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

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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

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Other Familiar TechnologiesFMCW / Doppler / Chirped / Barker

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∆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)

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TRENDS in RADAR and Remote Sensing

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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

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How Many Elements

PAVE PAWS - 31 Years Old

1,792 Passive Elements

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AESA Airborne

1000-3000+ (Active) Elements

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SBX

“8th Wonder of theWorld”RADOME: 103 FT HIGH

ANTENNA DIAMETER: 72 FT

45,056 T/R MODULES

RADAR: X-BAND PHASED ARRAY

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9

9th Wonder of the World?

DARPA ISIS

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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.

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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.

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Trend: Frequencies and Bandwidths Increasing

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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

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Baseband ASIC

RF ASIC with ceramic antenna array bonded directly on top of RFIC.

36 Element Array

Digital Moving Closer to the Antenna

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100100101…

010101100…

One Driver for Change: Multi-Function Radar

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“UK AIRBORNE AESA RADAR RESEARCH”, Dr. Stephen Moore, Radar Team Leader, Dstl, UK

Multiplexing Approaches• Time (sequence)• Frequency (Band, OFDM)• Space (subarray)• Simultaneous

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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

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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

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Active Electronically Steered Arrays (AESA)

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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

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More Functions May Require More Channels

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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)

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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

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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)

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“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

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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

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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

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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

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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)

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• 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

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+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

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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

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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

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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

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DSP

D/A

A/D

S21

CLK

DISTRIBUTED RADAR

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• 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

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Difference between MIMO and Phased Array

NOTE: MIMO Antennas can be co-located, or widely distributed

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“MIMO Radar with Colocated Antennas”, Jian Li and Petre Stoica, IEEE SIGNAL PROCESSING MAGAZINE SEPTEMBER 2007

MIMO: Radar vs. Comm’s

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TX

TX

RX

RX

Co-located AntennasWidely Spaced Reflectors

MIMO: Radar vs. Comm’s

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Widely Spaced AntennasCo-Located Reflectors

MIMO: Co-located Antennas

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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

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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

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Loss of capacity in comm’sLoss of resolution in radar

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The Need for More Channels

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• 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

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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.

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Questions

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