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Features of Microwave WPT• High power oscillators (kW~GW)
Magnetron, Gyrotron, etc. Inexpensive & easy maintenance.
• High energy conversion efficiency
DC-RF conversion efficiency is 50%~90% minimizing heat load.
• Phase controllability
Beam forming and steering by a phased array. No need of mechanical Beam forming and steering by a phased array. No need of mechanical
control.
• High transmittance though the atmosphere
Transmittable though clouds, fogs, and dielectric medium.
• Large beam divergence
Resulting in short transmission distance, large receiver area.
• Impact on human body
At some frequencies, resonantly absorbed by H2O molecules, resulting in
heating inside the body. Regal safety threshold for stationary exposures at
GHz ranges is 10 W/m2. (1% of solar radiation)3
Magnetron
Copper anode block
Resonating cavity
Operational principle 8-cavity magnetron
- Inexpensive, high power and very efficient ~ 80% of DC-AC conversion efficiency.- High output power of 100 kW@915 MHz has been obtained. - However, frequency is not precisely controllable and waveform/frequency is not stable.
A magnetic field parallel to a hot filament
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Field Effect Transistor (FET)
Source Gate Drain
Self-excited oscillation circuit with
Compact, light weight, efficient ~90%.Frequency is stable and precisely controllable.
Structure of a GaAs FET amplifier
eff g2f v Lπ=frequency
veff : mean electron velocityLg : gate length
Semiconductor GaAs Base
n-GaAs active layer
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Self-excited oscillation circuit with positive feedback
Comb-shape GaAs FET chip (NEC Corp.) 440×970 μm. 2 W output with Lg=0.5 μm, Wg=3mm@18 GHz.
Electron depletion region
GaN (Gallium Nitride) FETworks at 10 times higher voltages and higher electron mobility than GaAs transistors
Pow
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WPo
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Toshiba 6 GHz 174 W GaN Power FET
SiC, GaN high frequency devices• Broadcasting• Ground base for satellite communication• Cellular wireless infrastructure• High power radars• Public mobile radio• Military & aerospace
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Frequency /GHzFrequency /GHzFrequency /GHzFrequency /GHz
Pow
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WPo
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WPo
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Gyrotron JAEA Gyrotron SpecificationsFrequency 170 GHzMax Output Power 1.5 MWOutput Duration 0.1 ms – 1000 sBeam profile GaussianBeam waist 20 mmElectrical efficiency 60%
1MW Gyrotron (Japan Atomic Energy Agency)8
Power transfer to a model helicopter
light-weight & efficient rectenna receiver
Microwave-powered helicopter,1964
Raytheon Co. (USA) & Dr. William Brawn. 2.45 GHz.
Manufactured a rectenna array of 90% conversion efficiency .
It flew 10 hours at 18 m altitude.
10
High Power Transfer at Goldstone, US
Microwave power transmission demonstration at Goldstone, California, 1975
NASA JPL & Raytheon: 30kW, 2.45 GHz for 1mile distance @84% rectenna efficiency.
11
WPT to an airplaneActive phased array transmitter (1 kW)
MILAX (Microwave Lifted Airplane eXperiment), 1992
Kyoto Univ., Nissan Motors, etc. A plane flew for 40 sec, 400 m distance at 15 m
altitude. Tested active phased array, 2.4 GHz GaAs-FET amplifier, 4 bit-digital phase
shifter, micro-strip antenna.13
Rocket experiment in space
METS (Microwave Energy Transmission in Space) rocket experiment, 1993
Kyoto Univ., Kobe Univ. etc., in plasma environment in the ionosphere at 150~200
km altitude, power was sent from Mother ship to daughter ship using the same
transmission-reception system as MILAX ones.
14
Phased array antenna
θstr θstr
λ(δ/2π)
d
Concept of phased array antenna
strsin2d
λ δθ
π=
Adaptive array antennas for cell phone base. (Smart antenna) Directionality is designed to form a cell of communication area.
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Retro-directive function
α αα α
Sending back phase conjugation waves
λ(δ/2π)
d
sin2d
λ δα
π=
( )in 0 sinE E tω δ= + ( )out 0 sinE E tω δ= −
λ(δ/2π)
d
Pilot signal detection
Hardware retro-directiveSoftware retro-directive
17
Active control MPT system (Univ. of Tokyo)
2.45GHz
Target
5.8GHz
Receiver
System
2.45GHz
Pilot
Signal
5.8GHz
Energy
Beam
Transmitter
System
Phase
difference
Tracking
System
Digital phase
control
PC
18
Auto-tracking MPT system using an active phased array antenna.
