This document outlines research on improving the efficiency of power amplifiers for radar transmitters. It discusses using amplitude modulated waveforms and resonant supply modulation to efficiently transmit high peak power pulses while minimizing spectral emissions. Simulation and measurement tools were developed to characterize supply modulated power amplifiers. A resonant modulator circuit was designed and tested, demonstrating efficiency improvement. A GaN Doherty MMIC power amplifier was also fabricated and measured, achieving the highest reported efficiency to date for an X-band Doherty MMIC. Future work is proposed to further optimize efficiency through combined modulation and power combining architectures.

1. 12/14/2014
1
Headline
• Professor Zoya Popovic
• Professor Dragan Maksimovic
• Professor Dejan Filipovic
• Dr. Salvador Talisa
• Dr. Tibault Reveyrand
Welcome Committee
2

2. 12/14/2014
2
• Introduction
• Simulation and Measurement Tools (Ch. 3)
• Amplitude Modulated Waveform Design (Ch. 2)
• Resonant Supply Modulator Design (Ch. 4)
• Resonant Supply-Modulated Power Amplifier
Simulations and Measurements (Ch. 4)
• Doherty MMIC PA Design (Ch. 5)
• Conclusions and Future Work (Ch. 6)
Outline
3
• To efficiently transmit an amplitude modulated
radar pulse to confine spectral emissions
– Amplitude modulated pulse must have same
detection performance as a rectangular pulse
• Design a transmitter with a peak power mode
much higher (5-10 dB) than nominal operation
– Peak power mode accounts for <10% of time
Problem Description
4

3. 12/14/2014
3
Efficiency of A Single PA with Constant
Supply
5
Efficiency is proportional to input power
Efficiency of a Signal with a High Peak
to Average Power Ratio (PAPR)
6
Constant Supply
Vdd

4. 12/14/2014
4
Efficiency Improvement with Supply
Modulation
7
Modulated Supply
Supply modulation solves the problem
of constant DC power
Relevance to Radar
8
SPY1 -Surveillance (target detecting and
tracking) and control (fire control
and/or air control)
USS Lake Erie
(Cruiser)
USS Kidd
(Destroyer)
• 5 MW peak power
• 32 kW average power
• Over 4400 radiating elements
(not necessarily active)

5. 12/14/2014
5
• Introduction
• Simulation and Measurement Tools
• Amplitude Modulated Waveform Design
• Resonant Supply Modulator Design
• Resonant Supply-Modulated Power Amplifier
Simulations and Measurements
• Doherty MMIC PA Design
• Conclusions and Future Work
Outline
9
General Supply-Modulation
Measurements
10

6. 12/14/2014
6
Resonant Supply Modulated Bench
11
• 2 Arbitrary Waveform
Generators
• Microwave Signal
Generator
• Signal Analyzer
• Oscilloscope
• Digital Multimeters
• Power Supplies
• Three different time constants
– Sampling
– Carrier
– Envelope
• Time and frequency domain
– Spice, circuit envelope simulator, and
harmonic balance
• System level simulations
– VSS (AWR) and Ptolemy (Keysight)
Simulation Challenges
12

7. 12/14/2014
7
Ideal Supply Modulation in ADS
13
This work was done by Dr.
David Sardin
Ideal Supply Modulation in AWR
14
Required Steps for Envelope Path in Supply-Modulation Simulations
1. Solve the magnitude of the complex RF
input signal
2. Square and divide by 100 to solve the
instantaneous power level
3. Convert power level to dBm
4. Limit the maximum and minimum
values to within range of look-up table
5. Extract supply voltage from look-up
table based off of trajectory

8. 12/14/2014
8
Circuit Envelope Simulations with AWR
VSS (Validation)
15
Simulations were performed with a constant supply and an 18 MHz
OFDM signal to ensure that envelope simulators produced similar results.
Time-domain voltages and histograms gave us a degree of confidence that
VSS was performing correctly.
Ideal Supply Modulation Simulations
16
Constant Supply Modulated Final
Stage
Modulated Both
Stages
PAE=32% PAE = 47% PAE=52%

9. 12/14/2014
9
1. Generate supply
waveform with
trajectory (previous
slide)
2. Low-pass filter the
waveform
3. Generate pulse
width modulation
for high-side and
low-side switches
Modulating the Switching Supply
17
2
3
Jeong et al. "Wideband Envelope Tracking Power Amplifiers With Reduced Bandwidth
Power Supply Waveforms and Adaptive Digital Predistortion Techniques," Microwave
Theory and Techniques, IEEE Transactions on , vol.57, no.12, pp.3307,3314, Dec. 2009
• 5 point PAE
Decrease
• 1 point MSE
increase
Supply Modulation with a Switching
Supply
18
Thank you Yuanzhe Zhang

10. 12/14/2014
10
Full System Results
19
Total system efficiency: CPAE = 49%
• Introduction
• Simulation and Measurement Tools
• Amplitude Modulated Waveform Design
• Resonant Supply Modulator Design
• Resonant Supply-Modulated Power Amplifier
Simulations and Measurements
• Doherty MMIC PA Design
• Conclusions and Future Work
Outline
20

