Karoo Array Telescope Berm Shielding: Efficient Computational Modeling and Multicopter Measurement
The square kilometer array is planned to be the most sensitive radio telescope of the 21st Century. Electromagnetic site quietness is a critical element in achieving the full science goals. We evaluate the shielding effectiveness of a soil berm at the South African Karoo site. The berm is electrically large and computationally expensive to model. A hybrid GO/MoM model using FEKO is proposed. Simulated data are compared to full-scale multicopter measurements. Broadband antennas are built into the landing structure and their patterns are deembedded during postprocessing. Simulations and measurements over 100-900 MHz (vertically polarized) show that the berm becomes effective from the point where its height reaches ten wavelengths. Shielding effectiveness values in the range of 25 dB are predicted by an approximate perfect electrical conductor ground model; the validity of this approximation is investigated. A simple knife-edge model is shown to provide a useful estimate of likely shielding. The results show that 3-D berm optimization using computational techniques is possible.