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Transcript of 1/19 Periodic Structures and its Applications in Antennas Debabrata Kumar Karmokar Student ID:...
1/19
Periodic Structures and its Applications in Antennas
Debabrata Kumar KarmokarStudent ID: 42660130
Principal Supervisor: Prof Karu EsselleAssociate Supervisor: Prof Michael Heimlich
Course: COMP901 Academic Presentation and Writing Skills
2/19
Outlines:• What is a Periodic Structure?• Importance of Periodic Structures• What is a Leaky-Wave Antenna (LWA)?• Physics of LWA• Integration of Periodic Structures with Microstrip
LWA (MLWA)• Key Prior Research• Aims and Expected Outcome• Methodology• Task Plan, Current Position, and Progress • Conclusion
Department of Engineering, Faculty of Science
3/19
What is a Periodic Structures?• Periodic structure is finite or infinite repetition of unit cells in
one, two or three dimensions• Appear in nature in such forms as beehives, crystals, etc.
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Fig. 2. A finite beam on periodic simple supports
Fig. 3. Uniform planar PBG on microstrip substrate
Fig. 4. Periodic stubs on a microstrip line(Pozar, D. M., 2005 )
Fig. 1. A beehive(http://oneida.uwex.edu/2011/06/30/building-beehive/)
(Mead D. J., 1996)
(Gupta, S. K.)
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Importance of Periodic Structures
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(a) (b)
Big
Small
Fig. 5. Current magnitude distribution on the patches (a) without PBG and (b) with PBG (Zhang et al., 2004)
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What is a Leaky-Wave Antenna (LWA)?• LWA belong to the more general class of traveling wave antenna in which the
guided wave gradually leaks out into the surrounding space to produce radiation
• A wide-band microwave antenna that radiates a narrow beam whose direction varies with frequency
Department of Engineering, Faculty of Science
Fig. 6. The earliest example of a leaky-wave antenna (Oliner et al., 1993)
Broadside
EndfireBackfire+ z
+ x
- z
+ y
Radiation Microstrip lineSubstrate
Ground Plane
Feed point
Fig. 7. Basic microstrip leaky-wave antenna (MLWA)
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First Higher Order Mode of Microstrip Transmission Line (MTL) and Half-Width LWA
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Via
h
WW/2
Microstrip line
Substrate
Ground Plane
Fig. 8. Microstrip transmission line (MTL) and its first higher order mode
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Dispersion Diagram of MTL
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Fig. 9. Dispersion curves for the lowest mode and the first two higher modes in microstrip line (The microstrip line dimensions are: W = 3.00 mm, h = 0.635 mm, ϵr= 9.80) (Oliner et al., 1986)
EH1
EH2
EH0
Radiationregion
3.0
2.0
1.0
00 10 20 30 40
kc/ko
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Physics of LWA • A leaky-wave antenna supports a fast wave with
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x
z
Ey
The electric field Ey (x,z) on the aperture (x=0) that has the form of a leaky wave,
|𝛽|<𝑘0
𝐸𝑦 (0 ,𝑧 )=𝐴𝑒− 𝑗𝑘 𝑧 𝑧
Where the complex wavenumber of the leaky wave is given by𝑘𝑧=𝛽− 𝑗 𝛼
The field in the air region above the aperture (x>0) is given by
𝐸𝑦 (𝑥 , 𝑧 )=𝐴𝑒− 𝑗𝑘𝑧 𝑧 𝑒− 𝑗𝑘𝑥 𝑥
Where the vertical wavenumber is 𝑘𝑥=(𝑘02−𝑘𝑧
2 )1/2𝑘𝑥=𝛽𝑥− 𝑗𝛼𝑥
--------------- (1)
----- (2) ----- (3)
Fig. 10. An aperture with an electric field Ey (x,z) on it at x=0 (Jackson et al., 2008)
From Eq. 3 we get 𝛽𝛼=−𝛽𝑥𝛼𝑥 ----- (4)
The radiation angle is given by𝜃𝑟=𝑠𝑖𝑛− 1(𝛽 /𝑘0)θr
kz=β
x
k0kx
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Physics of LWA (contd.)
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𝛽𝛼=−𝛽𝑥𝛼𝑥 ----- (4)
Fig. 11. Ray diagram of power flow in the air region (a) exponential growth (b) exponential decay
000x
0
0x0x
(Jackson et al., 2008)
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Physics of LWA (contd.)
