Electro-mechanical radio frequency signal generator and method of operating an electro-mechanical radio frequency signal generator |
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申请号 | EP11290027.9 | 申请日 | 2011-01-19 | 公开(公告)号 | EP2479887A1 | 公开(公告)日 | 2012-07-25 |
申请人 | Alcatel Lucent; | 发明人 | Wiegner, Dirk; Templ, Wolfgang Dr.; | ||||
摘要 | The invention relates to a radio frequency, RF, signal generator (100), for providing an RF signal (RF_out), said RF signal generator (100) comprising: - at least two coupling elements (2; 41; 51), wherein each coupling element (2; 41; 51) comprises two coupling electrodes (3a, 3b) at least one of which is capable of performing a mechanical self-oscillation with a specific resonance frequency (fl, .., fN) and/or a specific attenuation to enable an electric coupling between said coupling electrodes (3a, 3b) which depends on said specific resonance frequency (fl, .., fN) and/or specific attenuation, - stimulating means (IG1, IG2, .., IGN) that are configured to selectively stimulate a mechanical self-oscillation of at least one of said coupling elements (2; 41; 51), and - signal processing means (22) configured to determine at least one parameter characterizing an actual resonance frequency and/or an actual attenuation exhibited by at least one coupling element (2; 41; 51) in response to a stimulation applied by said stimulating means (IG1, IG2, .., IGN). |
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权利要求 | |||||||
说明书全文 | The invention relates to a radio frequency, RF, signal generator for providing an RF signal. The invention further relates to a method of operating an RF signal generator. Conventional electronic RF signal generators usually are based on a non-RF input signal which is upconverted to an RF range, e.g. by multiplying the input signal with a corresponding local oscillator signal, which transforms the input signal in a per se known manner to the radio frequency range depending on the frequency of the local oscillator signal employed for multiplication. The conventional approach of providing and/or amplifying an RF signal comprises several disadvantages such as e.g. the introduction of nonlinearities and the like. Accordingly, it is an object of the present invention to provide an improved RF signal generator as well as improved signal amplification and an improved method of operating such an RF signal generator which do not suffer from the disadvantages of prior art systems. According to the present invention, regarding the above mentioned RF signal generator, this object is achieved by said RF signal generator comprising:
As the basic idea of the invention, the RF output signal is generated by composing its frequency components generated by means of at least two coupling elements, which act as mechanical oscillators at their resonance frequency each. When excited, at least one component of each coupling element oscillates at its resonance frequency, and via the change of its coupling between the coupling electrodes during an oscillation, the corresponding frequency component can be generated by modulating an externally applied supply voltage (providing electric power). This results in an "implicit" frequency upconversion. The employment of the self-resonance of the coupling elements in the RF signal generator according to the embodiments allow for a completely novel and disruptive approach for realization of a highly efficient RF signal generator: the RF output signal is generated by the combination of a plurality of spectral signal components which are generated by the controlled triggered self-oscillations of the coupling elements. According to an embodiment, the coupling elements are grouped in a number of sub-arrays, wherein each sub-array is characterized by specific physical parameters such as e.g. geometrical dimension, material, suspension of their coupling electrodes, wherein the physical parameters define the self resonance at a well-defined frequency and/or attenuation. Within this embodiment, all coupling elements of the same sub-array have the same resonance frequency and/or the same attenuation, within the limits of the manufacturing tolerance. According to a further embodiment, individual coupling elements are provided, each of which being characterized by specific physical parameters such as e.g. geometrical dimension, material, suspension of their coupling elements, wherein the physical parameters define the self resonance at a well-defined frequency and/or attenuation. Within this embodiment, all coupling elements may have an individual resonance frequency and/or attenuation, within the limits of the manufacturing tolerance. Combinations of both approaches (sub-arrays vs. provisioning individual coupling elements) are also possible. The concept according to the embodiments advantageously allows to overcome the currently available RF signal generator architecture, in particular by avoiding an upconversion process by means of multiplication with a local oscillator signal. Other components of conventional RF generation systems (e.g., digital-to-analog converters), which