News Column

Patent Issued for Satellite Transceiver

August 13, 2014



By a News Reporter-Staff News Editor at Journal of Engineering -- From Alexandria, Virginia, VerticalNews journalists report that a patent by the inventor Grotz, Joel (Betzdorf, LU), filed on March 19, 2009, was published online on July 29, 2014.

The patent's assignee for patent number 8792820 is SES Astra S.A. (Betzdorf, LU).

News editors obtained the following quote from the background information supplied by the inventors: "Satellite communication technology includes the transmission of radiofrequency signals from a satellite directly to antennas arranged at end-user premises. Such type of transmission is sometimes referred to as direct-to-home (DTH) satellite transmission, and usually implies the use of a satellite dish reflector with a low noise block (LNB) receiver. The satellite may for instance be a geostationary satellite orbiting the earth. Direct-to-home (DTH) satellite transmission offers specific advantages while involving specific technical requirements and challenges.

"The use of direct-to-home (DTH) satellite communications offers the following advantages. No terrestrial channel, such as a cable or wire, is required to provide communication to the end-user premises so that broadcast transmission can take place to virtually every place on earth. The use of high frequency signals in a line-of-sight (LOS) manner may provide high bandwidth and transmission rate communication.

"Direct-to-home (DTH) satellite communications also involve specific technical requirements and challenges. The receiving antenna's reflector must be as small as possible, to minimise the visual and aesthetic impact of the reflector without impairing quality of reception. Therefore, the receiving apparatus interacting with the reflector must be as efficient as possible, so as not to affect the signal quality. The receiver should also be as simple as possible to reduce its cost. At the same time, the setting up and adjustment of the orientation of the receiving antenna at the end-user side should be as easy as possible and the receiver should have a high tolerance to pointing errors.

"Radiofrequency signals broadcasted from satellites are often linearly polarized, for reuse of frequency bandwidth. That is, two orthogonally polarized signals on the same bandwidth are transmitted from the satellite. Misalignment of the polarization reception elements of the antenna and the polarization of the incoming signal affects the signal quality and is therefore undesirable.

"One way to avoid misalignment of the polarization reception elements of the antenna with respect to the polarization of the incoming signal is by mechanically rotating, i.e. tilting, the receiver to align the receiving elements with the polarization of the incoming signal. This usually requires either delicate manual adjustment procedures or relatively expensive electromechanical means for rotating the receiver. Such electromechanical steering means, which should usually be adapted for outdoor environments, i.e. arranged by the satellite antenna, may be subject to mechanical failures. Another way to cope with a misalignment of the polarization reception elements and the polarization components of the incoming signal is by using electronic means.

"U.S. Pat. No. 5,568,158 discloses an electronically adaptable polarization antenna feed apparatus. An electronic circuit is adapted to the apparatus for reception of polarized radiofrequency (RF) signals. Through the use of a combiner and variable gain amplifiers or attenuators, the signals from two orthogonally polarized signal paths are combined such that a maximum signal-to-noise ratio is obtained for a desired polarization.

"There is a constant need for improving such apparatus in view of the above-mentioned technical requirements and challenges, including, but not limited to, antenna pointing accuracy and polarization alignment."

As a supplement to the background information on this patent, VerticalNews correspondents also obtained the inventor's summary information for this patent: "The present invention aims at meeting or at least partially meeting the above-mentioned needs.

"According to the invention, a transceiver is configured for receiving linearly polarized signals from at least two geostationary satellites. The transceiver includes at least a first waveguide and a second waveguide configured to respectively form with a reflector two beam patterns with a maximum gain in angular directions different from each other. At one end of each one of the at least first waveguide and second waveguide, the transceiver includes two transceiving elements, i.e. transmitting and/or receiving elements, orthogonal to each other configured for respectively receiving, and/or transmitting, two orthogonal polarization components of the signals. The transceiver thus includes at least four transceiving elements configured for receiving, and/or transmitting, at least four corresponding signal components. The transceiver also includes at least four converting units each configured for converting, by using a common local oscillator, one of the at least four signal components to an intermediate frequency. The at least four converting units thus output at least four corresponding converted signal components. Furthermore, the transceiver includes a combining unit configured for linearly combining the at least four converted signal components, based on weights representing phase shifting and/or amplification of signal components. The transceiver includes a weight input unit configured for receiving the weights.

