Download Compact L- and S-Band GaN High Power Amplifiers

AN RFMD® WHITE PAPER
RFMD.
®
Compact L- and S-Band GaN High
Power Amplifiers
Dave Aichele, David W. Runton, Zoran Anusic, and Eric Schonthal
Key Concepts Discussed:
• Advantages and disadvantages of competing power amplifier technologies for radar applications.
• GaN power amplifiers are shaping the future of radar.
• Specific GaN solutions in production and proposed.
RF MICRO DEVICES®, RFMD®, Optimum Technology Matching®, and PowerStar® are trademarks of RFMD, LLC. All other trade names, trademarks and registered trademarks are the property of their respective
owners. ©2009, RF Micro Devices, Inc.
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Compact L- and S-Band GaN High Power Amplifiers
Contents
List of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Advancements in Radars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Industry Standard Power Amplifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
VED Amplifiers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
GaAs Amplifiers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Si Amplifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
The Wave of the Future: GaN Amplifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
RFMD Focuses GaN for Radar Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
RF3928: 300W at S-Band . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
RFHA1020: 350W at L-Band . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
RFHA1023: 250W at L-Band . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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Compact L- and S-Band GaN High Power Amplifiers
List of Figures
Figure 1. Long Range Surveillance L-Band Phase Array Radar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Figure 2. Radar Amplifier Technology Adoption Projections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Figure 3. Compact S-Band GaN HPA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Figure 4. RF3928 RF Performance from 2.7GHz to 3.5GHz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Figure 5. RFHA1020 RF Performance from 1200MHz to 1400MHz . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Figure 6. RFHA1023 RF Performance from 1200MHz to 1400MHz . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Figure 7. HPA Design Topology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Figure 8. GaN Model Source Pull, Load Pull . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Figure 9. Design NLM Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Figure 10. Compact L-Band GaN HPA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Figure 11. Pulsed RF Measurements and Affects of Pulse Width and Duty Cycle . . . . . . . . . . . . . . . 11
Figure 12. RFMD’s MicroShield Integrated RF Shielding Technology . . . . . . . . . . . . . . . . . . . . . . . . . 12
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Compact L- and S-Band GaN High Power Amplifiers
Introduction
1.
Civilian and military radar systems rely on amplifiers to
deliver pulsed and continuous wave power ranging from
mere watts, to hundreds of kilowatts for microwave and
millimeter frequencies. Radar use varies greatly because
it can identify the range, altitude, direction, or speed of
both moving and fixed objects such as ships, spacecraft,
guided missiles, motor vehicles, terrain, and weather.
Civilian uses include meteorological precipitation
monitoring,
radar
astronomy,
ground-penetrating
geological observation, and high-resolution imaging. In
military applications, radar is used in ground-penetrating,
ground/air surveillance, target tracking, rendezvous
systems, air-defense systems, antimissile systems, and
fire control.
Figure 1. Long Range Surveillance L-Band Phase Array
Radar
2.
3.
4.
Sensitivity:
Sensitivity is the essence of radar. Systems demonstrating improved detect and monitor capabilities,
capturing small, previously indistinguishable
objects, are replacing older technology.
Electronically Scanned Arrays:
Mechanically scanned antennas are being supplanted with electronically driven antennas which
demonstrate improvements in performance and reliability.
Image enhancement:
Advancements in computer processing and transmit/receive technologies allow newer radar systems
to generate higher resolution images.
Energy efficiency and increased power:
Reducing size and weight of complex radar systems
are direct results of higher efficiency and power.
Smaller size and weight are critical to increasing
possible civilian and military radar applications
where they were not feasible before. These advancements push radar manufacturers and component
suppliers to continue driving incumbent amplifier
technology towards power and efficiency.
Industry Standard Power Amplifiers
Some uses of radar cross over the civilian/military divide.
In the air, radar is used for controlling air traffic,
