Hindawi Publishing CorporationInternational Journal of Antennas and PropagationVolume 2013, Article ID 357418, 10 pageshttp://dx.doi.org/10.1155/2013/357418
Research ArticleExperimental Demonstration of Coexistence ofMicrowave Wireless Communication and Power TransferTechnologies for Battery-Free Sensor Network Systems
Satoshi Yoshida,1 Takumasa Noji,2 Goh Fukuda,3 Yuta Kobayashi,1 and Shigeo Kawasaki1
1 Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai,Chuo, Sagamihara, Kanagawa 252-5210, Japan
2 Tokyo Metropolitan University, 1-1 Minami-Osawa, Hachioji, Tokyo 192-0397, Japan3 Tokyo University of Science, 1-14-6 Kudankita, Chiyoda-ku, Tokyo 102-0073, Japan
Correspondence should be addressed to Satoshi Yoshida; [email protected]
Received 2 May 2013; Revised 24 July 2013; Accepted 4 September 2013
This paper describes experimental demonstrations of a wireless power transfer system equipped with a microwave bandcommunication function. Battery charging using the system is described to evaluate the possibility of the coexistence ofboth wireless power transfer and communication functions in the C-band. A battery-free wireless sensor network system isdemonstrated, and a high-power rectifier for the system is also designed and evaluated in the S-band. We have confirmed thatmicrowave wireless power transfer can coexist with communication function.
1. Introduction
Most electrical devices are powered by wires, but wired con-nections limit the mobility of portable devices and thepayloads of cars and spacecraft.There is thus a strong demandfor practical wireless technologies to reduce the weight ofcommunication and power-supply wiring. There are threewireless power transfer (WPT) categories: electromagneticcoupling type [1, 2], magnetic resonance type [3, 4], andmicrowave radiation type [5, 6]. Table 1 summarizes impor-tant features of each category. Coupling- and resonant-typeWPT devices using MHz frequencies have been reported [7,8], but such devices are not suitable for high-speed signal andcommand transfer or cannot transfer energy over distances ofseveral meters. Microwave WPT shows more promise, sincethe microwave band is commonly used in applications suchas wireless local area network and cellular network systems.Also, WPT-based microwave bands can transfer both energyand command signals over long distances.
The WPT systems using microwave or millimeter wavebands are categorized into three types, according to power
level. The first is the scavenging type, for targeting very weakpower densities [9–11] such as in wide coverage services, forexample, TV or radio broadcasting and cellular base stations[6, 12]. The second is an energy harvester type, for targetingweak power densities [13] such as narrow coverage area ser-vices, for example, wireless local or personal area networks,and othermobile terminals.The third is active energy transfersystems such as those used in space solar power stations[14, 15] and wireless charging of electric vehicles [5, 16].Other energy sources such as heat and vibration can alsobe harvested [17–19]. Table 2 summarizes these categories.Microwave rectifiers are a key device for realizing thesesystems, in particular diode-based microwave rectifiers [20–23]. These systems and rectifiers support only microwaveWPT functions and do not coexist with communicationfunctions.
We previously proposed a 4-bit digital phase shifter[24] and active integrated phased array antenna with beamsteering capability [25] for effective use of microwave energy,since propagation loss is large compared to other WPTconfigurations.
2 International Journal of Antennas and Propagation
Table 1: WPT classifications by principle.
Type Range Power delivery FunctionalityEM coupling Short High CommunicationMagnetic resonance Medium High/medium PowerMicrowave power transmission Long Medium/low Communication, sensors, and power
Table 2: WPT classifications by power level.
Type Source Available transferred power StructureScavenging Unknown (RF and mechanical) 𝜇W SimpleHarvesting Intentional and unknown (RF) mW Medium
EM power receiving Intentional (pair with RF powertransmission) W Complex
Microwave high powerfront end
Rectifier(RF-DC
converter)
ReceiverWPT
Data transmission
Baseband DSP
Baseband DSP
Battery or other
devices
Transmitter
Data DC
DC
Data Samefrequency
band
Figure 1: A conceptual illustration ofWiCoPT technology using themicrowave band.
