In general, radar antennas are installed on masts in relatively open areas to avoid signal sources or electromagnetic radiation caused by various interferences. To ensure stability and reliability during operation, a stable platform is configured for the specially designed radar antenna, which is unaffected to a certain degree. However, in practical applications, radar antennas may tilt due to external vibrations, structural stagnation, and installation errors during actual use. The tilt angle sensor can accurately measure the angular deviation caused by various reasons, transferring the angle signal in real-time in either digital or analog form. It can be directly connected to identify the corresponding signal display instrument and control system, achieving real-time detection and control of the radar antenna to ensure its normal and stable operation.

Satellite Automatic Tracking System

       The satellite automatic tracking system is used to ensure that the satellite launch antenna accurately points to the satellite while the vehicle is in motion. Its main equipment includes:

       (1) Antenna base, which uses unloading and energy storage methods to reduce the load inertia during antenna operation.

       (2) Servo, which uses position loop or speed loop control methods, employing analog hardware to improve circuit response speed and reduce dynamic lag error in the servo tracking system.

       (3) Data processing, which uses a dedicated mathematical solving platform to process error signals and dynamic signals of the carrier, calculating the control signals for the antenna.

       (4) Carrier measurement, which uses a combination of strapdown inertial navigation measurement and other measurement methods to measure the changes in the carrier, reflecting them in antenna tracking. Among them, fiber optic gyroscopes are new navigation instruments developed based on the principle of optical interference, becoming the ideal main component of the new generation of strapdown inertial navigation systems, used for precise direction finding of the intended object. Quartz flexible pendulum accelerometers are sensitive components made of fused quartz, with a flexible pendulum structure equipped with a feedback amplifier and a temperature sensor, used to measure linear acceleration along one axis of the carrier. The fiber optic gyroscope three-axis inertial measurement combination consists of three fiber optic gyroscopes and three quartz flexible pendulum accelerometers, capable of real-time output of the carrier's angular velocity, linear acceleration, linear velocity, and other data, with various working modes such as alignment, navigation, and heading attitude reference, used for combined navigation and positioning of moving carriers, while providing accurate data for the mechanical control device of the tracking antenna. For the moving communication system, its main performance requirements are: acceleration precision of 1×10^-4g; fiber optic gyroscope precision (bias stability) ≤1°/h; scale factor linearity ≤5×10^-4.

Satellite Communication System

      The role of the satellite communication system is to transmit television signals uplink to the satellite, which are then downlinked by the transponder to ground satellite receiving devices. Its main equipment includes: encoders/decoders, modulators/demodulators, up/down converters, high-power amplifiers, duplexers, and low-noise amplifiers.

"Moving Communication" System Working Principle

      During the movement of the carrier, changes in its attitude and geographical position can cause the originally aligned satellite antenna to deviate from the satellite, leading to communication interruption. Therefore, it is necessary to isolate these changes in the carrier to ensure that the antenna remains unaffected and always points to the satellite. This is the main problem that the antenna stabilization system needs to solve and is also the prerequisite for uninterrupted satellite communication for moving carriers.

   "Moving Communication" Tracking System is based on initial static conditions, where the GPS, theodolite, and strapdown inertial navigation system measure the heading angle, the longitude and latitude of the carrier's position, and the initial angle relative to the horizontal plane. Then, based on its attitude and geographical position, the satellite longitude automatically determines the antenna elevation angle relative to the horizontal plane, rotating the azimuth while keeping the elevation angle constant. It automatically aligns with the satellite in a signal maximization manner. During the movement of the carrier, the changes in the carrier's attitude are measured, and through mathematical platform calculations, converted into the antenna's error angle. The servo mechanism adjusts the antenna's azimuth angle, elevation angle, and polarization angle, ensuring that the antenna remains within the specified range of the satellite during the carrier's changes, allowing the satellite launch antenna to track geostationary satellites in real-time as the carrier moves. The system has two tracking modes: self-tracking and inertial navigation tracking. Self-tracking relies on satellite beacons for closed-loop servo tracking of the antenna; inertial navigation tracking uses gyroscopic inertial combinations to track the antenna based on the changes in the sensitive carrier. This tracking method is sometimes referred to as guidance. These two tracking modes can automatically switch based on the field situation. Once the system completes the star tracking and enters automatic tracking, it operates in self-tracking mode; at the same time, the inertial navigation system also enters the working state and continuously outputs data on antenna polarization, azimuth, and elevation. When the antenna beacon signal is interrupted due to obstruction or other reasons, the system automatically switches to inertial navigation tracking mode.

