Terahertz Radio Systems:

The Next Frontier?

Trevor BirdCSIRO ICT Centre, Marsfield, NSW

Presented at 2006 Workshop on the Applications of Radio ScienceLeura 15 – 17 February 2006

www.ict.csiro.auThis Presentation…

Why use terahertz or T-rays?Applications of THzExamples of THz radio systemsTHz imagingTHz indoor wireless systemKey THz technologyWork to be doneConclusion

www.ict.csiro.auWhat Is Terahertz?

1 THz = 1000 GHz or a wavelength of 0.3 mm (300 µm)Traditionally the spectrum from 300 GHz to 3 THz (ie 1 to 0.1 mm)In general use today from 100 GHz to 30 THzPart of the spectrum between millimetre-waves and the far-infrared (15 to 300 µm or 1 to 20 THz )

www.ict.csiro.auWhy THz?

Relatively unexplored frontier of the EM spectrumMost molecules have vibrational & rotational spectra in THz region Sub-mm resolution and good differential sensitivity in imaging dielectricsTHz interacts strongly with polar molecules –extreme sensitivity to water, penetrates non-polar molecules to a usable depth of a few mmPotentially safer for medical imaging than present methods, e.g. X-rays

www.ict.csiro.auExamples of Molecular Resonance

D-(+) glucose at room temperature D-(-) fructose at room temperature

Ref.: J-I Nishizawa et al, “Spectral measurement of terahertz vibrations of biomolecules using a GaP terahertz-wave generator with automatic scanning control”, J. Phys. D: Appl. Phys. 36 (2003) 2958–2961.

www.ict.csiro.auOptical versus RF Approach to THz

OpticalAvailability of sourcesMix down to THz rangeSize is an issue

Radio frequencyLack of natural sourcesMultiply-up microwave or mm-wave frequenciesGreater sensitivityPotentially compact systems

www.ict.csiro.auAn RF Engineering Approach

To make compact systems, components and devices need to be compatible in size to the wavelengthLikely to lead to greater system sensitivityLikely to lead to high level of integration and ultimately lower costAdvances in technology is making components and devices possible

www.ict.csiro.auTHz: Physical Properties - 1

www.ict.csiro.auTHz: Physical Properties - 2

1.E-081.E-071.E-061.E-051.E-041.E-031.E-021.E-011.E+001.E+011.E+021.E+03

1.E-01 1.E+00 1.E+01 1.E+02 1.E+03

Wavelength (microns)

Pow

er s

pect

ral d

ensi

ty

(W/c

m^2

/mic

ron)

T=280K T=300K T=500K T=1000K T=2500K

300GHz3THz30THz300THz3000THz

Frequency

www.ict.csiro.auTHz Applications

Detection of explosives, pollutants, bio-agents and drugsSecurityRemote sensing and radio astronomyMedicalMaterials assessmentFuture wireless communications

www.ict.csiro.auExplosive Detection Through Clothes

Example System: A single pixel system sensing presence of material by their spectral fingerprint through a barrier.

detector mat

eria

l

barriersource

www.ict.csiro.auSecurity

Security - images through walls/clothingThermography of the skin

Bright = ColdUpper Torso Reflects Sky

Dark=WarmLower Torso

Reflects Ground

Indoor images of person with concealed weapons

Millimetre-waves penetrate clothingConcealed objects block and reflect natural

emissions in different ways to the body

Images of people outdoorsPenetrates clothing and hair

*All mm-wave images taken by NGST using a 100 GHz camera

www.ict.csiro.auRemote Sensing & Radio Astronomy

Remote sensing of the atmosphere allows determination of pollutantsRadio astronomy done at high altitude to avoid absorption of the atmosphereSpectral lines of particular interest