11. 12/14/2014
11
Radar Spectrum Engineering Criteria
21
• Radar emissions are regulated by
National Telecommunications and
Information Administration
• In-band and out-of-band
bandwidth depends on rise and
fall times as well as frequency
modulation
• Spurious emissions cover infinite
bandwidth
Rectangular Pulse
22

12. 12/14/2014
12
Gaussian Pulse
23
Equalizing Total Pulse Energy
24
Gaussian pulse now fits
entirely inside a 1/TP filter

13. 12/14/2014
13
Range Resolution
25
Shorter pulses have smaller (better)
range resolution
Linear Frequency Modulation (Chirp)
26
Range resolution improvement is
proportional to time-bandwidth product

14. 12/14/2014
14
Chirp with a Gaussian Envelope
27
How Much Chirp Bandwidth is
Needed?
28

15. 12/14/2014
15
• A Gaussian shaped
chirp can be
designed to match
the detection
performance in terms
of both received
energy and range
resolution
• So why isn’t this done
already?
Conclusions About Waveform Design
29
• Class-C amplifiers are
typical for radar
transmitters because
they are efficient and
don’t need the supply
turned off
• Bottom of pulse
becomes more square
as transistor is biased
deeper in Class C
Pulse Shaping with a Class-C Amplifier
30

16. 12/14/2014
16
Summary of Theoretical Efficiency
Results
31
• Introduction
• Simulation and Measurement Tools
• Amplitude Modulated Waveform Design
• Resonant Supply Modulator Design
• Resonant Supply-Modulated Power Amplifier
Simulations and Measurements
• Doherty MMIC PA Design
• Conclusions and Future Work
Outline
32

17. 12/14/2014
17
General Supply-Modulation
Measurements
33
Resonant Supply Modulator
34Thank you Miguel Rodriguez

18. 12/14/2014
18
Drain Voltage with Switching Times
35
Shaping the Pulse
36
R = 220 Ω
L = 22 µH
C = 100 nF

19. 12/14/2014
19
Static Modulator Simulations
37
Resonant Modulator Static
Measurements
38Thank you Mauricio Pinto

20. 12/14/2014
20
• Introduction
• Simulation and Measurement Tools
• Amplitude Modulated Waveform Design
• Resonant Supply Modulator Design
• Resonant Supply-Modulated Power Amplifier
Simulations and Measurements
• Doherty MMIC PA Design
• Conclusions and Future Work
Outline
39
Resonant Supply-Modulated Power
Amplifier
40Thank you Scott Schafer
Composite Power Added
Efficiency (Total System)
TriQuint 150 nm GaN on SiC
f = 10 GHz

21. 12/14/2014
21
Amplitude-Weighting Pre-Distortion
41
• Initial simulation used a rectangular LFM with supply modulator used
for pulse shaping
• Pulse was too broad, so an amplitude pre-weight was calculated to
apply to the rectangular pulse
Simulated Results
42

22. 12/14/2014
22
Measured Results
43
• Measured modulator
efficiencies ranged
from 86-92%
• Better switches may
further improve
efficiency
Resonant Modulator Efficiency with
RFPA Load
44

23. 12/14/2014
23
Measured Time-Domain Results
45
RFPA Supply Power
46

24. 12/14/2014
24
Instantaneous Efficiency Comparison
47
• Introduction
• Simulation and Measurement Tools
• Amplitude Modulated Waveform Design
• Resonant Supply Modulator Design
• Resonant Supply-Modulated Power Amplifier
Simulations and Measurements
• Doherty MMIC PA Design
• Conclusions and Future Work
Outline
48

25. 12/14/2014
25
Variable Power Radar Project
49
• Mode 1: Normal rectangular pulses
• Mode 2: Fast and slow amplitude
modulation
• Mode 3: Temporary high power
rectangular pulses (5-10 dB increase)
Doherty Theory
50
• Two amplifiers, the carrier and
peaking, are treated as current
sources
• The carrier is always on and sees
ZC at low power levels
• When the carrier amplifier reaches
saturation, the peaking amplifier
turns on to load pull the carrier
amplifier
• Typical values are ZL = 25 Ω and
Z0 = 50 Ω

26. 12/14/2014
26
Doherty Amplifier Currents
51
ZL = 25 Ω
Z0 = 50 Ω
ZC = 100 Ω (low power)
ZC = 50 Ω (high power)
ZP = 50 Ω (high power)
Fabricated Doherty
52

27. 12/14/2014
27
Simulated Results of Doherty
53
On-Wafer Efficiency Measurements
54
9.9 GHz 10.1 GHz
Only four output powers and one bias level
were measured for yield testing.

