Department of Electronic Engineering Millimetre Wave and THz Research at QMUL Professor Xiaodong...
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Department of Electronic Engineering
Millimetre Wave and THz Research at QMUL
Professor Xiaodong ChenSchool of Electronic Engineering and
Computing ScienceQueen Mary University of London
Email: [email protected]
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Outline
Where am I from?
History of QMUL Group
Some New Topics
Summary
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Queen Mary, University of London
Queen Mary and Westfield College was founded in 1889, one of four major Colleges of University of London, ranked in12/13 place last year.
The newly merged Medical Hospital of the College was founded in 1373, the first teaching hospital in London!
Sir Peter Mansfield (Co-winner of 2003 Nobel prize in medicine (MRI)) was a graduate in physics at Queen Mary, University of London.
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Department of Electronic Engineering Queen Mary, University of London
Antenna & Electromagnetics Group (since 1968)
Networks Group Centre for Digital Music Multimedia & Vision Group
22 full staff + 10 teaching staff
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The Antenna and Electromagnetic Group
Prof. Clive Parini (Director of Graduate School) Prof. Xiaodong Chen (Director of Graduate Studies) Prof. Yang Hao Dr Robert Donnan (Lecturer) Dr Akram Alomainy (Lecturer)
Prof Peter Clarricoats, FRS (part time) Prof. Derek Martin (part time) Prof. Brian Collins (visiting professor) George Hockings (visiting professor)
10 Postdcotoral Research Assistants, 20 PhD Research Students
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Brief History: Major Milestones
1969-70 Analysis and Design of Corrugated Horns.
1973 First UK Compact Antenna Range. 1974 First text on Geometric Theory of
Diffraction. 1976 First use of Optimisation in Reflector
Antenna Design 1977 First Design of Array Feeds with Mutual
Coupling for Satellite Antennas 1982 First Design Tools for Shaped-beam
Antennas for Spacecraft Applications 1983 Reflector Surface Metrology using
Ultrasound or Millimetrewaves. 1984 First text on Corrugated Horns.
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1985:Reflector Design of James Clerk Maxwell Radio Telescope.
With a diameter of 15m the James Clerk Maxwell Telescope (JCMT) is the largest astronomical telescope in the world designed specifically to operate in the submillimeter wavelength region of the spectrum. The JCMT is used to study our Solar System, interstellar dust and gas, and distant galaxies. It is situated close to the summit of Mauna Kea, Hawaii, at an altitude of 4092m.
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1991:200GHz clean room operation of single offset CATR
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5GHz to 200GHz single offset CATR
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1992: Successful Measurement of Advanced Microwave Sounding
Unit -B
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Mounted on NOAA weather satellite AMSU-B uses passive radiometry to determine upper
atmospheric water vapour content
Swath width approx 2000Km
15km
50Km
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Orbit covers the globe (except near poles)
28.8°Earth rotationPer orbit
Orbit plane rotatesEastward 1° perday
530 miles
2 satellites cover the complete globe in 12 hours
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Passive radiometry around the water vapour absorption line (183.3GHz)
AMSU-B channels:-90GHz150GHz183GHz
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AMSU-B measured upper atmosphere water vapour
content
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AMSU-B QUASI-OPTICS
Mirrors and diochroic plates are used to select the various channels
Frequency 1
Frequency 2
Inputsignal
Diochroicplate
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New Tri-reflector CATR System (2005)Makes efficient use of main reflector
