Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01Q—ANTENNAS, i.e. RADIO AERIALS
  • H01Q3/00—Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system
  • H01Q3/26—Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system varying the relative phase or relative amplitude of energisation between two or more active radiating elements; varying the distribution of energy across a radiating aperture
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01Q—ANTENNAS, i.e. RADIO AERIALS
  • H01Q3/00—Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system
  • H01Q3/26—Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system varying the relative phase or relative amplitude of energisation between two or more active radiating elements; varying the distribution of energy across a radiating aperture
  • H01Q3/30—Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system varying the relative phase or relative amplitude of energisation between two or more active radiating elements; varying the distribution of energy across a radiating aperture varying the relative phase between the radiating elements of an array
  • H01Q3/34—Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system varying the relative phase or relative amplitude of energisation between two or more active radiating elements; varying the distribution of energy across a radiating aperture varying the relative phase between the radiating elements of an array by electrical means
  • H01Q3/36—Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system varying the relative phase or relative amplitude of energisation between two or more active radiating elements; varying the distribution of energy across a radiating aperture varying the relative phase between the radiating elements of an array by electrical means with variable phase-shifters
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01Q—ANTENNAS, i.e. RADIO AERIALS
  • H01Q3/00—Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system
  • H01Q3/26—Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system varying the relative phase or relative amplitude of energisation between two or more active radiating elements; varying the distribution of energy across a radiating aperture
  • H01Q3/30—Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system varying the relative phase or relative amplitude of energisation between two or more active radiating elements; varying the distribution of energy across a radiating aperture varying the relative phase between the radiating elements of an array
  • H01Q3/34—Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system varying the relative phase or relative amplitude of energisation between two or more active radiating elements; varying the distribution of energy across a radiating aperture varying the relative phase between the radiating elements of an array by electrical means
  • H01Q3/40—Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system varying the relative phase or relative amplitude of energisation between two or more active radiating elements; varying the distribution of energy across a radiating aperture varying the relative phase between the radiating elements of an array by electrical means with phasing matrix

Definitions

• a beamforming circuit for a phased array antenna of the coupled oscillator chain type is disclosed.
• the invention also relates to a phased array antenna system comprising such a circuit.
• the invention is intended in particular for applications in the fields of telecommunications, radars and medical imaging.
• the transmitter radiates in all directions and only a small fraction of this radiated power is picked up by the receiver.
• a large part of the radiated power is lost or, worse, it is reflected on different obstacles generating on the one hand fading due to destructive interference between contributions having followed different paths, and on the other hand a electromagnetic pollution affecting other users.
• the use of "intelligent" directional beam antennas can reduce this electromagnetic pollution and improve the quality of transmission, both in terms of increasing the signal-to-noise ratio on the receiving side by reducing the level of received interference or the increase of the radiated power on the transmitter side.
• Dynamic beam orientation can be achieved through the use of implanted antennas in a specific geometric configuration.
• the simplest configuration is that of the linear phased array, in which several antenna elements are aligned along a line (more rarely on a curve). Under these conditions, the orientation and the beam formation are obtained by controlling the amplitude and / or the phase of the radiofrequency signal supplying each of the radiating elements that constitute this network.
• FIG. 1 illustrates an antenna system comprising a linear phased array RPL, a CFF beam forming circuit and a radio frequency signal source SRF.
• the SRF source generates a radio frequency signal, which can be modulated to carry information.
• the CFF beamforming circuit comprises a radio frequency power divider DPRF which distributes the input signal from the source SRF between several outputs (five in the example of the figure).
• the distribution can be homogeneous or inhomogeneous, fixed or variable.
• a variable power distribution makes it possible to control the shape of the radiation pattern of the antenna system, in addition to its orientation.
• Each output of the power divider is connected to a respective phase shifter DP1 - DP5 introducing a variable phase shift which makes it possible to control the orientation of the radiation diagram of the antenna system; variable attenuators or amplifiers can also be provided to control the shape of this diagram, as an alternative or in addition to the use of a variable distribution power divider.