"The transceiver of the invention is suitable for receiving signals bearing the same content and originating from at least two different geostationary satellites. The signals are constructively combined to improve the signal quality. This enables to reduce the size of the receiving antenna's reflector, for instance the diameter of the satellite dish. As an equally suitable application, with no need to adapt or change the hardware equipment, such transceiver may also be used for receiving signals bearing different content and respectively originating from at least two different geostationary satellites.

"In addition, the same multi-waveguide transceiver of the invention may be used at different geographical areas on earth without requiring hardware modification. This enables to manufacture identical transceivers for use in different geographical areas. This particular advantage will be explained in more details below with reference to the Figures, but may be summarized as follows.

"The orthogonal polarization components of the signals transmitted from a satellite, such as a geostationary satellite, are projected on the earth with different angular orientations depending on the location on earth. Besides, let us consider two satellites positioned at different locations above the earth, such as at different locations on the geostationary orbit, and let us consider two different locations on earth from which the two satellites are viewed, namely a first location on earth and a second location on earth. The change from the first location on earth to the second location on earth of the angular orientation of the projected polarized components of the signals transmitted from each one of the satellites differs from each other.

"This means that a transceiver which would have two pairs of orthogonal receiving elements oriented to match, when located in one geographical area on earth, the orientation of the polarization components of the incoming signals, could not be simply tilted so as to match the orientation of the polarization components of the incoming signals in another geographical area on earth. Such a transceiver would have to be adjusted, by individually tilting each one of their pairs of receiving elements (this will be further explained with reference to the drawings, especially FIGS. 2 and 3).

"The transceiver of the invention provides a generic multi-waveguide transceiver for receiving linearly polarized satellite communication from two different satellites, wherein the transceiver need not be tailored to a particular geographical reception area.

"The weight-based combination in the transceiver of the invention does not only enable polarization matching to maximize the signal quality for reception by each waveguide or feed horn, but also enables additional fine-tuning of the directivity of the global beam formed by the plurality of waveguides. The possibility to adjust the directivity of the transceiver in a global manner by adjusting the weights used for combining the signal components enables to mitigate interference from other signal sources. It also enables to mitigate the effects of destructive interference in certain angular directions, upon reception, between the signals coming from the geostationary satellites themselves.

"The transceiver of the invention also enables adjustment of the polarization orientation to avoid potential cross polarization interference over the overall beam formed by the plurality of waveguides.

"In other words, the signal quality may be optimized both by polarization selection and directivity adjustment.

"In the transceiver of the invention, linearly combining the signals after downconverting them into an intermediate frequency allows the use in the combining unit of lower-frequency components, which are cheaper and less prone to affect the signal quality. The use of the same local oscillator for downconverting the signal components allows coherent combination in the combining unit. The complex weightings thus enable amplitude adjustment and phase shifting in a coherent manner, to provide constructive combination of the signal components.

"A further advantage of the invention is that different simultaneous satellite position constellations may be addressed with the same transceiver.

"According to one embodiment, the first waveguide, the second waveguide and the associated transceiving elements of the transceiver are included in a single housing.

"Integrating the two waveguides and the associated transceiving elements within a single housing enables to provide a robust transceiver wherein the first waveguide, the second waveguide and the associated transceiving elements are fixedly arranged with respect to each other. Since the use of a weight-based combining unit enables to compensate for the fixed positional relationship between the two pairs of transceiving elements, without any significant reduction of the signal quality, the same transceiver according to this embodiment may be used in different geographical areas. This is especially advantageous for use in different geographical areas wherein the projection of the polarization components of the signals transmitted from the two satellites are different for each satellite, and wherein the amount of angular variation of the projection of the polarization components from one location to the other is different depending on the considered satellite.

"This embodiment also addresses the following problem. Polarization alignment is a delicate problem for multiple satellite reception using a single integrated reception unit (a monoblock unit). Without the invention, the configuration of the single integrated unit should be adjusted at the time of design and manufacturing with a correct relative polarization orientation and polarization orientation difference corresponding to the satellites from which signals are to be received. In order to meet this requirement while still being able to manufacture a single integrated unit for use in a large geographical area (for economies of scale), an approach would be to sacrifice the adjustment accuracy, which would be undesirable. The embodiment of the invention does not require such undesirable adjustment.

"Besides, the mechanical, fixed adjustment of the polarization orientation of an antenna is prone to installation errors. It also requires mechanical or electromechanical means to enable to conveniently carry out such an adjustment, adding to the equipment costs needed for antenna mounting. This problem exists in particular for waveguide horn-based reception antennas which may require a tilting mechanism for accurate polarization adjustment.

