We propose a mode based approach for developing a parametric model to characterize RF propagation in conduits. The model considers a conduit as a lossy waveguide and defines the total received power as the sum of powers excited in propagating modes. The model's parameters are estimated from both the physical properties of the conduit material and an empirical data set. Underground conduits have significant value as wireless communication channels for condition based monitoring within the conduit. An enabler for this wireless sensor network application is based on characterizing the expected coverage range of wireless transceivers operating in the 2.4 GHz ISM band. Previous studies on modeling RF propagation in underground conduits have focused on conduits with diameters larger than 1.05 m. This motivated our measurement campaign to collect empirical data from underground conduits with varying diameters from 0.30 m to 1.37 m. The empirical data is used to predict the mode coupled powers which are model parameters that are analytically intractable. We observe that the proposed model provides a good estimate of received power in terms of contribution from dominant propagating modes.
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