This paper describes and discusses experimental demon-strations of wireless powering with communication tech-nology using microwave bands. Section 2 introduces twoconcepts of wireless powering technologies. Section 3 designsand evaluates a microwave rectifier suitable for the tech-nology and demonstrates a battery charging system usingWPT integrated with communication technology and beamsteering functions. Section 4 designs and evaluates a fullwireless and battery-free sensor network system.
2. Proposal and Design ofWiCoPT and WiSEnT
The main objective of our research group is to develop acompletely wireless sensor network system for use in reusablerockets. Toward this end, we have proposedwireless informa-tion/communication and power transmission (WiCoPT) andwireless sensor and energy transfer (WiSEnT) technologies.Simultaneous wireless power and data transfer at microwavefrequencies has been achieved in RFID applications. The dif-ferences between our proposal and RFID systems are thedelivered power, frequency band, and operating time width.Practical RFID applications use milliwatt-class power levels,several tens of MHz frequency bands, and millisecond-ordercommunication times, whereas our proposal uses watt-classpower levels, microwave frequency bands, and communica-tion/WPT time widths on the order of minutes or hours.
Microwave high powertransmitter
Rectifier(RF-DC
converter)
Sensor node
WPT
Communication
WPT
Communication
Sensor data Sensor data
Tx / Rx
Sensor
Base station
Differentfrequency
band
Tx/Rx
Figure 2: A conceptual illustration ofWiSEnT technology using themicrowave band.
Figure 1 shows a conceptual illustration of usingWiCoPTtechnology for wireless power and communication functions.The same frequency band is effectively used for both WPTand communication, since the WPT system utilizes theRF power of the modulated signal. To eliminate the localoscillator (LO) source on the receiver side, the transmitterdelivers the continuous wave (CW) signal, which is gener-ated, amplified, and combined with the modulated signal inthe microwave high-power front-end block. There are twomethods for obtaining both DC power and intermediatefrequency (IF) signals:
(1) use of a directional coupler before the rectifier toseparate DC and IF,
(2) use of a band-pass filter (BPF) after the rectifier toseparate DC and IF.
Sections 3.2 and 3.3, respectively, show examples ofmethods 1 and 2. The generated DC power charges batteriesor serves as a power supply for other devices. Inmethod 1, therectifier in the receiver operates solely as an RF-DC converter.In method 2, the rectifier acts as both a downconvertmixer and an RF-DC converter. IF signals of the frequencydifference between the modulated RF and nonmodulatedLO signal from the transmitter are used for communicationfunction.
Figure 2 shows a conceptual illustration of the WiSEnTtechnology, which is derived or produced from conven-tional wireless sensor network systems. The main difference
International Journal of Antennas and Propagation 3
D SG
RF in DC out
HEMT
Matching stub
Harmonicsfilter
Open circuit for fundamental wave
L3L2
L2DC cut RF cut
L5L4
L1
L6L7
A
Figure 3: Circuit diagram of a basic design of the C-band rectifierusing HEMT device.
between the WiSEnT technology and conventional wirelesssensor networks is whether DC power is wireless or wired.The base station has a microwave-band WPT transmitterand communication transceiver for sensor control and datareceiving, and the sensor node has amicrowave-band rectifierthat supplies DC power to sensor nodes. The sensor and datatransceiver operate using DC power and thus do not requirebatteries. The WPT and communication signal frequenciesare sufficiently different to avoid mutual interference. Theillustration shows only one sensor node, but more nodes willbe added in actual applications.TheWiSEnT technology thusrealizes a completely wireless sensor network.
3. Experimental Demonstration of WiCoPT
This section shows the microwave rectifier design and de-scribes potential integration with beam steering technologyand a battery charging demonstration of the WiCoPT tech-nology.
