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Reflections of the Future
Presented by: Bob CutlerAgilent Technologies Technology Leadership Organization
Copyright © 2013 Agilent Technologies
Trends in Radar Technology and their Impact on Test
ArchitecturesMonostatic
BistaticMultiStatic (Netted)
Angle / Time / Freq (Doppler)Space-Time Adaptive (STAP)
MIMOAdaptive/Cognitive
Imaging / Non-Imaging
Synthetic Aperture (SAR/ISAR/CSAR)
Synthetic Impulse and Aperture (SIAR)
Active / Passive
Multi-Mission:Multi-Function (MPAR or MFAR)
Time ScheduledFreq Scheduled (OFDM)Non-Radar (e.g.Comm’s)
AntennaMech. Steered
Passive Steered ArrayElectronic Steered Array
Digital ArrayDigital Beam Forming
Co-locatedDistributed
Tube / GaAs / GaN / SiGePhotonics
Active SignalsCW / FMCW / Pulsed / Chirped
Frequency HoppedCoded/Spread (e.g. Barker)
Impulse / UWBOFDM
Correlated / UncorrelatedOrthogonal
Signals of OpportunityBroadcast AM/FM/TV
Cellular
Categorizing Radar
April 18, 20132
DeploymentFixed Ground
AirborneLand Mobile
NavalSpace
Co-locatedDistributed
Man Portable
ApplicationSurveillance: Air/Sea/Land/Space
Air Traffic ControlFire Control
Ground Moving Target (GMTI)Imaging / Mapping
Navigation & Guidance(altimeters, terrain following, auto, autonomous ground vehicles, etc.)
WeatherWall/Ground Penetrating
Perimeter SecurityLaw Enforcement
Sports
PULSED RADAR Our Comfort Zone
April 18, 20133
Other Familiar TechnologiesFMCW / Doppler / Chirped / Barker
April 18, 20134
∆f
FREQ
TIME
TX RX POWERSPLITTERTarget Motion
FMCW: Frequency shift by delay (motion) Doppler: Frequency shift by motion only
Delayed Return
TX
RX
5
RADAR TRENDS
1. Digital continues to move closer to the antenna • Mechanically Steered > Electronically Steered Phased Array • Passive ESA (PESA) > Active ESA (AESA) > Digital Array Radar (DAR)• Steered Beams giving way to Digital Beam Forming (DBF)
2. Vacuum Electron Device (TUBES) giving way to Solid State.• Higher performance (GaAs, GaN, SiC)• Lower Cost (SiGe and even CMOS at mmWave)• MMIC, SoC, Radar-on-a-chip
3. Radar Engineers have Discovered Shannon• Applying “Information Theory” to radar• More sophisticated algorithms and signals• Signals adapt to detected targets and conditions.
4. Frequencies, Bandwidths, Resolution are increasing• Better Resolution• More Bands / Shared spectrum / Simultaneous operation on multiple bands• Smaller platforms (e.g. drones)
April 18, 20135
6
TRENDS in RADAR and Remote Sensing
April 18, 20136
4. Technology Sharing between Commercial and Government Sectors
• GaN for Cellular Base Stations
• CMOS and SiGe (ft > 100 GHz) for Radar
• CPU, GPU and FPGA technology
5. Architectures support multiple functions
• Search, track, fire control, Weather, Synthetic Aperture
• Communications
• Electronic Warfare (EW)
6. Spatially distributed radar systems are more common
• Elements of the radar system are at different locations (multistatic)
• MIMO (may be co-located or widely spaced)
7. Number of array elements is increasing
• Cost, size and power of each element decreasing (i.e. T/R modules are cheap)
• Higher levels of integration
• Conformal installation rather than planar
7
How Many Elements
PAVE PAWS - 31 Years Old
1,792 Passive Elements
April 18, 20137
AESA Airborne
1000-3000+ (Active) Elements
8
SBX
“8th Wonder of theWorld”RADOME: 103 FT HIGH
ANTENNA DIAMETER: 72 FT
45,056 T/R MODULES
RADAR: X-BAND PHASED ARRAY
April 18, 2013Confidentiality Label
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9
9th Wonder of the World?