usually add errors to the RF output signal, may also advantageously be omitted by employing the RF signal generator according to the embodiments. The concept according to the embodiments advantageously combines the benefits of a switched amplifier, namely high efficiency, digital control, wide band operation, and efficient parallel operation of fragmented frequency bands, with the benefits of the analogue amplifiers and upconverter modules, namely simplification or even avoidance of a reconstruction filter with its nonlinearities and matching losses. By means of the present embodiments, an external reconstruction filter for improving the RF output signal regarding its spectral properties can be simplified or even be completely avoided together with its related matching circuitry in a switched power amplifier. In difference to class-S switched amplifiers, the device according to the embodiments does not involve delta-sigma or comparable modulation. It features 100% coding efficiency. Thus, it contributes to an improved energy efficiency of a transmitter apparatus comprising the inventive RF signal generator while maintaining linearity. Additionally, by increasing the number of coupling elements, the supported signal bandwidth can be large, and is in particular not limited by a digital-to-analog converter. More specifically, since the RF signal generation according to the embodiments is based on a synthesis of the RF signal from its spectral components by means of the coupling elements, RF signals with fragmented frequency bands (i.e., signal components within the RF signal which comprise comparatively large frequency spacings of e.g. some hundred MHz up to several GHz) may be generated with a particularly high efficiency by providing and controlling coupling elements having resonance frequencies in the respective frequency ranges. E.g., a first number of coupling elements may be provided having resonance frequencies within a first RF range of e.g. 820 MHz to 860 MHz, whereas at least a second number of coupling elements may be provided having resonance frequencies within a second RF range of e.g. 2620 MHz to 2660 MHz thus offering a frequency spacing between both frequency bands of nearly 2 GHz. Generally, any number of coupling elements having arbitrary resonance frequencies and/or attenuations may be provided as long as the signal processing means may adequately control the various coupling elements, e.g. depending on the RF output signal to be generated. In general, each coupling element comprises at least two coupling electrodes, at least one of which is capable of performing a mechanical self-oscillation with a specific resonance frequency and/or a specific attenuation to enable an electric coupling between said coupling electrodes which depends on said specific resonance frequency and/or specific attenuation. Stimulating means are configured to selectively stimulate a mechanical self-oscillation of at least one of said coupling elements or its coupling electrode(s) capable of said mechanical self-oscillation. To ensure an efficient and precise RF signal generation, advantageously, signal processing means, which may also be configured to control the stimulating means, are configured to determine at least one parameter characterizing an actual resonance frequency and/or an actual attenuation exhibited by at least one coupling element in response to a stimulation applied by said stimulating means. Thus, the RF signal generator according to the embodiments advantageously offers a possibility for calibrating itself, which may e.g. be performed once after manufacturing, or preferably dynamically and/or periodically, e.g. during an ordinary operation of said RF signal generator in a target system such as an RF transceiver of a base station of a cellular communications network or the like. As already explained above, generally, the coupling electrodes of a coupling element form opposing parts, and at least one of those parts may mechanically oscillate (i.e., vibrate) relative to the other part or each other, respectively. In a preferred embodiment, the second opposing part (second coupling electrode) may also mechanically oscillate, preferably also with the resonance frequency of its opposing counterpart, i.e., the first coupling electrode. A distance between or an overlap of the two coupling electrodes determines the degree of coupling of the coupling element, which varies during the mechanical self-oscillation of the coupling element or its electrode(s), respectively. Typically, in a non-oscillating state (home state) of a coupling element, the coupling is comparatively low (preferably practically zero, according to an embodiment). Further preferably, the coupling elements are designed such that said coupling electrodes keep a spatial separation even in a tight coupling state in which their coupling is at its maximum, thus reducing mechanical wear. The coupling between the coupling electrodes may typically be based on electron emission or tunnelling effect; this results in a continuous dependency of the electric coupling with the distance or degree