Polarization controller, transmitter, computer-implemented method, computer program and non-volatile data carrier

Abstract

Based on a source signal (S), a polarization controller (110) controls a transmitter (100) to emit a modulated signal wave (RS) having a linear polarization of a selected orientation (Φ). The modulated signal wave (RS) is based on first and second modulated signals (SHAB, SVAB) with first and second polarizations respectively that have a relative phase relationship chosen such that the first and second modulated signals (SHAB, SVAB) radiated through respective orthogonal ports of a dual polarized antenna element (AE) of an antenna (160) are equivalent to the modulated signal wave (RS). To attain high power efficiency, the polarization controller (110) controls a respective bias level (B1, B2) in a power amplifying unit (140) amplifying the first and second modulated signals (SHAB, SVAB) such that the respective bias levels for the first and second modulated signals (SHAB, SVAB) depend on the selected orientation (Φ) of the linear polarization of the modulated signal wave (RS).

Description

[0001] Polarization Controller, Transmitter, Computer-Implemented Method, Computer Program and Non-Volatile Data Carrier

[0002] TECHNICAL FIELD

[0003] The invention relates generally to communication of linearly polarized radio signals. In particular, the present invention concerns a polarization controller according to the preamble of claim 1 and a transmitter including such a polarization controller. The invention also encompasses a computer-implemented method for controlling the proposed polarization controller, as well as a corresponding computer program and a storage medium containing such a computer program.

[0004] BACKGROUND

[0005] The polarization of an antenna describes the orientation of the electrical component of the electromagnetic fields in the far- field, or Fraunhofer, region from the antenna, where the electromagnetic field can be approximated locally as a plane wave. The electrical field can be described by a vector that is orthogonal to the propagation direction. To maximize the throughput and minimize the interference in a radio link between two points, which radio link employs polarized signal waves it is important to align the polarization of the two antennas to one another. A common solution to avoid the problem with polarization alignment is to use circular polarization, which is invariant to the roll off the antenna. However, some systems are designed for linear polarization, and here the polarization skew angle needs to be aligned between the antennas. Traditionally this is accomplished by rotating the entire antenna, or the antenna feed. However, alternatively, the electromagnetic field may be rotated by combining two orthogonal linear polarized waves.

[0006] In satellite communication systems the polarization of the radio link is determined in part by the satellites deployed and the regulatory filings for these satellites. The polarization is traditionally linear polarization for satellites operating in the Ku-band while circular polarization is most often used for satellites operating in X- and Ka-bands.

[0007] Traditionally Ku-band systems have been simple to manufacture and popular for broadcasting. Here, the polarization angle has been controlled by rotating the system, or the feed of the system, such that it aligns the polarization. This mechanical solution becomes impractical for smaller portable systems, especially for array antennas, where a mechanical rotation of the system, or the feed of the system, requires movement of relatively large components.

[0008] A more convenient solution is to have an aperture where the polarization orientation can be rotated by combining two antennas with orthogonal polarization by the means of a polarizer. The purpose of the polarizer is to excite each polarization of the antenna with the correct amplitude and phase to achieve the desired polarization when the two polarizations are combined. This can be achieved with passive waveguide components that separate the output from an amplifier, or signal source, into the two desired signals for the antennas. Such passive waveguide components usually include moving parts that must fulfil strict tolerance requirements, which renders them difficult to manufacture and increases the cost of the system. Figure 12 shows a block diagram of a transmitter with a passive polarizer 1220 that is controlled by a polarization control system 1210. The polarization control system 1210 is configured to set a desired polarization angle OCTR L with the aid of an electric motor 1212, which, in turn, is associated with an encoder 1215 feeding back a current polarizer angle a to the polarization control system 1210. The desired polarization angle OCTRL determines how orthogonal linear polarized signals S HA and SVA respectively from the polarizer 1220 are combined in an antenna 1260 that emits a signal wave at a particular polarization orientation. The linear polarized sig- nals S HA and SVA originate from a radio-frequency signal source 1205 that produces a source signal S, which is amplified in an amplifier 1240 to an amplified source signal SA, which, in turn is bandpass filtered in a filter 1230 to a bandpass limited signal SAF . The bandpass limited signal SAF is fed to a waveguide component, the polarizer 1220, that splits power to two output ports by rotating a septum 1225 in the assembly via a motor 1212. The power division between the two output ports of the polarizer 1220 is continuous and depends on the position of the septum 1225 set by the motor 1212. The relative phase between the two output ports of the polarizer 1220, which is either 0° or 180° likewise depends on the position of the septum 1225. A belt 1214 between the output shaft of the motor 1212 acts on a circular waveguide that contains the septum 1225 between the input and outputs of the polarizer 1220 to set a desired polarization angle OCTRL . The polarization control system 1210 may derive the desired polarization angle OCTRL from a positioning system 1270, which determines location data LD, e.g. based on a GPS receiver. Namely, a suitable orientation of the polarization typically depends on a direction relationship between the transmitter and the intended receiver, and the direction relationship, in turn, may be derived from the position and the direction of the transmitter.

[0009] A mechanical polarizer as shown in Figure 12 needs to have physical dimensions equivalent to several wavelengths, which for many frequency bands translates into relatively large sizes compared to the other components in a very-small-aperture terminal (VSAT), i.e. a two-way satellite ground station.

[0010] In the light of the above, it is desirable to replace the movingparts design with a completely electronic polarizer without any moving parts. Below follows same examples of such solutions.

[0011] US 6,181 ,920 shows a transmitter that provides a radio wave with selectable polarization. The transmitter includes antenna feeds that generate orthogonal radio waves having non-linear polarizations that corresponds to the selectable phase relationships of a first and a second modulating signals. A spatial combination of the non-linear radio waves to produce a linearly polarized radio wave that has an orientation corresponding to a selected phase relationship.

[0012] US 10,170,833 describes a transmitter or receiver that includes a phased array antenna system in which multiple characteristics of a transmitted or received beam can be controlled electronically. For example, in embodiments that include a transmitter, dual outputs of N signal modifiers can be connected to orthogonal inputs of N dual-orthogonally polarized antenna elements. Each signal modifier can modify the amplitude and phase of a communications signal in two parallel signal paths to produce two signal components each of which is an amplitude-modified / pha- se-shifted version of the communication signal. Multiple characteristics of the combined beam can be simultaneously controlled by setting the amplitude and / or phase-shift parameter values in the dual signal paths in the signal modifiers to combined values that individually affect each of the multiple characteristics of the combined beam.

[0013] JP 4 819 848 discloses a polarization control antenna and a calibration method for such an antenna. The polarization plane control antenna has: a distribution part which distributes input signals to two paths based on a specified polarization angle; a balance circuit which includes first and second quadrature hybrids connected to outputs of the distribution part; a polarization wave sharing antenna which transmits an output of the second quadrature hybrid with orthogonal polarization; first and second amplitude phase controllers which change the amplitude and phase of each signal that is converted by the first quadrature hybrid; a means for connecting to an output of the second quadrature hybrid and extracting calibration signals flowing in the output; a means for measuring the levels of the extracted calibration signals; and a controller which sets a polarization angle for the distribution part, and gain and phase coefficients for first and second amplitude phase parts.