3.1. Design and Evaluation of the Microwave Rectifier forWiCoPT. ASchottky diode is commonly used formicrowaverectifiers. The rectifier converts microwave energy to DCenergy used as a power supply for electrical or mechan-ical devices or for battery charging. We use a field-effecttransistor, in particular a high-electron-mobility transistor(HEMT), as a rectifying device. The rectifier utilizes theHEMT as a diode when the drain and source of the HEMTterminals are grounded.TheHEMT-type rectifier is easily in-tegrated into a monolithic microwave integrated circuit forfuture miniaturization.
Figure 3 shows a circuit diagram for a basic design of theC-band rectifier using a HEMT device. The rectifier designmethod is based on configuration with an input/output filter[26]. Open stubs using a 50Ω microstrip line are usedto configure the role of the input/output filter. A DC cutcapacitor and an RF cut inductor are placed at the inputand output port, respectively. The open stub near the DC cutcapacitor is an input matching network to the RF connector.L2 and L3 have an initial length of 𝜆/4, since impedance
from point A is open for a fundamental wave of 5.80GHzto flow the fundamental signal for the HEMT. L4 and L5,respectively, have an initial length of 𝜆/8 and 𝜆/4 as a filterwith ideal impedance of 0 and infinite for odd- and even-order harmonics.
Figure 4 shows pictures of fabricated rectifiers. C-bandrectifiers without and with a BPF are shown in Figures 4(a)and 4(b), respectively. The BPF is integrated with the C-band rectifier for WiCoPT operation. The BPF extracts IFsignals for data receipt. The center frequency of the BPFfor 20MHz and −3 dB bandwidth is 10MHz. An FHX76LPGaAs HEMT (Sumitomo Electric Devices Inc.) is used.The substrate material is RO4350B (Rogers Co.). Centerfrequency of the rectifier is 5.80GHz. The 5.8GHz rectifieris designed using the Advanced Design System (ADS) simu-lator (Agilent).TheAngelovmodel [27], a nonlinearmodel ofHEMTs, is used. Figure 5 shows simulated andmeasured loadresistance characteristics of the RF-DC conversion efficiencyunder conditions of 20 dBm input RF power and 5.80GHzfrequency. A fabricated rectifier without BPF is used forthe simulation and the measurement. The simulated andmeasured optimum load resistance is 439Ω and 470Ω, sincemaximum conversion efficiencies of 53.3% and 49.7% areobtained. Figure 6 shows simulated andmeasured DC outputpower and rectification efficiency of the fabricated rectifierusing a 5.80GHz CW signal. The maximum conversionefficiency of 53.3% and the maximum DC output powerof 328mW are simulated for input power of 22 dBm and30 dBm, respectively. The maximum conversion efficiency of49.7% and the maximum DC output power of 104mW aremeasured for input power of 20 dBm and 28 dBm, respec-tively. The BPF effect is negligibly small compared to the RF-DC conversion characteristics. During measurements, theoptimum load resistance of 470Ω is used. Conversion loss,defined as the power level difference between input RF andoutput IF signals, is measured.The conversion loss of 25.8 dBfrom 5.8GHz to 20MHz is obtained from the measurementwhile the input RF power level is 20 dBm.
A 5.8GHz rectifier forWiCoPT technology was thus suc-cessfully developed using the GaAs HEMT.