"In one embodiment, the weight input unit is configured for receiving the weights from an external unit. The external unit may be a set-top box.

"When setting up the satellite transceiver at an end-user home for instance, the user may be prompted to enter in, i.e. to provide to, the set-top box, directly or through a computer for instance, information regarding its location on earth. The information regarding the location may include the latitude or the longitude. Alternatively, or in addition, the location on earth may be derived from the address of the end user or the like. The address may be provided by the user at the time of setting up the transceiver.

"Based on the information indicating the location where the transceiver is set up, the set-top box may then provide, to the weight input unit of the transceiver, weights adapted to optimally receive linearly polarized signals from two or more given geostationary satellites by its plurality of pairs of receiving elements.

"The weights may also be automatically transmitted from an external unit such as a set-top box, based on information gathered through a satellite navigation system providing geospatial positioning information, such as the global positioning system (GPS), or the Galileo positioning system scheduled to be operational in the future.

"In one embodiment, the transceiver is configured for updating the weights after receiving them from the external unit, which may be a set-top box. This enables adjustment of the weights to optimally combine the polarization components transmitted from the satellite, to cope with potential positional errors when setting up the transceiver and the associated reflector. The fine-tuning also enables to adjust the weights to cope with interfering signals from other sources, or interfering obstacles in the line of sight (LOS) to search for the best combination, i.e. the combination of weights leading to the signal having the highest quality.

"In one embodiment, the first waveguide and the second waveguide have transceiving (receiving and/or transmitting) beam patterns with a maximum gain in angular directions separated by between 1, 5 and 10 degrees from each other. This enables to receive (or transmit) signals from two adjacent satellites on the geostationary orbit, which are separated by between 1, 5 and 10 degrees from each other with respect to the earth. Receiving signals from such satellites is advantageous in that the phase shift between the signals received from the two satellites may be relatively small (when receiving signals bearing the same content from the satellites).

"The invention also relates to a transceiver configured for transmitting linearly polarized signals to at least two geostationary satellites. The transceiver includes at least a first waveguide and a second waveguide configured to respectively form with a reflector two transmitting beam patterns with a maximum gain in angular directions different from each other. The transceiver also includes at one end of each one of the at least first waveguide and second waveguide, two transmitting elements orthogonal to each other configured for respectively transmitting two orthogonal polarization signal components, and thus forming at least four transmitting elements configured for transmitting at least four corresponding signal components. The transceiver further includes at least four converting units configured to output together the at least four corresponding signal components, by each converting into a carrier frequency, using a common local oscillator, one of at least four signal components to be converted. The transceiver yet further includes a splitting unit configured for outputting the at least four signal components to be converted, based on weights representing phase shifting and/or amplification. The transceiver also includes a weight input unit configured for receiving the weights.

"The invention also relates to the use of the above transceiver for receiving and/or sending linearly polarized signals from and/or to at least two geostationary satellites.

"The invention also relates to a computer program configured, when executed on the above transceiver, to cause instructions to be carried out to update the weights after receiving them from an external unit.

"The invention also relates to a set-top box, or a unit, configured for sending weights to and for use by a transceiver as described above.

"In one embodiment, the invention is applied to very small aperture terminals (VSAT) systems. VSAT systems are used for narrowband or broadband data communications with satellites on the geostationary orbit, including, but not limited to, two-way satellite real-time internet communication, video conferencing, etc.

"Polarization adjustment and alignment of VSAT terminals, earth station antennas, is a delicate, time-consuming and therefore expensive operation. The operation typically requires involving trained professionals upon installation of the terminals to ensure that polarization, azimuth and elevation of the antenna are accurately adjusted with respect to the incoming satellite signals. Moreover, after installation and throughout the lifespan of the terminals, subsequent verification and adjustment of the antenna alignment are usually required to compensate for movements caused by strong winds, vibrations, long-term deformations, or the like. For these verifications and adjustments, trained professionals are generally also involved to maintain the installation quality. The interferences resulting from badly pointed antennas and from cross-polarization is a technical problem, which the invention, according to one embodiment, helps to address."

For additional information on this patent, see: Grotz, Joel. Satellite Transceiver. U.S. Patent Number 8792820, filed March 19, 2009, and published online on July 29, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=8792820.PN.&OS=PN/8792820RS=PN/8792820

Keywords for this news article include: SES Astra S.A.

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Source: Journal of Engineering


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