[0014] US 10,971 ,815 reveals systems and methods of controlling signal polarization for an antenna system. The antenna system includes an ultrawide band or greater array of dual linear polarization elements. The antenna system also includes polarization synthesis networks. Each of the polarization synthesis networks is coupled to the first differential interface of the first element of a respective dual linear polarization element of the dual linear polarization elements and the second differential interface of the second element of the respective dual linear polarization element of the dual orthogonal linear polarization elements. Each of the polarization synthesis networks has a flat response for phase shift and amplitude over the ultrawide bandwidth.

[0015] US 2019 / 0221947 describes an apparatus that includes a phased array antenna panel and one or more dual-polarization beam former circuits mounted on the phased array antenna panel. The phased array antenna panel generally comprises a plurality of dual-polarization antenna elements. The plurality of dual-polarization antenna elements are generally arranged in one or more groups. Each dual-polarization beam former circuit may be coupled to a respective group of the dual-polarization antenna elements. Each dual-polarization beam former circuit generally comprises a plurality of transceiver channels. Each transceiver channel generally comprises a horizontal channel and a vertical channel. Each dual-polarization beam former circuit provides polarization rotation through bias current control in each of the vertical and horizontal channels.

[0016] In this design, the supply voltage to the transistor in the transceiver is fixed, while the current to the transistor may be adjusted. Such an adjustment alters the slope of the amplifier’s load line as well as the load being optimal for the circuit. Consequently, the current adjustment requires complex adaptations to the circuitry and it is complicated to apply the adjustment to an existing circuit. Thus, although solutions are known, as such, for controlling the orientation of an emitted linearly polarized signal wave, there is room for improvements, especially in terms of the overall efficiency.

[0017] SUMMARY

[0018] One object of the present invention is therefore to offer a solution that enables an energy-efficient transmission of modulated signal waves at a selected polarization orientation

[0019] Another object of the invention is to allow a cost-effective and volume-efficient design, for example suitable for inclusion in a VSAT or a terminal for ground-based communication.

[0020] According to one aspect of the invention, these objects are achieved by a polarization controller for controlling a signal generator to, based on at least one source signal, produce at least one pair of first and second modulated signals with first and second polarizations respectively and a relative phase relationship chosen, such that the at least one pair of first and second modulated signals radiated through respective orthogonal ports of at least one dual polarized antenna element of an antenna are equivalent to at least one respective modulated signal wave having a linear polarization of a selected orientation. Specifically, the polarization controller is configured to control a respective bias level in a power amplifying unit that amplify the first and second modulated signals such that the respective bias levels for each of the first and second modulated signals depend on the selected orientation of the linear polarization of the modulated signal wave.

[0021] This polarization controller is advantageous because, typically, the power amplifying unit is highly non-linear and the proposed polarization controller renders it possible to select a particular bias level that for a desired output power provides the best possible efficiency. As a result, the overall power consumption is Io- wered. The power consumption also becomes even and independent from the setting of the polarization orientation, which enables a low and even power usage.

[0022] The polarization controller may be configured to adjust the bias level in the power amplifying unit by adjusting a supply voltage to the power amplifying unit and thereby also altering the voltage to at least one transistor or amplifier module comprised in the power amplifying unit. For example, if the power amplifying unit contains a field effect transistor (FET), such an adjustment of the supply voltage to the power amplifying unit will result in an altered maximum drain-to-source voltage of the FET. Namely, the supply voltage determines the maximum voltage between the drain and the source of the transistor, or a power amplifier module that is based on FET technology. Depending on the type of amplification circuit used, the supply voltage to the power amplifying unit may or may not be identical to said maximum voltage. The amplifier module, in turn, may form part of a monolithic microwave integrated circuit (MMIC).

[0023] If the at least one transistor comprised in the power amplifying unit is an FET said transistor voltage is a drain-to-source voltage. In such a case, the adjusting of the supply voltage to the power amplifying unit may further cause a drain current to the at least one transistor to be altered. This is an advantageous because it enables the polarization controller to adjust the bias level in the power amplifying unit without requiring any complex connections to the unit. To existing amplifier modules, the proposed strategy is basically applicable with only minor modifications of the module’s DC-to-DC converter, where the DC-to-DC converter is arranged to provide supply voltage to the amplifier. For integrated circuits with a plurality of power amplifying modules, it is possible to provide a separate supply voltage to each power amplifying module.

[0024] The resulting lowered power consumption reduces the need for heat dissipation by the cooling the system, which decreases the cost and renders a more compact design possible.

[0025] According to embodiments of this aspect of the invention, the polarization controller is configured to control the respective bias levels of the power amplifying unit in different ways. For example, the bias levels may be controlled continuously as a function of the selected orientation of the linear polarization of the modulated signal wave. Alternatively, the bias levels may be controlled as a function of the selected orientation of the linear polarization of the modulated signal wave, which function is stepwise constant over predefined intervals of angles for the selected orientation of the linear polarization of the modulated signal wave. As yet another alternative, the bias levels may be controlled through a bias control signal that is common for both the power amplifiers irrespective of whether the control function is continuous or stepwise constant. Thus, there is a high degree of flexibility regarding how to assign appropriate bias levels for the power amplifying unit.

[0026] According to another embodiment of this aspect of the invention, the polarization controller is configured to obtain location data, for instance from a GNSS (global navigation satellite system) receiver and / or an IMU (inertial measurement unit), which location data reflect a current geographic location and a current orientation of the polarization controller. Further, based on the location data, the polarization controller is configured to determine the selected orientation of the linear polarization of the modulated signal wave. Consequently, the transmitter in a mobile terminal may for example automatically align itself with a polarization orientation of a receiver.

[0027] To automatically handle situations where at least one of the transmitter and the receiver moves during the signal transmission, the polarization controller is preferably configured to repeatedly obtain updates of the location data. If the location data of an obtained update differs by more than a threshold amount from the location data based on which a currently selected orientation of the linear polarization of the modulated signal wave has been determined, the polarization controller is further configured determine an update of the selected orientation of the linear polarization of the modulated signal wave based on the obtained updated location data. However, it may be necessary to update the selected orientation of the linear polarization also when the transmitter itself is stationary. For example, in a LEO (low Earth orbit) satellite system, and other non-geostatio- nary orbits, to follow a particular satellite, a ground based transmitter must typically adapt its polarization orientation continuously regardless of whether the transmitter moves or not. Preferably, therefore, the polarization controller is further configured to repeatedly obtain updates of directional data reflecting a current spatial direction to an intended receiver of the modulated signal wave, and determine an update of the selected orientation of the linear polarization of the modulated signal wave on the further basis of the obtained directional data.

[0028] According to yet another embodiment of this aspect of the invention, the polarization controller is configured to control a respective amplitude-phase relationship of a respective at least one pair of first and second basic signals based on which the at least one pair of first and second modulated signals are produced. Thus, the polarization controller may conveniently set the orientation of the linear polarization to a desired angle.