3.2. Evaluation of WiCoPT with Beam Steering. This sectiondescribes results of an experimental demonstration of a5.80GHz WiCoPT system with beam steering capability.Figure 7 shows a block diagram of the demonstration. Inthe demonstration, configuration of a directional coupler isapplied to show the validity of the configuration describedin Section 2. The transmitting side has horizontal 1D beamsteering capability using four phase shifters operating at5.80GHz. The phase shifter is a four-bit digital phase shifter[25]. A 4×4 circular patch array is used as four 1×4 subarrays.The 4×4 array is placed on a turntable so that the array beamis directed to the horn antenna when the beam is steered.Thearray antenna is designed using HFSS (Ansys Co.). Physicalparameters such as patch diameter and element spacing areoptimized by 3D electromagnetic field simulation.The phaseshifter is controlled by PXI hardware (National InstrumentsCo.).The LabVIEW software individually controls DC biases
4 International Journal of Antennas and Propagation
RF in
GaAs HEMT
DC out
(a)
RF in
DC out
(backside SMA)
IF BPF
GaAs HEMT
20MHz IF out
(b)
Figure 4: Fabricated C-band rectifier: (a) without BPF and (b) with BPF.
of the SPDT switches in the 4 phase shifters. The system canarbitrary create four-bit phase shifts, so beam direction is alsoarbitrary controlled digitally in the horizontal direction byadding phase shift between the element antennas.
The modulated baseband signal is upconverted to5.80GHz and equally divided into four branches. The modu-lation method is quadrature phase shift keying (QPSK), andthe sample rate is 1MSPS. A pseudonoise (PN) sequence oforder 14 is used as random data. A root-raised cosine filterwith alpha 0.5 is used in both the transmitting and receivingsides. The modulation/demodulation evaluation system ofthe PXI hardware is used. A 10 dB directional coupler is used
Input RF power (dBm)
0
10
20
30
40
50
60
Out
put D
C po
wer
(mW
)
0
20
40
60
80
100
120
Measured DC power (w/o BPF)Measured conv. effic. (w/o BPF)Measured DC power (w BPF)Measured conv. effic. (w BPF)Simulated DC power (w BPF)Simulated conv. effic. (w BPF)
RF-D
C co
nver
sion
effici
ency
(%)
0 10 20 30
Figure 6: Simulated and measured DC output power and rectifica-tion efficiency of the fabricated rectifier using a 5.8GHz CW signal.
in the demonstration to divide the received power for boththe demodulation and rectification parts, so 90%power of thereceived signal is used for rectification. The rectifier withoutBPF described in Section 3.1 is used. After rectification,DC power is consumed by a load resistance of 470Ω andconversion efficiency is measured. Total output RF power ofthe transmitting side is 36 dBm when the beam is centered.The distance between the antennas is 1m. Antennas on thetransmitting and receiving side are 4 × 4 circular patch arrayand horn antennas, respectively.
International Journal of Antennas and Propagation 5
Figure 7: Block diagram of the experimental demonstration of the WiCoPT technology with beam steering.
DC
outp
ut p
ower
(mW
)
0
10
20
30
40
Effici
ency
(%)
30
35
40
45
50
DC output powerEfficiency
Azimuth angle (deg)−60 −40 −20 0 20 40 60
Figure 8: Measured RF-DC conversion efficiency and DC outputpower when the beam is steered.
Figure 8 shows the measured RF-DC conversion effi-ciency and DC output power when the beam is steered. Over45% efficiency is obtained when the beam is steered from−20∘ to 35∘. Figure 9 shows the constellation of the receivedsignal. When the beam is steered to +35∘, the error vectormagnitude (EVM) and bit-error rate (BER) of the receivedsignal are 14.6% and below 6.1 × 10−5, respectively. When thebeam is steered to −20∘, EVM and BER of the received signalare 14.9% and below 6.1× 10−5, respectively.Themeasurementrange of the BER is limited to 6.1 × 10−5, due to the hardwarememory.
