What Are Methods for Antenna Tracking System?

Generally there are two modes for satellite tracking antenna including programming tracking and automatic tracking. Programming tracking is to drive tracking system based on the predicted satellite orbit information and antenna beam pointing information. Automatic tracking means that the earth station drives the tracking system to automatically aim the antenna at the satellite according to the beacon signal transmitted by the satellite. Because too many factors affect the satellite position, it is impossible to predict the satellite orbit for a long time, so most earth stations currently use automatic tracking methods. According to the tracking principle, automatic tracking can be divided into three types like step tracking, cone scan tracking and mono-pulse tracking. As you know that we are specializing in ground station antennas, so here we will not to introduce cone scan tracking which is for on the move antenna.

(a) Manual/Programme Tracking

(b) Mono–Pulse or Simultaneous Tracking

(c) Step Tracking

(d) Cone Scan Tracking

The first one needs operator intervention when tracking. The latter three techniques can be classified under the general heading of automatic tracking or auto tracking. These schemes represent closed-loop tracking systems and once satellite acquisition has been established, tracking continues with no operator intervention. All auto tracking schemes rely on the reception of a continuous beacon signal transmitted by the satellite. The received beacon signal is used to drive pointing error information which supplies control signals to the antenna drive servo mechanisms. The antenna is driven so as to attempt to minimise the pointing error and hence null the tracking error.

(a) Manual and programme steering of antenna tracking system

In the absence of an autotracking system, antenna pointing is either undertaken manually or using programmed steering. Manual tracking involves an operator controlling the movement of the antenna until the received signal strength is maximised. Programme steering uses prepared data describing the path of the satellite, seen from the earth station as a function of time. This information is fed to the antenna positioning servo system which points the antenna in the appropriate direction. Please click this page for learning more about programming tracking antenna from 1.8m to 13.0m with X-Y pedestal.

(b) Mono-Pulse or Simultaneous Tracking of antenna tracking system

Monopulse tracking is an advanced tracking system, which can determine the direction of the antenna beam deviating from the satellite within a pulse interval. When the antenna beam is aligned with the satellite, the antenna can only receive the “sum beam” signal, and the two “difference beam” signal outputs are zero; when the antenna beam deviates from the satellite, the monopulse tracking system can be divided into amplitude monopulse tracking system and phase monopulse tracking system. The amplitude monopulse tracking antenna consists of four feeds and a parabolic reflector. The four feeds deviate from the focus of the parabola and are arranged symmetrically, which will produce four independent beams deviating from the parabolic axis of symmetry. The phase monopulse antenna consists of four feeds and four reflectors. At this time, the four feeds will generate four independent beams parallel to the parabolic axis of symmetry. After the four beam amplitudes or phases are compared, a control signal can be generated to drive the antenna to automatically aim at the satellite. Antesly can provide antenna with mono-pulse tracking , please click this for learning further.

Diagram of mono-pulse tracking system

Advantage of mono-pulse tracking system

Mono-pulse tracking is a closed-loop system, which can obtain a complete angle error signal from each received pulse, and has the advantages of good real-time performance and high tracking accuracy. The tracking speed and tracking accuracy of the monopulse system are several orders of magnitude higher than those of the stepping system and the conical scanning system. Please click this page for learning more about mono-pulse tracking antenna.

Disadvantage of mono-pulse tracking system

Single pulse tracking requires antenna feed to have tracking fuzzy combiner (primary mode or high-order mode), which is complicated in design and high in cost. And the antenna will always be in motion, which increases the wear and tear of machinery and motors.

(c) Step Tracking of antenna tracking system

The principle of step tracking is shown in below. Step tracking refers to the constant adjustment of the antenna pointing to the increasing direction of the received signal at a fixed step. Step tracking is also called extreme value tracking. It is a step by step control of the antenna to rotate within the azimuth range and the elevation range, so that the antenna is gradually aligned with the satellite, and the system does not enter until the beacon signal received by the antenna reaches the maximum value, then the antenna will be in rest state. The control system always in rest or track alternately. In step tracking, the movement of the antenna can be divided into search step and adjustment step. The function of the search step is to determine the direction of antenna rotation. The adjustment step is to rotate the antenna one step in this direction. After searching the step action, the whole tracking system starts to work. It usually takes several search steps to determine the direction in which the antenna should rotate. After that, the antenna returns to its original position; then it rotates one step in the direction determined by the search step. This last step is called the adjustment step. The main difference between the adjustment step and the search step is that after the adjustment step, the antenna will not return to its original position, while the search step is different. The computer judges the increase or decrease of the receiving level within an appropriate integration time. If the receiving level increases, the antenna continues to rotate a small angle in the original direction; if the receiving level decreases, the antenna rotates in the opposite direction. The elevation direction and the azimuth direction are repeated alternately, so that the antenna beam can be gradually aligned with the satellite.

Diagram of step tracking system

Advantage of step tracking

The principle and equipment of step tracking are very simple with low in price, and can be easily connected to a computer, which can simplify the feed network. Step tracking can use general beacon receivers or digital receivers instead of complex mono-pulse tracking receivers. With the improvement of satellite position accuracy and the rapid development of microcomputers, more and more fixed ground stations tend to use step tracking.

Disadvantage of step tracking

The antenna beam controlled by step tracking cannot stay in the direction aimed at the satellite, but constantly swings around the direction, so the tracking accuracy is low. And because the antenna repeatedly rotates alternately on the elevation and the azimuth to realize the antenna beam is gradually aligned with the satellite, the tracking speed is slow.

Summary of satellite tracking systems

Tracking category	Remark	Performance	Application
Manual	Non-autotracking; Simple; Require operator	Tracking accuracy depends on operator -generally low	Many stations can turn to manual if other tracking methods fail
Programming	Non-autotracking; Simplistic with modern technology; Requires operator ; accuracy depends on orbit prediction	Tracking accuracy approaching 0.01° possible	Often regarded as back-up in case primary tracking system fails
Mono-pulse tracking	Autotracking Tracking information obtained in a single time frame;. 4 or 8 channel coherent receiver required; Expensive	Good tracking accuracy; typically 0.005°; Operational SNR (signal-noise ratio) -15 dB; Fast dynamic response	Widely used in many of larger earth stations; also shipborne terminals, sat-to-sat communication
Step-in tracking	Autotracking ; Sequential amplitude sensing system; Sensitive to AM interference; Simple low cost system ; single channel receiver;	Tracking accuracy of 0.01 ° have been obtained, typically <0.1°; Operational SNR (signal-noise ratio): -30-45 dB; Slow dynamic response	Widespread where lower accuracy acceptable and cost important; Many of the smaller earth stations, shipborne terminals

We believe you will have a learning about tracking modes like manual, programming tracking, step tracking, mono-pause tracking from above introduction. And we Antesky can provide antennas with such tracking modes. Please contact with us for your requirements via sales@antesky.com