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Department of Electronic Engineering Millimetre Wave and THz Research at QMUL Professor Xiaodong Chen School of Electronic Engineering and Computing Science.

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Presentation on theme: "Department of Electronic Engineering Millimetre Wave and THz Research at QMUL Professor Xiaodong Chen School of Electronic Engineering and Computing Science."— Presentation transcript:

1 Department of Electronic Engineering Millimetre Wave and THz Research at QMUL Professor Xiaodong Chen School of Electronic Engineering and Computing Science Queen Mary University of London

2 Department of Electronic Engineering Outline Where am I from? History of QMUL Group Some New Topics Summary

3 Department of Electronic Engineering 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.

4 Department of Electronic Engineering 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

5 Department of Electronic Engineering 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

6 Department of Electronic Engineering Brief History: Major Milestones Analysis and Design of Corrugated Horns. 1973First UK Compact Antenna Range. 1974First text on Geometric Theory of Diffraction. 1976First use of Optimisation in Reflector Antenna Design 1977First Design of Array Feeds with Mutual Coupling for Satellite Antennas 1982First Design Tools for Shaped-beam Antennas for Spacecraft Applications 1983Reflector Surface Metrology using Ultrasound or Millimetrewaves. 1984First text on Corrugated Horns.

7 Department of Electronic Engineering 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.

8 Department of Electronic Engineering 1991:200GHz clean room operation of single offset CATR

9 Department of Electronic Engineering 5GHz to 200GHz single offset CATR

10 Department of Electronic Engineering 1992: Successful Measurement of Advanced Microwave Sounding Unit -B

11 Department of Electronic Engineering Mounted on NOAA weather satellite AMSU-B uses passive radiometry to determine upper atmospheric water vapour content Swath width approx 2000Km 15km 50Km

12 Department of Electronic Engineering Orbit covers the globe (except near poles) 28.8° Earth rotation Per orbit Orbit plane rotates Eastward 1° per day 530 miles 2 satellites cover the complete globe in 12 hours

13 Department of Electronic Engineering Passive radiometry around the water vapour absorption line (183.3GHz) AMSU-B channels:- 90GHz 150GHz 183GHz

14 Department of Electronic Engineering AMSU-B measured upper atmosphere water vapour content

15 Department of Electronic Engineering AMSU-B QUASI-OPTICS Mirrors and diochroic plates are used to select the various channels Frequency 1 Frequency 2 Input signal Diochroic plate

16 Department of Electronic Engineering New Tri-reflector CATR System (2005) Makes efficient use of main reflector

17 Department of Electronic Engineering 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 operation using optical mirror technology

18 Department of Electronic Engineering 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

19 Summary of the Problem High-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 << D λ: signal wavelength D: reflector diameter Non-modular caustics 06/23 Analysing Qausi-optical system

20 Component Structure Modular Analysis GB expansion output plane reflector to be analysed reflected beams input plane } diffracted beams } GB expansion Previous reflector Introducing: DGBA (Diffracted Gaussian Beam Analysis)

21 Gaussian Beam Expansion expansion plane 09/23

22 Gaussian Beam Reflection s r   n  s i i i   r r    reflected beam incident beam incident beam: reflected beam: Gaussian beam optics: by Geometrical Optics: “lens formula”: 10/23

23 Gaussian Beam Diffraction - canonical problem - d half screen Gaussian beam 11/23

24 Gaussian Beam Diffraction - solution of the canonical problem - : Total diffracted field at the observation point : Unperturbed (incident) field at the observation point : Complex phase at the stationary point of the boundary-diffraction integrand : Complex phase at the (first) pole of the boundary-diffraction integrand : Shadow boundary 12/23

25 Gaussian Beam Diffraction - normal incidence - half screen z x y a z=-z 0 Q(x,y,z ) 000 P(x,y,z) s ^ s w 0 Gaussian beam amplitude (+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

26 DGBA test application: A Cassegrain-Gregorian Compact Antenna Range (CATR) – the spherical 90 GHz - 16/23 spherical 100 shaped feed 300

27 DGBA - Numerical Results - spherical tri-reflector CATR test case - field in the quiet zone (1200 from main reflector) 20/23

28 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 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 30 D S High-pass dichroic Porosity value High cut- off frequency Low cut- off frequency The final design: D = 2.16mm, S = 2.46mm, Thickness = 2.5mm

31 31 Measurement Transmission measurement above 75GHz was conducted by placing it in a quasi-optical measurement bench H

32 32 Results analysis - 1

33 Integration of DGBA and PMM Dual Channel Quasi-optical system

34 Integration of DGBA and PMM Results – 54GHz M1-54 M2 Horn dB Beamwidth Deg. Simulation. : H E Measured : H E-19.34

35 Integration of DGBA and PMM Results – 89GHz Dichroic Horn-89 M1-89 M dB Beamwidth Deg. Simulation : H E Measured : H E-19.69

36 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 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 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 39 Micro-klystron

40 40 Micro-klystron beam source PSD Experimental setup to test the scale down effect Experimental measured A-K voltage and current

41 41 Introduction – What is Pseudo-Spark Discharge? Occurs in special confining geometry In various gases such as helium, nitrogen, argon, et al Low pressure, mtorr, 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 Paschen curve and pseudospark regionSingle gap PSD geometry

42 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 43 Phase 1: Townsend discharge Seed electronsPre-dischargePlasma formation

44 44 Phase 2: Hollow cathode discharge Hollow cathode effectPlasma expansion Secondary emission

45 45 Phase 3: Superdense glow discharge Sheath contractionPrimary emissionConductive phase

46 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 47 PSD - Gas Ionisation 1. 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 48 PSD-2D Computational Model MAGIC 2D Model: Constant A-K voltage 10kV AK gap d=6mm Radius = 25mm Room temperature Insulator: 6mm thick Perspex Anode aperture: 0.5mm radius Anode thickness: 12mm Cathode aperture: 1.5mm radius Trigger radius: 1mm, cable outer radius: 6mm Nitrogen 100mTorr

49 49 PSD-2D Phase 1&2 Plasma formation at 30ns Plasma expansion at 50ns

50 50 PSD-2D Phase 3 Plasma expansion and emission at 80ns

51 51 PSD Process Detailed motion of all the particles in the system.

52 52 Simulation results Observed voltage between the anode and the cathode. Observed current at the anode aperture.

53 Department of Electronic Engineering 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.

54 Department of Electronic Engineering Thank you!

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