The BER is affected by the coupling factor of thedirectional coupler. The coupling factor should be deter-mined considering the balance between sensitivity of thereceiver and rectification efficiency. In the demonstration
shown in this section, a coupling factor of 10 dB is selectedsince communication quality is prioritized, such as BERof below 6.1 × 10−5, which is the measurement limitation.The measured BER deteriorates to 3.2 × 10−3 when a 20 dBdirectional coupler is used.Therefore, a coupling factor largerthan 10 dB deteriorates the BER, as in the PXI system. Fromthe viewpoint of rectification efficiency, the input RF powerof the rectifier in Figure 7 is considered to be around 17 dBmfrom Figures 6 and 8. The efficiency will degrade when acoupler with a coupling factor of less than 10 dB is used.Considering this trade-off, a coupling factor of 10 dB is used.
The beam steering function is thus effectively integratedwith the WiCoPT technology. Also, wireless communicationand power transfer are conducted simultaneously.
3.3. Battery Charging Demonstration Using WiCoPT. Fig-ure 10 shows a block diagram of the battery charging demon-stration using the WiCoPT technology. The concept is basedon the BPF configuration described in Section 2. To deliverboth DC power and data from the transmitter to the receiver,5.80GHz CW and 5.82GHz modulated signals are generatedon the transmitter side. To get high DC output power andcharge the battery, eight rectifiers are arranged in parallelon the receiver side. The 5.80GHz rectifier is equipped witha 20MHz BPF. Eight output signals from the BPF in therectifier are combined and input into the demodulator. DCout terminals of the rectifier are connected to the batterycharge control unit. To prevent overcharging, the control unitlimits the voltage and current to 3.9 V and 80mA. At thebeginning of charging, the control unit limits the currentto 80mA. If the output voltage reaches 3.9 V, which is thecharge finish voltage, the control unit stops current flow tothe battery. Output voltage of the rectifier changes since theload resistance, which corresponds with input resistance ofthe control unit, changes. The modulation method is QPSK,and the sample rate is 1MSPS. A root-raised cosine filter with
6 International Journal of Antennas and Propagation
−1 0 1
−1
0
1
Q
I
(a) +35 deg. beam steering
−1 0 1
−1
0
1
Q
I
(b) −20 deg. beam steering
Figure 9: Measured constellations of the received IF signals when the beam is steered.
Div
ider
SG
Mod.
8 re
ctifi
ers w
ith B
PF
SG
CombinerD
ivid
er
Batterychargecontrol
Battery
Combiner
Demod.
BPF out
DC out
4×4
circ
ular
pat
ch ar
ray
4×4
circ
ular
pat
ch ar
ray
2.40G
5.82G5.80G 5.80G
3.42G 16
ch A
MPs
20MHz5.82G+
Figure 10: Block diagram of the battery charging demonstration using the WiCoPT technology.
alpha 0.5 is used on both the transmitting and receiving sides.The modulation/demodulation evaluation system of the PXIhardware is used. The distance between the transmittingand receiving antennas is 40 cm. Total output power of thetransmitter side is 40 dBm and 31 dBm at 5.80GHz and5.82GHz, respectively. Input power of the rectifier at 5.8 GHzis calculated as 21.4 dBm considering propagation loss, cableloss, gain of the amplifier, conversion loss of the mixer, andinsertion loss of the combiner and divider.
TheRF-DC conversion efficiency ismeasured by compar-ing the consumed power of the load and input RF power ofthe rectifier. EVM and BER are also measured. Measurementis carried out in an anechoic chamber. Figure 11 showstime domain characteristics of the voltage and current atthe rectifier and the battery. It takes 20min to charge thebattery to 3.9 V. The battery charge control unit has operatednormally since charging current is initially limited to 80mAand finally to 0mA. Battery charging capability is confirmedfrom the evaluation. Input resistance of the unit changesduring charging, so an additional circuit will be requiredto obtain maximum RF-DC conversion efficiency in futureapplications.
Figure 12 shows constellations of the received signal.EVM and BER of 11.5% and below 6.1 × 10−5 are measured,respectively.TheBERmeasurement range is restricted to 6.1×10−5 due to the hardwarememory.We have thus validated theWiCoPT concept, including both communication and powerfunctions.