Active phased array transmitter
Transmitter specifications
Parameters valuesmicrowave frequency 5.8 GHzwavelength, λ 51.7mm
5-element active phased array antenna
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wavelength, λ 51.7mmtotal transmission power 3.5 Warray pitch, d 110 mm (d/λ=2)diameter of the array, D 330 mmSteering angle ,θ 9°Divergence angle ,θd 9°
Beam steering(x, y, z) = (160, 0, 1040)
(x, y, z) = (113, 113, 1040)
Computed beam steering
calculated measured
(x, y, z) = (80, 139, 1040)
(x, y, z) = (0, 160, 1040)
21
Theory of Rectenna Design
Antenna
Dipole and microstrip patch antennas are used because of
- simplicity of structure
- miniaturization in the size and weight
Schottky diode (SBD, Metal-semiconductor junction)
- low VT of 0.15-0.45 V 順方向電圧 (cf. 0.6-1.7 V in PN-junction diode)
- very fast switching action of 100 ps (10 GHz)
RECTENNA is the coined word for “RECTifier” and “antENNA”.
23
- very fast switching action of 100 ps (10 GHz)
dipole rectenna
Theory of Rectifier Circuit Design
R s
R LV g
+
-VL
+
-
I 1 I 2
I R
+-
I 1Input
Filter
Output
Filter
Output Smothing Capacitance
λ/4 Microstrip Line
ZW, β
R S
D C o
C 1RF-IN
Harmonic Filter
R L
24
input filter
- prevent any of harmonic wave from flowing back to the antenna.
- allow current flow at the fundamental frequency.
output filter
- reflect odd harmonics f, 3f, 5f ・・・.- allow even harmonics 0, 2f, 4f ・・・ to flow without any voltage drop
Block diagramIdeal equivalent circuit
Output Smothing Capacitance
and Lowpass FilterShottkey-Barrier Diode
Output Smothing Capacitance
and Lowpass Filter
λ/4 Microstrip Line
ZW, β
R S
D C o
C 1RF-IN
Shottkey-Barrier Diode
Harmonic Filter
R L
Rectification with a single diodenodeanti-node
VDC
VT
VBR
breakdown voltage VBR
thermal voltage VT
25
Rectification with a single diode
Typical diode V-I curve
VT
VBR
2T LV R
2Ld
V R
VT
VBR
Half-wave Rectification with a single series diode
Energy loss factors and conversion efficiency
Co
nv
ers
ion
Eff
icie
ncy
η
100%
Diode Max.
Efficiency
VR Effect
V f Effect
Higher order
Harmonics Effect
26
- η decreases with a decrease in Pin because fractional loss due to diode forward voltage
drop VT increases. (Vfeffect)
- When diode voltage Vd > VBR, η also decreases with Pin because reverse current is
induced. (VR
effect) It takes maximum when VDC ~VBR/2 or Vd ~VBR.
- At impedance matching condition with optimal external load RL, there is no reflected
wave.
Input Power P in
L
R
R
V
4
2
Co
nv
ers
ion
Eff
icie
ncy
2
BR
L4
V
R
Dipole Rectenna array on membranelight, thin, flexible & polarity free
Multi-directional dipole antenna (NASA Langley Research Center)
H-shape dipole on membrane(UT and JAXA/ISAS)
0.5λ
0.55λ
0.12λ
27
Polarity matching in reception antennaLinear polarization
Yaw angleΨ
No attitude (Yaw angle) changeNo attitude (Yaw angle) changeNo attitude (Yaw angle) changeNo attitude (Yaw angle) changeLinearly polarized waves (Generally longer transmission distance)
Horn antennaParabola antenna Patch antenna
With attitude (Yaw angle) changeWith attitude (Yaw angle) changeWith attitude (Yaw angle) changeWith attitude (Yaw angle) changeCircular polarized waves (independent of antenna attitude, wave polarity)
Circular polarized patch Circular polarized patch rectenna
Monopole/Dipole rectennaPatch rectenna
28
Micro-Strip Antenna (MSA) y
x
z
#4
#1
#3
#2
F
E
H
a
b
Polarization
29
・used for wireless communication receivers on aircraft, spacecraft, and automobile and for GPS receivers. ・directionality vertical to the antenna plane・Light weight, high power
Linearly polarized MSA
Interior electromagnetic field of
Rectangular MSA
a is normally half wavelength. It works as an
array of dipole antennas. The ground plate
reflect re-radiation. More volume(a*b*t),
more band width.
