Tracking design of a low-profile vehicle-mounted satellite communication antenna

In vehicle-mounted satellite communications, low-profile vehicle-mounted antennas have good concealment and usability, and have a wide range of application prospects. However, to achieve the best cost-effectiveness, the design of the antenna tracking controller is one of the key technologies. In the absence of heading guidance information, it is difficult to achieve a stable tracking control system for the vehicle-mounted antenna . A new tracking control strategy is proposed to solve this problem.

1 System composition

The antenna stabilization tracking control system is mainly composed of a tracking receiver , a controller, a driver , and an inertial device. The tracking receiver mainly provides the AGC level value of the satellite beacon; the controller mainly provides the operation and display interface and completes the implementation of the control strategy; the driver mainly completes the power amplification and controls the rotation of the motor; the shaft angle encoder mainly provides the real-time angle of the antenna azimuth and pitch; the inertial device mainly provides the disturbance information of the antenna carrier. The composition of the antenna control system is shown in Figure 1.

2 Tracking control strategy

The antenna system discussed here is a vehicle-mounted flat-panel antenna with asymmetric azimuth and elevation beam widths. The beam width of the elevation axis is relatively wide, and an electronic scanning method is adopted, supplemented by inclinometer positioning and gyro stabilization compensation, to achieve stable tracking of the elevation. The azimuth beam width is relatively narrow, so the tracking control strategy is mainly carried out for the azimuth.

The vehicle-mounted antenna control system has the ability to stabilize the carrier disturbance and solve the heading to achieve rapid capture and accurate tracking of satellite targets. In the implementation of the stabilization measures, this paper adopts the feedforward stabilization technology, using the carrier attitude information provided by the rate gyro installed on the vehicle body to solve the compensation signal for open-loop compensation; the solution of the heading information is based on the position of the AGC maximum point of the tracking receiver captured by the antenna as the relative heading initial point, and the heading offset obtained by the rate gyro integration is used to dynamically correct the orientation in real time.

2.1 Control loop design

The system uses the azimuth relative angle value of the maximum point of the AGC captured by the tracking receiver as the initial position, and uses the data provided by the rate gyros installed in the three orthogonal directions of the vehicle body to solve the disturbance components of the antenna azimuth and pitch generated by the vehicle body disturbance through coordinate transformation, and stably controls the antenna. At the same time, the output of the gyro is integrated to obtain the position offset, and then the position is compensated by the position loop. The control loop is shown in Figure 2. In Figure 2, θi is the target angular position; θo is the antenna angular position; KaWa(s) is the transfer function of the position loop amplification and correction link; KbWb(s) is the transfer function of the speed loop amplification and correction link; KcWc(s) is the transfer function of the speed feedback correction link; and f is the azimuth gyro output.

2.2 Tracking strategy

Scanning and tracking are the core parts of the technical implementation of this system. When the target satellite is set, the target angles of the antenna azimuth and pitch can be calculated through the current longitude and latitude of the antenna and the longitude of the target star. The antenna is guided into position according to the target angle, and the azimuth scan is performed with the current position as the center point. At the same time, the pitch is electronically scanned until the AGC is greater than the AGC threshold. When the antenna AGC is greater than the AGC threshold, the heading is set to zero, and the azimuth gyro speed Vf is sampled and integrated to obtain the change in the vehicle heading θf. This angle is superimposed on the step tracking command angle θi and used as the new command angle to climb the slope and find the maximum value. When the maximum value is found, the heading is reset to zero. Enter the tracking state and start the gyro output integral θf at the same time, and the integral iteration

Where θf(n) is the integral output; θf(n-1) is the last integral output; Vf(n) is the gyro output; and Vf(n-1) is the last gyro output.

The tracking status is divided into dynamic tracking (turning driving) and static tracking (straight driving). When the azimuth gyro value is greater than the critical value, dynamic tracking is performed, otherwise static tracking is entered. Dynamic tracking: When the azimuth gyro output value is greater than the critical value Vfo, the angle command uses the current angle plus the real-time θf as the command angle to make a position closed loop, and is assisted by speed compensation. Static tracking: With the maximum point of the AGC as the center, the azimuth mechanically slightly rotates the antenna platform to the left and right by a certain angle △θ±θf to obtain two AGCs: VAGC_l and VAGC_r. When VAGC_l=VAGC_r, it is aimed at the target; when VAGC _l>VAGC_r, the target is biased to the left, and the azimuth is rotated to the left by an angle of △θ±θf; when VAGC_l

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3 Design application and test results

The above design method is used in a vehicle-mounted flat-panel "mobile communication" antenna control system. After testing, the straight-tracking accuracy is 0.24 V. The turning tracking accuracy is 0.35 V. The accuracy calculation formula is detailed in the literature. The turning tracking test results are shown in Figures 4 and 5. The straight-tracking test results are shown in Figures 6 and 7.

4 Conclusion

The control strategy described in this paper uses an inclinometer and three rate gyros to achieve isolation of vehicle body disturbances and heading isolation through software, improving the cost-effectiveness of vehicle-mounted satellite communication antennas. The test results of the tracking algorithm show that the algorithm can meet the accuracy requirements and can be used as a tracking strategy for low-profile vehicle-mounted antennas and be promoted for use.