We have confirmed the validity of the WiCoPT technol-ogy using the two configurations described in Sections 3.2and 3.3 and shown thatmicrowave bandWiCoPT technologyis effective for future integration in WPT-based communica-tion systems.
4. Application of WiSEnT in CompletelyWireless Sensor Network
As an application of the WiSEnT technology, a wireless ther-mal sensor is powered byWPT technology using amicrowaveband.
4.1. Overview of the Demonstration Using WiSEnT. Figure 13shows a block diagram of a demonstration of the WiSEnT
International Journal of Antennas and Propagation 7
Elapsed time (min)
Volta
ge (V
)
2
3
4
5
6
7
Curr
ent (
mA
)
0
20
40
60
80
100
Output voltage of the rectifierOutput current of the rectifierCharging voltage of the batteryCharging current of the battery
0 10 20 30
Figure 11: Time domain characteristics of voltage and current at therectifier and the battery.
technology in a wireless thermal sensor. The base station andsensor node have WPT and communication functions. DCpower consumed in the sensor node is supplied byWPT fromthe base station using an S-band CW signal. Thermal sensordata are then sent back to the base station using the 400MHzband. The distance between the base station and the sensornode is 1.2m.The signal source in the base station consists ofa CW signal generator and an S-band high-power amplifier.The sensor node has an S-band rectifier, a thermal sensor,and a 400MHz band transceiver. DC power is provided bythe S-band rectifier to the thermal sensor and transceiver.There is no battery in the sensor node. A 4 × 4 circular patcharray antenna is used as both base station and sensor nodeantennas.
4.2. Design and Evaluation of S-Band Rectifier. One of thekey devices of the technology is a microwave rectifier thatcan supply watt-class DC power. Figure 14 shows the S-bandrectifier circuit. AnNPT25015GaNHEMT (Nitronex) is usedfor the rectifying element, since GaN HEMT has high break-down characteristics comparable with GaAs ones, makingthe GaN device preferable for high-power application. Drainand source terminals are grounded to be used as Schottkydiodes. A DC cut capacitor and an RF cut inductor are placedat the input and output terminals, respectively. Treatment ofthe harmonics is based on the design method described inSection 3.1. The design method shown in Section 3.1 is used.
Figure 15 shows simulated and measured results of theoptimal load resistance under the conditions of 30 dBm inputRF power at 2.25GHz. Optimal load resistance is 11Ω, andthe conversion efficiency is 10.8%. Figure 16 shows simulatedand measured input-output characteristics of the rectifier. A2.25GHz CW signal and 11Ω load resistance are used. Amaximum RF-DC conversion efficiency of 36.7% is obtainedwhen input power is 46 dBm. A maximumDC output power
−1 0 1
−1
0
1
Q
I
Figure 12: Constellations of the demodulated signal.
Signal source Rectifier
Sensor node
WPT
Communication
WPT
Communication
TransmitterSensor receiver
Thermalsensor
Base station
2.25GHz
1.2m
400MHz
Figure 13: Block diagram of WiSEnT system using a wirelessthermal sensor.
of 17.8W is obtained when input power is 47 dBm.Themeas-urement results agree well with the simulation results. Wehave thus successfully developed a high DC output power S-band rectifier for WiSEnT application.
4.3. Experimental Demonstration of WiSEnT. Table 3 showsa power diagram of the system. The total efficiency ofconversion from RF power of the base station to DC poweravailable in the sensor node is 0.35% when 47.6 dBm outputRF power from the base station is defined as the referencepower. Input RF power of the sensor node is 35.6 dB, whichcorresponds to 6.3% of the base station output power, consid-eringTx/Rx antenna gain, feed loss, and propagation loss. RF-DC conversion efficiency is calculated as 5.5% since powerconsumption of the thermal sensor of 200mW and RF inputpower of 35.6 dBm is considered. The RF-DC conversionefficiency is degraded since input resistance of the thermalsensor is not matched to the optimal load resistance of therectifier. The total efficiency value is not pessimistically lowsince the total efficiency will be increased by adding moresensor nodes. At least a 100W-class high-power amplifier orhigh gain antenna will be required to maximize performanceof the rectifier and exceed 10W DC power.