• each phase shifter feeds an antenna element
• EA1 - EA5. These elements are aligned at a distance of half a wavelength to minimize electromagnetic coupling
• Figure 2 provides an understanding of the formation and orientation mechanism of a radiation pattern.
• the amplitude of the total electric field radiated by the M antennas is:
• the reference DR identifies the radiation pattern emitted by the phased array; typically this diagram consists of a main lobe and several side lobes (only two are represented).
• the shape of the radiation pattern In addition to controlling the orientation of the radiation pattern, it is possible to influence the shape of the radiation pattern by acting on the amplitudes of the signals supplying the antennas. Moreover, since the elemental antenna is not isotropic, the shape of the radiation pattern also depends on its orientation: if we do not intervene on the amplitudes of excitation of the antennas, the central lobe widens when the value of the angle ⁇ increases.
• Articles [1] and [2] illustrate the state of the art in the field of conventional linear phased array antenna systems of the type shown in FIG.
• a disadvantage of this architecture stems from the complexity of the beam forming circuit, which comprises at least M phase shifters (one per antenna), each driven by a separate control signal.
• This figure shows a linear phased array antenna system in which the control circuit, or beamformer, essentially consists of a chain of electronic oscillators 01 - OM, which will be assumed by identical simplicity, coupled between they via respective coupling impedances Z c which, they too, will be assumed to be identical to each other. More precisely, each oscillator of the chain is coupled to its two nearest neighbors via an impedance, which can be purely resistive or reactive; Oscillators at the ends of the chain (O1 and OM) are coupled to their nearest single neighbor. At least said end oscillators have a free oscillation frequency that can be controlled; in practice, they will be voltage controlled oscillators (VCO). Preferably, all the oscillators will be VCOs, although only the two ends are actually controlled by respective control voltages V01, V02.
• VCO voltage controlled oscillators
• the different free frequencies of the oscillators are within a certain synchronization range. Under these conditions, within this range, the oscillators spontaneously synchronize with a phase relationship related to the initial distribution of their free oscillation frequencies. More precisely, if all the intermediate oscillators (02 - O (M-1)) have the same oscillation frequency f 0 while the end oscillators have free oscillation frequencies fo- ⁇ and fo + ⁇ , then an identical phase shift ⁇ is established between the adjacent oscillators. It can be shown that the phase shift ⁇ is independent of the number of oscillators constituting the network. Thus, by controlling only the free oscillation frequencies of the oscillators located at the two ends of the linear array (two control signals), it is possible to obtain a linear phase variation whose gradient depends on ⁇ .
• the architecture of FIG. 3 therefore makes it possible to orient the radiation pattern of a linear phased array antenna system, but not to modify its shape except to introduce variable attenuators, which would be contrary to the goal sought, namely a simplification of the control circuit.
• FIG 4 shows how the phase difference between two coupled oscillators depends on the difference between their free oscillation frequencies.
• the oscillators are two VCOs, coupled via a series RLC (resistive - inductive - capacitive) circuit.
• RLC resistive - inductive - capacitive
• the invention aims to remedy the disadvantages of the prior art by providing a beam forming circuit associating the simplicity of the architecture of FIG. 3 with a flexibility close to that of the conventional architecture of FIG. 1.
• An object of the invention making it possible to achieve this goal, is a beam forming circuit for a phased array antenna comprising a linear chain of coupled radio frequency electronic oscillators, in which at least two oscillators located at the ends of said chain present a variable free oscillation frequency, said circuit being characterized in that said oscillators are of differential type, each of them being adapted to generate a first oscillatory signal, said positive, and a second oscillatory signal, said negative, in opposition perfect phase.
• Radio frequencies means frequencies between 1 MHz and 300 GHz; this includes microwave or microwave (1 - 100 GHz) as well as millimeter wave (100 - 300 GHz).
