Adjustment of Satellite Communication Antenna Polarization Angle

Adjustment of Satellite Communication Antenna Polarization Angle: Linear Polarization and Circular Polarization

How to Adjust Horizontal/Vertical Polarization Angles

Adjustment Method for Linear-Polarization Signals: Ground Fixed Stations and SOTM Terminals

For linear-polarized signals, technicians typically adjust the polarization angle after completing azimuth and elevation alignment. Once the antenna is accurately pointed, the polarization adjustment can begin.
First, based on the satellite's orbital position and the geographic coordinates of the ground antenna, the azimuth, elevation, and polarization angle are calculated. After obtaining the required polarization angle, the technician rotates the antenna feed€”most commonly by rotating the LNB or the feed assembly€”to ensure that the antenna's receive/transmit polarization is properly aligned with the satellite's incoming signal.

This rotation aligns the ground antenna's horizontal or vertical polarization with the satellite's polarization orientation, minimizing cross-polarization interference and maximizing link performance.

If the LNB bracket includes a polarization scale, the technician can simply rotate the LNB to the calculated theoretical polarization angle indicated on the scale.
In addition, many modern fixed ground stations and SOTM antennas use automatic satellite acquisition. The antenna control unit (ACU) drives a motor to automatically rotate the feed (LNB) to the required theoretical polarization angle.

There is also a manual polarization adjustment method for rotating the antenna feed (LNB). For example:
Suppose a satellite transmits a horizontal-polarization signal at 12250.2 MHz and a vertical-polarization signal at 12250 MHz, and the ground antenna needs to align to the horizontal-polarization signal.
Horizontal and vertical polarizations are orthogonal to each other in space.
A well-designed antenna optimized for horizontal polarization has extremely low sensitivity to the vertical-polarized wave. When the antenna is perfectly aligned to horizontal polarization, its response to the vertical-polarized signal is theoretically zero.
Therefore, the goal of polarization adjustment is to:
Maximize the received power of the desired signal (12250.2 MHz, horizontal polarization).
Minimize the power of the undesired orthogonal signal (12250 MHz, vertical polarization)€”ideally making it disappear on the spectrum analyzer.
When these conditions are met, the antenna is perfectly aligned with the horizontal-polarization signal while achieving maximum suppression of the orthogonal vertical-polarization signal.

Manual Polarization Adjustment Procedure for Ground Station Antennasï¼š

· Preparation and Calculation: Input the local location and satellite longitude, and calculate the theoretical polarization angle.
· Equipment Connection and Setup: Properly connect the spectrum analyzer to the LNB output, and configure it to clearly observe the target signal as well as potential interference signals.
· Azimuth and Elevation Adjustment: Adjust the antenna's azimuth and elevation angles so that the antenna points toward the satellite.
· Polarization Angle Adjustment: Rotate the antenna feed (LNB) to the theoretical polarization angle to initially acquire the signal.
· Fine-Tuning Optimization (Core Loop): This is a precise and iterative process. By slightly rotating the LNB and monitoring the spectrum analyzer in real time, maximize the target signal power while minimizing the interference signal power to find the optimal peak point.

During manual polarization adjustment, continuously monitor the power of the horizontally polarized signal (desired signal) and the orthogonal vertically polarized signal (interference), and calculate the cross-polarization discrimination (XPD).

How is the antenna polarization angle adjusted for circularly polarized signals?

In fact, circularly polarized antennas do not require polarization angle adjustment; only the polarization state needs to be selected. Taking a Ka-band circularly polarized satellite communication portable station as an example:
The antenna of the portable station has only two polarization states: 0° and 180°. The feed (OMT or waveguide switch) is designed to switch between RHCP (right-hand circular polarization) and LHCP (left-hand circular polarization) operation modes. This is a simple two-option configuration rather than a finely adjustable angle.

During satellite acquisition, the user simply switches the feed between 0° and 180° manually; the antenna's polarization does not require motorized servo adjustment. It is important to note that if the circular polarization sense is incorrect (for example, using an LHCP antenna to receive an RHCP signal), signal loss can reach 25€“30€¯dB, causing the communication link to fail completely. During commissioning, only one of the two states (0° or 180°) can establish a valid connection, while the other will result in almost no signal.

ðŸ“¡ Why is the Antesky Flyaway Antenna Easier to Align Polarization in Engineering Applications?