Tracking of Moving Communication

       When the carrier is in motion, it is necessary to continuously track the satellite signal or satellite beacon signal. Different tracking methods can be adopted according to the needs of different systems. According to the tracking principle, automatic tracking can be divided into three types: step tracking, conical scanning tracking, and single pulse tracking.

Step Tracking

       Step tracking, also known as extremum tracking, involves controlling the antenna to make small angular step rotations in the azimuth and elevation planes, gradually aligning the antenna with the satellite. The system only enters a resting state after the received signal reaches its maximum value, and after a period, it resumes tracking, repeating this process. Figure 1 shows the principle block diagram of step tracking.

Figure 1 Principle Block Diagram of Step Tracking System

       In this method, the antenna's precession is divided into two types: search step and adjustment step. After the search step action, the entire tracking system begins to work, including sampling signal data, field strength memory, comparison, etc. After several searches and determining the direction in which the antenna should rotate, the antenna returns to its original position and then rotates one step towards the satellite. This final step is called the adjustment step. Therefore, the main difference between the adjustment step and the search step is that after the adjustment step action, the antenna does not return to its original position, while the search step does. Regardless of how many times the search step is executed, as long as the specified number of times is completed, the antenna returns to its original position, and then the antenna rotates one adjustment step. In actual systems, they can be separate or part of the same step.

       Single Pulse Tracking

       The characteristic of the single pulse tracking method is that the antenna beam is fixed, and within the interval of a pulse, the size and direction of the antenna beam's deviation from the satellite can be determined. This allows for the acquisition of error signals for the antenna's azimuth and elevation movements to drive the servo system, enabling the antenna to quickly align with the satellite. Single pulse tracking can be implemented using multiple horn methods and higher-order mode methods. The multiple horn method typically uses amplitude comparison and phase comparison. For parabolic antennas, multiple horns are usually configured to generate error signals for tracking using the amplitude comparison method. The higher-order mode method extracts higher-order modes generated in the feed waveguide as position error signals for tracking when the antenna's symmetry axis deviates from the satellite direction. The tracking speed and accuracy of the single pulse tracking system are several orders of magnitude higher than those of the conical scanning tracking system and the stepping tracking system, but it is complex and costly.

      Conical scanning tracking

      Conical scanning tracking involves the feed horn moving in a conical motion around the antenna's symmetry axis, or tilting and rotating the antenna's sub-surface, causing the antenna beam to rotate in a conical shape. When the antenna axis is aligned with the satellite, the beacon level will be modulated in amplitude by a very low frequency signal. The modulation frequency is the same as the beam rotation frequency, and the modulation depth is related to the distance the beam deviates from the satellite. A larger deviation results in a greater modulation depth; a smaller deviation results in a shallower modulation depth; no deviation results in a modulation depth of zero. The phase of the modulation is related to the direction of the beam's deviation, so the amplitude and phase of the modulation signal can be used to detect the pointing error of the antenna beam, and the direction and magnitude of the motor driving the antenna's rotation can be determined based on this pointing error.

      Comparison of three tracking systems

      From the perspective of the working principles of the three tracking methods, they are essentially the same, all comparing multiple AGC signals to determine the direction and magnitude of the motor's rotation. Stepping tracking samples separately in the azimuth and elevation planes and drives the motor to rotate the antenna within those planes; conical scanning tracking involves the feed making a conical motion under motor drive and comparing signal levels during this process to align with the satellite; single pulse tracking can determine the motor's rotation direction and magnitude within the time of a single pulse.

