PhD Research Student
Oluwafunmilayo Agunlejika, commonly called Funmi, is a research student within the School. She graduated with a Bachelor of Technology degree from Ladoke Akintola University of Technology, Ogbomoso, Nigeria and further studied for a M.Sc in Electronic and Electrical Engineering at the Obafemi Awolowo University, Ile-Ife, Nigeria.
Funmi is currently working on developing an electromagnetic solver based on the cylindrical Transmission Line Matrix (TLM) in the Communications Research Division.
Transmission Line Modelling of Cylindrical Radiating Structures
Oluwafunmilayo Agunlejika, James A. Flint and Robert D. Seager
Abstract- This paper gives the summary of an on-going research work on transmission line modellling of cylindrical radiating structures. The research focus on resolving the accurate and efficient representation issues associated with curved boundaries in Transmission Line Modelling (TLM) method. The research motivation and potential applications are briefly described
Keywords- Cylindrical mesh; Transmission Line Modelling; Radiating structures; Numerical Model; Electromagnetics
Transmission Line Modelling method (TLM) is a time domain numerical modelling method . TLM simulates the behaviour of a distributed system by employing a network of discrete transmission lines. The network structure is called the mesh, connecting junctions the nodes and the connecting lines between nodes are called link lines. The simulation produces a model of the electromagnetic wave propagating through the structure. The system is excited and the pulse travels along the link line. When the pulse is incident on one of the nodes, the energy is scattered isotropically in all four directions. The scattered pulses travel through the link lines and connect to adjacent nodes and the process is repeated. The field, current and voltage can then be determined at the required output point(s). Hoefer  described it as representing a true computer simulation of wave propagation in the time domain.
TLM has been known to be a versatile numerical tool in solving electromagnetic problems because of its stability, ease of application and capability for wideband applications. However, in standard Cartesian TLM, structures are represented in cubical form. Consequently, curved boundaries are represented with staircase approximations and so many discrete steps are required to represent smooth edges. Substantial work has been done to improve on the TLM method but the issues associated with accurate and efficient representation of curved boundaries remains a point of concern . The accurate solution of problems in electromagnetics ideally requires maximum conformity of the mesh to the structure being modelled. Material properties also have to be incorporated. There is an increasing demand for Electromagnetic Compatibility (EMC) for electronic devices worldwide and there are rapid developments in Ultra-wide band applications. These require accurate and efficient antenna design processes.
The approach to be used includes the definition of geometry, material type, appropriate boundary conditions and type of source excitation. The scattering equation for solving problems with cylindrical symmetry will be developed and a cylindrical curvilinear mesh for TLM applications will be developed. The mesh structure will be used to analyse cylindrical antennas and the results will be validated by comparing the results of simulation with both experimental and existing benchmark results.
Benefits and Application
The new technique that will be developed will allow structure conformity in modelling of arbitrary geometries and material properties, which will aim to produce more accurate results with lower simulation time. The results of this research work would enhance antenna design processes in telecommunication, EMC testing of equipment for commercial purposes and improve performance for defence applications. It will also bring about time efficiency in electromagnetic problem solving by reducing computational time and potentially open up a new area of research in UWB antennas.
 C. Christopoulos, The Transmission Modelling Method TLM, IEEE Press, New York, 1995
 WJR Hoefer, The transmission-line matrix method:theory and application IEEE transaction on microwave theory and techniques, Vol. 33, No 10, pp 882-893, October 1985.
 WJR Hoefer and Poman PM So, Electromagnetic simulator- The MEFISTO-2D Theory”, Canada, pg 1, 1998.