DARPA ISIS
April 18, 20139
The OS is launched like a satellite; once aloft it never lands until the end of its 10+ year lifetime. Within ten days it autonomously deploys to any designated worldwide location. The OS can maintain its station year-round withinlatitude bounds of -37° South to +55° North.
10
Test Implications
More modules to test – Cost of test, test times
Array calibration– Cost of test: test facilities, test times– New approaches to calibration and functional tests
(What worked for 3k elements probably might not be cost effective at higher element counts, and probably won’t scale to 300k)
– Accuracy and stability with longer test times.
Improve Measurement Throughput– Choose the right approach to test– Parallelize– Choose the right equipment – Optimize the software: Fill memory, empty during dead-time.– Optimize the test sequence: Fastest tests in the inner loops.
April 18, 201310
11
Trend: Frequencies and Bandwidths Increasing
April 18, 201311
60-100 GHz signals with 1-2 GHz bandwidth are no longer esoteric
Scopes have become an important tool for wideband RF signal analysis
Drivers and Enablers:– Smaller Platforms
(UAV)’s– Resolution (e.g. SAR)– Spectrum Availability
• More bandwidth available• Less crowded
– Improved Semiconductor Technology (SiGe / GaN / CMOS)
Wide bandwidth, multi-channel, Vector Signal Analysis
Consumer 60 GHz Technology
12
Baseband ASIC
RF ASIC with ceramic antenna array bonded directly on top of RFIC.
36 Element Array
Digital Moving Closer to the Antenna
April 18, 201313
100100101…
010101100…
One Driver for Change: Multi-Function Radar
April 18, 201314
“UK AIRBORNE AESA RADAR RESEARCH”, Dr. Stephen Moore, Radar Team Leader, Dstl, UK
Multiplexing Approaches• Time (sequence)• Frequency (Band, OFDM)• Space (subarray)• Simultaneous
15
Passive Electronically Steered Arrays (PESA)
• One Source of RF Energy• Klystron• Single Point of Failure• High Voltage Requirements
• TR Isolation• Circulator• Duplexer• Switch
• Power Distribution• Phase Shifters• One Receiver
• High Dynamic Range Requirements• Single Point of Failure
April 18, 201315
θ
θ
θ
θ
Sub
arra
y
High Power
TX
RX
θ
θ
θ
θ
Sub
arra
y
θ
θ
θ
θ
Sub
arra
y
16
Active Electronically Steered Arrays (AESA)
April 18, 201316
LowPower
TX
RX
Sub
arra
y
T/R
T/R
T/R
T/R
Sub
arra
y
T/R
T/R
T/R
T/R
Sub
arra
y
T/R
T/R
T/R
T/R
“T/R-Module Technologies Today and Possible Evolutions”,Patrick Schuh, et. al EADS
Brick
Tile
17
More Functions May Require More Channels
April 18, 201317
Sub
arra
y
T/R
T/R
T/R
T/R
Sub
arra
yT/R
T/R
T/R
T/R
Sub
arra
y
T/R
T/R
T/R
T/R
RX
LowPower
TX
RX
LowPower
TX
RX
More Channels enable:
• Simultaneous operation on multiple frequencies or bands
• Different functions on different sub-arrays
• Different Signals on Different parts of the array
• Co-located MIMO• Other advanced
functions
The Path to Digital Array Radar (DAR)
April 18, 201318
1 % e.g. 20 Channels for 2000 elements 10 % e.g. 200 Channels for 2000 elements 100%
“Advances in affordable Digital Array Radar”, Chris Tarran BSc CEng MIET Roke Manor Research Limited
Example: Purdue Prototype DAR System
April 18, 201319
Figure from “Digital Array Radar Panel Development”, William Chappell, Caleb Fulton. Purdue University
• DAR enabled by high levels of integration and Moore’s Law
• Ultimate in flexibility – Software Defined
• Signals can be modified in real time to task and condition
• Signals have bandwidth
• Likely to have a superset of performance specifications relative to AESA
Digital Baseband IQ RF
OFDM DAR (Concept)
April 18, 201320
“OFDM-based Digital Array Radar with Frequency Domain Mode Multiplexing”John P. Stralka, Northrop Grumman
OFDM Signals Have Noise-Like Pk/Avg ratiosTypically given as 10dB
© 2013 Agilent Technologies 21
38% 0dB above average of -2.3 dBm 21% 2 dB8.6% 4 dB1.4% 6 dB0.02% 8dB
% Time Exceeds Level
This is not an OFDM Signal.