[0029] According to another aspect of the invention, the above-mentioned objects are achieved by a transmitter for producing at least one modulated signal wave that has a linear polarization of a selected orientation when emitted from an antenna with at least one dual polarized antenna element connected to at least one respective pair of first and second output ports of the transmitter. The at least one respective pair of first and second output ports provide at least one respective pair of first and second modulated signals adapted to be transmitted via the antenna. The transmitter includes at least one signal splitter, a signal control- ler, a power amplifying unit and the proposed polarization controller. The at least one signal splitter is configured to receive a respective one of at least one source signal from a respective at least one radio-frequency signal source, and divide the respective at least one source signal into at least one respective pair of first and second source signal copies. The signal controller is configured to obtain the at least one respective pair of first and second source signal copies, and in response thereto, produce a respective at least one pair of first and second amplitude and phase adjusted signals. The power amplifying unit is configured to produce the at least one respective pair of first and second modulated signals based on the respective at least one pair of first and second amplitude and phase adjusted signals. The advantages of this transmitter are apparent from the discussion above with reference to the proposed polarization controller.

[0030] According to one embodiment of this aspect of the invention, the signal controller contains at least one first and second adjustable amplifier. The at least one first adjustable amplifier is configured to receive at least one first signal copy in the respective pairs of first and second source signal copies, and based thereon, produce an amplified version of the least one first signal copy, which amplified version has an amplitude whose magnitude depends on a first amplitude control signal. Analogously, the at least one second adjustable amplifier is configured to receive at least one second signal copy in the respective pairs of first and second source signal copies, and based thereon, produce an amplified version of the least one second signal copy, which amplified version has an amplitude whose magnitude depends on a second amplitude control signal. Thus, the transmitter may be tuned to a desired polarization orientation in a straightforward manner.

[0031] Preferably, to this aim, the signal controller includes at least one first and second phase shifters. The at least one first phase shifter is configured to receive the amplified version of the at least one first signal copy, and based thereon, produce the at least one first amplitude and phase adjusted signal whose phase angle relative to the first signal copy depends on a first phase control signal from the polarization controller. Analogously, the at least one second phase shifter is configured to receive the amplified version of the at least one second signal copy, and based thereon, produce the at least one second amplitude and phase adjusted signal whose phase angle relative to the second signal copy depends on a second phase control signal from the polarization controller.

[0032] According to another embodiment of this aspect of the invention, the at least one power amplifier includes at least one first and second power amplifier. The at least one first power amplifier is configured to receive the at least one first amplitude and phase adjusted signal, and based thereon, produce a respective at least one first bias-level adjusted signal whose bias level depends on at least one first bias control signal. Analogously, the at least one second power amplifier is configured to receive the at least one second amplitude and phase adjusted signal, and based thereon, produce a respective at least one second biaslevel adjusted signal whose bias level depends on at least one second bias control signal. Thus, the polarization controller may conveniently assign appropriate bias levels for the at least one power amplifying unit, for example as described above.

[0033] According to one embodiment of this aspect of the invention, the least one first bias control signal is configured to produce a respective at least one first bias-level adjusted signal by adjusting a supply voltage to the at least one first power amplifier thus causing a first maximum drain-to-source voltage of a first FET comprised in the at least one first power amplifier to be altered from a first to a second value. Analogously, the least one second bias control signal is configured to produce a respective at least one second bias-level adjusted signal by adjusting a supply voltage to the at least one second power amplifier thus causing a second maximum drain-to-source voltage of a second FET comprised in the at least one second power amplifier to be altered from a first to a second value.

[0034] Moreover, according to one embodiment of the invention, the first FET is arranged in the at least one first power amplifier such that the adjusting of the supply voltage to the at least one first power amplifier causes a first maximum drain current to the first FET to be altered from a first to a second value; and similarly, the second FET is arranged in the at least one second power amplifier such that the adjusting of the supply voltage to the at least one second power amplifier causes a second maximum drain current to the second FET to be altered from a first to a second value.

[0035] This reduces the adjustable voltage range of the maximal supply voltage somewhat, where the amount of reduction depends on the amplifier circuit design. In any case, if two DC-to-DC converters are used approximately equally an overall high efficiency is attained.

[0036] According to yet another embodiment of this aspect of the invention, the transmitter contains a filtering unit configured to receive the at least one respective pair of first and second modulated signals, and in response thereto, produce a respective at least one pair of first and second bandpass filtered modulated signals, which are adapted to be transmitted via the antenna. Hence, said modulated signals may for example be adapted for transmission via a single-antenna element antenna.

[0037] Preferably, the filtering unit, in turn, includes first and second bandpass filters. Here, the first bandpass filter is configured to receive a first bias-level adjusted signal in the at least one respective pair of first and second modulated signals, and based thereon, produce a first bandpass filtered signal in the at least one pair of first and second bandpass filtered modulated signals. Analogously, the second bandpass filter is configured to receive a second bias-level adjusted signal in the at least one respective pair of first and second modulated signals, and based thereon, produce a second bandpass filtered signal in the at least one pair of first and second bandpass filtered modulated signals.

[0038] According to still another embodiment of this aspect of the invention, the transmitter contains an antenna with at least one dual polarized antenna element connected to the at least one respective pair of first and second output ports of the transmitter. The at least one dual polarized antenna element is configured to emit the at least one modulated signal wave in response to the at least one respective pair of first and second modulated signals. Consequently, modulated signal waves may be sent to intended recipients, such as various satellite-based and / or ground based receivers, for example included in a microwave link.

[0039] According to another embodiment of this aspect of the invention, the transmitter contains at least two signal splitters each of which is configured to receive a respective source signal from a respective radio-frequency signal source and divide each of the source signals into a respective pair of first and second source signal copies. The radio-frequency signal sources employ a common frequency reference for producing the respective source signals. Thereby, synchronicity can be maintained in the system even though the radio-frequency signal sources may be mutually independent.

[0040] According to yet another aspect of the invention, the object is achieved by a computer-implemented method for controlling a signal generator to, based on at least one source signal, produce at least one pair of first and second modulated signals with first and second polarizations respectively and a relative phase relationship chosen such that the at least one pair of first and second modulated signals radiated through respective orthogonal ports of at least one dual polarized antenna element of an antenna are equivalent to at least one respective modulated signal wave having a linear polarization of a selected orienta- tion. The method is performed in processing unit of a polarization controller and involves controlling a respective bias level in a power amplifying unit, such that the respective bias levels for each of the first and second modulated signals depend on the selected orientation of the linear polarization of the modulated signal wave. The advantages of this method are apparent from the discussion above with reference to the proposed polarization controller.

[0041] According to a further aspect of the invention, the object is achieved by a computer program loadable into a non-volatile data carrier communicatively connected to a processing unit, where the computer program includes software for executing the above method when being run on the respective processing units.

[0042] According to another aspect of the invention, the object is achieved by a non-volatile data carrier containing the above computer program.

[0043] Further advantages, beneficial features and applications of the present invention will be apparent from the following description and the dependent claims.

[0044] BRIEF DESCRIPTION OF THE DRAWINGS

[0045] The invention is now to be explained more closely by means of preferred embodiments, which are disclosed as examples, and with reference to the attached drawings.