anticollision systems, altimetry, and flight-control. On the
sea, nautical radar is used to locate landmarks and other
ships and for ocean-surveillance systems. In all cases, as
these radar technologies and their requirements
advance, designers are seeking out next generation
amplifiers that offer advantages in power, bandwidth, and
efficiency over conventional technology.
Advancements in Radars
Manufacturers continue to make advancements to radar
systems to meet the requirements of their customers and
their environments and conditions. Several recent
advancements include:
WP101015
Current radar technology relies on conventional Vacuum
Electron Devices (VEDs), Gallium Arsenide (GaAs) and
Silicon (Si) solid state amplifiers to deliver power. Most
military and civilian radar systems operate in the following
microwave and millimeter frequencies: L-band (1GHz to
2GHz), S-band (2GHz to 4GHz), C-band (4GHz to 8GHz),
X-band (8GHz to 12GHz), ku (12GHz to 18GHz) and Kaband (26.5GHz to 40GHz). Power requirements vary from
single-digit watts to tens of kilowatts depending on the
amplifier used in the system. Below, technologies
providing current amplifier solutions for radar systems are
explained.
VED Amplifiers
VEDs consist of Traveling Wave Tubes (TWTs), Klystrons,
Magnetrons, Gyrotrons, and Cross Field Amplifiers (CFA).
VEDs are capable of working from the MHz range up to
hundreds of GHz and vary in power from watts to
hundreds of kilowatts. VED technology is 70 years-old,
however, and VEDs are complex to manufacture requiring
unique materials and skill sets. VED market share is
susceptible to next generation technologies that offer
comparable power levels at target frequencies with
robust solid state reliability.
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Compact L- and S-Band GaN High Power Amplifiers
GaAs Amplifiers
Si Amplifiers
GaAs amplifiers are used as pre-drivers, drivers, and final
stage amplifiers for radar systems that require high
efficiency while operating in microwave and millimeter
frequencies. GaAs amplifiers operate in the 5V to 28V
range. Power density limitations require either combining
these devices, or excluding them from use in higher
power radar applications where space limitations prohibit
power combining. Advancements in alternative
semiconductor technology for increased bandwidth,
power, and efficiency lure radar manufacturers away from
GaAs amplifiers.
Silicon amplifiers typically consist of silicon bipolar and
Laterally Diffused Metal Oxide Semiconductor (LDMOS)
technologies. These technologies are best known to
operate at 28V, with new improvements up to 50V. This
technology works well in VHF and UHF frequency ranges,
but can also work up to 3.5GHz. Packaged modules using
multiple die can offer power levels up to 1000W at 1GHz,
but typical power levels are less than 200W. The intrinsic
parasitic capacitance characteristics in this technology
limit the bandwidth performance and power capabilities.
This inherently limits potential improvements to efficiency
and power handling.
Figure 2. Radar Amplifier Technology Adoption Projections
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Compact L- and S-Band GaN High Power Amplifiers
The Wave of the Future: GaN Amplifiers
Gallium Nitride (GaN) amplifiers are deployed in military
radar systems where design, manufacture, and adoption
rates are increasing each year. For applications operating
in frequency bands less than 6GHz, radar manufacturers
recognize that this wide-band gap technology offers
significant advantages over existing Si and VED
amplifiers. Advantages include higher voltage and
broadband performance with high drain efficiency. There
is increased GaN manufacturing activity in the U.S. and
Japan toward higher frequency radar applications, (those
greater than 10GHz), with emphasis on improvements in
bandwidth, power output, and efficiency. These higher
frequency GaN solutions are encroaching on entrenched
GaAs and VED design slots and market share.
RFMD Focuses GaN for Radar Applications
GaN is relatively new to the market. Several established
RF companies have invested considerable resources to
develop a robust, reliable GaN semiconductor technology
targeting multiple markets. The pulsed and CW
performance from GaN radar systems are ideally suited
for both civilian and military applications. First generation
RFMD GaN technology was released as a 50V process
with power density greater than 5W/mm and respectable
power gain performance up to 6GHz. RFMD has
developed a family of high power, high efficiency,
broadband amplifiers that are positioned for L-band, Sband, and C-band radar applications.
Figure 3 shows a typical RFMD solution including the
partially matched power transistor, bias network, and oncircuit-board matching elements. The package is a
hermetically sealed bolt-down package for optimum