of overlap of the electrodes of the coupling element. The coupling may further be influenced by providing a specific vacuum or low-pressure environment or ionized media around the coupling electrodes. Moreover, the coupling may also be influenced by a specific shape of the opposing sections of the coupling electrodes (needle-type, spherical, and the like). A single coupling element, according to an embodiment, may have a maximum spatial dimension of 1 µm or less. A mobile part (e.g., electrode) of a coupling element typically may have a maximum dimension of 800 nm or less. The dimensions of a coupling element are also chosen with respect to the material from which the coupling element or its electrodes are made. According to a further embodiment, a few hundreds or even thousands of coupling elements per sub-array may be provided in order to be able to generate an RF output signal with adequate signal power. An overall number of coupling elements may well exceed ten thousand. Typically, according to a further embodiment, each coupling element has an individual stimulating generator means such as a coating with piezoelectric material; however, it is also possible to have a common stimulation generator means for a plurality of coupling elements. The RF signal generator according to the embodiments can e.g. be used as part of a transmitter arrangement, e.g. in base stations of mobile communication networks, in particular mobile telephony networks. The invention may be of particular use for radio transmitters in BTS (base transceiver stations) and User terminal equipment, defense systems, consumer electronics, and Software-Defined-Radio (SDR) and Cognitive Radio (CR) applications. According to a further preferred embodiment, said signal processing means are configured to individually determine an actual resonance frequency and/or an actual attenuation of all coupling elements which enables to precisely assess the actual operating parameters (resonance frequency, attenuation) of the coupling elements comprised within a specific RF signal generator. According to a further preferred embodiment, said signal processing means are configured to control a generation of said RF signal depending on an actual resonance frequency and/or an actual attenuation of said at least one coupling element. Thus, manufacturing variations, which may e.g. lead to deviations from a desired resonance frequency of specific coupling elements may be accounted for. For instance, if the signal processing means according to the embodiments comprise knowledge on an actual resonance frequency of every coupling element, groups of coupling elements may be formed, wherein the specific coupling elements being member of a group all exhibit the same resonance frequency or a resonance frequency being in a frequency range associated with said group. According to a preferred embodiment, said signal processing means are configured to determine a plurality of coupling elements which have an actual resonance frequency within a predetermined frequency range, and to define a sub-array of coupling elements associated with said predetermined frequency range from said plurality of coupling elements. By so defining sub-arrays, it can advantageously be ensured that each sub-array only comprises coupling elements which conform with the desired specific resonance frequency or resonance frequency range, respectively. According to a further preferred embodiment, said signal processing means are configured to simultaneously stimulate at least two coupling elements of said sub-array, whereby a signal power of the generated RF signal may be increased. Preferably, all coupling elements of a specific sub-array will simultaneously be stimulated to achieve a maximum RF output signal power. According to a further advantageous embodiment, during a manufacturing process of the RF signal generator, specifically of the coupling elements, a number of coupling elements may be produced which exceeds the nominal number of coupling elements that is required for achieving a specific RF output signal energy. After said step of manufacturing, a calibration as already explained above may be performed, whereby those coupling elements can be identified which actually comprise a resonance frequency within the desired frequency range. Usually, due to manufacturing tolerances, only a specific portion of the overall number of manufactured coupling elements will satisfy requirements regarding a specific resonance frequency or attenuation, and those identified coupling elements may be further used by the RF signal generator for RF signal generation. According to a further embodiment, said signal processing means are configured to determine such coupling elements, an actual resonance frequency and/or an actual attenuation of which is not within a predetermined frequency range and/or attenuation range, and to omit respective coupling elements when generating said RF signal, whereby the linearity of the generated RF output signal and an overall spectral quality of the RF output signal may be increased. According to a further embodiment, said