Transcript Outline - Tempest Home

High Power Millimeter Wave Grid Array
Sources*
Started 1 May 99
October 1999
S. A. Rosenau, C. Liang, W-K. Zhang(a), C. W. Domier(a), N. C. Luhmann, Jr.
Department of Electrical and Computer Engineering, University of California, Davis, CA 95616
(a) Department of Applied Science, University of California, Davis, CA 95616
A novel, broadband quasi-optical frequency multiplier system has been designed, simulated
and fabricated for high efficiency, high power millimeter wave applications. Initial proofof-principle doubler and tripler systems are being tested using a conventional 10 W Ka-band
TWT as the driver. Preliminary results have achieved > 6.7% and > 3.7% efficiency,
respectively, and generated > 410 mW output power at V-band and > 141 mW output power
at W-band with tunable bandwidths of 6.6 GHz and 2.5 GHz, respectively. Larger arrays
have been designed and are being fabricated. These arrays will be driven by an 80 W Ka–
band TWT and are expected to achieve 25% efficiency and 20 W output power at V–band
and 15% efficiency and 12 W output power at W-band. The long-term goal of this research
is a high power source using two microwave power module (MPM) drivers (200 W total)
and three frequency multiplier grid arrays. This is predicted to produce > 25 W cw output
power at V-band or > 15 W cw output power at W-band, and to offer dramatic savings in
size, weight and cost as compared to conventional coupled-cavity TWT sources. Eventual
systems could also employ the Millimeter Wave Power Module (MMPM), with an 18-40
GHz bandwidth, currently under development.
* This work has been supported by the US AFOSR under MURI '95 (Contract No. F49620-95-1-0253) and MURI '99
(Contract No. F49620-99-1-0297) and by the the US DOE (Contract No. DE-FG03-95ER54295).
MVE MURI 99 Kick-off Meeting
R. Barker, Technical Monitor
Introduction and Motivation
October 1999
Started 1 May 99
•
Low cost, high power, compact millimeter-wave sources are needed.
– Solid-State: Low cost and compact, but low power or low frequency.
– Electron Beam Devices: High power and high frequency, but become expensive and
bulky at high frequencies.
– Both technologies can provide inexpensive and moderately compact high power sources
at low frequencies.
•
High power microwave sources are available.
– Frequency Multipliers efficiently convert microwaves into millimeter-waves.
– Quasi-Optical Grid Arrays use quasi-optical power combining to achieve high power
handling (>100 W) with inexpensive solid-state devices in extremely compact (< 5 in3)
and extremely lightweight (< 2 lb.) systems.
– Overmoded waveguide mounting structures permit larger, more efficient and higher
power quasi-optical grid arrays.
•
Frequency Multiplier Grid Arrays create inexpensive, compact, high power systems
by converting high power low frequency sources into high power high frequency
sources.
– Simulations predict a Frequency Multiplier Grid Array based source capable of
generating > 20 W at V-band and > 12 W at W-band (when driven by a 80 W source).
MVE MURI 99 Kick-off Meeting
R. Barker, Technical Monitor
Project Overview
October 1999
Started 1 May 99
•
The prototype systems currently being fabricated and tested are designed to explore
the basic physics of frequency multiplier grid arrays in overmoded waveguides.
– Initial proof-of-principle prototype systems driven by a pulsed 10 W TWT have achieved
excellent preliminary results.
– New wafer designs currently being fabricated explore physics of grid array unit cell
dimensions and varactor device layout.
– New fixture designs reduce losses inherent in current biasing techniques (doublers).
– New filter/ matching techniques and designs are being fabricated and tested.
•
The next stage in development explores the challenges of increased drive power.
– Larger arrays will be fabricated to handle higher input powers.
– Heat generation by the array will be measured and heat dissipation systems designed and
evaluated.
– EM simulations and experiments will be performed to evaluate the effects and optimize
the performance of significantly overmoded waveguides.
– New fixtures will be fabricated to incorporate the results of these experiments and new
designs.
•
The long-term goal of this project are high power cw sources.
– High output powers: > 20 W at V-band and > 12 W at W-band.
– High multiplication efficiencies: > 25% for doublers and > 15% for triplers.
– Broadband: Tunable bandwidths of 60 - 70 GHz and 90 - 110 GHz.