Singly ionized nitrogen 1461 GHzCarbon monoxide 1267 GHz

Examples: CONDOR installed in Atacama, Chile

• CO N+ Deuterium Observation Receiver

Herschel Space Observatory

www.ict.csiro.au

Radio Astronomy – Herschel Space Observatory

The Herschel Space observatory is a space telescope designed to observe in the sub-millimetre (terahertz) and far-infrared bandsThe Observatory employs both direct and heterodyne instruments to meet a number of imaging requirements:

HIFI – Single pixel heterodyne receiver for high spectral resolution observationsPACS and SPIRE – Large arrays of bolometers for photometry and low resolution spectroscopy

Due for launch in 2007 and will be located at the 2nd Lagrangian point of the Earth-Sun system 1.5M km from Earth

The direct detector instruments provide large instantaneous field of view imaging through large focal plane arrays, whereas the heterodyne instrument provides high spectral resolution for spectroscopic type observations

www.ict.csiro.auVisual and THz Images of Skin Cancer

Visual image THz image

Histology

www.ict.csiro.auThe Benefits of THz Images

Shows depth and extent of a tumourIncreases the certainty of removal surgery – Moh’s micrographic techniqueReduces the cost of the surgeryGives a unique signature of inter- and intra-molecular interactionsTHz properties of bio-materials well documentedExcellent differential sensitivity to dielectrics

www.ict.csiro.auDental Imaging

www.ict.csiro.auDepth of Penetration in Human Tissue

Reference: Fitzgerald et al., Leeds Uni.

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5 0.75 1 1.25 1.5

Frequency, THz

Pene

tratio

n de

pth,

mm Skin

Striated muscleTooth enamelCortical boneDe-ionised water

www.ict.csiro.auPenetration in Fatty Human Tissue

1.00E-02

1.00E-01

1.00E+00

1.00E+01

1.00E+02

1.00E+03

0.01 0.1 1 10 100 1000

Frequency, GHz

Pene

trat

ion

dept

h, m

m

?

www.ict.csiro.auTrend to THz Frequencies

Use of the radio spectrum has seen the upper frequency for communications increasing about a decade every 20 yearsAt this rate, by 2020 0.5 to 1 THz will be used for wireless communication

1.E+05

1.E+06

1.E+07

1.E+08

1.E+09

1.E+10

1.E+11

1.E+12

1900 1920 1940 1960 1980 2000 2020

Year

Radi

o Fr

eque

ncy

Hz

Marconi

Radio comms

Satellite comms

LMDS

THz

(T.S. Bird 2004)

www.ict.csiro.au

Millimetre-wave Imaging

www.ict.csiro.auHow Does Passive Imaging Work?

Measures thermally-generated mm-wave radiation from objects

The “Black Body” curve shows the The “Black Body” curve shows the dependence of thermallydependence of thermally--generated generated

radiation intensity on wavelengthradiation intensity on wavelength

200

GH

z

The observed image results from a The observed image results from a combination of emitted and reflected combination of emitted and reflected

radiationradiation

www.ict.csiro.auAdvantages

Safe for humansNo electromagnetic interferenceCovert operation – can “see” through obstacles like smoke, dust, fog and clothingCan operate day and/or night

Passive millimetre-wave image through fog (taken by Northrop Grumman with a 100 GHz camera)

www.ict.csiro.auEarly Imaging Systems

Mostly Focal Plane Detector Arrays – 1000’s of Receiving ElementsPrincipal similar to Digital Visible-light Camera Very expensive and bulky – based on MMIC technology

NGST’s PMMW (100GHz) Video Camera1040 GaAs MMIC Receivers

US$17,000,000

Trex PMMW (75-94 GHz) Video Camera1000 GaAs MMIC LNAs

25,000 Sb-based MMIC DetectorsUS$1,000,000

www.ict.csiro.auRecent Developments - 1

Brijot Imaging – based on scanned sub-array (released in April 2005).Claim to have US$100 million in backorders.Based on Lockheed Martin technology (development cost US$200 million over 10 years).