[0046] Figures 1-2 show block diagrams of transmitters according to embodiments of the invention, which transmitters employ single-antenna element antennas;

[0047] Figures 3a-6b show diagrams illustrating how the bias levels of power amplifiers in a transmitter may be controlled depending on a selected orientation of a linearly polarized modulated signal wave according to embodiments of the invention; Figures 7-8 show block diagrams of transmitters according to embodiments of the invention, which transmitters employ antenna arrays;

[0048] Figures 9-10 illustrate, by means of flow diagrams, a general and a preferred method respectively according to the invention of controlling the polarization orientation of an emitted signal wave;

[0049] Figure 11 shows a diagram exemplifying how the efficiency of a power amplifier may vary as a function of the maximum output power for different bias tunings;

[0050] Figure 12 shows a block diagram of prior-art transmitter with controllable polarization orientation;

[0051] Figure 13 shows a graph that exemplifies how the bias level in the power amplifying unit may be adjusted by adjusting the supply voltage to the power amplifying unit and thus altering a voltage to a transistor in the power amplifying unit according to one embodiment of the invention; and

[0052] Figure 14 illustrates a scenario where the transistor in the power amplifying unit is an FET and the adjusting of the supply voltage to the power amplifying unit causes both a maximum drain-to- source voltage and a maximum drain current to the FET to be altered.

[0053] DETAILED DESCRIPTION

[0054] Figure 1 shows a block diagram of a transmitter 100 according to one embodiment of the invention, which transmitter 100 employs an antenna 160 with a single-antenna dual polarized antenna element AE. The transmitter 100 is adapted for producing a modulated signal wave RS that has a linear polarization of a selected orientation when emitted from the antenna 160. The transmitter 100 contains a signal generator 10 and a polarization controller 1 10. As will be discussed below, the transmitter 100 preferably also includes a positioning system 170.

[0055] The polarization controller 110 is configured to control the signal generator 10 to produce a pair of first and second modulated signals S HAB and SVAB respectively. The pair of first and second modulated signals S HAB and SVAB have first and second polarizations respectively, which preferably are orthogonal to one another, e.g. horizontal and vertical, and are produced based on a source signal S from a radio-frequency signal source 105, which, typically, carries an information / payload signal.

[0056] The first and second modulated signals S HAB and SVAB have such relative phase relationship that when they are radiated through respective orthogonal ports of the dual polarized antenna element AE of the antenna 160 the first and second modulated signals S HAB and SVAB are equivalent to a modulated signal wave RS having the linear polarization of the selected orientation. To accomplish this, the polarization controller 110 is configured to control the relative phase relationship between the first and second modulated signals S HAB and SVAB , for example via control signals CAI , CA2 , C PH I and C PH2 , where a first amplitude control signal CAI sets an amplitude of a first basic signal SI A of a first signal copy S1 of the source signal S, a second amplitude control signal CA2 sets an amplitude of a second basic signal S2A of a second signal copy S2 of the source signal S, a first phase control signal C PH I sets a phase of the first basic signal SI A and a second phase control signal C PH2 sets a phase of the second basic signal S2A.

[0057] According to the invention, the polarization controller 1 10 is further configured to control a respective bias level in a power amplifying unit 140 in the signal generator 10 which power amplifying unit 140 amplifies the first and second modulated signals S HAB and SVAB , and which control is effected via at least one control signal B1 / B2. As will be discussed below, the polarization controller 1 10 is configured to control the bias levels of the first and second modulated signals S HAB and SVAB , such that the respective bias levels depend on a desired output power and the selected orientation of the linear polarization of the modulated signal wave RS.

[0058] Figure 1 1 shows a diagram exemplifying how the efficiency of a power amplifier may vary as a function of the maximum output power for different bias tunings. In the diagram of Figure 1 1 , a first graph PA1.0 illustrates the efficiency q as a function of the output power P OUT for a power amplifier that is tuned to be optimized for maximum output power. A second graph PA0.2 illustrates the efficiency q as a function of the output power P OUT for a power amplifier that is tuned to be optimized for an output power being 80 % lower than the maximum output power, i.e. a factor 0.2 thereof. Not surprisingly, the tuning optimized for the output power being 80 % lower than the maximum output power is more efficient up to a particular output power P OUT equal to P B . In short, the amplifier tuning associated with the second graph PA0.2 achieves an overall better efficiency for all output levels until it saturates and cannot provide any additional power, which happens around the output power P B . Consequently, for output power levels above P B , it is favorable to change to the amplifier tuning associated with the first graph PA1.0 that is optimized for maximum output power. Actually, due to signal linearity requirements, i.e. the relationship between input and output power, the output level at which it is most favorable to change bias tuning is likely to occur at an output power PO UT somewhat below the output power P B . In any case, it is this change of bias tunings that is exploited in the present invention and constitutes the rationale behind the polarization controller’s 110 control of the respective bias levels of the power amplifying unit 140.

[0059] Figure 13 shows a graph where the horizontal axis represents a voltage VDS to a transistor, for example the drain-to-source voltage of an FET included in a power amplifying unit controlled by the polarization controller 110. The vertical axis shows a current I D to the transistor, for example the drain current of said FET. According to one embodiment of the invention, the polarization controller 110 is configured to control the bias level of a power amplifying unit by adjusting, for example lowering, a supply voltage to the power amplifying unit. This, in turn, causes a maximum drain-to-source voltage VDS of the FET to be altered from a first value Vosim to a second value Vos2m, which is lower than the first value Vosim. As a result, an operating point for the FET may be shifted from a first value OPi to a second value OP21 such that the operating point is better suited for a lower output power. Technically, a maximum drain current I DI to the FET may remain unaltered. Typically, however, as will be discussed below with reference to Figure 14, an adjustment of the supply voltage to the power amplifying unit also results in that the maximum drain current I DI to the FET is altered.

[0060] Figure 14 shows a graph corresponding to that of Figure 13, where the labels and units defined that also are shown in Figure 13 are the same as described above with reference to Figure 13. Figure 14, however, illustrates a situation where the adjustment of the supply voltage to the power amplifying unit causes both the maximum drain-to-source voltage VDS of the FET to be altered from the first value Vosim to the second value Vos2m, and the maximum drain current I DI to the FET to be altered from a first value loim to a second value Io2m. This is beneficial, since the slope of the load line for a thus adjusted operating point OP22 may be equal to the slope of the load line for an original operating point OP1 , and this namely greatly facilitates the circuit design to enable the proposed adjustment of the bias level.

[0061] Most preferably, the power amplifying unit includes a variant of FETs referred to as High-electron-mobility transistors (HEMTs or HEM FETs), which are also known as heterostructure FETs (HFETs) or modulation-doped FETs (MODFETs). It should be noted, however, that a wide range of alternative transistor types may also be employed according to embodiments of the invention, for example, bipolar transistors, CMOS (Complementary Metal Oxide Semiconductor) transistors or any kind of lll-V group type of semiconductors, e.g. GaN transistors.

[0062] Figures 3b, 4b, 5b and 6b exemplify different bias levels B1 and B2 for power amplifiers generating the first and second modulated signals SHAB and SVAB for different total output power levels POUT and orientations for the polarization angle <t> according to embodiments of the invention. Depending on the polarization angle the total output power level POUT is composed of output power from POUTI and POUT2 from the first and second modulated signals S HAB and SVAB respectively as is apparent from the graphs in Figures 3a, 4a, 5a and 6a.

