Classifications

• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03F—AMPLIFIERS
  • H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
  • H03F3/54—Amplifiers using transit-time effect in tubes or semiconductor devices
  • H03F3/56—Amplifiers using transit-time effect in tubes or semiconductor devices using klystrons
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03F—AMPLIFIERS
  • H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
  • H03F3/54—Amplifiers using transit-time effect in tubes or semiconductor devices
  • H03F3/58—Amplifiers using transit-time effect in tubes or semiconductor devices using travelling-wave tubes

Definitions

• This invention relates to an amplifier equipped with microwave tubes with progressive uncles (TOP) which constitute the last stage of telecommunications transmitters used in ground-satellite and satellite-ground links. They can also be used in other types of transmitters intended for example for military, scientific, metrology, telecommunications, terrestrial links, radio-relay systems, etc.
• TOP progressive uncles
• Figure 1 shows the block diagram of this last stage which comprises a microwave tube 10 of the TOP type attacked by a signal Ue which is a modulated electromagnetic wave coming from a preamplifier 12 and low level stages, This signal is of l order of a few tens of milliwatts at a frequency included in a “telecommunication” band, for example 12.75 - 14.50 GHz.
• the amplifier drives a load which is in this example a transmitting antenna 14.
• a power supply 15 supplies the various high voltages necessary for the operation of the tube.
• the TOP 10 is with a depressed collector. Its output is on a rectangular or coaxial guide, for example WR 75.
• a filter 16 at the output of the TOP is imposed by "telecommunications" standards; it makes it possible to avoid the emission of undesirable frequencies which would be generated due to the non-linearities of the TOP.
• a circulator 18 after the filter 16 prevents any untimely reflection of microwave energy towards the tube.
• a first coupler 20 at the output of the circulator 18, followed by the appropriate transitions and cables, makes it possible to make available on a front face of the amplifier, a sample of the output power Ps of the amplifier for measurement, if necessary, by the user.
• a second coupler 22 at the output of the circulator, followed by a high frequency (HF) detection 24 and suitable cables and transitions, allows the generation of a signal representative of the output power Ps, necessary for the proper functioning of the control device and regulation (not shown in the figure) of the TOP.
• HF high frequency
• a third coupler 26 followed by another HF detection 28 likewise allows the generation of a signal representative of the reflected power Pr by the user, in this example by the transmit antenna 14.
• This reflected power signal is often implemented in a threshold system, which makes it possible to save all the equipment in the event of significant mismatching of this use.
• the second 22 and third 26 couplers are, of course, associated with tables and, for example, calibration cards.
• Figure 2 shows the simplified diagram of a traveling wave tube 30.
• a relatively thin, cylindrical electron beam 32 emitted by a TOP cathode 34 circulates along the axis ZZ 'of a metal helix 36.
• An RF input signal to be amplified is injected at a first end 38 of the propeller, at frequency F.
• the interaction between the electron beam 32 and the electromagnetic signal propagating on the propeller 36 is such that the electrons regroup in periodic packets, at the frequency F, and cede their energy to the radiofrequency (RF) input signal which happens to be thus amplified and extracted at the other end 40 of the helix (RF output).
• RF radiofrequency
• the electrons thus yield 20 to 30% of their energy to the input RF signal. This percentage of energy transfer (20 to 30%) is called "electrical efficiency".
• the electrons After leaving the helix, the electrons enter a collector 42 where they should dissipate, in thermal form, the 80 to 70% of their remaining kinetic energy.
• the collector 42 is brought to a potential Vc which makes it possible to slow down the electrons before they hit the walls of the collector.
• the maximum value of the collector voltage Vc is imposed by the prohibition on reflecting electrons towards the helix.
• Figure 2 illustrates this phenomenon.
• the electrons enter the helix at the speed Vi corresponding to a voltage of 10 Kv. After yielding 2 kW, they exit the propeller at a lower speed V 2 , which corresponds to 8 Kv since the beam is 1 A.
• the voltage Vc of the collector has been chosen to be equal to 6 kV relative to the cathode. No electron is therefore reflected.
• the collector voltage Vc could even have been chosen much lower, for example at 2 Kv, value beyond which the electrons would have been reflected.
• the electrons do not exit at the speed V 2 , but with a dispersion of velocities, often quite wide, around V, hence the margin taken in the choice of Vc.
• the braking of the electrons by the collector voltage Vc reduces the energy to be dissipated thermally on the walls, and therefore the energy taken from the high voltage supply of the electron beam.
• the overall yield then becomes more important.
• FIG. 3 shows such a traveling wave tube comprising a four-stage collector E1, E2, E3, E4.
• the role of the first stage E1 is to brake and collect the slowest electrons, the last stage E4, at the bottom of the collector, the fastest electrons.
• FIG. 4 represents a section in the area of the electrodes E1, E2, E3 and E4 of the collector of such a TOP tube with four stages.
• the electron beam 32 at the outlet of the propeller 36, arriving in the area of the collectors, disperses along direct paths 52 (in solid lines) and secondary paths 54 towards the four electrodes.
• the lines in dotted lines show the equipotentials 56.