thermal contact. The package houses the GaN transistor
die, splitting and combining networks, matching, and
stabilization circuitry.
The impedance at the package pin for the device is
typically 15Ω to 25Ω. This higher impedance allows the
circuit board matching elements to remain compact as
shown in Figure 3. The wide-dimension, low-impedance
matching traces, typical in silicon-based solutions, which
take up significant amounts of circuit board area, are not
required. For radar applications requiring several devices
combined in parallel to achieve multi-kilowatt amplifiers,
the cost benefits of module size reduction alone
represent a significant advantage. Indeed, equivalent
silicon-based solutions may have a footprint 10 times
larger.
Figure 3. Compact S-Band GaN HPA
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Compact L- and S-Band GaN High Power Amplifiers
RF3928: 300W at S-Band
performance for the RF3928 covering the full 2.7GHz to
3.5GHz band. This broadband performance represents
fixed circuit board tuning with no adjustments to bias or
tuning component changes.
RFMD’s RF3928 was designed for operation from 3GHz
to 3.5GHz and provides over 300W of pulsed peak power,
with peak gain greater than 9dB and peak drain
efficiency of 46% to 52% over that frequency range.
All measurements were taken under pulsed conditions
using a 100μsec pulse at 10% duty cycle. Power droop
across the pulse width is typically 0.2dB indicating that
the thermal properties of the GaN device and package
are not limiting performance.
Previously RFMD has shown that this amplifier topology is
very flexible and can achieve wide bandwidth (25%
bandwidth) while providing high-output power and
efficient operation. Figure 4 presents board tuned
Figure 4. RF3928 RF Performance from 2.7GHz to 3.5GHz
RF3928 Gain/Efficiency vs. Frequency, Pout = 54.5dBm
(Pulsed 10% duty cycle, 100uS, Vd = 50V, Idq = 440mA)
16
56
Gain (dB)
Gain
Eff
54
14
52
13
50
12
48
11
46
10
44
9
42
8
40
7
38
6
Drain Effficiency (%)
Fixed tuned test circuit
15
36
2700
2800
2900
3000
3100
3200
3300
3400
3500
Frequency (MHz)
.
Figure 5. RFHA1020 RF Performance from 1200MHz to 1400MHz
RFHA1020 Gain/Efficiency vs. Frequency, Pout = 55.4dBm
(Pulsed 10% duty cycle, 100uS, Vd = 50V, Idq = 440mA)
18
66
64
Fixed tuned test circuit
16
62
15
60
14
58
13
56
12
54
11
52
10
50
9
48
8
Gain
46
Eff
7
44
6
1200
Drain Effficiency (%)
Gain (dB)
17
42
1220
1240
1260
1280
1300
1320
1340
1360
1380
1400
Frequency (MHz)
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Compact L- and S-Band GaN High Power Amplifiers
Summary
RFHA1020: 350W at L-Band
RFMD has developed the RFHA1020 to provide high
power at L-band frequencies. This part uses the same
circuit topology and package as the RF3928, but provides
high power performance from 0.9GHz to 1.4GHz,
optimized from 1.2GHz to 1.4GHz (performance
evaluation is included in Figure 5).
RFMD has developed a portfolio of high power matched
amplifier products to provide solutions for next generation
military and civilian radar applications. Wide bandwidth,
high output power, and high efficiency operation enable
simplification of high-power radar system modules.
Design using GaN devices allows for multiple bands to be
covered by a single matched design, reducing size and
complexity of the overall multi-kilowatt amplifier. The
resulting designs allow for tighter integration through
smaller system footprints and reduced cooling needs,
which leads to enhanced device efficiency and lower
operational costs.
RFHA1020 provides high-output power from 0.9GHz to
1.4GHz and output power greater than 300W over the
entire frequency band, while optimized output power of
350W is achieved from 1.2GHz to 1.4GHz. Power gain
ranges from 13.6dB to 15.5dB, and peak drain efficiency
ranges from 50% to 63%.
RFHA1023: 250W at L-Band
RFMD’s RFHA1023 provides a lower power output
solution at L-band operating at 36V. This part
incorporates in package pre-matching in a bolt down highthermal conductivity solution.
Figure 6 provides measured data on the performance of
this part under the same pulsed conditions previously
discussed. The RFHA1023 achieves 250W peak output
power over the same 1.2GHz to 1.4GHz, 15% bandwidth,
while maintaining greater than 13dB gain at peak power.
Peak drain efficiency ranges from 52% to 64% and small
signal gain exceeds 14dB with power gain ranging from
13.2dB to 14.6dB at 250W output power.
Figure 6. RFHA1023 RF Performance from 1200MHz to 1400MHz
RFHA1023 Gain/Efficiency vs. Frequency, Pout = 54dBm
(Pulsed 10% duty cylce, 1mS, Vd = 36V, Idq = 440mA)
18
68
Fixed tuned test circuit
66
16
64
15
62
14
60
13
58
12
56
11
54
10
Gain
52
Eff
9
50
8
1200
Drain Effficiency (%)
Gain (dB)
17
48
1220
1240
1260
1280
1300
1320
1340
1360
1380
1400
Frequency (MHz)
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Compact L- and S-Band GaN High Power Amplifiers
Appendix
Figure 7. HPA Design Topology




