A Printed Rampart-Line Antenna with a Dielectric Superstrate for UHF RFID Applications

1. A Printed Rampart-Line Antenna with a Dielectric Superstrate for UHF RFID Applications Benjamin D. Braaten Gregory J. Owen Dustin Vaselaar Robert M. Nelson Cherish Bauer-Reich Jacob Glower Brian Morlock (PacketDigital LLC) Michael Reich (CNSE) Aaron Reinholz (CNSE) North Dakota State University

2. Topics • Introduction • Background • Design Process • Design Example • Conclusion North Dakota State University

3. Introduction • Interest in RFID has recently grown tremendously in many areas [1]-[5]: • supply chain management [6]-[8] • RFID security [9]-[10] • UHF antenna design [11] • back-scattering analysis [12]-[14] • Types of systems [1] • passive • semi-passive • active North Dakota State University

4. Introduction • Our work focused on the antenna design of a passive RFID tag. • On a passive tag the antenna is typically connected directly to the rectifier. • thus antenna impedance and rectifier impedance directly effect the read range • Antenna characteristics (gain, input impedance and resonant frequency) can be effected by nearby conducting and non-conducting objects [15]-[21]: • Isotropic and anisotropic superstrates • Surface placement of tag • Other RFID tags North Dakota State University

5. Introduction • Several advantages are gained by using a superstrate [18]: • Protection against heat, physical damage, and the environment (moisture, sun) • Several examples include: • Electronic car tolling [22] • Livestock tracking [23]-[24] North Dakota State University

6. Background • The max theoretical read range of a passive RFID tag can be written as (using Friis’s eqn.) [25]: where North Dakota State University

7. Background The layout region can contain many different designs and be located on many different surfaces [27]-[38]: North Dakota State University

8. Antenna Design Process First start with determining the electrical length of each segment of a rampart line antenna. North Dakota State University

9. Antenna Design Process The length of the kth segment is written as: This then gives the entire length of the dipole as:

10. Antenna Design Process For the rest of this paper we assumed the following symmetry: Same length Same length North Dakota State University

11. Antenna Design Process Next, start with the rampart line antenna and use a CAD program to determine N: Design for the application Located here

12. Antenna Design Process Then define pivot points to fit the antenna on the space provided and define an inductive loop for input impedance:

13. Antenna Design Results • Operating frequency of 920MHz • 60mil substrate with permittivity of 4.25 • 60mil superstrate with permittivity of 4.0 • Results in N=12 • Gr=4.3dBi North Dakota State University

14. Antenna Design Results • Layout a): (H=2985mils and W=1522mils) • Gr=2.62dBi • Zin=10.527+j139.263 • Layout b): (H=2746mils and W=1540mils) • Gr=2.97dBi • Zin=36.93+j139.737

15. Antenna Design Results • The printed boards on 5mil FR4 and BT substrate, resp. • Type F and Type PFC epoxy was used to attach straps • Cured at 50C for 8hrs. • Both layouts with both substrates and epoxy were tested. North Dakota State University

16. Measurement Results The test structure

17. Measurement Results The read range results

18. Etheta Ephi Measurement Results Several normalized-pattern results

19. Measurement Results Simulated gain and input impedance results: North Dakota State University

20. Conclusion • A design process based on a Rampart line antenna has been presented • Yields antennas with: • high gain, • flexible impedance values, • high space filling and • constant impedance • Two designs have been validated with measurement and shows to yield a comparable read range to tags applied to other applications. North Dakota State University

21. Questions Thank you for listening North Dakota State University

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