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HYBRID T-MATRIX METHOD FOR ELECTROMAGNETIC SCATTERING FROM MULTIPLE LEAF STRUCTURES
- Foliage structures are one of the most abundant types of obstacles present in rural wireless communications environments. These foliage obstacles are composed of leaves, branches and trunks, which act as complex scatterers to propagating radiowaves operating in such environments, which may degrade the performance of radio systems. The proper understandings of such interactions are necessary to predict effects on radio systems, and helps to ensure their reliable performance in such complex environments. One element of these foliage obstacles are their leaf structures. These leaf structures generally have complex geometries, which make it challenging to find an exact solution to their scattered fields. These leaf geometries can be approximated as thin dielectric disks for deciduous leaves, or as thin dielectric cylinders for coniferous leaves [I]. From these simplified leaf geometries, approximate analytical methods may be used to evaluate the scattered fields . In this work, we use a hybrid method of moments (MoM) Transfer matrix (T-matrix) model to describe the scattering from multiple leaf structures, which greatly reduces the solution time. The T-matrix is a matrix representation of the electromagnetic scattering in terms of the incident and scattered wave spherical wave expansion modes . This T-Matrix formulation is only dependent on the scatterer properties – its dielectric properties, size, and shape - and is independent of the incident fields. This means that for a particular scattering object, the T-matrix only needs to be calculated once, and can be reused for succeeding computations. This makes the T-matrix formulation well suited in modeling the electromagnetic scattering from multiple leaf objects, which typically have similar leaf shapes and sizes for a certain tree species. In this work, the T-matrix is evaluated by directly solving the scattered fields from multiple incident plane wave directions using FEKO, a commercially available method of moments solver. As the T-matrix for a certain scattering geometry does not change with the incident wave, several sets of overdetermined equations for each scattered wave coefficient in terms of the unknown rows of the T-matrix and the incident wave coefficients. The T-matrix rows are found from the least squares solution of these overdetermined equations. The scattering from a collection of multiple identical leaf geometries with varying positions and orientations are found by applying a superposition approximation of the scattered fields from each of the individual leaf geometries from the T-matrix method. The scattered fields are compared with the method of moments solution of the multiple leaf geometry. It was found that the superposition of the hybrid T-matrix provides a very accurate model for the scattering from multiple leaf structures at a fraction of the time.
Co, Paul Jason
- 8th AUN/SEED-Net Regional Conference on Electrical and Electronics Engineering