λ
Wilkinson combiners at input and output of
devices, 50Ω impedance at the package leads
λ
λ
Two stage quarter-wave impedance
transformation for broader bandwidth
Ω
Ω
High dielectric substrates for impedance
transformation to present optimum load / source
impedance to device
Isolation resistors to prevent odd-mode
oscillations
Figure 8. GaN Model Source Pull, Load Pull
Source (5ohm chart) 1.2GHz to 1.4GHz
Load (5ohm chart) 1.2GHz
1 2GHz to 1.4GHz
1 4GHz
Gain 30dBm 20 cell 5ohm
1.0
0.8
0
2.
0
0.
4
p2
p3
Swp Max
1.4e+009
6
0.
0
0.
6
0.8
1.0
2.
4
3.
p1: Freq = 0.9 GHz
Stability = 1
1.4e+009
r 3.60116
3 60116 Ohm
0
3.
x 1.10298 Ohm
0.
p1
Pout Eff 35dBm 5ohm 20cell SrcB HIGH
Swp Max
1.4e+009
1.2e+009
r 1.28968 Ohm
x 0.725037 Ohm
0
4.
4.
5.0
0
5.0
0. 2
0.2
10.0
5.0
4.0
3.0
2.0
1.0
0.8
0.6
0.4
0
0.2
10.0
p2: Freq = 1.2 GHz
Stability = 1
10.0
5.0
4.0
3.0
2.0
1.0
0.8
0.6
0.4
0.2
10.0
0
p1: Freq = 0.9 GHz
Stability Index = 1
p2: Freq = 1
1.2
2 GHz
Stability Index = 1
-10.0
0
-4
.
S(1,1)
Lowband 1p2GHz at dev Z 5ohm low band
SCIR1()
Stability 20 cell 5ohm
LPCS(50,40,5)
Eff 1p2 35 20cell SrcB 2
.0
-2
-0.8
-1.0
LPCS(22,18,1)
Gain 1p4 30dbm
LPCS(23,19,1)
Gain 1p1 30dBm
-0.8
.0
0
2.
LPCS(45,35,5)
Eff 1p4 35 20 cell Src B 2
LPCS(54,53,0.5)
Pout 1p2 35 20 cell SrcB 2
-1.0
-3
.6
LPCS(53,52,0.5)
LPCS(53
52 0 5)
Pout 1p4 35 20cell SrcB 2
LPCS(55,45,5)
Eff 0p9 35 20 cell SrcB 2
-0
.6
0
LPCS(24,20,1)
Gain 0p9 30dbm
Swp Min
9e+008
.0
.4
-3
-0
- 5.
.0
WP101015
-0
LPCS(56,54,0.5)
LPCS(56
54 0 5)
Pout 0p9 35 20 cell SrcB 2
-4
p3: Freq = 1.4 GHz
S bili = 1
Stability
red – input circuit, green - stability
•
•
•
1.2e+009
r 3.41804 Ohm
x -0.976928 Ohm
0
.4
2
-0.
-5.
-0
-10.0
9e+008
2
r 0.361034
Ohm
-0 .
x 0.343082 Ohm
SCIR2()
Stability 20 cell 5ohm
Swp Min
9e+008
p3: Freq = 1.4 GHz
Stability Index = 1
S(2,2)
Lowband 1p2GHz at dev Z 5ohm high band
Pink – output circuit, grey - stability
GaN Non Linear Model (NLM) used to generate source and load contours
Source contours generated for Pin = +10dBm
Load contours generated for Pin = +41dBm
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Compact L- and S-Band GaN High Power Amplifiers
Figure 9. Design NLM Simulation
•
•
•
•
EM simulation used to design splitter/combiner networks
GaN Non Linear Model (NLM) used to estimate RF performance over
frequency
Ideal bias networks (lossless
(lossless, broadband) used for simulation
NLM provides isothermal results (short pulse)
.
Figure 10. Compact L-Band GaN HPA
Compact application circuit for L-band 350W solution: 2” x 2”
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Compact L- and S-Band GaN High Power Amplifiers
.
Figure 11. Pulsed RF Measurements and Affects of Pulse Width and Duty Cycle
μ
μ
μ
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Compact L- and S-Band GaN High Power Amplifiers
Figure 12. RFMD’s MicroShield Integrated RF Shielding Technology

Demonstrated a compact 350W L-band power amplifier

Design completed using non linear model results exclusively

Package matched to 25 Ω at the input and output lead

Application real estate including bias networks and occupies a 2 inch by 2 inch area

Optimized for 1.2GHz to 1.4GHz, but can operate with 31% bandwidth

For long pulse widths and duty cycles 0.4dB to 0.6dB drop in peak power performance
1.2GHz to 1.4GHz (200MHz, 15% bandwidth)
•Peak Pout 350W
•Peak efficiency 52% to 64%
•Gain at peak power 13.5dB to 15.5dB
•Linear gain 14.5dB to 16.0dB
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