28. 12/14/2014
28
• Introduction
• Simulation and Measurement Tools
• Amplitude Modulated Waveform Design
• Resonant Supply Modulator Design
• Resonant Supply-Modulated Power Amplifier
Simulations and Measurements
• Doherty MMIC PA Design
• Conclusions and Future Work
Outline
55
• Gaussian-shaped radar waveforms have similar
detection performance to rectangular waveforms
and are efficiently transmitted with a supply-
modulated Class-B PA while exhibiting better
spectrum
• A test bench and simulation environment was
developed to characterize supply-modulated PAs
• A variable pulse-width resonant modulator
demonstrates PA efficiency improvement in both
simulations and measurements
• An X-Band GaN Doherty MMIC PA has the highest
measured performance of any X-Band Doherty
MMIC to our knowledge
Conclusions
56

29. 12/14/2014
29
• Apply resonant modulator to a high-efficiency
switched-mode PA for efficiency improvement while
monitoring out-of-band spectral content
• Study how best to use a resonant modulator in a
phased array
• Test devices for reliability at temporary peak power
mode with load modulation
• Employ peak power mode in a power combined
architecture
• Measure X-Band Doherty MMIC with resonant
modulator and test variable mode radar pulses
Future Work
57
Publications
58
Patents:
• Zai, Andrew H., Cesar A. Lugo, Matthew D. Sharp, and Minhtri T. Ho. Adaptive Interference Canceller in a Digital Phase Array. The Johns
Hopkins University, assignee. Patent US 8,817,927
Theses:
• Zai, Andrew H. The Steered Auxiliary Beam Canceler for Interference Cancellation in a Phased Array. Thesis. Virginia Polytechnic Institute and
State University, 2011.
Journals:
• A. Zai, M. Pinto, M. Coffey, and Zoya Popovic. "Supply-Modulated Power Amplifiers for Radar Transmitters with Amplitude-Modulated Pulses.“
Transactions on Microwave Theory and Techniques. (Submitted)
• Rodriguez, M.; Roberg, M.; Zai, A.; Alarcon, E.; Popovic, Z.; Maksimovic, D., "Resonant Pulse-Shaping Power Supply for Radar Transmitters,"
Power Electronics, IEEE Transactions on , vol.29, no.2, pp.707,718, Feb. 2014
Conferences:
• Zai, A.; Li, D.; Schafer, S; Popovic, Z. "High-Efficiency X-Band MMIC GaN Power Amplifiers with Supply Modulation" Microwave Symposium
Digest (IMS), 2014 IEEE MTT-S International, June 2014
• Zai, Andrew; Campbell, Charles; Popovic, Zoya. Supply-Modulated Power Amplifiers for Amplitude Modulation Radar Transmitters. GOMAC
Tech Conference 2014, Charleston, SC.
• Zai, Andrew; Popovic, Zoya. Supply-Modulated Power Amplifiers for Amplitude Modulation Radar Transmitters. Proceedings of USNC–URSI
National Radio Science Meeting, Boulder, CO.
• Schafer, Scott; Litchfield, Michael; Zai, Andrew; Popovic, Zoya; Campbell, Chuck, "X-band MMIC GaN power amplifiers designed for high-
efficiency supply-modulated transmitters," Microwave Symposium Digest (IMS), 2013 IEEE MTT-S International, June 2013
• Jang, Haedong; Zai, Andrew; Reveyrand, Tibault; Roblin, Patrick; Popovic, Zoya; Root, David E., "Simulation and measurement-based X-
parameter models for power amplifiers with envelope tracking," Microwave Symposium Digest (IMS), 2013 IEEE MTT-S International , vol., no.,
pp.1,4, 2-7 June 2013
• Dongxue Li; Rodriguez, M.; Zai, A.; Sardin, D.; Maksimovic, D.; Popovic, Z., "RFPA supply modulator using wide-bandwidth linear amplifier with
a GaN HEMT output stage," Control and Modeling for Power Electronics (COMPEL), 2013 IEEE 14th Workshop on , vol., no., pp.1,6, 23-26 June
2013
• Nanzer, J.A.; Zai, Andrew H., "Correction of frequency uncertainty in wide field of view interferometric angular velocity measurements,"
Microwave Symposium Digest (MTT), 2012 IEEE MTT-S International , vol., no., pp.1,3, 17-22 June 2012

30. 12/14/2014
30
• Lindsey
• Mom, Dad, Colette, and Natalie
• Zoya
• Current and past group members
• The CoPEC Group
Acknowledgments
59
Questions?
60
Don’t make measurements on
Mondays or Fridays!

31. 12/14/2014
31
Backup
61
Simulated PA Gain
62

32. 12/14/2014
32
Ensuring Stability
63
Simulated Load-Pull Results
64
Optimal impedance for
efficiency is about 100 Ω
Imaginary part of optimal impedance is
resonated out by a resonant stub.

33. 12/14/2014
33
High-Level Block Diagram of Doherty
65
66

34. 12/14/2014
34
On-Wafer Gain Measurements
67
9.9 GHz 10.1 GHz
Only four output powers and one bias level
were measured for yield testing.