Research On Automatic Tracking Algorithms For Mobile Satellite Antenna

With the rapid developments of satellite communication and the increasing demands for mobile communication, vehicle satellite communication which mainly transmits multimedia broadband data acquires universal attention, where automatic tracking technologies of antenna are the key points to guarantee communication quality. This paper studies thoroughly on the automatic tracking speed and accuracy, correspondingly presenting the improved algorithms on purpose.Step tracking is widely used in mobile satellite antennas because of its simple devices and stable performance. However, since the step size makes an irreconcilable conflict between the tracking speed and the tracking accuracy, an improved algorithm using variable step size is proposed in this paper: there is a big step size when the antenna is far away from the goal orientation while there is a smaller one when it’s nearer. Meanwhile, basic step tracking method is too simple to assure the accuracy of the direction judgement during the vehicle movements. In this paper, it applies one way of bidirectional search to avoid the misjudgment generally. Besides, based on the improved algorithm of one-dimensional step tracking, this paper presents a two-dimensional step tracking algorithm which drives the antenna along the direction of power gradient relative to the azimuth and the elevation.Fast beamforming of a phased array antenna is the kernel to achieve the accurate tracking. To improve the effectiveness and reliability of an electronic beam scanning, a new fast beamforming algorithm based on simultaneous perturbation stochastic approximation (SPSA) is proposed. It estimates the gradient of the received power simply relative to the phase difference between two adjacent phase shifters, for the difference remains the same in a uniform array. All phase shifters are updated simultaneously according to the gradient. In contrast with presented electronic beamforming that is generally used the elevation scan, the improved algorithm is successfully extended to the two-dimensional beam scan.On the improved algorithms both in step tracking and electronic beam scan, a large number of simulation experiments are conducted verifying the good performance obtained. Besides, the paper discusses the combination of step tracking and beamforming in detail, and makes lots of experiments as well to validate its availability. It makes the whole tracking process a right thing.