Modal Analysis of Thermal Noise from Lossy Dielectric Medium

The modal characterization of the thermal noise generated by lossy dielectric media can be used to improve the design of antenna arrays and improve the overall system performance. In this paper we study the thermal noise generated above a circular ground plane by a lossy semi-infinite medium. To do so, we consider an array of infinitesimal dipoles above the ground plane. The fields generated by the dipoles in presence of the finite ground plane are computed using the Method of Moments and used to compute the power dissipated by the dielectric medium. Combining the fluctuation-dissipation theorem to Lorentz reciprocity, the noise correlation matrix at the location of the dipoles is obtained. Using this matrix, we apply the eigenmode decomposition to obtain a modal representation of the noise. From there, we study the behaviour of the different modes and the dependence on the size of the ground plane. We show that increasing the size of the ground plane decreases the noise power and increases its coherence, potentially facilitating its filtering.