MVE MURI 99 Kick-off Meeting
R. Barker, Technical Monitor
State-of-the-Art in Moderate/High Power
Frequency Multipliers
Started 1 May 99
October 1999
Efficiency Array Size
(devices)
Output
Frequency
Output
Power
2x
66 GHz
500 mW
9.5 %
760
BNN
2x
66 GHz
2.1 W
7.5 %
1760
SQBV
3x
99 GHz
5W
2%
3100
MSQBV
3x
93 GHz
91 mW
10 %
1
(waveguide)
ISIS
2x
88 GHz
280 mW
14 %
1 (whisker
contacted)
Crowe et al.
Schottky
varactors
2x
262 GHz
10 mW
24 %
1 (whisker
contacted)
Goals:
Rosenau
Schottky
varactors
2x
66 GHz
410 mW
6.7 %
56
20 W, 25 %, 2100 dev.
Rosenau
SQBV
3x
96 GHz
77 mW
2.4 %
250
Rosenau
MQBV
3x
90 GHz
141 mW
3.7 %
270
Author
Devices Harmonic
Jou
Schottky
varactors
Qin
Liu
Rahal et al.
Staecker, et. al.
MVE MURI 99 Kick-off Meeting
R. Barker, Technical Monitor
12 W, 15 %, 6150 dev.
Varactor Grid Arrays
October 1999
Started 1 May 99
Elect ric Wall
a=400 µm
y
W
Varactor
Di ode s
b=400 µm
w=30 µm
E
Magnet ic
Wall
Magnet ic b
Wall
E
x
z
Indu cti ve
Le ads
Elect ric Wall
a
• Frequency multiplier grid arrays are composed of arrays of varactor devices.
• Frequency doublers use biased single sided devices:
Schottky, BNN, RTD or other varactor devices.
• Frequency tripler grid arrays use un-biased devices
with symmetric dc characteristics:
back-to-back arrays of MQBV, SQBV, SSQBV or other QBV devices.
C
V
C
V
MVE MURI 99 Kick-off Meeting
R. Barker, Technical Monitor
Started 1 May 99
Quasi-Optical Frequency Multiplier
Grid Arrays
Input Matching
Network
Input
Filter
Grid
Heat
Output
Array Spreader Filter
RF
Input
•
•
October 1999
Output Matching
Network
RF
Output
Overmoded waveguide is employed to reduce diffraction losses, contain input and
output signals and provide a mounting structure for quasi-optical grid array
elements.
Quasi-Optical Grid Array elements include:
–
–
–
–
Varactor Grid Array, to provide frequency multiplication
Filters, to isolate input and output signals
Matching Networks, to impedance match waveguide to GaAs based array
Heat Spreader, to remove heat to waveguide walls for dissipation outside the system
MVE MURI 99 Kick-off Meeting
R. Barker, Technical Monitor
Quasi -Optical Over-Moded Waveguide
Frequency Multiplier Grid Arrays
Started 1 May 99
•
•
•
October 1999
Overmoded waveguide is employed to reduce diffraction losses, contain input and output
signals and provide a mounting structure for quasi-optical grid array components.
Broadband quasi-optical filters have been developed and are in use. New filter design
techniques are currently being investigated.
High power, cw operation planned using advanced cooling systems like the
CVD diamond heat spreader shown above.
MVE MURI 99 Kick-off Meeting
R. Barker, Technical Monitor
Power Distribution in Waveguides
October 1999
Started 1 May 99
Incident Pow er
Heat Generated
Tripled Pow er
Reflected Pow er
Eff iciency
40
0.06
35
0.05
30
25
0.04
20
0.03
15
0.02
10
0.01
5
0
0
0
0.2
0.4
0.6
0.8
Efficiency per unit cell (in %)
Power per unit cell (in Watts)
0.07
E(x)
d
a
x
Eff iciency per unit
Dielectric-loaded waveguide with fundamental
mode (LSE10) electric field profile.
1
Distance across w aveguide (in cm)
•
•
•
Incident power in a metal waveguide follows a sine2 distribution across the long dimension.
Varactor device performance varies with incident power, resulting in reduced efficiency.
