (RFID)– Enable supply chain automation.
• Item level tagging– Each and every item has it own tag with
unique ID.– Tag is usually passive.
Frequency Bands in RFID
• LF (<135 kHz)
• HF (13.56 MHz)
• UHF (860 – 960 MHz)
• Microwave (2.45 GHz)
Frequency Band in RFID
• LF (<135 kHz)
• HF (13.56 MHz)
• UHF (860 – 960 MHz)
• Microwave (2.45 GHz)
HF vs UHF
Proposal Formulation
Merge HF and UHF
Dual Frequency Antenna
(With frequency ratio ≈ 70)
Current Technology
• Microstrip patch antenna– Too low frequency ratio (< 5).
• Common aperture antenna– Dual feed point
Brain Storming
• Merging a HF antenna and an UHF antenna.
• Idea:– A HF multi-turn coil antenna.– A UHF planar dipole.– A transmission line to separate both
the above antennas.
Design Aim (1)
• Antenna impedance equals to the complement of the input impedance of the RFID chip at UHF operation– Design frequency: 960 MHz– Chip impedance: 17 - j150Ω – Design aim: 17 + j150Ω
• A resonance point at HF.– Parallel resonance.– Zero reactance and infinite resistance.
Design Aim (2)
• A single feed antenna.– Avoid modification on existing chip
• Reasonable antenna size and cost.– Not the focus of this paper.– The final design must not be larger than
14400 mm square.
A Simple HF RFID Antenna
• A multi-turn planar spiral antenna.
A Simple UHF RFID Antenna
• A dipole with matching network.– RFID chip is usually capacitive. The matching
network is to transform the antenna into inductive to enable conjugate matching.
An Initial Picture
• Feed point chosen to be at B.
Final Design
Chip
Final Design (1)
• Transmission line to transfer the HF coil antenna impedance to very high value (ideally open circuit).
Final Design (2)
• Overlapping loops to provide high capacitance.
Chip
Final Design (3)
• A gap to prevent the UHF antenna shorting the HF antenna. A patch on the bottom provides path for UHF operation.
Chip
Final Design (4)
• DC path for rectifier circuit (some type).
Chip
Simulation
• Using Ansoft HFSS
• Simulated impedance (at 960 MHz):– 24 + j143Ω– Very near to the target of 17 + j150Ω
• Resonance near 13.56 Mz
Fabrication
• On double-sided FR4
Measurement Setup
SMA Connector(At the chip location)
HF Testing
• Transmission measurement: Resonance at HF.
UHF Testing (1)
• Impedance measurement: Matching impedance with respect to RFID chip.
UHF Testing (2)
• At 960 MHz:– 50 + j135Ω
• Balance to unbalance problem– BALUN needed.
• Pattern in good agreement
Future Work
• Miniaturization.– To fit in small objects.
• Actual testing with RFID chips.– To obtain performance (read range)
measurement.
Conclusion
• a detailed design for a high frequency ratio dual-frequency antenna.