To achieve stable and reliable satellite communications, the earth station antenna must be accurately aimed at the distant satellite. The process of satellite pointing is a process of continuous searching and approaching, and its goal is to make the center of the antenna beam accurately point to the satellite, so as to obtain the maximum signal reception and transmission efficiency.
The satellite alignment of earth station antennas is the key to ensuring the stability of satellite communication links. Currently, the commonly used alignment modes include the following five:
- Beacon tracking
- Carrier tracking
- Reference satellite tracking
- Program tracking
- Manual tracking
This article will focus on one of the common and efficient automatic satellite tracking methods – beacon tracking.
In previous blogs, we showed another three tacking methods including Program Tracking, TLE Tracking, and Vector Tracking in details as well.
- Introduction to Beacon Tracking
Beacon tracking is the most commonly used and most reliable automatic satellite tracking method for satellite communication terminals. The satellite will continuously transmit a dedicated beacon signal in the downlink, which is usually a narrow-band, high-power continuous wave signal with a fixed frequency and polarization.
The beacon parameters of each satellite are provided by the satellite operator and can be found on the relevant website. The following are examples of beacon parameters of some high-orbit satellites under China Satcom:
Satellite beacon
Taking ChinaSat 10 as an example, there are two beacon signals in the Ku band:
- Frequency: 12745 MHz, horizontal polarization;
- Frequency: 12741 MHz, vertical polarization;
- Advantages of Beacon Tracking
The beacon signal is independently transmitted by the satellite and has nothing to do with the user’s business data. Even if the business is interrupted, the beacon signal still exists and the antenna can still keep tracking the satellite. This gives beacon tracking the following advantages:
- High reliability: not affected by user data interruption;
- Strong stability: can always be used for star alignment;
- High precision: precise control is achieved through AGC voltage feedback.
I’m sure you’re familiar with the principles of telemetry tracking antennas. They have multiple feeds and employ mono-pulse tracking technology. The antenna feeds generate sum and difference beams. The sum beam is used to receive signals, while the difference beam is used to detect deviations in the antenna’s pointing direction. This tracking method offers high accuracy, fast response, and strong anti-interference capabilities. However, its drawbacks are significant: high cost and complex equipment.
In actual applications, considering the cost and volume limitations, most satellite communication antennas use a single feed and beacon receiver AGC voltage feedback method for beacon tracking.
- Composition and workflow of beacon tracking system
3.1 Beacon tracking system connection structure
A beacon tracking system typically includes the following components:
- Antenna;
- LNB (Low Noise Converter);
- Beacon receiver;
- Antenna Controller (ACU);
Take Anesky 7.3m receive only antenna as example, we had done factory accepeance for 1 set of 7.3m antenna last year. The connection is shown in the following figure:
Beacon tracking connection
3.2 Basic process of beacon tracking
3.2.1. Beacon signal reception
The satellite continuously transmits beacon signals, which are received by the ground antenna and sent to the beacon receiver.
3.2.2. AGC circuit operation
The AGC (Automatic Gain Control) circuit inside the beacon receiver will automatically adjust the gain according to the strength of the received beacon signal to keep the amplitude of the output signal stable within a certain range. The stronger the signal, the smaller the AGC gain and the higher the output AGC voltage; the weaker the signal, the larger the AGC gain and the smaller the output AGC voltage.
Input power and beacon output
In the figure, the AGC voltage output by the satellite signal receiver is proportional to the power of the satellite signal, showing a linear relationship. The figure below shows the test results of a certain model of satellite signal receiver, where the signal power unit is dBm and the AGC unit is voltage V.
.
There is a stable linear relationship between the AGC voltage and the input signal power, and this characteristic is the core basis of beacon tracking.
3.2.3. Antenna scanning and signal detection
The antenna controller ACU drives the antenna to scan a small range in the azimuth and elevation directions and records the AGC voltage values at different angles.
- Parabolic antennas usually use conical scanning;
- Phased array antennas often use stepped scanning.
3.2.4. Peak tracking and alignment
During the scanning process, the ACU will record the AGC voltage values under different pointing directions. The ACU will look for the maximum value of the AGC voltage and assume that this point corresponds to the position where the antenna beam is pointed at the satellite. The ACU will then adjust the antenna to this angle and continue to make fine adjustments near it to maintain the satellite pointing state.
- Key parameters for beacon tracking
The effectiveness of beacon tracking depends on several key parameters:
- Beacon frequency and polarization: need to match satellite parameters;
- Signal capture range: determines the frequency range of signal detection;
- Processing delay : generally around 2ms, affecting response speed;
- Amplitude stability: reflects the stability of the AGC output, usually within ±0.25 dB;
- Refresh cycle: determines the tracking frequency and real-time performance;
The following table shows the basic parameter indicators of a typical beacon receiver:
| Parameter | Range | Notes | |
| Beacon
type |
Frequency | 950MHz ~ 2200MHz | |
| Input power | -95dBm ~ -20dBm | ||
| Capture bandwidth | ± 50KHz~ ± 245KHz | Stepin 1kHz | |
| Operation threshold | CN0 ≤ 42dBc/Hz | ||
Basic parameter indicators of beacon receiver
Where beacon frequency = satellite transmission frequency – LNB local oscillator frequency. For example, if you use an LNB with a local oscillator frequency of 11300 MHz to receive the 12745 MHz beacon of ChinaSat 10, the frequency should be set to 12745 – 11300 = 1445 MHz.
Since the beacon signal is a continuous wave without modulation, the energy is highly concentrated in a very narrow bandwidth. The bandwidth of a typical beacon receiver is usually on the order of tens of kHz. The extremely narrow bandwidth can suppress noise and interference to the maximum extent, significantly improve the signal-to-noise ratio (SNR) of the beacon signal, and facilitate accurate tracking.
The processing delay represents the response speed of the beacon receiver, and the processing delay is generally around 2ms;
Amplitude stability represents output stability, that is, the fluctuation range of the output AGC voltage when the input beacon signal power remains unchanged. Generally speaking, the amplitude stability of the beacon receiver can reach within ±0.25dB.
- Digital AGC signal processing
In order to simplify the design of the ACU and reduce its demand for external analog signal processing, the beacon receiver usually has its own ADC sampling circuit to convert the analog AGC voltage signal into a digital AGC voltage, and then transmit the digitized AGC voltage to the antenna controller ACU through the asynchronous serial port.
This design improves the system’s integration and reliability.
Digital AGC beacon reception
The beacon tracking method based on AGC voltage has become one of the most mainstream satellite tracking methods in satellite communication terminals due to its high cost-effectiveness, stable performance and easy implementation .
This beacon tracking method is widely used in small or medium-sized VSAT terminals, airborne/vehicle-mounted/ship-mounted/portable stations and other scenarios.
Antesky Science Technology Inc. was built in 1985, we’re mainly engaged in the design and manufacture of satellite communication large satellite dish,VSAT antenna,TVRO antenna, Portable flyaway antenna and relevant control and tracking system. We have a selected range of antenna in the frequency band, such as C-band, Ku-band, X-band, L-band, S-band, Ka-band, DBS-band.
If you are looking for any other satellite communication dish or related accessories, please send Antesky an inquiry via sales@antesky.com. Thanks!
