Periodic Structures and its Applications in Antennas

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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

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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

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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

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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 𝛼The 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)

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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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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

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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

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Q & A

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