• chain of coupled oscillators is meant a set of oscillators provided with an order relation, in which each oscillator is coupled to its two nearest neighbors, except the first and the last oscillator, which are coupled only to each other. 'to their only closest neighbor.
• the coupling can be done, generally, via an electrical circuit, purely resistive, purely reactive or both resistive or reactive. Electromagnetic coupling may also be considered in some cases. Typically, but not necessarily, the coupling strength can be the same between all pairs of oscillators.
• the phased array of the invention may be linear. It can also be a two-dimensional network constituted by a plurality of linear sub-networks. It can also be a two-dimensional network matrix structure in which each oscillator feeds several antenna elements forming the same row or the same column of the matrix.
• All the oscillators in the chain can be identical to each other, although this is not essential.
• all oscillators may be voltage controlled oscillators.
• the circuit may also comprise a plurality of multiplexers for selecting, from each oscillator, one or the other of said first and second oscillatory signals.
• Such a circuit may also comprise a control system of said multiplexers adapted to:
• the circuit may comprise, in place of the multiplexers, a plurality of modulators (for transmission operation) or demodulators (for reception operation ), each of said oscillators being connected to a respective modulator or demodulator to serve as a local oscillator.
• the beam forming circuit may also comprise a system for distributing to said modulators a baseband signal, said distribution system being adapted to: in a first state, distribute said signal to all modulators with the same phase; and, in a second state, distributing an inverted signal to every alternate modulator.
• the beam forming circuit may also comprise a system for forming a baseband signal: in a first state, by directly adding the signals demodulated by said demodulators; and in a second state, adding said signals after inverting those from one demodulator out of two, alternatively.
• said modulators may be vector modulators and said baseband signal may be a vector signal comprising a component I and a Q component in quadrature.
• Said modulators / demodulators may be Gilbert cell modulators / demodulators, or more generally, translinear, preferably operating in differential mode.
• the oscillators can be coupled to their nearest neighbors via variable resistors, preferably in the form of field effect transistors.
• variable resistors preferably in the form of field effect transistors.
• Such a circuit may also comprise a control system for symmetrically and in opposite directions to vary the free oscillation frequencies of the two said oscillators at the ends of the chain, and to vary the values of said variable resistors while keeping them equal between they.
• Another object of the invention is a phased array antenna system comprising a beam forming circuit as described above, as well as a plurality of antenna elements arranged to form a phased array powered by said circuit.
• Figure 2 the principle of controlling the orientation of the radiation pattern of such an antenna system
• Figure 3 is a block diagram of a phased array antenna system of the coupled oscillator chain type, known from the prior art
• FIG. 4 a graph illustrating the phase difference between two coupled oscillators as a function of the difference between their free oscillation frequencies
• Figure 5 is a block diagram of an antenna system according to a first embodiment of the invention.
• FIG. 6 the electrical diagram of a voltage controlled oscillator realized in MOS technology used for the implementation of the system of FIG. 5;
• FIG. 7 is a block diagram of an antenna system according to a second embodiment of the invention.
• FIGS. 8A and 8B respectively, the block diagram of a vector modulator used for implementing the system of FIG. 7, and a Gilbert cell forming part of such a modulator;
• FIG. 9 a graph illustrating the phase shift between two oscillators coupled across a resistor, as a function of the value of said resistor and for three different differences between their free oscillation frequencies;
• Figure 10 is a block diagram of an antenna system according to a third embodiment of the invention.
• Figure 1 the block diagram of an antenna system operating in reception, according to a fourth embodiment of the invention.
• the present inventors have realized that it is possible to overcome the limitations of the beamforming circuit of FIG. 3 and to obtain almost arbitrary phase shifts - and thus almost total variability in beam misalignment angle.
• antenna - simply by replacing the "single output" oscillators with differential oscillators.
• FIG. 5 illustrates a linear phased array antenna system according to a first embodiment of the invention.
• the circuit of control (or beamformer) of this system is constituted by a plurality of identical voltage controlled differential (VCO) oscillators (five, in the example shown in the figure, but the number could be much higher, for example understood between eight and several tens) VC01 - VC05.