Absorber
Field Magnetude
QUIET ZONE
Field Magnetude
QUIET ZONE
TRI-REFLECTOR RANGE
SINGLE REFLECTOR
RANGE
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300GHz Tri-reflector CATR Demonstrator Currently under test
at QM*Spherical Main reflector diameter = 1M*Shaped subreflectors of order 350mm in diameter* rms error on all reflectors about 8 microns* Quiet zone size is 75% of main reflector diameter.* Spherical main reflector permits manufacture of large sizes with 1 micron rms for 1 THz operationusing optical mirror technology
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New Research Topics:
Antenna Technology Wireless Communications/GPS EM Healthcare Quasi-optics and Millimetre Wave
New analysis algorithm –DGBA Quasi-optical components/system
High Power THz Generation
Summary of the ProblemHigh-frequency methods of analysing reflectors
Analysis Objective: modular, efficient analysis tool
Physical Optics (PO) GTD
• Simple
• Flexible
• Non-singular fields+
• Ray-based method
• Numerically efficient
• Inefficient for λ << Dλ: signal wavelength
D: reflector diameter
• Non-modular
• caustics
06/23
Analysing Qausi-optical system
Component Structure Modular Analysis
GB
exp
ansi
on
output plane
refle
ctor
to b
e an
alys
ed
reflected beams
input plane
}
diffracted beams
}diffracted beams
GB
expansion
Prev
ious
re
flect
or
Introducing: DGBA(Diffracted Gaussian Beam Analysis)
Gaussian Beam Expansion
expa
nsion
plane
f x y A
w x mL jn x
w y L j y
mnnm
( , )
( ) exp( )
( ) exp( )
09/23
Gaussian Beam Reflection
sr
n
x si
i
i
h
hr
rx
x
h
reflected beam
incident beam
incident beam:
1 12q R
jwi i
i
reflectedbeam:
1 12q R
jwr r
r
Gaussian beam optics: • w wr i
Rrby Geometrical Optics:
1 1 1
R R fr i “lens formula”:
10/23
Gaussian Beam Diffraction- canonical problem -
d
half screen
Gaussian beam
11/23
Gaussian Beam Diffraction - solution of the canonical problem -
U P Ui Pj jk d ys d yp
j jk d ys d yp
x xsx xs
( ) ( )erfc( ( ( ) ( ))
/)
erfc( ( ( ) ( ))/
);
112 0
1 1 2
12 0
1 1 2
U P( )
U Pi ( )
: Total diffracted field at the observation point
: Unperturbed (incident) field at the observation point
k d ys0 : Complex phase at the stationary point of the boundary-diffraction integrand
k d yp01 : Complex phase at the (first) pole
of the boundary-diffraction integrand
xs : Shadow boundary
12/23
Gaussian Beam Diffraction- normal incidence -
half screen
z
x
y a
z=-z0
Q(x ,y ,z )0 0 0
P(x,y,z)s
s
w0
Gaussian beamamplitude (+1)
• Boundary diffraction theory gives asymptotic solution• GO incident beam is complemented by a diffracted field in terms of complementary error functions
• Solution is valid for normal incidence within the paraxial
region
13/23
DGBA test application:A Cassegrain-Gregorian Compact Antenna Range
(CATR) – the spherical tri-reflector @ 90 GHz -
16/23
spherical
100l100l
shapedshaped
feed
300l
DGBA - Numerical Results- spherical tri-reflector CATR test case -
-50
-40
-30
-20
-10
-1 -0.5 0 0.5 1
DGBA; E-planeDGBA; H-planePO; E-planePO; H-plane
field
in d
B
radius in m
co-polar
x-polar
field in the quiet zone (1200l from main reflector)
20/23
28
Dichroic Dichroics are well known for their frequency selective
characteristics at millimeter and sub-millimeter wave frequencies
There are two basic types of dichroic mirrors: Patch and Slot.
29
Two channel Quasi-Optical Network (QON)
Two channels: 54GHz (oxygen lines) and 89GHz (atmospheric windows)
High pass dichroic (transmits at 89GHz and reflects at 54GHz) is needed to achieve high pass QO system
M1-54
H-54
M1-89
H-89
M2
D
30
DS
High-pass dichroic Porosity value
High cut-off frequencyLow cut-
off frequency
The final design: D = 2.16mm, S = 2.46mm, Thickness = 2.5mm
31
Measurement Transmission measurement above 75GHz was
conducted by placing it in a quasi-optical measurement bench
H
32
Results analysis - 1
Integration of DGBA and PMM
Dual Channel Quasi-optical system
Integration of DGBA and PMM
Results – 54GHz
M1-54
M2
Horn-54
-8.68dB Beamwidth Deg.