• Recent measurements carried out within the framework of improvements in the implementation of TOP in telecommunications transmitters have shown that it exists, for example, in the case of a TOP with collector two-stage depressed, a relationship between the high frequency output power Ps of the TOP and the collector current. Indeed, the current Here generated by the first stage E1 of the collector is a unique and increasing function of the modulation rate of the beam current and therefore of the output power Ps at high frequency.
• a first object of the invention is to simplify the measurements of the output powers of a tube microwave amplifier. Another object is to reduce the cost of the amplifier by eliminating parts and adjustments necessary in the state of the art for measuring the power of microwave tube amplifiers.
• the invention provides a method for measuring the RF output power of a microwave tube amplifier, the tube comprising an electron gun providing an electron beam, a RF circuit for interaction between an RF signal and the electron beam, the RF circuit having an amplified RF signal output, a collector having at least two electrodes for collecting the electron beam, these electrodes being respectively separated from the barrel by increasing distances, the first electrode being closest to the barrel, characterized in that the RF output power at the output of the amplified RF signal is determined from the measurement of the current Here, coming from the first electrode, a calculation of the power RF output being effected by a predetermined relationship between said current Here and the output power of the amplifier.
• the simplification proposed therefore consists in replacing the direct measurement and / or the HF detection of the RF output power Ps by the sole measurement of the current Here of the first electrode of the collector of the tube.
• This measurement of Here is sufficiently precise to satisfy the indication of power on the front face of the amplifier and especially for the needs of controlling the entire supply of the TOP, the processing logic of the amplifier and the various signal processing.
• the invention also relates to a microwave tube amplifier, the tube comprising an electron gun providing an electron beam, an RF circuit for interaction between an RF signal and the electron beam, the RF circuit having a signal output.
• Amplified RF a collector having at least two electrodes for collecting the electron beam, these electrodes being respectively separated from the barrel by increasing distances, the first electrode being the closest to the barrel, characterized in that it comprises first means for measuring the current Here from the first electrode and second means for determining the RF output power from the measurement of this current Here.
• TOP traveling wave tube
• FIG. 5 shows the block diagram of an amplifier according to the invention comprising a TOP
• FIGS. 7a, 7b, 7c and 7d show variation curves of the output power Ps as a function of the current of the first electrode of a four-stage TOP;
• FIG. 8 shows a circuit for measuring the collector current of the amplifier of Figure 5 according to the invention.
• FIG. 5 shows a block diagram of an amplifier 70 according to the invention comprising a TOP.
• the amplifier 70 comprises the microwave tube 10 of the TOP type with a depressed collector driven by an RF input signal coming from the preamplifier 12.
• the amplifier drives through the filter 16 and the circulator 18 the transmit antenna 14.
• a power supply 72 supplies the various high voltages necessary for the operation of the tube.
• the amplifier further comprises a circuit 74 for measuring the current Here coming from the first electrode E1 of the TOP.
• FIG. 6a represents a curve 80, of the output power
• FIG. 6b represents a curve 64 the output power Ps as a function of the current Here of a TOP of nominal power 750W operating in the band C.
• FIG. 6c represents another curve 88 of the output power Ps as a function of the current Here of the TOP of FIG. 5b of 750W operating in the frequency band 12.75-14.5 GHz.
• FIG. 8 shows a circuit for measuring the collector current Here of the first stage E1 of the TOP 10 of the amplifier of FIG. 5 according to the invention.
• the high voltage power supply 72 supplies, through a transformer TX1, an alternating voltage U1 to a high voltage rectifier bridge P1 comprising rectifying diodes D1, D2, D3, D4 supplying the high direct voltage Vc1 and the current Here of the first electrode E1 from the TOP.
• a current transformer TX2 of the measurement circuit 74 comprises a primary 120 in series with a wire 122 for supplying alternating current to the high-voltage rectifier bridge P1 and a secondary 124 generating an alternating voltage Uc1 proportional to the alternating current in the representative wire 122 Here the current for supplying the electrode E1.
• the voltage Uc1 after rectification by a bridge P2 of diodes D6, D7, D8, D9 is amplified by a conventional operational amplifier A1 which supplies, at its output Sa, a voltage Us1 proportional to the current Here of the first electrode E1.
• the processing circuit 76 of known type establishes the relationship, as described above, between the voltage Us1 output of the detector 74 representative of the current Here and the output power Ps of the amplifier
• This processing circuit 76 can be a computer using for example a microprocessor or any other computing device.
• the third coupler 26 for the measurement of the reflected power, Pr, by the user, can also be omitted insofar as the circulator 18 protects the TOP.
• the amplifier according to the invention has the following advantages:

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• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Amplifiers (AREA)
• Microwave Amplifiers (AREA)

Applications Claiming Priority (3)

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• 2002
  • 2002-03-29 FR FR0203974A patent/FR2837997B1/fr not_active Expired - Fee Related
• 2003
  • 2003-03-18 WO PCT/FR2003/000861 patent/WO2003084057A2/fr not_active Ceased
  • 2003-03-18 US US10/509,381 patent/US20050174169A1/en not_active Abandoned
  • 2003-03-18 EP EP03725302A patent/EP1490965A2/de not_active Withdrawn

Non-Patent Citations (1)

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