I NTEGRATED C OHABITATION OF M ULTIPLE M INIATURE A NTENNAS Presented by: Raheel M. Hashmi PhD Student, 42664675 Supervised by: Prof. Karu P. Esselle Department of Engineering Macquarie University, Sydney 13 th June 2012 1/24
Outline • Introduction: SKA & Phased Array Feeds (PAFs) • PAFs: What? Why? Limitations? • EBG Structures: A Possible Remedy • Research Objectives & Outcomes • Project Plan & Progress • Conclusions 2/24
Square Kilometer Array • To be the largest Radio Telescope in history o Location: Australia, New Zealand & South Africa o Reflector dishes & aperture arrays over 3000 KMs o Revolutionary discoveries in astronomical science • Unparalleled Scalability ASKAP Antennas at Murchinson Radio Observatory (Courtesy: ATNF, CSIRO) o Scaling current technology: Not Feasible!! o High design complexity & cost barriers • Main Objectives: • Large Collecting Area Smart Feeds: Multi-Beam • Greater Field-of-View Phased Array Feeds (PAF) Australia’s Telescope Compact Array (Courtesy: ATNF, CSIRO) 3/24
Artist’s Impression of SKA dishes spread over the Radio -Quiet zone in Western Australia (Courtesy: Swinburne Astronomy Productions/SKA) 4/24
Phased Array Feeds Designs BYU/NRAO Dipole Feed Phased Array Feed Demonstrator Checker-Board Connected Array • DRAO, Canada • CSIRO, Australia • BYU/NRAO, USA • ASTRON, the Netherlands • Planar Connected Arrays • Thickened Dipoles • Vivaldi Elements • Dense Focal Plane Sampling • Linear Polarization • Dense Focal Plane Sampling • Orthogonal Polarizations • Frequency Ratio 1.3:1 • Orthogonal Polarization • Frequency Ratio 2:1 • Frequency Ratio 3:1 • Simple & Low-cost Structure 5/24
Outline • Introduction: SKA & Phased Array Feeds (PAFs) • PAFs: What? Why? Limitations? • EBG Structures: A Possible Remedy • Research Objectives & Outcomes • Project Plan & Progress • Conclusions 6/24
Why PAFs? • Wide-Angle High-Resolution Radio Camera • A Phased Array Feed offers: o Adaptive Multi-beam Receiver (Multi-Pixel Feed) o Complete coverage of available Field-of-View o Sensitivity & Survey Speed (SVS) greater than Single-Pixel Feed o Improved Radiation and Aperture Efficiencies Model of PAF illuminating a Reflector Dish (B. D. Jeffs et al., 2009) • Governing Factors (B. D. Jeffs et al., 2009 ) : SVS/unit Cost max.(SVS) & min.(Cost) SVS N b . b . B . (A eff / T sys ) 2 No. of Solid angle Effective Aperture / beams per beams System Temperature System (a) Primary pattern of reflector (b) Feed pattern by PAF Bandwidth (B. D. Jeffs et al., 2009) Sensitivity 7/24
Design Constraints & Objectives • Constraints No. of Beams (N b ) Signal Processing : tradeoff relationship o System Bandwidth (B) Cost : strictly constrained variable o Beam Solid Angle ( b ) Field of View : controllable but design-time variable o Effective Aperture (A eff ) Reflectors & Effective Illumination : controllable variable o System Temperature (T sys ) Design Complexity & Cost : controllable variable & o • Objective “Maximize Sensitivity of Radio Telescope” 8/24
Mutual Coupling & T sys System model of Phased Array Feed based receiver (K. F. Warnick et al., 2009: BYU/NRAO Arecibo Telescope Progress) • LNA’s inherent noise: <50 Kelvin (strictly ) requirement for radio astronomy • Inter-Channel mutual coupling • Independent LNA design: Insufficient!!! • Result: Decreased Sensitivity 9/24
Scan Blindness & Surface Waves • Physically: Common-Mode Currents (CMC) o Differential Beam-Forming with Common-Mode loading o Large input mismatch at certain scanning angle • Scan Blindness: What and When? o Floquet Mode = Propagation Const. of supported Mode For a function ‘R’ periodic in ‘z’ with period ‘L’: Common-mode currents on Connected Array at 1.7 GHz R(z) = e -j z U(z) R(z + L) = e -j (z+L) U(z + L) (above) and 0.9 GHz (below) (S. G. Hay and O’Sullivan, 2008) by Fourier Series l.h.s. becomes e -j z U(z) = A n e -j(2 π n/L)z . e -j z R(z) = A n e -j nz : n = + 2 π n/L n , L i.e. periodicity breaks (B. Munk, 2009) 10/24
Outline • Introduction: SKA & Phased Array Feeds (PAFs) • PAFs: What? Why? Limitations? • EBG Structures: A Possible Remedy • Research Objectives & Outcomes • Project Plan & Progress • Conclusions 11/24