[0063] Figure 3b shows a diagram illustrating how first and second bias levels B1 and B2 of first and second power amplifiers 141 and 142 respectively in the power amplifying unit 140 of Figure 1 are controlled depending on the selected orientation for the polarization angle <t> for different values of the total output power level POUT between a minimum value Pmin and a maximum value Pmax respectively. Here, the polarization controller 110 is configured to control the first and second bias levels B1 and B2 respectively of the power amplifying unit 140 continuously as a function of the selected orientation <t> of the linear polarization of the modulated signal wave RS. Each of the bias levels B1 and B2 varies between a respective minimum and maximum value Bmin and Bmax, which are both positive and non-zero. The first bias level B1 has its maximum value Bmax for the polarization angle <t> = 90° and its minimum value Bmin for the polarization angle <t> = 07180°, and the second bias level B2 has its maximum value Bmax for the polarization angle <t> = 07180° and its minimum value Bmin for the polarization angle <t> = 90°.

[0064] Figure 4b shows a diagram illustrating one embodiment of the invention where the first and second levels B1 and B2 are equal to one another for all polarization angles Here, the polarization controller 110 is configured to control the first and second bias levels B1 and B2 respectively of the power amplifying unit 140 either through a bias control signal B1 / B2 being common for both the power amplifiers 141 and 142 in the power amplifying unit 140, or two identical control signals, i.e. B1 = B2. Analogous to the above, the bias control signal B1 / B2 is a continuous function of the selected orientation <t> of the linear polarization of the modulated signal wave RS.

[0065] Figure 5b shows a diagram illustrating one embodiment of the invention where the first and second bias levels B1 and B2 of first and second power amplifiers 141 and 142 are different from one another except around the polarization angles <t> = 45° and 0) = 135°.

[0066] Specifically, the polarization controller 1 10 is here configured to control the first and second bias levels B1 and B2 respectively of the power amplifying unit 140 through control signals being functions of the polarization angle which functions are step- wise constant over predefined intervals of angles for the polarization angle For example, each of the predefined intervals may extend over 18° as exemplified in Figure 5b. Each of the bias levels B1 and B2 varies between a respective minimum and maximum value Bmin and Bmax, which are both positive and nonzero. The first bias level B1 has its maximum value Bmax for the polarization angle <t> = 90° and its minimum value Bmin for the polarization angle <t> = 07180°, and the second bias level B2 has its maximum value Bmaxfor the polarization angle <t> = 07180° and its minimum value B min for the polarization angle <t> = 90°.

[0067] Figure 6b shows a diagram illustrating one embodiment of the invention where the first and second bias levels B1 and B2 are equal to one another for all polarization angles Hence, the polarization controller 110 is here configured to control the first and second bias levels B1 and B2 respectively of the power amplifying unit 140 either through a bias control signal B1 / B2 being common for both the power amplifiers 141 and 142 in the power amplifying unit 140, or two identical control signals, i.e. B1 = B2. Analogous to the embodiment illustrated in Figure 5b, the control function is stepwise constant over predefined intervals of angles for the polarization angle For example, each of the predefined intervals may extend over 9°.

[0068] Referring again to Figure 1 , according to one embodiment of the invention, the polarization controller 110 is configured to obtain location data LD reflecting a current geographic location and a current orientation of the polarization controller 1 10. The location data LD may originate from a positioning system 170 in the transmitter 100. The positioning system 170, in turn, may include a GNSS receiver 171 , e.g. adapted to receive signals from one or more of the Galileo system, the GPS, GLONASS (Global' naya Navigatsionnaya Sputnikovaya Sistema) and the BeiDou Navigation Satellite System, and / or an IMU 172. Based on location data LD, the polarization controller 110 is configured to determine the selected orientation <t> of the linear polarization of the modulated signal wave RS based on the location data LD. Consequently, depending on where an intended receiver of the modulated signal wave RS is located, the polarization controller 110 may automatically derive a most suitable polarization angle 0).

[0069] To allow movements of the transmitter 100 and / or the receiver, the polarization controller 110 is preferably further configured to repeatedly obtain updates of the location data LD. If the location data LD of an obtained update differs by more than a threshold amount from the location data LD based on which a currently selected orientation <t> of the linear polarization of the modulated signal wave RS has been determined, the polarization controller 110 is configured to determine an update of the selected orientation <t> of the linear polarization of the modulated signal wave RS based on the obtained updated location data LD. As a result, the transmitter 100 and the receiver may maintain alignment of the polarization also if their mutual positions vary during the signal transmission.

[0070] Further, even though the location data LD remains unaltered, it may be necessary to change the selected orientation <t> of the li- near polarization of the modulated signal wave RS. Namely, the receiver, which may be carried by a satellite system with non- geostationary orbits may have altered its position. In such a case, the selected orientation <t> of the linear polarization of the modulated signal wave RS needs to be changed in response to an altered directional relationship between the position reflected by the location data LD and a spatial direction to the intended recipient of the modulated signal wave RS.

[0071] According to one embodiment of the invention, the polarization controller 110 is further configured to repeatedly obtain updates of directional data DD, for instance via radio messages, which directional data DD reflect a current spatial direction to an intended receiver of the modulated signal wave RS. The directional data DD may either indicate the spatial direction as such, or specify position coordinates for the intended receiver, so that the polarization controller 1 10 may calculate the spatial direction based on its own position derived from the location data LD. The polarization controller 110 is then configured to determine an update of the selected orientation <t> of the linear polarization of the modulated signal wave RS on the further basis of the obtained directional data DD.

[0072] In addition to the above, the transmitter 100 includes a signal splitter 120 configured to receive the source signal S the radiofrequency signal source 105 and divide the source signal into a pair of first and second source signal copies S1 and S2 respectively.

[0073] According to one embodiment of the invention, the signal controller 130 in the transmitter 100 contains first and second adjustable amplifiers 131 and 132 respectively. The first adjustable amplifier 131 is configured to receive the first signal copy S1 , and based thereon, produce an amplified version SI A of the first signal copy S1. The amplified version SI A has an amplitude whose magnitude depends on the first amplitude control signal CAI from the polarization controller 110. Analogously, The se- cond adjustable amplifier 132 is configured to receive the second signal copy S2, and based thereon, produce an amplified version S2A of the second signal copy S2. The amplified version S2A has an amplitude whose magnitude depends on the second amplitude control signal CA2 from the polarization controller 1 10.

[0074] According to one embodiment of the invention, the signal controller 130 also contains first and second phase shifters 133 and 134 respectively. The first phase shifter 133 is configured to receive the amplified version SI A of the first signal copy S1 , and based thereon, produce the first amplitude and phase adjusted signal S HA whose phase angle relative to the first signal copy S1 depends on a first phase control signal CPH I . Analogously, the second phase shifter 134 is configured to receive the amplified version S2A of the second signal copy S2, and based thereon, produce the at least one second amplitude and phase adjusted signal SVA whose phase angle relative to the second signal copy S2 depends on the second phase control signal C PH2.

[0075] According to one embodiment of the invention, the power amplifier 140 of the transmitter 100 further contains first and second power amplifiers 141 and 142 respectively.

[0076] The first power amplifier 141 is configured to receive the first amplitude and phase adjusted signal S HA , and based thereon, produce a first bias-level adjusted signal S HAB whose bias level depends on a first bias control signal B1. Analogously, the second power amplifier 142 is configured to receive the at least one second amplitude and phase adjusted signal SVA, and based thereon, produce a second bias-level adjusted signal SVAB whose bias level depends on a second bias control signal B2.