H
tGround
Impedance Matching between MSA and output
ρ 0
a
x
y
ε r
F
G
S
R
R : Radiator element
S : dielectoric Substrate
G : Ground
F : Feeding point
Output impedance Z varies from 0
(center) to several hundred ohms
(open boundary) depending on the
feeding point location ρ0. Design ρ0
to have 50 Ω impedance.
30
G
S
R
ρ 0
a
x
y
ε r
F
b
Tf
Fm
ρ 0
x
y
ε r
l s
l 0
w
b) Coplanar Feeding Method
a) Backside-Coaxial Feeding Method
c) ElectroMagnetic (EM) Coupling Feeding Method
to have 50 Ω impedance.
0150 tan
2Z
a
ρπ = − Ω
for 0.15< ρ0/a<0.85
a
ρ0
MSA Rectenna Design
Antenna Array (Right Face)
Dielectric
Medium
Combine
Patch antenna and rectifier circuit are
printed on a substrate which requires low
dielectric constant (εr = 1.2~5.0) and low
dielectric loss (tanδ=10-3~10-4), such as
the Teflon-fiberglass substrate.
31
Rectifier Array (Rear Face)
Cupper (Ground)
Cupper (Antenna)Cupper (Rectifier)
MAS rectenna array
The size of antennas in its resonance
direction is λg/2.
r
gε
λλ 0=
Rectifier Circuit for MSA rectenna
Output Smothing Capacitance
λ/4 Microstrip Line
ZW, β
R S
D C o
C 1RF-IN
Harmonic Filter
R LFeeding Point
(DC out)
Stub
LPF
OutputTransmissionLine
Chip
Condenser
DiodeRF IN
Feeding Point
(DC out)
Stub
LPF
OutputTransmissionLine
Chip
Condenser
DiodeRF IN
32
Diode
Chip Condenser
Stub
Feeding
pointRF-IN
Stub
Output Smothing Capacitance
and Lowpass FilterShottkey-Barrier Diode
An example of rectifier
The equivalent circuit is the same as
previous.
Stubs are used as capacitors for
input and output filters.
Flexible Patch Rectenna on a felt pad
light, thin, flexible, polarity free & efficient
Patch rectenna on felt (UT)
Rectification efficiency
Wearable patch antenna (NICT)
Patch rectenna on felt (UT)
33
Observation System for Gas Pipeline Network Using Unmanned Airship
Specifications of power and propulsion systems
Endurance
Thrust Force
Propulsion Power
Energy for 10h Cruise
10
584
8.17
224
h
N
kW
kW·h
Unmanned Airship (Unmanned Airship (Unmanned Airship (Unmanned Airship (φφφφ30m x 8m). 30m x 8m). 30m x 8m). 30m x 8m). Recharge with 10hr intervalsRecharge with 10hr intervalsRecharge with 10hr intervalsRecharge with 10hr intervals (power (power (power (power stations at every 100stations at every 100stations at every 100stations at every 100----200 km.)200 km.)200 km.)200 km.)
Energy for 10h Cruise
Microwave Power 30GHz
Energy Charging Time
Rectenna Efficiency
Rectenna Max. Power
Density
Rectenna Weight Density
Rectenna Surface Area
Rectenna Total Weight
Fuel Cell Energy Density
Fuel Cell Weight
224
200
1.1
0.5
1.5
1.5
60
90
500
450
kW·h
kW
h
-------
kW/m2
Kg/ m2
m2
kg
Wh/kg
kg
35
Solar Power Satellite (SPS) system
1 GW Class SSPS Concept
Panel 2 km × 1.9 kmOutput power 1 GWOrbit GeosynchronousPowerPowertransmission 5.8 GHz
Total weight 20,000 tonsProblems ・EM interference with aircrafts,
birds.・cost of electricity・terrestrial energy balance
1 GW Class SSPS Concept in JAPAN
36
Summary of Microwave WPT
MW class oscillators are available at inexpensive price. Frequency is stable and phase is controllable.
High power of MWT was demonstrated on the ground and in space.
A microwave beam can be formed and steered by a phased
37
A microwave beam can be formed and steered by a phased array antenna, without mechanical gimbaling.
Non-mechanical Automatic tracking is realized through a retro-directive function.
Rectifying antenna (Rectenna) using a single SBD rectifyer and patch antenna is simple, light weight, inexpensive and flexible.