Brijot BIS-WDS Prime (quoted price: US$60,000. NB indications are that true price

is closer to US$100,000)

94 GHz Brijot image

www.ict.csiro.auRecent Developments - 2

Millivision – uses a large sub-array and a rotating wedge to scan. Poor image quality and user interface.Other major players are Smiths Detection (Farran), QinetiQ and Trex

Millivision Vela-125 (US$60,000)

Smiths Detection – Tadar (no price info available)scan takes 6 seconds

94 GHz Millivision Vela-125 image

www.ict.csiro.auThe CSIRO Approach - Differentiation

200 GHz operation compared with 94 GHz operation for most other systems

Smaller aperture size and/or improved angular resolutionPossibility of greater stand-off distance

Heterodyne receivers enable us to obtain distance information (for an active system)Links with radioastronomy(including patented Mills Cross-like imaging system)

www.ict.csiro.auCross-Correlation Imager

CSIRO Patent Applied

www.ict.csiro.auCSIRO Imaging Demonstrator

Target Specifications

Focal distance = 40 metresDepth of field > ± 10 metresHalf-power beamwidth < 0.30o, corresponding to 20 cm resolution at 40 m rangeScan range > ±7o, corresponding to 5 x 5 m field of view at 40 m rangeFrame rate = 1 complete frame in less than 30 secondsMinimum detectable temperature difference in scene < 5K

www.ict.csiro.auCSIRO Imaging Demonstrator

Assembly of the imaging demonstrator (7 September 2005)

www.ict.csiro.auThe CSIRO Approach

PLL DRO

11.5 GHz

LNALNA

4th Harmonic Mixer

LORF

BasebandBPF

BasebandAmp

IF AMP

IF AMP

184.5-192 GHz

Fan-

Beam

Ant

enna

Fan-

Beam

Ant

enna

Motor Drives &Shaft Encoders

4th Harmonic Mixer

LO

RF

LNALNA

x 4FrequencyMultiplier

x 4

FrequencyMultiplier

10 MHzREF. OSC

0 - 360Dig. PhaseShifter

0 - 360Dig. PhaseShifter

DrvA

Power Divider

IF AMP BPF

IF AMP BPF

PHASE SWITCH4-quadrant Multiplier

90 deg3 dB

Quadrature Hybrid

0 deg3 dB

In-Phase divider

184.5-192 GHz

CORRELATOR4-quadr.Multiplier

CORRELATOR4-quadr.Multiplier

I

Q

SYNC. DEMOD4-quadr.Multiplier

BasebandBPF

BasebandAmp SYNC. DEMOD

4-quadr.Multiplier

Cont

rol &

Dat

a Acq

uisit

ion

Com

pute

r

ADC

ADC

0.5 - 8 GHz

0.5 - 8 GHzIF

IF

DrvA

DrvA

Integrated Rx Module

Integrated Rx Module

www.ict.csiro.auPillbox Antenna

Imaging system needs an antenna with a scanning fan-beam radiation patternProposed and patented novel design that uses multi-reflector “pill-box” antenna

Beam scans as thesubreflector rotates

FeedAperture

(Reference: SG Hay, JW Archer, GP Timms & SL Smith, IEEE Trans. AP, Aug., 2005)

www.ict.csiro.au180-200 GHz Receiver

Design, fabrication, micro-assembly and test complete on 2 modules.Module comprises:

2 x 180-205 GHz LNAs; Sub-harmonic LO Mixer (LO @ 46 GHz); 30-65 GHz LO MPA

LNALNA

184.5-192 GHz

4th Harmonic Mixer

LO

RF

IFDrvA

Integrated Rx Module

Reference: JW Archer & MS Shen, Microwave and Optical Technology Letters, 20 December 2004

www.ict.csiro.au0.5 – 8 GHz Analogue Correlator

PLL DRO

11.5 GHz BasebandBPF

BasebandAmp

AMP

AMP

10 MHzREF. OSC

A

PHASE SWITCH4-quadrant Multiplier

90 deg3 dB

Quadrature Hybrid

0 deg3 dB

In-Phase divider

CORRELATOR4-quadr.Multiplier

CORRELATOR4-quadr.Multiplier

I

Q

SYNC. DEMOD4-quadr.Multip

BasebandBPF

BasebandAmp SYNC. DEMO

4-quadr.Mult

A

AD

Uses IF phase switching, with synchronous demodulation at baseband, to minimize effect of high 1/f noise associated with the output of the multiplier chips.Two wideband analogue multipliers packaged in connectorized metal blocks.InP Multiplier MMIC chips provided courtesy of the ATNF.

