2.45 GHz Low Power Rectenna Design for Wireless Sensor

1
2.45 GHz Low Power Rectenna Design for Wireless
Sensor RFID Applications

• Ph.D. Candidate Yunlei Li
• Advisor Jin Liu
• 9/10/03

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Outline

• Introduction
• Rectifier
• Antenna
• System
• Conclusion

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Radio Frequency Spectrum
Frequency Wavelength Band designation Wireless sensor RFID applications
30-300 kHz 10-1km LF (low frequency) LF RFID Passive IC tag inductive coupling
300-3000 kHz 10-1km MF (medium frequency) MF RFID Passive IC tag inductive coupling
3-30 MHz 100-10m HF (high frequency) HF RFI D Passive IC tag Inductive coupling (6.78 MHz, 13.56 MHz, 27.125 MHz)
30-300 MHz 10-1m VHF (very high frequency) Wireless sensor Active RFID
300-3000 MHz 1m-10cm UHF (ultra high frequency) Wireless sensor Active RFID transceivers (315, 433, 868, 915, 2450 MHz)
3-30 GHz 10cm-1cm SHF (super high frequency) 5.8 GHz Active RFID Beamed microwave power transmission
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Electromagnetic Power Transmission

• RF Power launched through electromagnetic waves
  by an antenna
• ? c/f
• Near field the area from the antenna to the
  point where the electromagnetic field forms at a
  distance of D lt?/2?
• Far field The area after the point at which the
  electromagnetic wave has fully formed and
  separated from the antenna at a distance of D
  lt?/2?

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RF Power Transmissionnear field

• Passive RFID tag
• Inductive Coupling (transformer effect)
• Energy in magnetic field strength
• Coil antennae
• Reader-gt transponder Power data
• Transponder-gt reader Data back by load modulation

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RF Power Transmissionfar field

• Friis Transmission Equation
• PrPtGtGr?2/(4?R)2
• Pr Receiveded power
• PtTransimitted power GtTransimitter
  antenna gain
• Gr Receiver antenna gain
• R Transmission distance

Calculated received power Assuming Gt20dB,
Gr10dB
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Rectenna RF to DC Conversion

• Rectenna element RectifierAntenna
• Frequency reflecting plane
• Dipole or patch antenna
• Microwave low pass filter
• Schottky barrier diode
• Low pass filter passing DC
• Load resistor
• Applications
• Wireless power transmission between space and
  earth
• high power Rectenna array

• Wireless sensor (GAP4S) long range RFID
• Low power Rectenna used to
• convert RF power to DC to
• charge a battery or big Cap
• Performance Goal-high efficiency
• Overall efficiency ?oDC output power/incident RF
  power
• gt85 (high power optimized load)
• Conversion efficiency ?cDC output
  power/(incident RF power-reflected RF power)
• gt90 (high power optimized load)

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Rectifier/RF Detector

• Single diode

• Voltage doubler

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Schottky Diode

• Equivalent circuit of a
• Schottky diode
• Rj0.026/IT, ITIsIb
• Isdiode saturation current, a
• function of barrier height
• Ibexternal applied bias current
• Cjdiode junction capacitance
• Lp, CpParasitic inductor Cap
• RsParasitic resistance representing losses
• Voltage sensitivity of a diode in mV/?W
• ?20.52/(IT(1?2Cj2RsRj)(1Rj/RL))

• N-type
• Low Rs
• External bias (High barrier, low Is)
• High flicker noise
• P-type
• High Rs
• Zero bias (low barrier, high Is
• Low flicker noise

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Low pass filter for better efficiency
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Microstrip Patch Antennas
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Radiation performance of single layer patch
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Microstrip Patch Array
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Hybrid-Ring Coupler

• Hybrid ring coupler to split powers from the
  input to two outputs
• Power split ratio
• Note there is an upper limit on line impedance
  of about 150 ? for many microstrip transmission
  lines

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Gain of Microstrip Patch Array

• The Maximum gain of a microstrip phase 2nx2m
  array
• GdB10log(4?A/?2)-?(D1D2)/2
• AD1D2
• D1effective width of the uniformly spaced array
• D2effective height of the uniformly spaced array
• ?attenuation in dB per unit length of a 50 ohm
  transmission line being used in the monolithic
  feed A typical value of ? is 0.4dB/ft for a 50
  ohm microstrip line on 1/32th-in (0.794mm) Teflon
  fiberglass at 2.2 GHz

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System Design

• Monolithic Integration of rectenna (antenna
  array with rectifier) with RF detector
• Impedance matching of patch antenna (or antenna
  array) to the input of the rectifier using
  corporate feed network
• Ring coupler to split power from antenna to
  rectenna and demodulator separately to maintain
  8dB power split ratio
• Use single diode rectifier to maximize efficiency
  of the Rectenna
• Use voltage doubler detector to maximize its
  voltage for better demodulation
• Ring coupler isolate the Rectenna Detector and
  allow separate impedance matching network design

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Conclusion

• A 2.4GHz low power Rectenna detector will be
  designed and simulated with ADS
• The system will be monolithically integrated onto
  a single circuit board
• A high gain patch antenna array boosts the power
  level at the input of the Rectenna for better
  power conversion efficiency
• A hybrid ring coupler is used to divide the power
  between Rectenna and detector
• The system implements a key RF front end for
  GAP4S wireless sensor system