RF generator is configured to provide an RF signal which comprises a plurality of spectral components, and wherein for each spectral component at least one coupling element, preferably a plurality of coupling elements, is provided, which comprise a resonance frequency that is associated with the respective spectral component. According to a further embodiment, said stimulating means comprise a plurality of stimulating impulse generators, wherein groups of coupling elements, or preferably single coupling elements, are assigned to a respective stimulating impulse generator. Thus, either individual coupling elements may be stimulated in an isolated manner, or advantageously a simultaneous stimulation of several coupling elements may be effected. According to a further preferred embodiment, the stimulating means comprise a piezoelectric element, in particular a piezoelectric coating on a coupling electrode of a coupling element, wherein said stimulating impulse generator is configured to apply a predetermined voltage to the piezoelectric element to excite an oscillation of the coupling electrode. Depending on the specific configuration of the signal processing means, it is also possible to stimulate a self oscillation of one or more coupling elements by applying a voltage signal comprising a specific pulse shape to the piezoelectric element(s) provided for stimulating the respective coupling elements. By defining specific pulse shapes for the voltage control of the stimulating generators, an even more precise generation of the desired RF output signal is enabled. According to a further advantageous embodiment, the coupling electrodes of a coupling element comprise two opposing and/or partially overlapping sections, wherein said sections are designed to maintain a special separation even in a tight coupling state between said coupling electrodes, which advantageously reduces a mechanical wear. A further solution to the object of the present invention is given by a method of operating radio frequency signal generator according to claim 11. The inventive method comprises the steps:
According to a further embodiment, said signal processing means individually determine an actual resonance frequency and/or an actual attenuation of a plurality, or preferably of all, coupling elements, which enable a very precise control of individual coupling elements. According to a further embodiment, said signal processing means control a generation of said RF signal depending on an actual resonance frequency and/or an actual attenuation of said at least one coupling element, which can e.g. be periodically determined according to the embodiments or once after a manufacturing process of the radio frequency signal generator. According to a further embodiment, said signal processing means determine a plurality of coupling elements which have an actual resonance frequency within a predetermined frequency range, define a sub-array of coupling elements associated with said predetermined frequency range from said plurality of coupling elements, and simultaneously stimulate at least two coupling elements of said sub-array. According to a further embodiment, said signal processing means determine such coupling elements, an actual resonance frequency and/or an axial attenuation of which is not within a predetermined frequency range and/or attenuation range and omit respective coupling elements when generating said RF signal. Further features, aspects and advantages of the present invention are given in the following detailed description with reference to the drawings in which:
The ends of the reeds 3a, 3b facing away from the respective opposing reed 3a, 3b are attached to a suspension 4a, 4b each. Within the present embodiment, common suspensions 4a, 4b for all reeds 3a, 3b of each respective one side of the coupling array 1 are used. All coupling elements 2 according to the embodiments are deigned such that at least one coupling electrode 3a, 3b is capable of performing a mechanical self-oscillation with a specific resonance frequency and/or a specific attenuation to enable an electric coupling between both coupling electrodes 3a, 3b of a specific coupling element 2 which depends on said specific resonance frequency and/or specific attenuation. Within the present embodiment depicted by Further within the present embodiment depicted by The actual number N of sub-arrays and the number of coupling elements 2 per sub-array inter alia depends on a required bandwidth, a required frequency resolution, a required signal output power for the RF output signal to be generated by the array 1 and the electrical characteristics of the coupling contacts. Within each sub-array SA1-SA4, according to a preferred embodiment, the coupling elements 2 have the same physical dimensions and properties (within the manufacturing tolerances), and therefore exhibit the same resonance frequency and the same attenuation. In the exemplary array 1 shown by Since each sub-array (or group) of coupling elements represents a distinct resonance frequency, which according to the present embodiment is given by wherein E