www.ict.csiro.auData Acquisition

I and Q outputs fed into an ADC card taking around 300 samples per second.Averaging 5 to 10 samples per pixel to improve signal-noise ratio.50 ms per pixel (taking into account time to move subreflector and adjust phase shifters).25 x 25 pixels => 31 seconds per scan

Stepping time(small %)

Adjust phase shifters(goal: 10 ms)

Acquire valid data(20 – 30 ms)

TTL Pulse

Breakdown for each pixel

www.ict.csiro.auImaging Demonstrator – Early results

2D scan at 185 GHzFrame rate: 1 frame per 30 secondsActive system (70 mW source at a distance of 4 mplaced next to the antenna to illuminate the scene)Small metal plate at 4 m, (i) uncovered and (ii) covered with a piece of cloth

Source antenna(stepped horn)

metal plate

(i) 2D unprocessed image of metal plate

(ii) Same as (i) with plate covered with cloth

www.ict.csiro.au

Towards Real-time THz Imaging- THz ‘Camera’

www.ict.csiro.auPassive Imaging?

Desirable from cost, system simplicity and invasiveness standpoints but S/N seriously limited by:

Black-body radiation characteristics

Detector and array efficiency and system loss

LNA availability – useful gain/noise to ~300GHz only

www.ict.csiro.auActive Imaging?

Improved S/N but:More complex and costlySimilar system constraints though coherent detection availableLow THz electronic source powers for illumination & mixer LO driveHigh source cost Limited source bandwidths, ~ 60GHz around 650GHz windowPossible exposure issues, though THz non-ionizing

www.ict.csiro.auImaging Methods

ActiveAbsorption – transmission measures variation of lossScattering – measures reflectance and

PassiveThermal – measures the radiation based on body temperature and the differencesRadiometer - minimum detectable temperature

inttB

TMDT

IF

sys=

www.ict.csiro.auDirect vs Coherent Detection

Incoherent - Direct DetectionThe signal is converted direct to baseband and all phase information is lostLower complexity than heterodyneLow spectral resolutionGood scalability to large array sizesCan be very wideband => greatly improves SNR for thermal imagingie Cryogenic bolometers are extremely sensitive detectors in the sub-millimetre region

Coherent – Heterodyne Detection A mixer is used to shift the signal to a more convenient frequencyPhase/Frequency/Spectral information is availableHigh spectral resolutionLimited scalability due to requirement of local oscillator signal and mixer for each element

BSNR /1∝

www.ict.csiro.auIncoherent and Coherent Detection

Incoherent

Coherent/ Heterodyne

www.ict.csiro.auDirect vs Coherent Detection

1e-020

1e-018

1e-016

1e-014

1e-012

1e-010

1e-008

1e+011 1e+012 1e+013

Noi

se E

quiv

alen

t Pow

er W

/Hz^

0.5

Frequency (Hz)

Theoretical Comparison of Heterodyne and Direct Detectors

HeterodyneDirect with NEP_elect = 10^-9

Direct with NEP_elect = 10^-11Direct with NEP_elect = 10^-13

100GHz 1 THz 10 THz

The key advantage of heterodyne over direct detection is that much greater SNR’s can be achieved for a given incident signal power

www.ict.csiro.auHeterodyne Detection at THz

Local oscillator – limited availability of power sources, could be generated optically