• VCO voltage controlled differential
• oscillators other than the two extremes could have a constant free oscillation frequency.
• FIG. 6 illustrates the wiring diagram of a conventional VCO in MOSFET technology, of the single cross-pair type.
• the active part of this circuit consists of two N-MOS transistors T1 and T2 coupled in such a way that the gate signal of T1 is taken from the drain of T2 and vice versa.
• the transistors are biased downwards by means of a current mirror MC.
• Their drains are connected to a line maintained at the potential Vcc via respective LRC circuits, in which the capacitance (CV1, CV2) is realized by means of a VARACTOR diode so as to depend on a control voltage.
• the operation of such a circuit is known per se and described, for example, by [6].
• VCO structures are known from the prior art and can be applied to the invention.
• Each oscillator has two output terminals, for two differential signals Vd1, Vd2 in phase opposition.
• the phases of the positive and negative differential voltages present on the i th VCO (VCOi) are denoted respectively ⁇ , and ⁇ ⁇
• the adjacent oscillators are coupled together by coupling impedances Z c connected between their output terminals.
• Each oscillator is associated with a respective multiplexer MUX ' i which makes it possible to apply the signal having the phase ⁇ , or else ⁇ ⁇ to the input of a respective power amplifier HPAi, the output of which is connected to an element of antenna, or radiator, EAj, which can be for example of the electromagnetic horn type or "patch".
• Each multiplexer is controlled by a respective control signal.
• this signal can take two values represented by 0 and 1; when the signal is equal to 0, the multiplexer MUXi selects the "positive" output signal of the oscillator VCOi, that is to say ⁇ , and when the signal is equal to 1, it selects the "negative" output signal , ie ⁇ ⁇ ⁇ ⁇
• the maximum phase shift that can be obtained between two adjacent oscillators eg ⁇ ⁇ , and ⁇ + 1 or ⁇ and ⁇ ⁇ + ⁇
• the fact of having complementary phases makes it possible to widen the depointing dynamics. Indeed, it is possible to imagine several scenarios.
• Scenario 1 0 ° ⁇ ⁇ + 90 ° (0 ° ⁇ eEmax ⁇ + 30 o ).
• phase shift values can be obtained by controlling the free oscillation frequencies of the two oscillators placed at the ends (VC01 and VC05). Under these conditions, all the control voltages of the multiplexers are identical to select only the signals having a phase ⁇ or else ⁇ ⁇ .
• Scenario 2 -90 ° ⁇ ⁇ 0 ° (-30 o ⁇ e E max ⁇ 0 °).
• This phase shift ⁇ 3 ⁇ is obtained thanks to the controls of the two oscillators located at the ends VC01 and VC05. Under these conditions, this phase shift ⁇ 3 ⁇ [-90 °, 0 °] lies in the operating range of the synchronized oscillators (-90 ° ⁇ 3 ⁇ ⁇ 90 °).
• ⁇ ⁇ 3 2.
• the signals applied to the antennas will therefore be taken alternately on the positive phase and the negative phase. It is therefore possible to vary the angle of misalignment of the antenna beam in the range of -90 ° to + 90 °, so 180 °, with only two "forbidden regions" around ⁇ 30 °. If the antenna beam is not too narrow, these forbidden areas have few practical consequences.
• control signal Vi for each multiplexer, and therefore for each oscillator, plus two V01 and V02 signals controlling the free frequencies of the two oscillators placed at the ends of the chain.
• phase shifts the phases to be retained are alternately ⁇ and ⁇ ⁇ + 1 or the inverse ⁇ , and ⁇ , + ⁇ . This implies that the control voltages applied to two multiplexers corresponding to adjacent antennas are of opposite signs.
• V1 and V2 are respectively applied to the even and odd multiplexers.
• V1 is a reference and to control only V2, thus limiting the control number to three (V2, V01, V02), which is perfectly acceptable from a system point of view.
