Full-Wave Analysis of Thermal Noise in Antenna Arrays on Top of Layered Medium

Observations made using antenna arrays are often limited by the noise coming from the antenna system itself and from the environment. In demanding applications such as radio astronomy, the thermal noise emitted by the multilayered substrate below the antenna array may become significant and needs to be properly characterized. Both the intensity of the noise at each port and the correlation of the noise at pairs of ports need to be quantified. In this article, we provide a spectral formulation to calculate the noise correlation matrix of antenna arrays. The method is based on the propagative and evanescent plane wave spectrum emitted by each pair of active antenna ports into the lossy layered medium and thus can be implemented as a postprocessing step combined with any full-wave numerical solver. This formulation allows us to account for layered media with different physical temperatures at each layer. Numerical examples are provided using square kilometer array (SKA) stations lying on a finite ground plane, itself lying on a layered semi-infinite soil. The behaviors of noise power and noise correlation coefficients are studied for different positions of the antennas on the ground plane. This is done considering multilayered soil with different moisture levels. A very good agreement with the commercial software FEKO is observed regarding the evaluation of the noise correlation coefficients. Moreover, the efficiency of the algorithm in terms of computation time is shown by comparison with FEKO. The direction-dependent system noise temperature picked up by a full SKA station in the presence of the soil is also given.