A Metamaterial-Based Series Connected Rectangular Patch Antenna Array for UHF RFID Readers Benjamin D. Braaten Sayan Roy* Sanjay Nariyal Masud A. Aziz Bilal Ijaz Muhammad M. Masud ECE Department North Dakota State University Fargo, ND, USA.

1) Introduction and Background 2) The Metamaterial-Based UHF RFID Antenna 3) Measurement and Simulation Results 4) Discussion and Guidelines 5) Conclusion Topics

Introduction and Background The proposed metamaterial-based UHF RFID reader antenna: The design consists of the following features: 1) Rectangular patches 2) Inter-digital capacitors 3) Tuning stub 4) Series fed array Reference: S. Paulotto, P. Baccarelli, F. Frezza and D. R. Jackson, “A microstrip periodic leaky-wave antenna optimized for broadside scanning,” IEEE International Symposium on Antennas and Propagation, June 9-15, 2007, pp

The Manufactured Prototype a = 2.15 mm b = mm c = 3.1 mm d = 23.6 mm e = 32.0 mm f = 6.2 mm g = 5.6 mm h = 13.0 mm j = 8.87 mm k = 41.4 mm m =55.95 mm n = 5.6 mm p = mm q = 8.8 mm W = mm H = 83.5 mm Finger spacing = 0.8 mm Finger width = 0.4 mm Finger length = 0.5 mm Substrate: Thickness: 1.58 mm Permittivity: 4.3 (FR4)

S-parameters of a Single Array A resonant frequency of 920 MHz can be observed.

Series Fed-arrays Under Test Texas Instruments Passive UHF RFID tag [1]: Read sensitivity: - 13 dBm Write sensitivity: -9 dBm [1] Texas Instruments, [online],

Series Fed-arrays Under Test Two UHF RFID reader antennas, mounted on a Styrofoam block, connected in series in the anechoic chamber, formed as a travelling wave antenna.

Coverage results Good coverage up to cm.

Normalized fields at 920 MHz x-z plane y-z plane

Simulated Surface Currents at 920 MHz

Antenna Design

Design Guidelines 1) Simulated S-parameters for a single metamaterial-based RFID reader antenna for various values of m (stub length). 2) The stub width n was also varied in a similar manner and no change in the resonant frequency was observed. 3) Similarly, the dimensions of the patch were increased and decreased by 15% and very little change in resonant frequency was observed.

1) The S-parameter results in this work show that a compact UHF RFID reader antenna can be developed for near-field UHF RFID applications. 2) The read-range measurements show that spatially broad near-field coverage can be achieved by connecting multiple antenna in series. This coverage can also be observed from the simulated fields. 3) The simulated currents show that this antenna supports current on the radiating patches and the matching stub. Discussion

1) A new metamaterial-based UHF RFID reader antenna has been presented. 2) This antenna can be connected in series for broad near- field coverage at 920 MHz. 3) Measurement and simulation results were compared. 4) Initial discussion and guidelines on designing the antenna have been presented. Conclusion

Thank you for listening! Questions?