8 International Journal of Antennas and Propagation
RF in DC out
GaN HEMT
Matching circuit
Harmonicsfilter
Open circuit for fundamental wave
Figure 14: A circuit of the S-band high-power rectifier.
0
5
10
15
20
Load resistance (ohm)
RF-D
C co
nver
sion
effici
ency
(%)
1 10 100 1000
MeasurementSimulation
Pin = 30 (dBm)
Figure 15: Simulated and measured results for optimal load resis-tance.
Figure 17 shows the measurement setup in an anechoicchamber. Two4× 4 arrays, theGaN rectifier, a thermal sensor,and ice for cooling the sensor are shown.
Figure 18 shows measured data from the thermal sensor,with sensor data and rectifier output voltage corresponding tothe sensor supply voltage. In the demonstration, the thermalsensor is cooled by ice to show normal operation of thesensor. RF output is stopped and the sensor is cooled from910 to 1035 s. At 1040 s, RF output and the sensor start. Sensordata show a temperature around 25∘C, which corresponds toroom temperature. After the cooling, the sensor data showa temperature around 0∘C. Measurement of the system isconducted in an anechoic chamber.We have thus successfullydemonstrated a completely wireless sensor network systemusing the WiSEnT technology.
5. Conclusion
We have proposed the WiCoPT and WiSEnT technologiesand provided experimental demonstrations of the feasibility
Input RF power (dBm)
Out
put D
C po
wer
(W)
RF-D
C co
nver
sion
effici
ency
(%)
0
10
20
30
40
50
60
0 10 20 30 40 50
Measured DC powerMeasured conv. effic.Simulated DC powerSimulated conv. effic.
Figure 16: Simulated and measured input-output characteristics ofthe rectifier.
Figure 17: Measurement setup in an anechoic chamber.
for the coexistence of WPT and communication in a battery-free wireless sensor network system. 5.80GHz GaAs HEMTrectifiers with a 20MHz BPF were designed and evaluatedfor WiCoPT technology. Output DC power was 50mWwith efficiency of 49.7%. The fabricated rectifier was usedfor a WiCoPT demonstration. 400mW output power wasobtained and 1MSPS QPSK communication with 11.5% EVMwas conducted. A high output power 2.25GHz GaN HEMTrectifier was designed for WiSEnT technology. A maximumoutput DC power of 17.8W was measured. A battery-freewireless sensor network was created using the rectifier asa WiSEnT technology demonstration, and a wireless sen-sor network was realized by the WiSEnT technology. Ourproposed technologies should be effective for a wirelesspower system integrated with communication functions infuture wireless sensor network applications such as cars andspacecraft.
International Journal of Antennas and Propagation 9
Table 3: Power diagram for the demonstration.
Amount of change at each term Power level (dBm) Power level (W) Total efficiency (%)Signal source (dBm) 47.6 47.6 57.5 100Feed loss (dB) 1.5 46.1Tx antenna gain (dBi) 14.9 61.0Propagation loss (dB) 39.1 21.9Rx antenna gain (dBi) 14.0 35.9Feed loss (dB) 0.3 35.6Rectifier RF input (dBm) — 35.6 3.6 6.3RF-DC conversion (%) (rectifier) 5.5 — —Supplied DC power (dBm) (thermalsensor) — 23.0 0.20 0.35
Elapsed time (s)
Sens
or d
ata (
deg)
Out
put v
olta
ge o
f the
rect
ifier
(V)
00 500 1000 1500
10
20
30
40
Sensor data Output voltage of the rectifier
Figure 18: Measured data of the thermal sensor and output voltageof the rectifier.
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