is Young's modulus, p is a specific mass of a coupling electrode, d is a thickness of the coupling electrode, 1 is a length of the coupling electrode, there is a plurality of N sub-arrays (only four of which are shown in Thus, instead of utilizing an upconversion process as proposed by conventional RF signal generating systems, the RF signal generator 100 ( For instance, a coupling element 2 ( The oscillation of the coupling electrodes (i.e., reeds) 3a, 3b of a coupling element 2 (compare Further, the area 5b, which surrounds reed 3a and in which significant electron tunneling may occur from reed 3a to an opposing reed, has bent downward towards to the opposing reed 3b in the course of the self-oscillation, such that the free end of reed 3b is now within the area 5b; therefore a significant tunnelling current will flow from reed 3a to reed 3b. In Summary, in the deflected state of However, the principle according to the embodiments is not limited to a DC voltage supply for the opposing coupling electrodes 3a, 3b of a coupling element; an AC voltage supply may also be used which offers a further degree for shaping the spectral properties of generated RF output signals. Moreover, although the configuration depicted by Alternatively or additionally, it is also possible to have an analyzing unit (not shown) integrated in the signal processing unit 22, wherein the analyzing unit identifies spectral components of an RF input signal (not shown) to be amplified by the device 100. This RF input signal may e.g. be directly fed to the signal processing unit. Based on the input signal information 21, the signal processing unit 22 calculates a pulse form and/or timing for stimulating pulses which excite respective self-oscillations of specific coupling elements 2 ( In the example shown by In response to the stimulating pulses, the coupling elements 2 ( The amplitude of the stimulating pulse determines the power of the spectral component and the timing determines its phasing. The calculation of the pulse form and timing is based on the spectral input information 21 which is e.g. provided on baseband level as explained above, and/or a fed back sample (see feedback loop 23) of the so generated RF output signal RF_out, and a reference clock 24. The resonance frequencies of the coupling elements 2 within the sub-arrays SA1, .., SAN are fixed and have been designed to correspond to desired frequency components for the RF output signal RF_out to be generated. In the example shown by Alternative or additionally, the feedback loop 23 may also pick up a signal portion at an output of the antenna network 25, which enables to include the antenna network 25 into a linearization process employing said feedback loop 23. The supply voltage applied between the supply input 26 and a further reference potential such as analog ground potential, here a direct current (DC) supply voltage, effects a current through the coupling array 1, which depends on the electrical coupling within the sub-arrays SA1-SAN of the coupling elements 2 ( As an example, an inventive RF signal generator 100 according to a preferred embodiment may provide a frequency resolution in equal steps of between 1 kHz and 50 kHz, with a typical width of a resolved frequency interval of between 1 MHz and 100 MHz. The center frequency of the RF output signal RF_out to be generated may e.g. range between 500 MHz and 10 GHz. For example, with a frequency resolution of 50 kHz and a width of MHz, the coupling array 1 comprises about 1000 sub-arrays, i.e. N=1000. The base structures of the coupling electrode 3a are a layer (or coating) supporting electron emission 35 ("emission layer") and a piezoelectric (piezoactive) layer (or coating) 32. The emission layer 35 is directly attached to the coupler contact 31 to electrically connect the emission layer 35 to a voltage supply (not shown) and faces the other reed (compare The piezoactive layer 32 may be electrically contacted at its left (exposed) end via a first piezo contact 33a, and at its right (covered) end via a second (window) contact 33b reaching through the upper insulating layer 34b. The second (window) contact 33b is electrically connected via the metallization 37 to a metallization contact 36 in the region of the coupler contact 31 such that the areas of immediate connection to an external piezo voltage supply, namely the first contact 33a and the metallization contact 36, are well reachable and are not exposed to deflection during a reed oscillation thus not affecting the self-oscillation. By applying a voltage across the piezoelectric coating 32, the piezoelectric coating 32 may e.g. be contracted whereas the emission layer 35 remains at its original length, resulting in an upward-bending of the reed 3a at its free right end. After the voltage application has ended, the reed 3a will oscillate at its resonance frequency, causing a coupling varying with the resonance frequency. Note that the reed 3a may comprise an additional layer, in particular in order to deposit both the emission layer and the piezoactive layer as coatings on the additional layer, and/or to