Mixer – Schottky diodes, hot electron bolometers (HEB), superconductor–insulator-superconductor (SIS)

www.ict.csiro.auSchematic of Active THz Imager

Object

Processor

THz imager

Opticalcamera

Dichroic filter

Baffle

Tx

Focal plane array

T.S. Bird and D. Rabanus 2004

www.ict.csiro.auIntegrated Focal-plane Arrays

Focal plane fields and conjugate matchingNeed to match the focal fields of the lens or reflector Can correct for errors in reflectors or lensesAllow formation of multiple beamsDetectors need to be connected to the antenna elements

Example: SIS 200 GHz Array, T ~ 100K each element

Ref. de Lange et al, NSF & NASA

www.ict.csiro.auPossible Focal Plane Array

Heterodyne ArrayLO Generation

Mode Locked Laser

Optical Filter(selects 2

harmonics with terahertz

separation)

Optical Amplifier

Divider(coupler)

Silicon Lens

AntennaHEB Mixer

Optical Fibre

MgO

Source: S. Hanham 2005

www.ict.csiro.auImage Reconstruction

Measure both amplitude and phasePhase is difficult to measure accurately at THz

Amplitude only measurements and reconstruct the phaseSee Greg Hislop’s paper this afternoon on phase retrieval

Horizontal Displacement (mm)

Ver

tical

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emen

t (m

m)

Correct Phase

0 5 10 15

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Progressive Projections' Phase Estimate

0 5 10 15

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-2

-1

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Reconstructed phaseCorrect phase

www.ict.csiro.au

THz Indoor Wireless Local Area Network

www.ict.csiro.auTHz Indoor Wireless Link

Frequency - 600 GHzDistance – 10 mAntenna gain

Access point – 30 dBiComputer – 19 dBi (20 mm antenna @ 50% efficiency)

Power – 1 mW at both access and computerRx bandwidth – 40 GHz (6.7%)Receiver noise figure – 5dB (~950K)Waveguide losses - 3 dB at each endQPSK + Turbo coding

www.ict.csiro.auTHz Wireless LAN

Fibre backbone

Multibeam access point antenna

PC card antenna

www.ict.csiro.auBit Error Rate 600 GHz Wireless

1E-21

1E-18

1E-15

1E-12

1E-09

1E-06

0.001

1

0 10 20 30 40

Data rate, Gbps

Bit

Erro

r Rat

e

10m5m

www.ict.csiro.auTHz Technology

Antennas and transmission linesComponentsDetectorsSources

www.ict.csiro.auAntennas & Transmission Lines

Many conventional microwave/ millimetre wave antennas can be used eg horns, reflectors, lensesAim to minimize long metallic structures to reduce lossPrinted metallic structures eg microstrip are unsuitableNew electromagnetic-based materials may be suitable

electromagnetic bandgap (EBG)metamaterials

www.ict.csiro.auElectromagnetic Bandgap Components

Metallic Ground Plane

Woodpile EBG Material

Double Slot Antenna

y

z

x

d2

Metallic Ground Plane

Woodpile EBG Material

Double Slot Antenna

y

z

x Metallic Ground Plane

Woodpile EBG Material

Double Slot Antenna

y

z

xy

z

x

d2d2

Development of passive low-loss components

WaveguidesFiltersCouplers

New properties of materialsElectromagnetic methods for these structures

EBG woodpile antennaRef. Weily et al., IEEE Trans., AP-52, 2004

Electromagnetic bandgap waveguide

www.ict.csiro.au

Electromagnetic Bandgap (EBG) Components

Input waveguide Output waveguideInput waveguide Output waveguide

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Input waveguide Output waveguideInput waveguide Output waveguide

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Input waveguide(P1)

Output waveguide(P3)

Output waveguide (P2)

12.2 12.3 12.4 12.5 12.6 12.7 12.8 12.9 13 13.1−25

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Output waveguide(P3)

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Input waveguide(P1)

Output waveguide(P3)

Output waveguide (P2)