Q: What’s this signal’sPeak-to-Average Ratio?
A: It depends!
Only exceed 8dB above average .02% of the time. However, we have observed peaks up to 8.5dB above average.
So, how often can you get away with driving the amplifier into saturation?
Band Limited Gaussian Noise
8.5 dB
Pulsed Sine vs Complex Modulated Signals
April 18, 201322
Need wideband to characterize the pulse
Can use narrowband swept to measure the spectrum.
Can improve SNR of spectrum by using narrow RBW’s
Need accurate, wide-band digitizers to capture signal without loss of information.
Cannot improve SNR of spectrum by narrowing RBW
Spectrum of a periodic signal
Spectrum of a signal without cyclostationary components
23
Trend: RF Shifting from Tubes to Solid StateFrom GaAs to GaN
GaN provides higher power levels, greater robustness– Test impact: power supplies, drive levels, and loads (pads)
SiGe/CMOS with Ft’s >> 100 GHz– Low Cost, High levels of integration
Efficiency an issue– Thermal Management– Spectral splatter / Emissions– Pre-distortion
April 18, 201323
24
Pre-Distortion
Waveform Fidelity– e.g. Chirp Linearity– Pulse Shape
Emissions– Spectral splatter
Efficiency– Higher Power Added Efficiency (PAE)– Module to Module Gain Match?
Implementations– Linear (equalization) or Non-Linear– Adaptive (comm’s) or– Lookup table or– Pre-computed Waveforms
April 18, 201324
Many design automation and test tools exist today
• Simulation tools such as SystemVue and ADS
• Digital Predistortion Algorithms
• X-Parameter Measurements for characterizing and modeling non-linear devices (PNA-X)
25
• How will new radar signal fidelity/accuracy be defined? Measured?• For comm’s signals we use demodulator based error-vector
magnitude (EVM)• Impairments impacting radar signal fidelity
– Phase noise – AM/PM Conversion– Intermodulation Distortion– Amplifier Gain/Phase Stability
(thermal or power supply)– Additive Noise– Spurious– Baseband IQ modulation Errors
(e.g. gain/phase imbalance)
TX/RX Signal Fidelity
April 18, 201325
+Meas(t)
Reference Waveform Generator
-+
Ref(t)
Err(t)RMS
Digital CommSignals
+Meas(t)
Stored or Measured Reference Waveform
-+
Ref(t)
Err(t)RMS
Any Signal
Normalize and Align
DistortionSuite and/or Power Sweeps
April 18, 201326
Vector Signal AnalyzerMeasure with Live Signals
Network AnalyzerMeasure with Power-Swept Tones
AM/AM, AM/PM, Power Statistics, EVM AM/AM, AM/PM, S and X Parameters
27
Impact of Digital Moving Closer to the Antenna
Functionality becoming software defined• New capabilities added to existing designs • Upgrades to deployed equipment (no return to factory for test)• May need to verify performance drivers, not specific implementations
Signals are not fixed by design, and may not be fixed during operation (adapt to target and conditions)
• Change with function• Pre-compensate based on channel
(target, clutter, jamming, etc)
Signals convey information
April 18, 201327
28
Impact of Digital Moving Closer to the Antenna• No Analog S21 Measurements (for DAR)
• Signals may be amplitude modulated (linearity)
• Signals Have Bandwidth (flatness, spurious)
• DSP TTD vs Phase/Gain Shift (for DAR)
• Digital Plumbing (interconnects)
• More Channels to Test
• Performance Metrics(new plus some old)
• Calibrations
• Test Modes
• Test Points
• Test Methods
April 18, 201328
DSP
D/A
A/D
S21
CLK
DISTRIBUTED RADAR
April 18, 2013
Confidentiality Label
29
30
• Phased Array: Single Waveform
• Multistatic: One or more illuminators. Signal Processing at each RX
• MIMO: Receive different linear combinations of TX signals with Joint Processing
Rx
Multistatic radar
Tx
SP SPSP SP
Radar Architectures
a
Phased array radar
Tx / RX
MIMO-radar(Multi Input Multi Output)
SP/Rx
Tx
MIMO Concept
s0
TX
h00 r0 ...