Alternative waveguides offer potential solutions:
– photonic band gap (PBG) materials
– dielectric-loaded waveguide
– metal disk-loaded waveguide
MVE MURI 99 Kick-off Meeting
R. Barker, Technical Monitor
Schottky Varactor Devices
October 1999
Started 1 May 99


2
b
___
a
a
___
b
1
C diode
R diode
C parasitic
C bias
L strip
R strip
•
•
•
MVE MURI 99 Kick-off Meeting
Frequency doubler grid arrays using
Schottky varactors fabricated by MartinMarietta have been tested.
Cmin = 15 fF, Cmax = 60 fF resulting in
Cmax/Cmin = 4
Rs = Rdiode + Rstrip = 6 Ω
R. Barker, Technical Monitor
Preliminary Frequency Doubler Results
October 1999
Started 1 May 99
Schottky diodes, fabricated by Martin-Marietta (Baltimore), were used in an
overmoded waveguide frequency doubler grid array.
Eff iciency
Simulated Ef ficency
Instantaneous
7
12
6
10
5
0.3
8
0.2
6
4
Efficiency (%)
Output Pow er (W)
0.4
14
Efficiency (%)
Output Pow er
Tuned
4
3
2
0.1
0
0
1
2
3
4
5
6
7
2
1
0
0
8
30
Input Pow er (W)
32
33
34
35
Input Frequency (GHz)
• 410 mW output power at 66 GHz
• 6.7 % efficiency at 63 GHz
(reduced efficiency caused by fixturing)
• 56 devices
• 7.3 mW per device
MVE MURI 99 Kick-off Meeting
31
• 6.6 GHz (10%) tuned output bandwidth
• 3.6 GHz (6%) instantaneous output
bandwidth
R. Barker, Technical Monitor
Started 1 May 99
Frequency Doubler Grid Array
Designs in Fabrication
Bias Method
Double Bias Line
Resistor Network on Chip
Standard Off-Chip
Standard Off-Chip
Standard Off-Chip
Standard Off-Chip
Standard Off-Chip
•
•
•
Number
of Devices
168
168
168
84
140
136
560
a/b
Ratio
1
1
0.5
1
1.5
1
1
Max. Operating
Frequency (GHz)
82
82
82
82
82
103
207
October 1999
Fixture
Waveguide
K-band
K-band
Ka-band
Ka-band
Ka-band
Ka-band
Ka-band
Two designs investigate a new method of providing bias to the array (see following
viewgraph). These designs will be housed in a new, larger fixture currently being fabricated.
Three designs vary the shape of the unit cell. This will allow experimental investigation into
the physics of this aspect of grid array technology. The values a and b are the width and
height, respectively, of the unit cell. Values of a/b less than one result in tall, thin unit cells,
values greater than one result in short, fat unit cells.
Two designs are have smaller dimensions. This allows higher frequency operation. In order
to avoid potential grating modes caused by the diode grid, the largest grid dimension must be
less than an effective half wavelength of the highest frequency signal.
MVE MURI 99 Kick-off Meeting
R. Barker, Technical Monitor
Started 1 May 99
New Frequency Doubler Diode
Bias Techniques
Wavegui de Wall
Double Bias Line
•
•
•
•
•
Wavegui de Wall
Waveguide Wal l
October 1999
Waveguide Wal l
Resistor Network on Chip
Previous arrays required n + 1 bias lines for an n  m array.
Two new bias techniques both result in only two bias connections.
Fixture provides one connection resulting in only one bias line penetrating the
waveguide wall.
Double bias line design uses two closely spaced bias lines.
Resistor network on chip design places the resistive voltage divider on the grid
array substrate.
MVE MURI 99 Kick-off Meeting
R. Barker, Technical Monitor
Frequency Tripler Grid Arrays
October 1999
Started 1 May 99
A Superlattice Barrier structure has been successfully employed for high frequency multiplication efficiency. By
using a back-to-back layout configuration, SSQBV Varactors have symmetric C-V characteristics, therefore, are
natural triplers. Simulations have been performed using the HP HFSS 3-D EM code and the HP MDS code to
optimize the unit cell size and metal lead width.
