1. ANALYSIS OF CONSTRAINTS IN SMALL UHF RFID TAG DESIGN
Mun Leng Ng
Auto-ID Adelaide
School of Electrical & Electronic Engineering
University of Adelaide
Australia

2. Introduction on RFID
What is RFID?
RFID basic components:

3. RFID Tag
Consist of
Basic requirement: - Compact - Reliable - Inexpensive

4. The Constraints Bandwidth limitation on impedance matching
Tag antenna size constraint towards impedance matching

5. Bandwidth Limitation

6. Bode-Fano Limit

7. Bode-Fano Limit (cont)

8. Application of Bode-Fano Limit on RFID
Allocated bandwidths for RFID:
Others: China: 917 – 922 MHz (Temporary license can be applied) Australia: 918 – 926 MHz

9. Application of Bode-Fano Limit on RFID
3 different cases considered:

10. Application of Bode-Fano Limit on RFID
Assume R = 1 k, C = 1 pF
R = 10 k, C = 1 pF (for less power consuming tag chip in practice)

11. Tag Antenna Size Constraint

12. A Simple Loop Antenna
Single-turn circular loop antenna:

13. Overall Circuit
Qant = (2f L)/Rr
Qchip = f0/f

14. Results
When Qant = Qchip: D = 9.65 cm Impedance of antenna approximately times impedance of chip
If R = 10 k, C = 1 pF: D = 4.48 cm Smaller difference between tag antenna and chip impedances

15. Copper foil tuning strap for impedance matching
A Simple RFID Tag
Copper foil tuning strap for impedance matching
Butterfly antenna
(a modified bow-tie)

16. A Simple RFID Tag (cont)
Simplified equivalent circuit:

17. Another Simple RFID Tag
Consists of a circular loop antenna with a very simple matching network
FRONT
REAR

18. Conclusion