[0077] It is generally advantageous if the polarization controller 110 is configured to effect the above-described procedure in an automatic manner by executing a computer program. Therefore, the polarization controller 110 may include a memory unit 117, i.e. non-volatile data carrier, storing a computer program 118, which, in turn, contains software for making processing circuitry in the form of at least one processor 115 in the polarization controller 1 10 execute the actions mentioned in this disclosure when the computer program 118 is run on the at least one processor 115.

[0078] Figure 2 shows a block diagram of a transmitter 100 according to one embodiment of the invention, which transmitter 100, similar to the embodiment of Figure 1 , employs an antenna 160 with a single-antenna element AE. All components, units and signals in Figure 2 that also occur in Figure 1 designate the same components, units and signals as described above with reference to Figure 1 .

[0079] Thus, in summary, the transmitter 100 according to one embodiment shown in Figure 2 differs from the transmitter 100 according to one embodiment shown in Figure 1 in that in Figure 2, the transmitter 100 includes a filtering unit 150. The filtering unit 150 is configured to receive the first and second modulated signals S HAB and SVAB respectively and in response thereto produce first and second bandpass filtered modulated signals S HABF and SVABF respectively, which are adapted to be transmitted via the antenna 160 in place of the first and second modulated signals SHAB and SVAB . It may be preferable if the modulated signal wave RS is produced based on the first and second bandpass filtered modulated signals S HABF and SVABF respectively instead of being based directly on the first and second modulated signals S HAB and SVAB because in the former case fewer harmonics and less spurious signals are included in the modulated signal wave RS.

[0080] Figure 7 shows a block diagram of a transmitter 100 according to one embodiment of the invention, which transmitter 100 employs an antenna 161 with an array of antenna elements AE1 , AE2, ... , AEn organized in a feed network, which antenna elements AE1 , AE2, ... , AEn are configured to emit a respective modulated signal wave RS1 , RS2, ... , RSn. All components, units and signals in Figure 7 that also occur in Figure 1 designa- te the same components, units and signals as described above with reference to Figure 1.

[0081] In summary, the embodiment shown in Figure 7 differs from the embodiment shown in Figure 1 in that in Figure 7, a signal splitter 1200 is included that divides the source signal S from the radio-frequency signal source 105 into 2n signal copies, e.g. 2048 signal copies. Analogously, the transmitter 100 includes a signal controller 135 configured to obtain respective pairs of first and second source signal copies S1 S2; S3, S4; S(2n-1 ), S2n, and in response thereto produce respective pairs of first and second amplitude and phase adjusted signals. To this aim, the signal controller 135 contains n copies of the signal controller 130, each of which, in turn, contains the above-described first and second adjustable amplifiers 131 and 132 respectively and first and second phase shifters 133 and 134 respectively.

[0082] Analogously, a power amplifying unit 145 is configured to produce respective pairs of first and second modulated signals based on the respective pair of first and second amplitude and phase adjusted signals, which power amplifying unit 145, in turn, contains n copies of the above-described first and second power amplifiers 141 and 142 respectively.

[0083] Preferably, each of the 2n adjustable amplifiers and the 2n phase shifters in the signal controller 135 as well as each of the 2n power amplifiers in the power amplifying unit 145 is individually controllable. Therefore, the signal controller 135 may have inputs configured to receive amplitude control signals CAI , CA2n and phase control signals C PH I , . . . , C p H2n , and the power amplifying unit 145 may have inputs configured to receive bias control signals PAI , PA2 ; PAS , PA . . . ; PA(2n-D , PA2n .

[0084] The transmitter 100 further contains a polarization controller 110, which is configured to produce the amplitude control signals CAI , . . . , CA2n j the phase control signals C PH I , . . . , C H2n and the bias control signals PAI , PA2 ; PAS , PA4 ; . . . ; PA(2n-i ) , PA2n to the signal controller 135 and the power amplifying unit 145 respectively.

[0085] Figure 8 shows a block diagram of a transmitter 100 according to one embodiment of the invention, which transmitter 100, similar to the embodiment of Figure 8 employs an antenna 161 with an array of antenna elements AE1 , AE2, ... , AEn organized in a feed network. All components, units and signals in Figure 8 that also occur in Figures 1 and / or 8 designate the same components, units and signals as described above with reference to these figures.

[0086] In summary, the embodiment shown in Figure 8 differs from the embodiment shown in Figure 7 in that in Figure 8, a set of radiofrequency signal sources 105i , 1052, ... , 105nare included where for example n equals 1024, which radio-frequency signal sources 105i , 1052, ... , 105nproduce respective different source signals Si , S2, ... , Sn. Moreover, signal splitters 121 , 122, .., 12n are included that divide each of the source signals Si , S2, ... , Sninto a respective pair of signal copies Sn , S12; S21 , S22; ... ; Sni, Sn2 respectively. The radio-frequency signal sources 105i , 1052, ... , 105nemploy a common frequency reference CLK for producing the respective source signals Si , S2, ... , Sn, which common frequency reference CLK may originate from a clock generator 180.

[0087] For improved quality of the emitted modulated signal waves RS1 , RS2, ... , RSn, each of the embodiments shown in Figures 7 and 8 may also include a respective filtering unit 150, which is configured to receive the pairs of first and second modulated signals from the power amplifying unit 145, and in response thereto, produce respective pairs of first and second bandpass filtered modulated signals.

[0088] It should be noted that, similar to the embodiments of the invention discussed above with reference to Figures 4b and 6b, the bias control signals B1 and B2 may be common for the first and second power amplifiers 141 and 142. Analogously, therefore, two or more of the above control signals PAI , PA2; PAS, PA PA(2n-i), PA2n may be pairwise common for two or more of the 2n power amplifiers in the power amplifying unit 145 of the embodiments shown in Figures 7 and / or 8.

[0089] In order to sum up, and with reference to the flow diagrams in Figures 9 and 10, we will now describe a general and a preferred method respectively according to the invention for controlling the polarization orientation <t> of the at least one emitted signal wave RS or RS1 , RS2, ... , RSn respectively.

[0090] In the flow diagram of Figure 9, in a first step 910, a selected orientation <t> for the polarization of the at least one signal wave to be emitted is determined, for example based on location data LD from a positioning system.

[0091] Then, in a step 920, a desired output power of the at least one signal wave to be emitted is determined. Based thereon, in turn, in a step 930, respective amplitudes and phases are calculated for each of the at least one pair of modulated signals based upon which the at least one signal wave is to be produced. Alternatively, the respective amplitudes and phases may be derived from a lookup table.

[0092] In a subsequent step 940, respective bias levels are determined for each of the amplifiers that amplify the at least one pair of modulated signals, for example as described above with reference to Figures 3a to 6b.

[0093] Thereafter, in a step 950, source signal(s) is / are obtained, and based thereon, the at least one pair of modulated signals are produced, which are amplified and phase adjusted in agreement with steps 910 to 940. A step 960, following step 950, checks if the signal transmission shall end, for example in response to an operator command; and if so, the procedure ends. Otherwise, the procedure loops back to step 950 for continued production of the at least one pair of modulated signals. The flow diagram in Figure 10 is a slight modification of the flow diagram in Figure 9. Specifically, the flow diagram in Figure 10 includes a step 1045 between steps 940 and 950. In step 1045, it is checked if the location data LD and / or the directional data DD has been updated to differ by more than a threshold amount from the location data LD and / or directional data DD respectively based on which a currently selected orientation of the linear polarization of the modulated signal wave has been determined. If so, the procedure loops back to step 910; and otherwise, step 960 follows.