• SYC a control system
• This system could be criticized for providing no advantage over the use of non-differential VCOs coupled to each other, to which differential amplifiers or follower or inverter amplifiers controlled by an identical control system would be associated. to the one described here.
• SYC preferably digital and for example microprocessor.
• This system could be criticized for providing no advantage over the use of non-differential VCOs coupled to each other, to which differential amplifiers or follower or inverter amplifiers controlled by an identical control system would be associated. to the one described here.
• it is necessary to ensure very high accuracy on the phase and therefore a very great control of the propagation time of the different signals. This is very difficult taking another architecture than the one proposed.
• the main limitation of the system of Figure 5 is that it does not allow to transmit data efficiently. Indeed, because of the non-idealities of voltage-controlled oscillators, the synchronization frequency of the overall system depends (slightly) on the frequencies imposed by the oscillators placed at the ends. This variation, however small, can be troublesome for an application such as data transmission for which the frequency of the carrier must be stable. However, it is perfectly acceptable in the field of radar, where bursts of frequencies are sent in different directions.
• the multiplexers MUX 1 are replaced by vector modulators MV 1, preferably of the translinear type with Gilbert cell.
• FIG 8A illustrates the structure, known per se, of such a modulator.
• the radiofrequency carrier is of differential type, consisting of two sinusoidal signals in phase opposition, P + and P-; the VC01 - VC05 differential oscillators naturally provide these signals and thus serve as local oscillators.
• a quadrator CQ circuit decomposes both the positive phase and the negative phase of the carrier into two components in quadrature, that is to say out of phase by 90 ° - what are called the components "I” and "Q" (PI + , PQ +, PI-, PQ-).
• the two positive and negative phases of carrier I are provided to a first Gilbert CG1 cell, where they are multiplied by a first baseband signal Si (t), which contains a first half of the information to be transmitted.
• the two phases, positive and negative, of the carrier Q are supplied to a second cell of Gilbert CG2, where they are multiplied by a second baseband signal SQ (Î.), which contains a second half of the information to be transmitted.
• the baseband signals are of the differential type, such as the P + / P- carrier. For the sake of simplicity, this is not shown in FIGS. 7, 8A and 10,
• the output signals of the two Gilbert cells are summed, generally by means of a radiofrequency transformer, not shown, to form the (unipolar) output signal of the differential modulator, SO (t).
• the Gilbert cells are known, for example, from [7, 8],
• Figure 8B illustrates the wiring diagram of a Gilbert cell in MOS technology. It consists of two differential amplifiers formed by pairs of transistors coupled by their sources (Q1 / Q4; Q3 / Q5) whose outputs are connected in phase opposition. The sources of these transistors are connected to the drains of a third differential pair (Q2 / Q6); therefore, the output currents of the first two differential pairs linearly depend on the drain currents of the third pair, as well as their respective input voltages (V1 + / V1-; V2 + / V2-).
• the differential output signal, VOG is taken between the drains of Q1 / Q3 and Q4 / Q5, connected together in pairs.
• vector modulators can be used to reverse the signals sent to every other antenna element, so as to allow an orientation of the antenna beam beyond the conventional range. ° - + 30 °.
• the beam forming circuit of FIG. 7 comprises an SD system for distributing to the modulators the baseband vector signal (Si; S Q ), this distribution system being adapted to:
• the orientation of the radiation pattern is obtained by a very simple digital processing of the baseband signal.
• / SQ baseband signals may be constant at intervals, and be used only for the orientation of the radiation pattern.
• non-vector modulators typically constituted by a simple Gilbert cell.
• a circuit of the type illustrated in FIG. 7 could also be realized by using non-differential coupled oscillators, since it is the modulators that introduce the phase shifts of 180 ° allowing the orientation of the beam over a wide range of directions.