Antesky 1.0-2.4 Meter Flyaway antenna is engineered with practical field deployment requirements in mind, making polarization alignment significantly more efficient:

€¢ Precise Feed Polarization Scale

Antesky 1.0-2.4 Meter Flyaway antenna: The linear-polarized feed is equipped with a ±90° mechanical scale, perfectly matching the engineering workflow described in this article€”allowing technicians to €œcoarsely set the polarization angle according to the theoretical value.€

€¢ Optional Motorized Polarization Adjustment (for Fixed or Transportable Stations)

For users who need quicker setup, remote operation, or reliable repeatability (such as government, broadcast, emergency communications, or fixed ground stations), Antesky antenna can be configured with:
A polarization adjustment motor
Controller-based automatic positioning to the specified polarization angle

€¢ 0°/180° Quick-Switch Circular Polarization Feed
For circular-polarized configurations, the antenna uses a feed design that supports instant switching between RHCP and LHCP.

€¢ High Cross-Polarization Isolation
The feed system is optimized to provide excellent cross-polarization isolation, ensuring strong co-pol performance while suppressing unwanted cross-pol signals€”matching the XPD requirements outlined earlier in the article.

Conclusion

This article systematically elaborates on the theoretical foundations and practical methods for adjusting the polarization angle of satellite communication antennas. By analyzing the characteristics of linear and circular polarization in different application scenarios, we recognize the critical impact of polarization alignment on communication quality. Linear polarization systems require precise polarization angle adjustment to ensure maximum signal reception and interference suppression, whereas circular polarization systems simplify the installation process through rotational direction matching.

From personal experience I would add:

Aligning linear polarisation with only the wanted signal being observed and measured

If you are trying to align linear polarisation and only have the wanted signal being measured it is definitely not possible to align the polarisation with sufficent accuracy by adjusting for maximum signal strength, as the maximum is very wide.

One possibility is to misalign the polarisation by a considerable amount till a significantly lower level, but accurately recordable level, is observed. Record the this level accurately and also mark the angle on the feed throat. Then repeat the process on the other side of the maximum. Then carefully rotate the feed to a final position half way between the two marked positions. At this point, for a receive only antenna you are finished. If it is transmit antenna you can now contact the network operations center (NOC) and ask for permission to transmit. They will ask you to transmit a low level CW (unmodulated) carrier and they will observe what cross-pol interference you are causing. Hopefully this will be acceptably very low but they may ask for small adjustments for you to make. If they do ask you to make manual adjustments do it under phone contact with the NOC and be very patient and be prepared to wait for the NOC to make accurate measurements, which each may take several seconds to stabilise and record.

Read here About co-polar and cross-polar linear feed assemblies

If you have a spectrum analyser and can observe multiple carriers over say 70 - 200 MHz you can try boldly rotating the feed and watching for cross polar carrier levels (typically visible in-between your wanted polarisation carriers), which will rapidly drop to zero as you go through the sharp cross-polar null. This is not always the case if there is little or no traffic on the opposite polarisation.

If you have a spectrum analyser and can observe the satellite beacons then prepare a note of the status of the various beacons and their frequencies. From this you can determine what polarisation you are using and also verify the satellite identily!. For example, a satellite might transmit one circular polarisation beacon on one frequency and one linear polarisation beacon on another frequency.
Note that if you are looking at a circular polarisation satellite beacon and you have a linear polarisation receive system, then your measured level will be about same level, all the way round, as you adjust your linear polarisation rotation.

Never transmit until you are certain of the satellite identity, your polarisation is approximately right and you are in phone contact with the NOC for permission so they can see your signal come up in the right place. If in any doubt or loss of phone link, turn off your transmit right away.

Regarding circular polarisation

Read here How to set up circular polarisation

Feed systems vary. Many types comprise a linear polarisation OMT that combines two rectangular waveguides one TX, the other RX) into a single short circular or square cross-section waveguide. Between this and the feed horn is a polariser tube which contains a row of slots, pins or similar devices. This line is set at 45 deg to the linear polaristions of the OMT. Depending on which way (+45 deg or -45 deg) the OMT to polariser junction is set makes the feed operate clockwise transmit or anticlockwise transimt and the opposite on receive.

Which circular polarisation you are set to will be confusing. Note that one way will work perfectly and the other way not at all. So if you can't find the wanted signal at all then try the opposite polarisation. Confusion is common due to the circular polarisation changing each time the signal is reflected (once for front fed antennas, twice for Cassegrain or Gregorian geometries. Documentation is often not clear about the +45 or -45 deg and scales may be marked 0 - 360 or +/-180.
Don't worry, just try one way is if no good try the other. Once it works document or photograph carefully so you can repeat at other sites.