s1
RX
r1 ...
h01
h10
h11
[ ][ ]=[ ] s0
s1
r0
r1
h00 h01
h10 h11
What’s Received: R = HS
Solving for S (comm’s): S = H-1R
Solving for H (radar): H = S-1R
32
Difference between MIMO and Phased Array
NOTE: MIMO Antennas can be co-located, or widely distributed
April 18, 201332
“MIMO Radar with Colocated Antennas”, Jian Li and Petre Stoica, IEEE SIGNAL PROCESSING MAGAZINE SEPTEMBER 2007
MIMO: Radar vs. Comm’s
April 18, 201333
TX
TX
RX
RX
Co-located AntennasWidely Spaced Reflectors
MIMO: Radar vs. Comm’s
April 18, 201334
Widely Spaced AntennasCo-Located Reflectors
MIMO: Co-located Antennas
April 18, 201335
TX
TX
RX
RX
Co-located AntennasMultiple Reflectors
Targets are Point ReflectorsCo-Located Antennas Allow Direction Finding(Reflectors of interest are within the beam pattern)
Under certain MIMO conditions, the Rank of the channel matrix indicates the number of targets in a range cell
RangeResolution
MIMO: Radar vs. Comm’s signals
COMM’s
• Data rate greater than supported by the modulation (bandwidth)
• Antennas Generally Co-located at TX and at RX (except wide-spaced multi-BTS)
• Takes advantage of multi-path in the environment
• Adaptive TX to optimize data transfer
• Signals Convey information after channel response is known. Preamble used for measuring the channel response.
RADAR• Range, Angle, Doppler resolution greater
than supported by waveform or array size
• Antennas my be:Co-LocatedSpaced at TXWide-Spaced at RX
• Takes advantage of multi-path in the target, targets (multiple per range cell, or clutter)
• Adaptive TX to optimize resolution, put more energy on target, minimize interference (target in another range cell, clutter)
• Signals don’t convey information, the channel is the thing. Signals designed to simplify receiver processing – orthogonal codes or frequencies
April 18, 201336
37
Test Implications for MIMO
Separating Hype from Reality– Did I achieve the advertised improvement
in performance?– If not, why not?
Models and Simulation– Need better target, propagation and clutter models based on MIMO implementation– Antenna models (antenna correlation – good for phased arrays, bad for MIMO)– Simulating waveform correlation under various conditions (e.g. Doppler)
Performance is now a function of N different signals M different receivers– Are the signals accurate (high fidelity)– Are they coupled (e.g. through a common power supply)– If the signals are orthogonal by design, has the orthogonality property been
compromised (time/frequency misalignment, phase noise, distortion)– Simulating radar return – Each receiver needs a different signal
April 18, 201337
Loss of capacity in comm’sLoss of resolution in radar
38
The Need for More Channels
April 18, 201338
• Radars have more transmit and receive channels
• Multiplexing instruments with fewer channels may not be optimal, or may not work, depending on the application
• High parallel channel counts can lead to faster test times
• Channels may need to be synchronous and phase coherent (e.g. for beam forming or MIMO)
• May need scalable solutions for production flexibility
• Size and space constraints
PXI and AXIe modular systems may offer benefits as they are easier to expand.
The system shown above contains 2 12GS/s waveform generators (AWGs) and
24 1.6 GHz IF/Baseband digitizers
M8190A
M9703A
PXI
AXIe
39
Summary
• Frequencies and Bandwidths are going up• Number of array elements are increasing
• Digital is moving closer to the antenna• Signal complexity is increasing and becoming more adaptive• Processing algorithms are growing very sophisticated. Need
to verify during development, may not need to test during production
• Size is going down (and up!)• Multifunction radars have more complicated test requirements• Test involve generating and analyzing full bandwidth, multi-
channel signals with complex and dynamic modulation.
April 18, 201339
Questions
April 18, 2013Confidentiality Label
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