      Single pulse tracking has high accuracy and speed, but the system is complex and costly, generally suitable for places with high precision requirements; conical scanning can meet the general system's accuracy requirements, but its structure is relatively complex, has significant signal loss, and the tracking speed is also relatively slow; stepping tracking has speed and accuracy that fall between the two, and the entire system is relatively simple, making it easier to implement, thus achieving widespread application.

       Stabilization technology

　　For mobile communication systems, if there is only tracking, the antenna can easily lose the signal under large fluctuations of the carrier, leading to communication interruptions. Therefore, an antenna stabilization system is necessary to isolate the interference caused by carrier movement. There are two implementation methods for vehicle-mounted antenna stabilization systems: 1. Physical platform stabilization; 2. Inertial stabilization.

       (1) Physical platform stabilization isolates the vehicle-mounted antenna from the vehicle body through a stabilization platform, so the motion of the vehicle body is isolated from the vehicle-mounted antenna system. This is equivalent to fixing the vehicle-mounted antenna to the ground plane, making it easy to achieve precise satellite alignment, and once aligned with the satellite, no further adjustment of the antenna's direction is needed. This method divides the vehicle-mounted antenna stabilization system into a stabilization platform system and an antenna servo system. The antenna's stabilization for satellite alignment relies on the stabilization platform, has poor autonomy, is complex, and has relatively high costs.

       (2) Inertial stabilization utilizes information from gyroscopes, GPS, etc., on the carrier to establish a mathematical platform through coordinate transformation, calculating the correction amount for the servo system. The system is widely used due to its simple structure, good reliability, small size, low cost, and ease of maintenance.

     "Mobile Communication" vehicles can transmit digital television, broadcasting, and data signals bidirectionally via satellite at speeds of 20 to 100 km/h, ensuring uninterrupted broadband multimedia satellite communication for moving carriers.

"Mobile Communication" system features

"Mobile Communication" has the following advantages in live broadcasting:

       (1) During the broadcasting process, it uses autonomous tracking to track satellites, fully utilizing the characteristics of satellite communication's large coverage area, strong anti-interference capability, and stable lines, enabling point-to-point, point-to-multipoint, and point-to-main station mobile satellite communication.

       (2) The "Mobile Communication" vehicle has flexible and mobile broadcasting characteristics, ensuring fast and real-time static and dynamic live broadcasts.

       (3) The automatic reacquisition time is short, allowing for quick recovery of communication after exiting a communication blind spot.

       (4) Compared to OFDM "directionless" mobile microwave equipment, the "Mobile Communication" vehicle does not require operators for receiving and transmitting equipment to work under harsh environmental conditions, saving manpower and material resources, and reducing electromagnetic radiation pollution.

       (5) The reduction of nodes in the signal transmission process improves the quality and reliability of the broadcast.

       (6) It can reduce the operating costs of live broadcasts in large-scale, complex scenarios.

However, due to current technological limitations, "Mobile Communication" still has some shortcomings, mainly:

       (1) In complex broadcasting environments (too many or too high buildings, bridges, mountainous areas, etc.), signal interruption may occur.

       (2) When using two "Mobile Communication" vehicles to transmit different television image signals, it is difficult to achieve seamless connection without flash points during image broadcasting (both vehicles encountering flash points simultaneously).

       (3) Signal transmission between the "Mobile Communication" vehicle and the mobile signal collection vehicle is not easy (the direction and position of both vehicles are constantly changing).

Advantages of AgileLight series fiber optic gyroscopes used in mobile communication

       The AgileLight series fiber optic gyroscopes have stable performance, can withstand shocks and various harsh environments, and have significant price advantages. They can serve as key components in low-cost fiber optic gyroscope inertial navigation systems or be used in servo systems, making them an ideal choice for mobile communication systems.