Electronic Band-Gap Structures • Engineered materials designed to have structural periodicity – Originally a domain of Solid State Physics – Composed of metal, dielectrics, or both – Assist/ Impede flow of EM waves of certain wavelengths – Periodicity on the order of half-wavelength or more • Applications – High Gain & Directive Antennas – Frequency Selective Surfaces (FSS) – Waveguides & Filters – High-Impedance Loading 1D, 2D and 3D EBG Structures (Joannopolous et al., 2008) 12/24
Applications Partially Reflective Surfaces: Metallic Loading High Impedance Ground Plane (A. P. Feresidis et al., 2005) (R. F. J. Broas et al., 2005) Frequency Selective Surface (B. Munk, 2000) High Gain 1-D EBG Resonator Antenna (A. R. Wiley et al., 2005) Optimized PRS-EBG Resonator Antenna (Y. Ge et al., 2007) 13/24
Band-Gap Theory • Defect-Mode Transmission Model (Jecko B. et al., 2007) • Fabry-Perot Cavity Model (Y. Ge et al., 2012) • Gain & Directivity Enhancement o Tangential dimensions of EBG Layer o Cavity Height o Magnitude & Phase of cavity reflection coefficient o Capacitive/Inductive loading of EBG layers o Current Issues: o Narrow radiation bandwidth (~300 – 700 MHz) o Limited Beam-Steering support (~20-30 degrees) 14/24
Outline • Introduction: SKA & Phased Array Feeds (PAFs) • PAFs: What? Why? Limitations? • EBG Structures: A Possible Remedy • Research Objectives & Outcomes • Project Plan & Progress • Conclusions 15/24
Research Objectives • Enhance radiation bandwidth of EBG resonant structures – Engineering reflection phase gradient of the Partially Reflecting Surface (PRS) by loading – Multivariable Optimization for PRS loading patterns • Eliminate Scan Blindness & Mutual Coupling – Applying high-impedance loading for CMC suppression – Evaluating EBG superstrate effects for distant placement of elements • Conserve planar low-cost structural advantage • Increase array gain & beam steering angle • Extract empirical models to assist design processes • Integrating the findings to develop EBG focal plane array prototype 16/24
Expected Outcomes • Wide Radiation Bandwidth of EBG-PRS Resonant Structures • Improved Radiation Efficiency • Higher Reflector Illumination Effeciency Suppression of Surface Currents Less Power Transfer Mismatch • Reduction of Noise Increased Sensitivity • • Possibility to use Sparse Arrays for dense sampling 17/24
Outline • Introduction: SKA & Phased Array Feeds (PAFs) • PAFs: What? Why? Limitations? • EBG Structures: A Possible Remedy • Research Objectives & Outcomes • Project Plan & Progress • Conclusions 18/24
Project Milestones Period Milestones From To Mar 2012 Aug 2012 Extensive Literature Review & Skill Enhancement Sep 2012 Feb 2013 Achieving Wide Radiation Bandwidth for EBG Structures Mar 2013 Aug 2013 Elimination of Scan Blindness & Mutual Coupling Sep 2013 Nov 2013 Formulating Analytical Basis & Data Reorganization Dec 2013 Mar 2014 Optimizing EBG structures for Gain Enhancement & Beam Steering Apr 2014 Aug 2014 Fully integrated PAF design verification and prototype fabrication Sep 2014 Feb 2015 Experimental measurements of prototype and Thesis development Mar 2015 Thesis submission & Examination 19/24
Delivery Schedule Deadline Deliverable Detailed Research Proposal Aug 2012 Prototype A: Wide Radiation Bandwidth EBG surfaces Feb 2013 Reporting results in IEEE Conferences Feb 2013 Prototype B: EBG Focal Plane Array free of Scan Blindness & Aug 2013 Mutual Coupling Empirical Models for Trend Analysis Dec 2013 Jan 2013 Reporting results in IEEE Letters/Journals Prototype C: Fully Integrated and Optimized Focal Plane Array Aug 2014 Reporting of results in IEEE Conferences/Journals Dec 2014 Mar 2015 Thesis Document 20/24
High-Level Execution Plan 1 2 3 Years Months 1-3 4-6 7-9 10-12 13-15 16-18 19-21 22-24 25-27 28-30 31-33 34-36 Literature Review Software Training Simulation Development Investigative Analysis Physical Measurements EBG Incorporation Formalization & Optimization We are Gain Enhancement here Prototyping & Fabrication Thesis Development Publication Process Project Kick-off: 1 st March 2012 Project Completion: 30 th March, 2015 21/24
Outline • Introduction: SKA & Phased Array Feeds (PAFs) • PAFs: What? Why? Limitations? • EBG Structures: A Possible Remedy • Research Objectives & Outcomes • Project Plan & Progress • Conclusions 22/24
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