A. S. Hoenshel and R. Mittra EMC Lab Pennsylvania State University University Park, PA 16802

1. A Parametric Study on the Platform Tolerance of RFID Antennas and their Performance Enhancement with Artificial Magnetic Conductors A. S. Hoenshel and R. Mittra EMC Lab Pennsylvania State University University Park, PA 16802

2. Electronic Toll Collection Access Control Animal Tracking Inventory Control Tracking Runners in Races! RFID Antenna Applications

3. Small Size Planar UHF Frequency Allocation Europe 866-869 MHz North America 902-928 MHz Impedance Matching ASIC Chip: High Capacitive Value, Small Resistive Value Environmental Conditions RFID Antenna Design Challenges

4. Mounting Materials Cardboard (er=2.5) Glass with No Loss(er=3.8) Glass with Loss(er=2.5) and Loss Tangent 0.002 Plastic (er=4.7) Performance Enhancement using Artificial Magnetic Conductors (AMCs) Two Planar-Inverted F-Antenna Designs Scope of Presentation

5. Characteristic Impedance Power 3-Dimensional Radiation Patterns Maximum Directivity Antenna Parameters Investigated * * where Umax is the radiation intensity in maximum direction and Prad is the total radiated power where Za = Ra + j Xa is the antenna impedance and Zs = Rs + j Xs is the source impedance * Source: Constantine A. Balanis. Antenna Theory, Analysis and Design, New Jersey, (Third Edition) John Wiley and Sons.

6. Open-Ended Stub PIFA Design ASIC Chip: Zc=10-j160 [W] at 867 MHz Zc=10-j150 [W] at 915 MHz Zc=10-j145 [W] at 940 MHz 62mm 51mm • Dual-band Frequency Operation • Gap Dimension and Stub Dimension Used to Tune • Platform Tolerance • Dominating Horizontal Current Distribution 5mm 3mm = 2.35 * Source: M. Hirvonen, K. Jaakkola, P. Pursula, and J. Saily, “Dual-Band Platform Tolerant Antennas for Radio-Frequency Identification,” IEEE Trans. Antennas Propag., vol. 54, no. 9, pp. 2632 - 2637, Sept. 2006.

7. Open-Ended Stub PIFA Design • Mounting Materials • Dimensions • 900 mm x 900 mm • (4 x 4) • Thickness=13 mm • Cardboard (er=2.5) • Glass(er=3.8) • Plastic(er=4.7) • Tag Dimension • 62 mm x 51 mm 62mm 51mm 5mm 3mm = 2.35

8. Impedance [867/915 MHz] Open-Ended Stub PIFA Design

9. Power (867 MHz) Power (915 MHz) Power (940 MHz) No Material 83.49 64.92 74.07 Cardboard(er=2.5) 54.53 86.28 80.5 Amount Increased -28.96 21.36 6.43 No Material 83.49 64.92 74.07 Glass (er=3.8) 54.81 80.72 72.9 Amount Increased -28.68 15.8 -1.17 No Material 83.49 64.92 74.07 Plastic (er=4.7) 58.3 85.72 72 Amount Increased -25.19 20.8 -2.07 Power Open-Ended Stub PIFA Design *Design Goal: Power > 40% at Selected Frequencies

10. Radiation [867 MHz] Open-Ended Stub PIFA Design No Material Cardboard Glass Plastic

11. Directivity at 867 MHz [dB] Directivity at 915 MHz [dB] Directivity at 940 MHz [dB] No Material 2.2637 2.6293 2.7450 Cardboard(er=2.5) 2.8511 3.1605 3.6968 Amount Increased 0.5874 0.5313 0.9518 No Material 2.2637 2.6293 2.7450 Glass(er=3.8) 3.8117 4.4925 5.9277 Amount Increased 1.5480 1.8632 3.1826 No Material 2.2637 2.6293 2.7450 Plastic(er=4.7) 4.7619 5.3194 6.1712 Amount Increased 2.4983 2.6901 3.4261 Directivity Open-Ended Stub PIFA Design

12. Inductively-Coupled Feed Loop PIFA Design ASIC Chip: Zc=10-j150 [W] at 915 MHz Zc=10-j145 [W] at 940 MHz • Dual-band Frequency Operation Achieved • Gap dimension between loop and radiators is used to tune • Platform Tolerance • Reduced Current on Ground Plane

13. Inductively-Coupled Feed Loop PIFA Design • Mounting Materials • Dimensions • 200 mm x 200 mm • ( x ) • Thickness=5 mm • Cardboard (er=2.5) • Glass with No Loss(er=3.8) • Glass with Loss(er=2.5) and Loss Tangent 0.002 • Tag Dimension • 54 mm x 45 mm