Woodpile EBG

90° bend 3-dB coupler

Ref.: Weily et. al., Electronic Lett., 2006, pp. 42-43.

www.ict.csiro.auEBG Horn Antenna Array

See Andrew Weily’s poster tomorrow

Ref.: Weily et. al., submitted IEEE TAP, 2005.

www.ict.csiro.auHorns for THz

CSIRO designed profiled smooth-walled horns at 0.84 and 1.7 THzSimpler to make than conventional corrugated hornsGood Gaussian beam properties

1.7 THz horn

1mm

0.84 THz hornPhotos provided by D. Rabanus, U. Cologne

www.ict.csiro.auSmooth Walled Horn at 840 GHz

Comparison of theory and experiment

Plot provided by D. Rabanus & C. Granet

www.ict.csiro.auTHz Focal Plane Antenna Arrays

Horn arrays in use todayPlanar antennas can suffer from substrate mode problems where the electrically thick substrate leads to radiation becoming trapped in the substrateSolutions to this problem are: EBG substrate, membrane substrate or a substrate lens

www.ict.csiro.auTHz Detectors

Source: Gerecht et al, IEEE Trans MTT, V47,12, Dec 1999

www.ict.csiro.auHot Electron Bolometers

HEB is a thermal superconducting device that responds to temperature (power)A thin strip of superconductor is cooled to its transition temperature between its superconducting and normal states. At this transition temperature its

I-V characteristic is non-linearThe received THz and LO signals modulate the temperature and hence the resistance of the superconductor at the lower beat frequency

Bolometer Diagram

www.ict.csiro.auTHz Sources

Examples: Virginia Diodes Inc., multiplier chain, 0.8mW (~$50k) ELVA BWO,10mW (~$90k)

NASA report 50mW for micro-fabricated TWT

Source: Douglas Paul, Cavendish Lab

www.ict.csiro.auExample of Present State of the Art

F. Rodriguez-Morales et al, “A Terahertz Focal Plane Array Using HEB Superconducting Mixers and MMIC IF Amplifiers,” IEEE Microwave and Wireless Letters, Vol. 15, No. 4, April 2005.

A FPA of 3 elements operating at 1.6 THzUses a double slot antenna with integrated HEB mixerLO provided by gas terahertz laser simultaneously illuminating all three elementsEach element has an individual lens to provide focusing and overcome the substrate mode problem associated with planar antennas

www.ict.csiro.auFocal Plane Array at 2.52 THz

Reference: A. Lee and Q. Hu, "Real-time, continuous-wave terahertz imaging by use of a microbolometer focal-plane array," Opt. Lett. 30, 2563-2565 (2005)

www.ict.csiro.auWork To Be Done

New more powerful, less complex sourcesnow usually laser-based but solid-state source performance is improving at near-THz frequenciesa ‘natural’ THz source

Improve sensitivity and availability of THz detectorsReduce losses in componentsReduce cost

integrated circuits and componentscombine RF and optics

Bio-medical effectsSpectrum allocationStandards for applicationsFind a ‘killer’ application for THz

www.ict.csiro.auConclusion

Overview of THz technologyDescribed some work underway in AustraliaFocal plane arrays for faster imagingTo be successful THz imaging will need to overcome technology and cost issues600 GHz wireless local area network is technically feasibleGaps in many technology areasCostTHz is still looking for the killer application for take-off

www.ict.csiro.auAcknowledgements

CSIRO ICT Centre staff who provided slides and pictures, particularly

Christophe GranetKieran GreeneAndrew HellicarGreg TimmsGreg Hislop

My collaborators:Stephen Hanham, Sydney UniversityAndrew Weily, Karu Esselle & Barry Sanders, Macquarie University

David Rabanus, University of ColognePeter de Maagt, ESTEC

www.ict.csiro.au

Questions?For more information, see www.csiro.au or contact:

Trevor BirdChief ScientistCSIRO ICT CentreTel: +61 2 9372 4289Email: trevor.bird@csiro.au