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Explore the design process of a novel UHF RFID antenna system using a dielectric superstrate, leading to improved gain and flexible impedance values for better RFID applications. Results, analysis, and conclusion included.
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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
Topics • Introduction • Background • Design Process • Design Example • Conclusion North Dakota State University
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
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
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
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
Background The layout region can contain many different designs and be located on many different surfaces [27]-[38]: North Dakota State University
Antenna Design Process First start with determining the electrical length of each segment of a rampart line antenna. North Dakota State University
Antenna Design Process The length of the kth segment is written as: This then gives the entire length of the dipole as:
Antenna Design Process For the rest of this paper we assumed the following symmetry: Same length Same length North Dakota State University
Antenna Design Process Next, start with the rampart line antenna and use a CAD program to determine N: Design for the application Located here
Antenna Design Process Then define pivot points to fit the antenna on the space provided and define an inductive loop for input impedance:
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
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
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
Measurement Results The test structure
Measurement Results The read range results
Etheta Ephi Measurement Results Several normalized-pattern results
Measurement Results Simulated gain and input impedance results: North Dakota State University
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
Questions Thank you for listening North Dakota State University