14. Impedance Inductively-Coupled Feed Loop PIFA

15. Impedance Inductively-Coupled Feed Loop PIFA

16. Power (915 MHz) [%] Power (940 MHz) [%] Free Space 86.09 41.45 Cardboard 16.29 6.5 Cardboard Optimized 61.19 31.69 Free Space 86.09 41.45 Glass 24.06 9.48 Glass Optimized 56.59 69.36 Free Space 86.09 41.45 Glass with Loss 11.65 23.81 Glass with Loss Optimized 61.6 52.55 Power Before and After Optimization Inductively-Coupled Feed Loop PIFA *Design Goal: Power > 40% at Selected Frequencies

17. Directivity at 915 MHz[dB] Directivity at 940 MHz[dB] No Material 5.4033 5.1851 Cardboard (er=2.5) 5.3529 4.6835 Amount Increased -0.0504 -0.5016 Directivity at 915 MHz[dB] Directivity at 940 MHz[dB] No Material 5.4033 5.1851 Glass No Loss (er=3.8) 5.3148 5.1188 Amount Increased -0.0885 -0.0663 Directivity at 915 MHz[dB] Directivity at 940 MHz[dB] No Material 5.4033 5.1851 Glass With Loss (er=2.5) and loss 0.002 5.2634 5.1851 Amount Increased -0.1399 0 Directivity & Radiation Inductively Coupled Feed Loop PIFA 867 MHz No Material 867 MHz Cardboard

18. PEC Ground Reflects Half the Radiation Gain can be increased by 3 dB Image Currents Can Cancel Currents in Antenna Limitation on distance between ground and radiating elements (/4) Reflection Coefficient of -1 Performance Enhancement with Artificial Magnetic Conductors • PMC Ground • Image Currents In Phase with Original Currents • PMC is reflective • Low Profile Antennas • High Impedance Surface • Current is filtered at selected frequencies so tangential magnetic field is small while electric field is still large • Suppression of Surface Waves=>Minimizes Backlobe • Reflection Coefficient of +1

19. Fabrication of AMCs GA Input Parameter Output Configuration of AMC

20. FSS Layer FSS Unit Cell /2 x  /2 FSS Layer Reflection Phase Crosses 0 at 939 MHz

21. Directivity [dB] Directivity [dB] 915 MHz 867 MHz 940 MHz 940 MHz PEC Ground PEC Ground 4.0235 4.3255 4.1707 3.8399 AMC Ground AMC Ground 5.6650 4.6120 4.7566 4.9485 Increased Increased 0.5885 1.3395 0.9167 Directivity AMC Open-Ended Stub PIFA Inductively-Coupled Feed Loop PIFA 0.7778

22. Radiation [867 MHz]AMC Open Ended Stub PIFA Inductively Coupled PIFA PEC AMC PEC AMC

23. Optimization Open-Ended Stub PIFA Design

24. STUB 2.8 Imaginary 867 MHz [W] Real 867 MHz [W] Power 867 MHz [%] Gap 2.6 157.45 40.29 63.56 Gap 2.5 142.94 3.55 29.90 Gap 2.4 153.95 26.54 77.39 Gap 2.2 131.14 2.66 10.70 Gap 2.1 128.29 2.69 9.23 Optimization Open-Ended Stub PIFA Design Note: 915 MHz and 940 MHz were not able to be sufficiently matched. *Design Goal: Power > 40% at Selected Frequencies

25. Dimension [mm] Imaginary 915 MHz [W] Real 915 MHz [W] Imaginary 940 MHz [W] Real 940 MHz [W] Power 915 MHz [%] Power 940 MHz [%] 8.90 164.15 0.07 169.24 3.27 0.92 17.11 9.10 164.23 0.06 170.52 4.52 0.78 20.97 9.20 162.70 0.24 166.82 1.47 3.64 9.68 9.25 166.60 2.98 171.89 0.51 26.83 2.44 9.30 158.90 0.14 163.86 1.29 3.11 10.70 9.40 163.04 0.13 167.28 4.80 1.90 26.83 9.50 163.52 0.17 168.06 4.42 2.34 23.91 Optimization Inductively-Coupled Feed Loop PIFA Design *Design Goal: Power > 40% at Selected Frequencies

26. Work in Progress 30 mm x 30 mm Unit Cell 3 x 3 Unit Cells for /2 x  /2 FSS 16 mm x 16 mm Unit Cell 6 x 6 Unit Cells for /2 x  /2 FSS

27. Summary • Open-Ended Stub PIFA Design showed to be platform tolerant in numerous cases • Each case was thoroughly examined • Inductively-Coupled Feed Loop PIFA was very sensitive to platform • An optimization was done for each mounting material • The AMC ground plane did improve the directivity and reduce the backlobe for both antenna cases • An optimization needed to be done using the AMC for both antenna cases because the impedance was altered significantly in each case • The Open-Ended Stub Design was optimized to sufficient operation but the Inductively-Coupled Feed Loop PIFA could not be tuned for sufficient operation