# Design and Implementation of Attitude Stabilization System for Marine Satellite Tracking Antenna
## 1 Introduction  
Marine Satellite Tracking Antenna (MSTA) is an important shipboard device, which is responsible for establishing the communication between ships and geostationary satellites. The antenna dish of MSTA has to be directed at the geostationary satellite whatever the ship would rotate, due to ocean waves, as shown in Figure 1. To guarantee that high-quality satellite signal can be received by the antenna dish, the tracking angle error should be as small as possible. For the Ka-band MSTA under development (the latest technology in MSTA), the Root Mean Square (RMS) value of tracking angle error should be less than 0.2 deg under the condition that the maximum ship rotation velocity is about 26.2 deg/s. To realize this end, the design of attitude stabilization system of Ka-band MSTA, including algorithm, software and hardware, is very challenging. Now, there are several different kinds of MSTA in the market, such as L-band, C-band and Ka-band MSTA, which are mainly divided according to the frequency range of received satellite signals. For example, the frequency range of the satellite signals received by the L-band and C-band MSTA is typically below 8 GHz, which is a relatively low frequency in field of satellite communication and also means that the tracking angle error of the antenna dish of MSTA can be relatively large, around 2 deg. However, the Ka-band MSTA, as the latest technology of MSTA, requires a high-accuracy tacking system. This is becaue the frequency range of the received satellite signals is from 26.5 GHz to 40 GHz, which enables greater volumes of data traffic to be transmitted. There is currently a great need for high bandwidth communication from those latest applications, such as high-definition television and broadband network, which means Ka-band MSTA has a massive market. Several research works have been done in the field of attitude control of MSTA. In [1], two generalized predictive control algorithms are used to control \(x\) and \(y\) axes of a two-degree-of-freedom robot, which is an earth station antenna related to be the HDF pedestals (High Dynamic Full Motion Leo Satellite Tracking Pedestals). In [2], a Fault Tolerant Control (FTC) system is proposed for the satellite tracking antenna. The FTC system maintains the tracking functionality by employing proper control strategy. A robust fault diagnosis system is designed to supervise the FTC system. The employed fault diagnosis solution is able to estimate the faults for a class of nonlinear systems acting under external disturbances. Fuzzy logic is used in [3] to cope with the uncertainty and nonlinear nature of the attitude control of shipboard tracking antenna. The simulations demonstrated the effectiveness of the design, which has been implemented on some antennas. In [4], a digital servo system of the Permanent Magnet Synchronous Motor (PMSM) is implemented in the satellite antenna position control. The novel control system based on Digital Signal Processing (DSP) and Complex Programmable Logic Device (CPLD) modules is proposed to satisfy the requirements of the high performance servo system. In [5], an attitude stabilization controller based on \(\mathcal{H}_{\infty}\) mixed-sensitivity synthesis method is proposed to realize high accuracy of tracking control of MSTA. Experimental results show that the tracking accuracy can be improved to \(\pm\)0.3 deg, which is five times higher than that by the conventional controller. These research works have contributed a lot to the design of attitude stabilization system of MSTA, but there still exist some points that can be improved. The designed attitude control system of MSTA is fundamentally an attitude stabilization system, which is also applied in many other systems, besides MSTA system. In [6], two fault-tolerant control (FTC) schemes for spacecraft attitude stabilization with external disturbances are proposed. The effectiveness of the proposed schemes against actuator faults is demonstrated in simulation.