• the use of differential oscillators is very advantageous in that it makes it possible to use Gilbert's cell modulators, which reject the frequency of the carrier of the spectrum of the modulated signal thus avoiding all the problems of frequency recombination. Indeed, either a carrier P (t) characterized by a pulse COR and a baseband signal S (t), pulse o) s ⁇ w P.
• a carrier P (t) characterized by a pulse COR and a baseband signal S (t), pulse o) s ⁇ w P.
• the active components of the modulator must be polarized, a DC component is superimposed on these two signals.
• the second has the additional advantage of allowing the use of the entire signal generated. This means that there is no created signal that is not used, as in the case where one uses a multiplexing leading to discard half of the generated signals.
• the embodiment of FIG. 7 remains affected by the problem of the drift of the synchronization frequency, which depends on the difference imposed between the free oscillation frequencies fo, fo2 of the end VCOs, driven by the control signals V01, V02.
• a first solution may consist in injecting into the oscillator chain a signal from a phase-locked loop, the frequency of which is very stable. The disadvantage of this solution is the additional complexity involved.
• phase shift between two adjacent oscillators does not depend solely on the free oscillation frequency difference between the two end oscillators, but also on the strength of their coupling.
• the phase shift can be modified by acting on the value of this resistor.
• FIG. 9 shows the dependence of ⁇ as a function of R c for different values of the frequency difference f01-f02.
• FIG. 10 shows a circuit similar to that of FIG. 7, but in which the coupling impedances have been replaced by MOSFETs Mp1, Mn1-Mp4, Mn4 operating in an ohmic zone and acting as voltage-controlled variable resistors, the voltage of grid Vg serving as control signal.
• the variation of ⁇ over the entire desired range can be obtained by keeping f 01 -f 02 in a limited range.
• f 0 -f 02 can take only three values: 0, for a zero misalignment angle, + ⁇ , for a positive misalignment angle, and - ⁇ for a negative misalignment angle, any other variation being obtained in acting on the coupling resistances by applying a timely voltage to the grids of the MOSFETS.
• a control system SYC preferably digital, for example microprocessor, generates the appropriate control signals.
• the coupling resistances can be realized using other types of transistors, for example junction field effect (JFET) or high electron mobility (HEMT). They may be part of more complex coupling circuits, for example also comprising reactive elements.
• JFET junction field effect
• HEMT high electron mobility
• variable coupling resistor has been described with reference to a modulator circuit; it can also be applied to a multiplexer type beam forming circuit (FIG. 5) or even to a circuit using non-differential oscillators, of the type shown in FIG.
• FIG. 11 shows a portion (the first two antenna elements EA1, EA2, and the corresponding sections of the beam forming circuit) of such a system.
• the vector modulators MVi are replaced by demodulators, also vector, DM1, DM2, also based on Gilbert cells.
• Each demodulator receives as input the differential sinusoidal signal generated by the respective local oscillator (VC01, VC02) as well as the signal picked up by an antenna element EA1, EA2, and outputs a demodulated signal of the type vectorial: S / SQI, S
• the phase shift ⁇ between the different local oscillators has repercussions on the demodulated signals; in addition, the signals from different demodulators have an additional phase shift due to the spatial shift between the respective antenna elements.
• the antenna pattern can be oriented in the range ⁇ 30 °.
• the combination system of FIG. 10 just like the SD distribution system of FIG. 10, the combination system of FIG.
• FIG. 11 the connections between antenna elements and demodulators have been shown to be direct, but in a known manner amplifiers, filters, or even frequency converters can be provided on the paths of the signal signals. 'antenna.
• the beam forming circuit of the invention is particularly suitable for monolithic integration, for example in N-MOS or C-MOS technology.

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• 2010
  • 2010-12-23 FR FR1005095A patent/FR2969834B1/fr not_active Expired - Fee Related
• 2011
  • 2011-12-14 WO PCT/IB2011/055670 patent/WO2012085768A1/fr not_active Ceased
  • 2011-12-14 EP EP11807775.9A patent/EP2656437A1/de not_active Withdrawn

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