1/19 Periodic Structures and its Applications in Antennas Debabrata Kumar Karmokar Student ID: Principal Supervisor: Prof Karu Esselle Associate 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. Department of Engineering, Faculty of Science 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 ( (Mead D. J., 1996) (Gupta, S. K.)

4/19 Importance of Periodic Structures Department of Engineering, Faculty of Science (a) (b) Big Small Fig. 5. Current magnitude distribution on the patches (a) without PBG and (b) with PBG (Zhang et al., 2004)

5/19 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 Endfire Backfire + z + x - z + y Radiation Microstrip line Substrate Ground Plane Feed point Fig. 7. Basic microstrip leaky-wave antenna (MLWA)

6/19 First Higher Order Mode of Microstrip Transmission Line (MTL) and Half-Width LWA Department of Engineering, Faculty of Science Via h W W/2 Microstrip line Substrate Ground Plane Fig. 8. Microstrip transmission line (MTL) and its first higher order mode

7/19 Dispersion Diagram of MTL Department of Engineering, Faculty of Science 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 = mm, r = 9.80) (Oliner et al., 1986) EH 1 EH 2 EH 0 Radiation region k c /k o

8/19 Physics of LWA A leaky-wave antenna supports a fast wave with Department of Engineering, Faculty of Science x z EyEy The electric field E y (x,z) on the aperture (x=0) that has the form of a leaky wave, Where the complex wavenumber of the leaky wave is given by The field in the air region above the aperture (x>0) is given by Where the vertical wavenumber is (1) (2) (3) Fig. 10. An aperture with an electric field E y (x,z) on it at x=0 (Jackson et al., 2008) From Eq. 3 we get (4) The radiation angle is given by θrθr kz=βkz=β x k0k0 kxkx

9/19 Physics of LWA (contd.) Department of Engineering, Faculty of Science (4) Fig. 11. Ray diagram of power flow in the air region (a) exponential growth (b) exponential decay (Jackson et al., 2008)

10/19 Physics of LWA (contd.) Department of Engineering, Faculty of Science Fig. 12. Ray diagram for a finite leaky-wave propagation Fig. 13. Field level of a typical leaky-wave having and (Jackson et al., 2008)

11/19 Department of Engineering, Faculty of Science Fig. 14. Normalized complex propagation constant for a microstrip line (Line dimensions are: W = 11 mm, h = mm, r = 2.2) (Liu et al., 2008) The radiation angle is given by Physics of Leaky-Wave Antenna (contd.)

12/19 Integration of Periodic Structures with microstrip LWA (MLWA) Department of Engineering, Faculty of Science 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

13/19 Key Prior Research Department of Engineering, Faculty of Science ReferencesApproachContributions 1.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): Series of short circuits with long rectangular guide Main lobe scans from to 41 0 Poor radiation in broadside 2.Park, W.-Y. and S. Lim (2011). "Multi-Beam Leaky-Wave Antenna: Design, Analysis, and Experiments." Electromagnetics 31(4): Right-/left-handed meta surface with defected ground surface One beam steered from -8 0 to Another beam is fixed at 59 0 (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): 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 Gain is comparatively lower at broadside

14/19 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 Department of Engineering, Faculty of Science

15/19 Department 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.)

16/19 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 Department of Engineering, Faculty of Science 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

18/19 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 Department of Engineering, Faculty of Science

20/19 Department of Engineering, Faculty of Science