Far-field Pattern Analysis Based on Piecewise Aperture Field Integration for Leighton Chajnantor Telescope Antenna under Gravity and Wind Load

The Caltech Submillimeter Observatory telescope will be relocated from Mauna Kea, Hawaii to Chajnantor Plateau, Chile, refurbished there and renamed the Leighton Chajnantor Telescope (LCT). At the new site, the open-air environment, as well as the high altitude, will amplify the influence of gravity and wind load on structural deformation, thus affecting the antenna's radiation characteristics, which can be characterized by a far-field pattern. To quickly and accurately compensate for the effect of reflector structural deformation on the far-field pattern of LCT's antenna, we propose a far-field pattern quick calculation method (FPQCM) to analyze the antenna's radiation characteristics under gravity and various wind loads, which combines the optical path difference calculation method on the aperture plane, the piecewise Zernike polynomial function, and the piecewise aperture field integration method. Through extensive experimental comparisons with the numerical method based on physical optics and physical theory of diffraction, it is validated that the proposed FPQCM significantly reduces the time by more than 100 times for acquiring the far-field patterns while maintaining the accuracy of the main figure of merits at the highest frequency (i.e., 856 GHz). In addition, we analyzed the far-field pattern of the antenna at different zenith angles, gravity, and winds of different strengths and directions by FPQCM, which provided guidance for performing more precise control through an active surface optimization system after LCT resumes operation, thus facilitating the acquisition of higher surface accuracy and better observation effect.