A Computationally Efficient Reciprocal Effective Roughness Model for Diffuse Scattering

Ray tracing (RT) has become central to site-specific electromagnetic propagation modeling in complex, dynamic environments. Yet its computational burden grows sharply as high-fidelity digital twins of these environments scale to millions of facets whose material parameters must be continuously updated as the environment changes. The challenge is amplified at mmWave and sub-THz frequencies, where surface roughness becomes comparable to the wavelength and so diffuse scattering can account for up to 40% of the power, making accurate yet tractable models essential. The popular Effective Roughness (ER) approach offers physical consistency but becomes increasingly costly when highly directive lobes are required or when environment parameters change or must be iteratively tuned. This communication introduces a directive, reciprocal diffuse scattering model that preserves the structure of the Effective Roughness (ER) model while enabling an order-of-magnitude reduction in computational cost. Validation across eight materials shows comparable accuracy, with a slight average improvement, demonstrating a scalable and physically meaningful solution for RT in scenarios where diffuse scattering is relevant.