better control the mechanical properties (such as the resonance frequency via a dominant specific mass) of the reed 3a. It is also noted that piezoelectric multilayer structures may be applied instead of a single piezoactive layer 32. Note that the resonance frequency of a coupling element and here the coupling electrode 3a, in accordance with the invention, is typically in the GHz range. On the outer surface of the torsion unit 52, there is a first coupling surface 57, which covers about one third of the torsion unit's circumference. Further, on the inner surface of the jacket 53, there is a second coupling surface 58, covering about one tenth of the inner surface's circumference. The first coupling surface 57 and the second coupling surface 58 have about the same area size here. As such, the components 57, 58 represent coupling electrodes in the sense of the present invention. The coupling surfaces 57, 58 are connected to a combined (preferably DC) power supply and an RF signal output (see contacts 44a, 44b). During an oscillation, the two coupling surfaces 57, 58 vary their overlap (and distance), and thus the coupling varies with the resonance frequency of the torsion oscillation, wherein an electric RF signal having a frequency component of the self-oscillation of the torsion unit 52 is obtained. The proposed embodiments realize a highly efficient and highly linear RF signal generation which advantageously does not require a D/A converter or an upconversion module any more, in contrast to state of-the-art RF power signal generator or - transmitter architectures. Moreover, a reconstruction filter is not required with the inventive RF signal generator 100. A large signal bandwidth of the RF output signal RF_out ( Impulse generators IG1', ..., IG4' are also provided, which are controlled by the signal processing means 22 of the RF signal generator 100 as already explained above. As symbolized by arrows pointing from the respective stimulating generators IG1', ..., IG4' to single coupling elements or coupling electrodes thereof, according to the present and particularly preferred embodiment, each coupling element depicted within Since In contrast to the ideal system of For example, a first coupling electrode 300a of a third coupling element of the array A1 is shorter than its neighbour coupling electrodes, and thus the coupling electrode 300a comprises a resonance frequency which is too high as compared to its neighbouring coupling electrodes of the subarray A1. The same holds true for the second electrode 300b of the respective coupling element. Within the second subarray A2, a further coupling electrode 301a is substantially larger than its neighbouring electrodes, which leads to the effect that said coupling electrode 301a has a lower resonance frequency than its neighbouring coupling electrodes of the same array A2. Moreover, further similar deviations from an ideal state of the coupling electrodes 302a, 303a of the third array A3 are depicted by As an exception, the coupling elements of the fourth array A4 basically exhibit the desired resonance frequency and as such are comparable to the ideal configuration of According to a particularly preferred embodiment, in a first method step 200, cf. the flow-chart of For optimum precision, within step 200, each single coupling element of the RF signal generator 100a is stimulated individually, which has the effect that the generated RF output signal RF_out ( After assessing the actual resonance frequency of all coupling elements within step 200 ( In the next step 210, when generating an RF output signal by stimulating the coupling elements of subarray A1, which are associated with a first specific spectral component of the desired RF signal, the signal processing means 22 will only control the first, the second, the fourth and the fifth coupling element of subarray A1 thus omitting the third coupling element comprising the defective electrodes 300a, 300b, in the course of generating the RF output signal. This advantageously avoids generating too high signal frequencies, which would be the case when also stimulating the coupling element with the defective electrodes 300a, 300b. Although the fifth coupling element of subarray A1 does not comprise an ideal form and thus resonance frequency, either, however, its deviation from the desired resonance frequency is comparatively small, i.e. smaller than that of the third coupling element, so that it can be employed for RF signal generation within the desired tolerances. Thus, according to a preferred embodiment, the signal processing means 22 may rather - at best - activate the electrodes 300a, 300b in such cases, where typically coupling elements of the second subarray A2 would be activated, because, due to their manufacturing variations, the resonance frequency of the coupling element 300a, 300b is within the range of the desired resonance frequency for the coupling elements which are associated with the second subarray A2. Likewise, the coupling elements 302a, 303a comprise a to low resonance frequency as compared to the further coupling elements of the