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Fig. 12. Ray diagram for a finite leaky-wave propagation
Fig. 13. Field level of a typical leaky-wave having and2/3/ 0 k 02.0/ 0 k
(Jackson et al., 2008)
(Jackson et al., 2008)
11/19Department of Engineering, Faculty of Science
Fig. 14. Normalized complex propagation constant for a microstrip line (Line dimensions are: W = 11 mm, h = 0.508 mm, ϵr= 2.2) (Liu et al., 2008)
The radiation angle is given by
𝜃𝑟=𝑠𝑖𝑛− 1(𝛽 /𝑘0)
Physics of Leaky-Wave Antenna (contd.)
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Integration of Periodic Structures with microstrip LWA (MLWA)
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Fig. 15. (a) The 3D view of the periodic half-width MLWA (b) The layout of this periodic half-width MLWA
Fig. 17. ML over a ground plane with periodic lattice of apertures (Gagnon et al., 2006)
(Li et al., 2010)
Fig. 16. Reconfigurable half-width MLWA
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Key Prior Research
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References Approach Contributions1. Yuanxin, L., X. Quan, et al. (2011). "The Half-
Width Microstrip Leaky Wave Antenna With the Periodic Short Circuits." Antennas and Propagation, IEEE Transactions on 59(9): 3421-3423.
Series of short circuits with long rectangular guide
• Main lobe scans from 1440 to 410
• Poor radiation in broadside
2. Park, W.-Y. and S. Lim (2011). "Multi-Beam Leaky-Wave Antenna: Design, Analysis, and Experiments." Electromagnetics 31(4): 247-257
Right-/left-handed meta surface with defected ground surface
• One beam steered from -80 to +100
• Another beam is fixed at 590
(Frequency range: 3.9 to 4.2 GHz)
3. Kempel, L., E. Rothwell, et al. (2011). Theoretical analysis of a varactor-loaded half-width leaky-wave antenna. General Assembly and Scientific Symposium, 2011 XXXth URSI
Application of varactors with half-width leaky-wave antenna
• The varactor controls the complex wavenumber
• Same pointing direction of the main lobe across 1 GHz
4. Ouedraogo, R. O., E. J. Rothwell, et al. (2011). "A Reconfigurable Microstrip Leaky-Wave Antenna With a Broadly Steerable Beam." Antennas and Propagation, IEEE Transactions on 59(8): 3080-3083
Connection of lumped capacitors at the free edge of the antenna through computer controlled switch
• Obtained the placement of main beam at several selected angles
• No position of main beam at backfire and endfire
• Optimizer failed to fiend switching configuration at -800
• Gain is comparatively lower at broadside
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Aims and Expected Outcome• To design 1D, 2D and 3D periodic structures capable of
supporting the leaky-wave antennas• To make more energy efficient antenna using PBG structures• To integrate these periodic structures with leaky-wave
antennas• Designing leaky-wave antennas that can scan the main beam
from endfire to back fire• To develop leaky-wave theory in connection to solid state PBG
theory• To provide experimental evidence supporting the claims in the
proposed branch
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15/19Department of Engineering, Faculty of Science
Fig. 18. Half-width MLWA: endfire to backfire scanning capability (Expected outcome of this research)
Aims and Expected Outcome (contd.)
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Methodology• Calculation of initial dimensions of the periodic structure• Mathematical modelling of the antenna system• Analysis of the modelled system• Optimization methods development• Observation of the electric current distribution • Study the effect of change in geometry of the periodic
structures• Fabrication and testing of entire assembly • Post processing of measured and simulated results• Comparison of the simulated results with practical data
Department of Engineering, Faculty of Science
17/19
Task Plan, Current Position, and Progress
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Task 2- Research Equipment and Software Training
Task 6- Data Analysis
Task 8- Post Processing Task 7- Fabrication
Task 9- SummarizationTask 10- Thesis Writing and Submission
Task 1- Literature Review
Task 3- Mathematical Modeling Task 4- Integration of Periodic Structure Task 5- Simulation
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We are here
Progress: Basic knowledge on LWA Prior research and scope in the field from journals and conference papers Training on CST Microwave Studio and HFSS
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Conclusion• MLWA provide excellent properties• Low profile, minimal weight, simple fabrication• MLWA have wide range of applications • Number of limitations in the previous research– Broadside scanning– Endfire and backfire scanning
• Successful completion of this project should overcome most of the limitations
• Development of a novel periodic leaky-wave antenna for continuous scanning from endfire to backfire through broadside
Department of Engineering, Faculty of Science
19/19
Q & A
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20/19Department of Engineering, Faculty of Science