# Re-Optimized Design for the ADR-Based Dual-Loop Controller of 100 m Class Aperture Radio Telescope
## 1 Introduction  
The fully steerable reflector radio telescope plays a crucial role in radio-astronomy observations because of its larger observational sky coverage and longer observational time (integration time). For higher sensitivity and angular resolution, the antenna aperture of a single-dish radio telescope becomes larger and larger. The 100 m \(\times\) 110 m Green Bank Telescope (GBT) and the 100 m aperture Effelsberg Radio Telescope are the biggest fully steerable antennas in service. Xinjiang Astronomical Observatory, CAS is building the larger aperture QiaTaid Radio Telescope (QTT), which has a 110 m aperture dish and works at frequencies from 115 MHz up to 115 GHz [1]. Pointing accuracy is a crucial index, as important as the angular resolution and sensitivity of a fully steerable radio telescope. The pointing accuracy of large-aperture antennas is required to be a few arcseconds; e.g., QTT required an initial pointing accuracy of better than 2.5 arcsec and about 1 arcsec ultimately, which is challenging. In addition, astronomical observation also requires the antenna to switch fast between the goal and calibrator when operating at higher-frequency observations or VLBI [2]. The good dynamic performance of the antenna's servo system implies a shorter settling time, a tiny/zero overshoot for switching, meaning higher observation efficiency for the antenna. Making an antenna's aperture larger makes its sensitivity and resolution higher; however, it requires higher pointing accuracy at the same frequency, consequently asking for better servo control performance. Comparing the pointing accuracy, blind pointing accuracy is more closely related to the antenna's mechanical performance, and improvement in it is regarded as a better way to achieve high-accuracy pointing and is more meaningful [3]. An antenna's pointingperformance is beset by various challenges [4]. The negative effect of an imperfect antenna structure, such as uneven track and axis-related errors, can be reduced by astronomical pointing correction [5; 6]. In addition to an antenna's imperfect structure, antennas built outdoors are subject to nonlinear friction [7; 8] and many environmental disturbances, like wind gusts and temperature, which make the antenna's servo control accuracy challenging. The design of a better main-axis controller is regarded as a way to reduce the negative effects, and thus, improve the antenna servo system's performance. Electromechanical servo systems like antennas apply the current, velocity, and position to a three-loop control structure. The velocity- and position-loops are more relevant to the antenna's servo performance; so, they are crucial to the antenna's high-precision pointing control. Traditionally, integer-order proportional-integral-derivative (IOPID) controllers are employed in each loop; however, IOPID cannot simultaneously meet the requirements for the tracking accuracy and stability of a servo control system. Therefore, compound control based on IOPID and/or advanced control algorithms has been researched and utilized for antenna-pointing control. Advanced control algorithms can reduce major issues and increase the performance of the servo system, so their utilization is the major way to improve pointing control performance [9]. The advanced algorithms used for antennas mainly include linear quadratic Gaussian (LQG)/H\({}_{2}\), H\({}_{\infty}\), quantitative feedback technique (QFT), disturbance observer-based control (DOBC), equivalent input disturbance approach (EID), active disturbance rejection control (ADRC), sliding mode control (SMC), etc. LQG/H\({}_{2}\) controllers are well studied for achieving high-performance control of antennas under disturbances. In [10], [PERSON] et al. compared and studied the tracking and disturbance rejection performances of a feedback controller and LQG controller for the Deep Space Network (DSN) antenna. In [11], [PERSON] et al.