Ante nna L ead
2000 Å Al in- site
super lat tic e barr ier
1500 Å n GaAs
super lat tic e barr ier
1500 Å n Ga As
super lat tic e barr ier
1500 Å n Ga As
super lat tic e barr ier
1500 Å n Ga As
40Å AlAs
10 Å Ga As
40Å AlAs
10 Å Ga As
40Å AlAs
10 Å Ga As
40Å AlAs
Meta l
Active Region
n+
Subst rat e
Isola tion
E
1  m n+ GaAs
supe rlattic e bar rie r str uc ture
Subst rat e
17 -3
doping 1x10 cm
Undope d
18 -3
doping 4x10 cm
12 -2
 doping 2.3x10 cm
T op Vie w
Superlattice Schottky Quantum Barrier Varactor (SSQBV) Structure
Cross Se cti onal Vie w
Back-to-back Layout Configuration of Varactor
C
Antenna
Leads
Bac k-t o-Back
Varac tor Diodes
Parasitic F ield s
Between F ing ers
C-V Curv e
Ed ge Eff ect
V
E Fi el d
C pp
Cg
I
Cg
I-V Curv e
D iode Active
Regio n
+
V
Monolithic Frequency T ripler Array
MVE MURI 99 Kick-off Meeting
n Reg ion
Rs
3-D EM Simulat ion and Device Simulation
R. Barker, Technical Monitor
Preliminary Frequency Tripler Results
October 1999
Started 1 May 99
Multiple Quantum Barrier Varactor (MQBV) devices, fabricated at Rockwell Science
Center, were used in an overmoded waveguide frequency tripler grid array.
200
3.5
4
3
2.5
100
2
1.5
50
1
Output Pow er (mW)
Eff iciency (% )
0
0.5
0
0
1
2
3
4
Efficiency (%)
150
3
Efficiency (%)
Output Power (mW)
3.5
2.5
2
1.5
1
0.5
0
30
32
33
34
Input Frequency (GHz)
Input Pow er (W)
• 141 mW output power at 90 GHz
• 3.7 % efficiency
(reduced efficiency due to low yield)
• 270 devices
• 0.5 mW per device
MVE MURI 99 Kick-off Meeting
31
• 2.5 GHz (3%) tuned output bandwidth
R. Barker, Technical Monitor
Started 1 May 99
Frequency Tripler Grid Array
Designs in Fabrication
100 0 
n+ GaAs
Antenna Lead
150 0 
n G aAs
AlGaAs barrier
150 0 
n G aAs
AlGaAs barrier
150 0 
n G aAs
AlGaAs barrier
150 0 
n G aAs
AlGaAs barrier
150 0 
n G aAs
Met al
Active Region
n+
Substrat e
Isolation Mesa
Si 3 N4
E
New Varactor Layout
•
•
•
200 Å AlGaAs
1500 Å n GaAs
200 Å AlGaAs
1500 Å n GaAs
200 Å AlGaAs
1500 Å n GaAs
200 Å AlGaAs
1500 Å n GaAs
1  m n+ GaAs
1  m n+ GaAs
GaAs Subst rate
Substrat e
-3
cm
-3
doping 1x1017 cm
17
-3
undoped
-3
doping 4x1018 cm
cm
undoped Al.45 Ga.55 As
C ross S e cti on al Vi e w
2000 Å Al in-situ
18
doping 5 x 10
doping 1 x 10
Top Vie w
October 1999
18
doping >5 x 10
-3
cm
MQBV Profile
-2
 doping 2.3x1012 cm
SQBV Profile
New frequency tripler grid array designs are in fabrication.
Both MQBV and SQBV devices are being fabricated.
An improved varactor layout has been developed utilizing advanced
fabrication techniques.
– Planarized technique improves metal layer design.
– Mesa etch improves isolation and device performance.
MVE MURI 99 Kick-off Meeting
R. Barker, Technical Monitor
Quasi-Optical Output Structure
October 1999
Started 1 May 99
Electromagnetically
Transparent
Thermal Epoxy
Quasi-Optical Grid Array
Heat Spreader
Output Filter/Matching Network
Conductive
Thermal Epoxy
Heat Sunk Metal
Waveguide Walls
Frequency
Selective Surface
A new technique has been implemented which incorporates a heat spreader,
output filter and output matching network in a single device. This results in
reduced complexity and lower insertion loss resulting in greater efficiency of
the frequency multiplier system.
MVE MURI 99 Kick-off Meeting
R. Barker, Technical Monitor