Multi-frequency Full-wave Simulations of Vegetation Using a Hybrid Method

In this paper, we study wave propagation in vegetationat multiple frequencies using a hybrid method. Firstly, themultiple scattering within a single plant is captured using theHigh-Frequency Structure Simulator (HFSS) for extracting theT-matrix of the plant in vector cylindrical waves. Secondly, theFoldy-Lax equations are applied with the extracted T-matricesto consider the multiple scattering among different plants. Theaccuracy of the hybrid method is verified by comparing the scatteringresults from 9 wheat plants with direct HFSS simulations.The hybrid method is implemented with parallel computing usinga physical iterative method to perform full-wave Monte Carlosimulations of a wheat field with up to 169 plants at L-, S- andC-bands. The impact of the gaps and the plant structure on themicrowave propagations are studied by assessing the scatteredfields and the resulting non-uniform transmission at differentregions. The results are compared with modeling results usingthe classical radiative transfer equations (RTE), and two majordifferences are observed: (1) the transmission calculated fromthe hybrid method is much larger than that of the RTE, and (2)the full-wave simulation results show much weaker frequencydependence than RTE with a saturation as frequency increases.