[0094] The process steps described with reference to Figures 9 to 10 may be controlled by means of a programmed processor. Moreover, although the embodiments of the invention described above with reference to the drawings comprise processor and processes performed in at least one processor, the invention thus also extends to computer programs, particularly computer programs on or in a carrier, adapted for putting the invention into practice. The program may be in the form of source code, object code, a code intermediate source and object code such as in partially compiled form, or in any other form suitable for use in the implementation of the process according to the invention. The program may either be a part of an operating system, or be a separate application. The carrier may be any entity or device capable of carrying the program. For example, the carrier may comprise a storage medium, such as a Flash memory, a ROM (Read Only Memory), for example a DVD (Digital Video / Versatile Disk), a CD (Compact Disc) or a semiconductor ROM, an EPROM (Erasable Programmable Read-Only Memory), an EEPROM (Electrically Erasable Programmable Read-Only Memory), or a magnetic recording medium, for example a floppy disc or hard disc. Further, the carrier may be a transmissible carrier such as an electrical or optical signal which may be conveyed via electrical or optical cable or by radio or by other means. When the program is embodied in a signal, which may be conveyed, directly by a cable or other device or means, the carrier may be constituted by such cable or device or means. Alternatively, the carrier may be an integrated circuit in which the program is embedded, the integrated circuit being adapted for performing, or for use in the performance of, the relevant processes.

[0095] Variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

[0096] The term “comprises / comprising” when used in this specification is taken to specify the presence of stated features, integers, steps or components. The term does not preclude the presence or addition of one or more additional elements, features, integers, steps or components or groups thereof. The indefinite article "a" or "an" does not exclude a plurality. In the claims, the word “or” is not to be interpreted as an exclusive or (sometimes referred to as “XOR”). On the contrary, expressions such as “A or B” covers all the cases “A and not B”, “B and not A” and “A and B”, unless otherwise indicated. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

[0097] It is also to be noted that features from the various embodiments described herein may freely be combined, unless it is explicitly stated that such a combination would be unsuitable.

[0098] The invention is not restricted to the described embodiments in the figures, but may be varied freely within the scope of the claims. Any subject-matter falling outside the scope of the claims is provided for information purposes, only.

Claims

Claims1. A polarization controller (110) for controlling a signal generator (10) to, based on at least one source signal (S; Si , S2, Sn), produce at least one pair of first and second modulated signals (SHAB , SVAB ; SHABF , SVABF) with first and second polarizations respectively and a relative phase relationship chosen such that the at least one pair of first and second modulated signals (SHAB , SVAB ; SHABF , SVABF) radiated through respective orthogonal ports of at least one dual polarized antenna element (AE; AE1 , AE2, AEn) of an antenna (160; 161 ) are equivalent to at least one respective modulated signal wave (RS; RS1 , n) having a linear polarization of a selected orientation characterized in that the polarization controllerconfigured to: control a respective bias level (B1 ; B2) in a power amplifying unit (140; 145) amplifying the first and second modulated signals (SHAB , SVAB ; S HABF , SVABF) such that the respective bias levels (B1 ; B2) for each of the first and second modulated signals (S HAB , SVAB ; SHABF , SVABF) depend on the selected orientationof the linear polarization of the modulated signal wave (RS).

2. The polarization controller (110) according to claim 1 , wherein the polarization controller (110) is configured to control the respective bias levels (B1 ; B2) of the power amplifying unit (140; 145) continuously as a function of the selected orientationof the linear polarization of the modulated signal wave (RS).

3. The polarization controller (110) according to claim 1 , wherein the polarization controller (110) is configured to control the respective bias levels (B1 ; B2) of the power amplifying unit (140; 145) as a function of the selected orientationof the linear polarization of the modulated signal wave (RS), which function is stepwise constant over predefined intervals of angles for the selected orientationof the linear polarization of the modulated signal wave (RS).

4. The polarization controller (110) according to any of claims 2 or 3, wherein the polarization controller (1 10) is configured to control the respective bias levels (B1 ; B2) of the power amplifying unit (140; 145) through a bias control signal being common for a pair of power amplifiers (141 , 142) comprised in the power amplifying unit (140; 145).

5. The polarization controller (110) according to any one of the preceding claims, wherein the polarization controller (1 10) is configured to: obtain location data (LD) reflecting a current geographic location and a current orientation of the polarization controller (110), and determine the selected orientationof the linear polarization of the modulated signal wave (RS) based on the location data (LD).

6. The polarization controller (110) according to claim 5, wherein the polarization controller (110) is further configured to: repeatedly obtain updates of the location data (LD), and if the location data (LD) of an obtained update differs by more than a threshold amount from the location data (LD) based on which a currently selected orientationof the linear polarization of the modulated signal wave (RS) has been determined determine an update of the selected orientationof the linear polarization of the modulated signal wave (RS) based on the obtained updated location data (LD).

7. The polarization controller (110) according to any of claims 5 or 6, wherein the polarization controller (110) is further configured to: repeatedly obtain updates of directional data (DD) reflecting a current spatial direction to an intended receiver of the modulated signal wave (RS), and determine an update of the selected orientation of the linear polarization of the modulated signal wave (RS) on thefurther basis of the obtained directional data (DD).

8. The polarization controller (110) according to any of the preceding claims, wherein the polarization controller (110) is further configured to control (CAI , CA2 ; CPHI , C PH2) a respective amplitude-phase relationship of a respective at least one pair of first and second basic signals (SHA; SVA) based on which the at least one pair of first and second modulated signals (S HAB , SVAB ; SHABF , SVABF) are produced.

9. The polarization controller (110) according to any of the preceding claims, wherein the polarization controller (110) is configured to control the respective bias level (B1 ; B2) in the power amplifying unit (140; 145) by adjusting a supply voltage to the power amplifying unit (140; 145) and thus altering a voltage (VDS) to at least one transistor comprised in the power amplifying unit (140; 145).

10. The polarization controller (110) according to claim 9, wherein the at least one transistor comprised in the power amplifying unit (140; 145) is a field effect transistor, said voltage (VDS) to the at least one transistor is a drain-to-source voltage and the adjusting of the supply voltage to the power amplifying unit (140; 145) is further configured to cause a drain current ( I D) to the at least one transistor to be altered.

11. A transmitter (100) for producing the at least one respective modulated signal wave (RS; RS1 , RS2, RSn) according to any one of the preceding claims that has a linear polarization of the selected orientationwhen emitted from the antenna (160; 161 ) with the at least one dual polarized antenna element (AE, AE1 , AE2, AEn) connected to the at least one respective pair of first and second output ports of the transmitter (100), which at least one respective pair of first and second output ports provide the at least one respective pair of first and second modulated signals (SHAB, SVAB ; SHABF, SVABF) adapted to be trans-mitted via the antenna (160; 161 ), characterized in that the transmitter (100) comprises: at least one signal splitter (120; 121 , 122, 12n; 1200) configured to receive a respective at least one source signal (S; Si , S2, Sn) from a respective at least one radio-frequency signal source (105; 105i , 1052, 105n) and divide the respective at least one source signal into at least one respective pair of first and second source signal copies (S1 , S2; S1 - S2n; Sn - Sn2), a signal controller (130; 135) configured to obtain the at least one respective pair of first and second source signal copies (S1 , S2; S1 - S2n; S11 - Sn2) and in response thereto produce a respective at least one pair of first and second amplitude and phase adjusted signals (S HA ; SVA) , a power amplifying unit (140; 145) configured to produce the at least one respective pair of first and second modulated signals ( S HAB, SVAB ; S HABF , SVABF ) based on the respective at least one pair of first and second amplitude and phase adjusted signals (S HA; SVA) , and the polarization controller (1 10) according to any one of the preceding claims.

