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Radio astronomical observations put stringent requirements on the tracking and pointing accuracy of radio telescope antennas. High inertia, low stiffness, underdamped, and multi-resonant frequencies of a large aperture radio telescope's antenna make the high-accuracy control difficult. It is not easy to satisfy control performance using only conventional PID controllers. A low-order Active Disturbance Rejection-based double-loop controller for large antenna is designed in this paper and tested on the Green Bank Telescope model. First, the first-order Linear Active Disturbance Rejecting Controller (LADRC) cascading a first-order low-pass filter and a notch filter is designed for the antenna's velocity loop to achieve the dual-objective optimal velocity tracking. Second, the position loop controller is designed to realize the antenna's position-tracking control by combining the PD controller and a low-pass filter. Further optimization of the position-loop controller helps improve the dynamic performance of the system. The simulation results indicate that the response curves of the proposed PD-LADRC control are smother than those of the Quantitative Feedback Theory (QFT) based controller; the settling time of the PD-LADRC system is 10.1 s and reduces by about 8.2 s than that of the QFT. While using a better position controller reduces settling time to 5 s. The PD-LADRC system also has better wind-disturbance rejection; the worst disturbance response reduces at the gearbox by 68.3% and 60% at the dish, and the recovery time reduces by more than 15 s than the QFT-based controller. In addition, besides easier parameter tuning, the proposed PD-LADRC has better robustness to systematic parameter perturbations and minor tracking error rms in position tracking. [ABSTRACT FROM AUTHOR]

In 21 cm experimental cosmology, accurate characterization of a radio telescope’s antenna beam response is essential to measure the 21 cm signal. Computational electromagnetic (CEM) simulations estimate the antenna beam pattern and frequency response by subjecting the EM model to different dependencies, or beam hyperparameters, such as soil dielectric constant or orientation with the environment. However, it is computationally expensive to search all possible parameter spaces to optimize the antenna design or accurately represent the beam to the level required for use as a systematic model in 21 cm cosmology. We therefore present the Model for Emulating Directivities and Electric fields of Antennas ( MEDEA) , an emulator that rapidly and accurately generates far-field radiation patterns over a large hyperparameter space. MEDEA takes a subset of beams simulated by CEM software, spatially decomposes them into coefficients on a complete, linear basis, and then interpolates them to form new beams at arbitrary hyperparameters. We test MEDEA on an analytical dipole and two numerical beams motivated by upcoming lunar lander missions, and then employ MEDEA as a model to fit mock radio spectrometer data to extract covariances on the input beam hyperparameters. We find that the interpolated beams have rms relative errors of at most 10 ^−2 using 20 input beams or less, and that fits to mock data are able to recover the input beam hyperparameters when the model and mock are derived from the same set of beams. When a systematic bias is introduced into the mock data, extracted beam hyperparameters exhibit bias, as expected. We propose several extensions to MEDEA to potentially account for such bias.

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.