Simulation. : H-21.51 E-20.92
Measured : H-20.09 E-19.34
Integration of DGBA and PMM
Results – 89GHz
Dichroic
Horn-89
M1-89
M2
-8.68dB Beamwidth Deg.
Simulation : H-21.44 E-21.22
Measured : H-19.15 E-19.69
36
One of the most difficult components to realise in sub-millimeter bands is the THz sources.
THz sources can be broadly divided into three categories: Solid state sources; Vacuum tube sources; Optical style sources.
Each of them has its strength and weakness.
THz sources
37
Overview: State of the art
THz-emission power as a function of frequency Solid line: Conventional THz sources; Ovals: recent THz sources *1: M. Tonouchi, ‘Cutting-edge terahertz technology’, Nature photonics, Feb, 2007
BWO
Gyrotron
38
Solid state sources: are limited by reactive parasitics, or transit times (RC) rolloff, or heavy resistive losses;
Vacuum tube sources: suffer from physical scaling problem, metallic losses and need for extremely high fields;
Optical style sources: the photon energy level (~meV) too close to that of lattice phonons, needing cryogenic cooling.
Overview: Physical limitations
39
Micro-klystron
40
Micro-klystron beam source
PSD Experimental setup to test the scale down effect Experimental measured A-K voltage and current
41
Introduction – What is Pseudo-Spark Discharge?
electron beam
anode
insulator
hollowcathode
deff
• Occurs in special confining geometry• In various gases such as helium, nitrogen, argon, et al• Low pressure, 50-500mtorr, self-sustained, transient hollow cathode discharge, for a gap separation of
several mm• High quality electron beam and ion beam extraction before and during the conductive phase
(pd)min
pd [torr x cm]
VB [V]
0 2 4 6 8 10 12 14 16
200
400
600
800
1000
1200
1400vacuum breakdown
p seu d osp ark reg ion
pseudosparkregion
Paschen curve and pseudospark regionSingle gap PSD geometry
42
PSD Process Phase 1: Townsend discharge
- low current pre-discharge- plasma formation
Phase 2: Hollow cathode discharge- hollow cathode effect- plasma expansion
Phase 3: Superdense glow discharge (conductive phase)- high-current phase (10 kA cm-2 )
43
Phase 1: Townsend discharge
Seed electrons Pre-discharge Plasma formation
44
Phase 2: Hollow cathode discharge
Hollow cathode effect Plasma expansion Secondary emission
45
Phase 3: Superdense glow discharge
Sheath contraction Primary emission Conductive phase
46
PSD Numerical Simulation
MAGIC: Particle-In-Cell and Monte-Carlo Collision (PIC-MCC)Ref: C.K. Birdsall et al, Computer Phy. Comm 87, 1995.
47
PSD - Gas Ionisation1. Electron-induced ionisation
2. Ion-induced ionisation
The cross section depends on:1. The energy of the impact electron;2. The gas type.
For different gases, the cross sections are different functions of impact electron energy. The functions can be achieved from experimental results.
48
PSD-2D Computational Model
MAGIC 2D Model:Constant A-K voltage 10kVAK gap d=6mmRadius = 25mmRoom temperature
Insulator: 6mm thick PerspexAnode aperture: 0.5mm radiusAnode thickness: 12mm
Cathode aperture: 1.5mm radiusTrigger radius: 1mm, cable outer radius: 6mm
Nitrogen 100mTorr
49
PSD-2D Phase 1&2Plasma formation at 30ns
Plasma expansion at 50ns
50
PSD-2D Phase 3
Plasma expansion and emission at 80ns
51
PSD Process
Detailed motion of all the particles in the system.
52
Simulation results
Observed voltage between the anode and the cathode. Observed current at the anode aperture.
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Summary
MM/THz technology becomes increasingly beneficial to our society. MM/THz technology has been advancing over one century – an old and young topic.
New applications have posed many technical challenges in MM/THz technology – needing fresh blood of microwave engineers.
Solutions lies in understanding and innovation in methodology and technology.
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Thank you!