Fast far-sidelobe modeling for centimeter to sub-millimeter astrophysical observations

Next-generation centimeter to sub-millimeter telescopes require exquisite control over instrumental far-sidelobe response to accurately measure faint signals like the Cosmic Microwave Background B modes. Because existing electromagnetic modeling methods are computationally expensive, we developed a novel, diffraction-based beam modeling method for rapid and low-cost calculations. We applied this methodology to model the BICEP3 far-sidelobes and found good qualitative agreement with in situ beam measurements. Using this validated simulated beam, we calculated the sidelobe temperature pickup for a specific observation scenario: scanning near the slopes of Cerro Toco in the Atacama Desert. This rapid, predictive framework is most valuable as a tool for optimizing instrument baffling and identifying efficient scan strategies during the conceptual design phase.