subarray A3, which means that the signal processing means 22 could stimulate the coupling elements 302a, 303a in such cases, where frequency components are to be generated which comprise a lower frequency than emitted by first, third and fifth coupling elements of the subarray A3. For instance, the coupling elements 302a, 303a may be employed when generating frequencies which typically would be emitted by coupling elements of the first subarray A2. Thus, by individually assessing the actual resonance frequency of all coupling elements, the signal processing means 22 can advantageously re-order the various coupling elements regarding their actual resonance frequency. As a result, the signal processing means 22 may advantageously determine only such coupling elements for stimulation which have the corresponding desired actual resonance frequency. The afore-mentioned embodiments enable an advantageous calibration process of the coupling elements of the RF signal generator 100a which effects a particularly precise RF signal generation. For instance, the calibration process explained above with reference to Alternatively or in addition, in low-load phases where the required RF output signal energy is lower than the maximum possible signal energy, different groups of coupling elements may be utilized to generate the desired RF output signal, and the signal quality of a so obtained RF output signal may be assessed. If a specific group exhibits a particularly poor signal quality, e.g. regarding spectral shape, it may be concluded that one or more coupling elements which are associated with the currently used group of coupling elements comprise substantial deviations from their desired operating parameters. By altering the scheme according to which coupling elements are associated with a specific group to be used next for signal generation, defective coupling elements may be identified in an iterative process. A specific advantage of this variant is the fact that a regular RF signal generation, is not required to be interrupted for identifying defective coupling elements. According to a further preferred embodiment, the signal processing means 22 ( According to a further preferred embodiment, said signal processing means 22 are configured to simultaneously stimulate at least two coupling elements of a sub-array, whereby a signal power of the generated RF signal RF_out may be increased. Preferably, all coupling elements of a specific (constructive or virtual) sub-array will simultaneously be stimulated to achieve a maximum RF output signal power. According to a further advantageous embodiment, during a manufacturing process of the RF signal generator 100, 100a, specifically of the coupling elements 2, a number of coupling elements may be produced which exceeds the nominal number of coupling elements that is required for achieving a specific RF output signal energy. After said step of manufacturing, a calibration 200, 210 ( According to a further embodiment, the signal processing means 22 are configured to determine such coupling elements, an actual resonance frequency and/or an actual attenuation of which is not within a predetermined frequency range and/or attenuation range, and to omit respective coupling elements when generating said RF signal, whereby the linearity of the generated RF output signal and an overall spectral quality of the RF output signal may be increased. According to a further embodiment, the RF generator 100, 100a is configured to provide an RF signal RF_out which comprises a plurality of spectral components, and wherein for each spectral component at least one coupling element 2, preferably a plurality of coupling elements, is provided, which comprise a resonance frequency that is associated with the respective spectral component. According to a further embodiment, the stimulating means comprise a plurality of stimulating impulse generators IG1, .. , IG1', .., IG4', wherein groups of coupling elements, or preferably single coupling elements, are assigned to a respective stimulating impulse generator. Thus, either individual coupling elements may be stimulated in an isolated manner, or advantageously a simultaneous stimulation of several coupling elements may be effected. Instead of providing constructive sub-arrays SA1, SA2, .. ( The aforedescribed embodiments of the RF signal generator and the method of operating such RF signal generator are not limited to coupling elements as depicted by The description and drawings merely illustrate the principles of the invention. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described or shown herein, embody the principles of the invention and are included within its spirit and scope. Furthermore, a11 examples recited herein are principally intended expressly to be only for pedagogical purposes to aid the reader in understanding the principles of the invention and the concepts contributed by the inventor(s) to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. Moreover, all statements herein reciting principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to encompass equivalents thereof. |