12. The transmitter (100) according to claim 11 , wherein the signal controller (130) comprises: at least one first adjustable amplifier (131 ) configured to receive at least one first signal copy (S1 ) in the respective pairs of first and second source signal copies (S1 , S2), and based thereon, produce an amplified version (SI A) of the least one first signal copy (S1 ), which amplified version (SI A) has an amplitude whose magnitude depends on a first amplitude control signal (CAI ) , and at least one second adjustable amplifier (132) configured to receive at least one second signal copy (S2) in the respective pairs of first and second source signal copies (S1 , S2), and based thereon, produce an amplified version (S2A) of the least one second signal copy (S2), which amplified version (S2A) has an amplitude whose magnitude depends on a second amplitudecontrol signal (CA2) .

13. The transmitter (100) according to claim 12, wherein the signal controller (130) comprises: at least one first phase shifter (133) configured to receive the amplified version (SI A) of the at least one first signal copy (S1 ), and based thereon, produce the at least one first amplitude and phase adjusted signal (SHA) whose phase angle relative to the first signal copy (S1 ) depends on a first phase control signal (CPHI ) , and at least one second phase shifter (134) configured to receive the amplified version (S2A) of the at least one second signal copy (S2), and based thereon, produce the at least one second amplitude and phase adjusted signal (SHA) whose phase angle relative to the second signal copy (S2) depends on a second phase control signal (CPH2) .

14. The transmitter (100) according to any of claims 11 to 13, wherein the at least one power amplifying unit (140) comprises: at least one first power amplifier (141 ) configured to receive the at least one first amplitude and phase adjusted signal (SHA) , and based thereon, produce a respective at least one first bias-level adjusted signal (S HAB) whose bias level depends on at least one first bias control signal (B1 ), and at least one second power amplifier (142) configured to receive the at least one second amplitude and phase adjusted signal (SVA) , and based thereon, produce a respective at least one second bias-level adjusted signal (SVAB) whose bias level depends on at least one second bias control signal (B2).

15. The transmitter (100) according to claim 14, wherein: the least one first bias control signal (B1 ) is configured to produce a respective at least one first bias-level adjusted signal (SHAB) by adjusting a supply voltage to the at least one first power amplifier (141 ) thus causing a first maximum drain-to-source voltage (VDS) of a first field effect transistor comprised in the atleast one first power amplifier (141 ) to be altered from a first value (VDsim) to a second value (VDS2m), and the least one second bias control signal (B2) is configured to produce a respective at least one second bias-level adjusted signal (SVAB) by adjusting a supply voltage to the at least one second power amplifier (142) thus causing a second maximum drain-to-source voltage (VDS) of a second field effect transistor comprised in the at least one second power amplifier (141 ) to be altered from a first value (Vosi m) to a second value (VDS2m).

16. The transmitter (100) according to claim 15, wherein: the first field effect transistor is arranged in the at least one first power amplifier (141 ) such that the adjusting of the supply voltage to the at least one first power amplifier (141 ) causes a first maximum drain current ( I D) to the first field effect transistor to be altered from a first value ( I DI ) to a second value ( I D2) , and the second field effect transistor is arranged in the at least one second power amplifier (142) such that the adjusting of the supply voltage to the at least one second power amplifier (142) causes a second maximum drain current ( I D) to the second field effect transistor to be altered from a first value ( I DI ) to a second value ( I D2) .

17. The transmitter (100) according to any of claims 14 to 16, further comprising a filtering unit (150) configured to: receive the at least one respective pair of first and second modulated signals (S HAB, SVAB ) and in response thereto produce a respective at least one pair of first and second bandpass filtered modulated signals (S HABF ; SVAB F) which are adapted to be transmitted via the antenna (160; 161 ).

18. The transmitter (100) according to claim 17, wherein the filtering unit (150) comprises: a first bandpass filter (151 ) configured to receive a first bias-level adjusted signal (S HAB) in the at least one respectivepair of first and second modulated signals (SHAB, SVAB) , and based thereon, produce a first bandpass filtered signal (S HABF) in the at least one pair of first and second bandpass filtered modulated signals, and a second bandpass filter (152) configured to receive a second bias-level adjusted signal (SVAB) in the at least one respective pair of first and second modulated signals (SHAB, SVAB) , and based thereon, produce a second bandpass filtered signal (SVABF) in the at least one pair of first and second bandpass filtered modulated signals.

19. The transmitter (100) according to any of claims 11 to 18, further comprising an antenna (160; 161 ) with at least one dual polarized antenna element (AE, AE1 , AE2, AEn) connected to the at least one respective pair of first and second output ports of the transmitter (100), which at least one dual polarized antenna element (AE, AE1 , AE2, AEn) is configured to emit the at least one modulated signal wave (RS; RS1 , RS2, RSn) in response to the at least one respective pair of first and second modulated signals (S HAB, SVAB ; SHABF, SVABF) .

20. The transmitter (100) according to any of claims 11 to 19, wherein: the transmitter (100) comprises at least two signal splitters (121 , 122, 12n) each of which is configured to receive a respective source signal (Si , S2, Sn) from a respective radio-frequency signal source (105i , 1052, 105n) and divide each of the source signals (Si , S2, Sn) into a respective pair of first and second source signal copies (Sn - Sn2), and the radio-frequency signal sources (105i , 1052, 105n) employ a common frequency reference (CLK) for producing the respective source signals (Si , S2, Sn).

21. A computer-implemented method for controlling a signal generator (10) to, based on at least one source signal (S; Si , S2, Sn), produce at least one pair of first and second modulatedsignals (SHAB, SVAB ; S HABF, SVABF) with first and second polarizations respectively and a relative phase relationship chosen such that the at least one pair of first and second modulated signals (SHAB, SVAB ; SHABF, SVABF) radiated through respective orthogonal ports of at least one dual polarized antenna element (AE; AE1 , AE2, AEn) of an antenna (160; 161 ) are equivalent to at least one respective modulated signal wave (RS; RS1 , RS2, RSn) having a linear polarization of a selected orientation, which method is performed in processing unit (115) of a polarization controller (1 10), and is characterized by: controlling a respective bias level (B1 ; B2) in a power amplifying unit (140; 145) such that the respective bias levels (B1 ; B2) for each of the first and second modulated signals (S HAB, SVAB ; S HABF, SVABF) depend on the selected orientationof the linear polarization of the modulated signal wave (RS).

22. A computer program (118) loadable into a non-volatile data carrier (117) communicatively connected to a processing unit (115), the computer program (118) comprising software for executing the method according to claim 21 when the computer program (118) is run on the processing unit (115).

23. A non-volatile data carrier (117) containing the computer program (118) of the claim 22.

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