1. Microwave Imaging using Indirect Synthetic Reference Beam Holography
Presentation to Calgary University - October 2005
Microwave Imaging using Indirect Synthetic Reference Beam Holography
Dr. M. Elsdon
CEIS, Northumbria University, Newcastle-upon-Tyne, NE1 8ST, UK

2. Introduction Overview of Northumbria University Imaging Group
Overview of Holographic Imaging
Describe Northumbria University’s Imaging Technique – Indirect Holography
Applications of this technique:
Antenna fields
Concealed Metal Objects
Dielectric Objects,
Breast Cancer Detection

3. ABOUT ME Dr. Michael Elsdon
BEng (Hons) Electronic and Communication Engineering
PhD ‘Compact Microstrip Antennas’
July 2005: Post-Doctoral Researcher
Microwave Imaging Research Group, Northumbria University, UK
Project: ‘Microwave Imaging of Breast Cancer’

4. Research Overview
Work of group based upon patented invention of Northumbria University: ‘Synthetic Reference Beam Holography’
Exploits the advantage of NOT requiring direct measurement of phase.
Mathematical Reconstruction enables phase to be ‘deduced’
VNA replaced with Diode Detector – LOW COST
Applications:
Antenna Radiation Pattern Measurement
Airport Security
Medical Imaging

5. Holographic Approach For Imaging
1. DIRECT HOLOGRAPHY:
Measure amplitude and phase of scattered signal
Reconstruct Image using Mathematical Techniques
Requires VNA - EXPENSIVE

6. Requires Only Simple Diode Detector
2. INDIRECT HOLOGRAPHY:
3D Images can be reconstructed from Amplitude of scattered signal
Requires only SCALAR measurements
Requires Only Simple Diode Detector
- INEXPENSIVE

7. Indirect Holography Two Stage Process: Stage 1:
Illuminate Object with reference wave to form Hologram (Intensity Pattern)
Stage 2:
Reconstruct Image of Original Object using post-processing software

8. Stage 1: Formation of Intensity Pattern
Illuminate object with coherent reference wave
Combine reflected signal with reference signal
Form Intensity Pattern – Hologram
Record Intensity of Hologram

9. Intensity Pattern Formation – Experimental Arrangement for Data Collection
Object
RX Probe
Controller
TX Probe
Power Meter
Intensity Pattern
I (x,y)
Microwave
Source
Directional
Coupler
Variable Attenuator
Phase Shifter
Position
Control
Synthetic
Reference Wave
Hybrid
Tee

10. Stage 2: Image Reconstruction
Take Fourier Transform of Recorded Intensity Pattern
Filter Fourier Transform to remove unwanted terms
Take Inverse Fourier Transform
Perform Back-propagation and IFT to produce image at selected depth

11. 1. Intensity Pattern
2. Fourier Transform

12. Synthesized Reference Wave separates required term from origin
Problem: Difficult to produce sufficient offset to separate terms of Fourier Transform
Synthesized Reference Wave separates required term from origin
Spectral Representation of Off-axis Hologram:

13. 3. Filter off Unwanted Terms
4. Re-centre remaining term
Measurement Plane Image

14. 5. Back-propagate to selected depth and perform IFT
ORIGINAL IMAGE
At Object Plane

15. History of Microwave Imaging Research at Northumbria
Imaging of Antenna Radiation Characteristics
Imaging of Concealed Metal Objects
Imaging of Plastic Objects
Breast Cancer Detection

16. 1. Antenna Radiation Characteristics
Parabolic Dish
Data Collection System

17. Reconstructed Near-Field
Magnitude
Phase

18. 2. Imaging of Concealed Metal Objects
Uncovered Triangle:
Triangle Covered with Cloth:

19. Intensity Pattern Formation – Experimental Arrangement for Data Collection
Object
RX Probe
Controller
TX Probe
Power Meter
Intensity Pattern
I (x,y)
Microwave
Source
Directional
Coupler
Variable Attenuator
Phase Shifter
Position
Control
Synthetic
Reference Wave
Hybrid
Tee

20. Typical Intensity Pattern

21. Linear Phase Shift Applied to Synthetic Reference Wave
Plane Wave Spectrum

22. Reconstructed IMAGE

23. Problem of Previous Example:
Terms in PWS overlap if object is tilted, can’t separate terms
Can only image objects that are FLAT

24. SOLUTION:
Apply 2D phase shift to reference wave

25. PWS with 2D Phase Shift
Tilted Objects do not cause terms to overlap

26. 3. Imaging of Dielectric Objects

27. Recorded Intensity Pattern
F.T of Intensity Pattern

28. Reconstructed IMAGE

29. 4. Imaging of Breast Cancer - Crude Phantom
εr1 = 30, εr2 = 2, d1 = 35mm, h = 10cm, x = y = 40cm,
dx = dy = 1cm, f = 8.6GHz

30. Photo of Breast Phantom

31. Photo of Experimental Setup

32. Recorded Intensity Pattern
F.T of Intensity Pattern

33. Reconstructed IMAGE

34. Benefits of Northumbria University’s Technique
Provides 3D Holographic Image from “Single –View” 2D Scan
Employs Patented Synthetic Reference Beam Electronically
Hologram “Created” in Software
Compact Microwave Network Compared to External Offset Reference Beam Antenna Geometry
Low-Cost
Simple Square-Law Detector in Lieu of Vector Analyser
Phase Retrieval via Mathematical Reconstruction Process

35. Microwave Imaging Research Group Northumbria University
Dr David Smith, Team Leader & Inventor of Synthetic Reference Beam Holography
Dr Michael Elsdon, Post - Doctoral Researcher
Dr Mark Leach, Post - Doctoral Researcher
Prof. Stephen J Foti, Consultant
Mr M. Joy, PhD Student

36. Acknowledgements Engineering and Physical Science Research Council
(EPSRC)
Wellcome Trust
Newcastle University Medical School
Prof. T. Lennard (Royal Victoria Infirmary)
Mr Peter Elsdon, Technical Consultant