US2866115A - Transit time modulator - Google Patents

Transit time modulator Download PDF

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Publication number
US2866115A
US2866115A US675103A US67510357A US2866115A US 2866115 A US2866115 A US 2866115A US 675103 A US675103 A US 675103A US 67510357 A US67510357 A US 67510357A US 2866115 A US2866115 A US 2866115A
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United States
Prior art keywords
collector electrode
electrode
electrons
grid
transit time
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Expired - Lifetime
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US675103A
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English (en)
Inventor
Noel W Ledbetter
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LENKURT ELECTRIC CO Inc
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LENKURT ELECTRIC CO Inc
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Priority to BE568458D priority Critical patent/BE568458A/xx
Application filed by LENKURT ELECTRIC CO Inc filed Critical LENKURT ELECTRIC CO Inc
Priority to US675103A priority patent/US2866115A/en
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Publication of US2866115A publication Critical patent/US2866115A/en
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J25/00—Transit-time tubes, e.g. klystrons, travelling-wave tubes, magnetrons
    • H01J25/78—Tubes with electron stream modulated by deflection in a resonator
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03C—MODULATION
    • H03C3/00—Angle modulation
    • H03C3/30—Angle modulation by means of transit-time tube

Definitions

  • This invention relates to apparatus for modulating the phase or frequency of an electric signal by varying the transit time or transmission delay of the signal through an electron tube.
  • an improved transit time modulator comprises an electron tube having means for forming an electron beam, means for varying the intensity of the electron beam responsive to an input carrier signal, means for producing a variable transverse deflection of the electron beam responsive to an input modulating signal, and output means for producing an output electric signal responsive to the variations in the intensity of the electron beam.
  • the output means is disposed in slanting relation to the beam so that as the beam is deflected transversely responsive to the modulating signal the effective length of the beam and the transit time of the signal passing through the tube are varied.
  • the output means includes an electrode surface that lies along a segment of aparabola having its axis disposed perpendicular to the middle of the mean path followed by the electron beam between the deflection means and the output means. Also, means are provided for maintaining a substantially field-free drift space in which the electron beam moves at substantially constant velocity between the deflection means and output means.
  • Fig. 1 is a schematic diagram of an improved transit time modulator
  • Fig. 2 is a longitudinal section showing one construction of a drift space shield and collector electrode'for the improved transit time modulator
  • Fig. 3 is a transverse section taken alongline 3-3 of Fig. 2;
  • Fig. 4 is a fragmentary perspective view showing another construction of the drift space shield and collector electrode.
  • an improved transit time modulator employs a novel electron tube contained in an evacuated envelope 1.
  • a conventional electron ,gun comprising a cathode 2 and accelerating electrode 3 is operable to produce within envelope 1 an electron beam, represented in the drawing by broken line 4.
  • the electron gun also includes a conventional control electrode 5 for varying the intensity of the electron beam responsive to an input electric signal supplied between the control electrode and the cathode as hereinafter explained.
  • Conventional electrostatic deflection electrodes 6 and 7 are provided for producing a variable transverse deflection of beam 4 responsive to another inputelectric signal.
  • the electron beam can be deflected through a range of angular directions.
  • broken line 4 reppresents a mean or undeflected path of the electron beam while broken lines 4 and 4" represent the extreme up- Patented Dec. 23, 1958 Ward and downward deflections of the beam, respectively.
  • a collector electrode 8 is disposed in slanting relation to the electron beam, as shown, so that deflection of the beam by the deflection electrodes moves the electron beam along the slant of the collector electrode and varies the length of the electron path between the control electrode 5 and the collector electrode 8.
  • a substantially field-free drift space through which the electrons move at substantially constant velocity, is provided between the deflection electrodes and the collector electrode.
  • This field-free drift space may be defined, for example, by an electron permeable grid 9 disposed just in front of collector electrode 8, as shown, and a lateral shield 10.
  • Grid 9 serves two principal purposes. First, it prevents variations in the potential of collector electrode 8 from having a substantial effect on the transit time of electrons traveling between the deflection electrodes and the collector electrode. Second, it improves the fre quency response of the tube by providing an electrostatic shield between the collector electrode and the electrons approaching the collector electrode until such approaching electrons are closely adjacent to the collector electrode.
  • collector-electrode 8 and grid 9 which are closely adjacent to each other lie substantially along a segment of a parabola having its axis disposed perpendicular to the mean or undeflected path 4 of the electron beam between the deflection electrodes and the collector electrode.
  • Accelerating electrode 3, grid 9, and transverse shield 10 are electrically connected together and maintained at the same constant electric potential. Deflection electrodes 6 and 7 are maintained at the same average potential as accelerating electrode 3. Consequently, except for the transverse deflecting potential applied between deflection electrodes 6 and 7 as is hereinafter explained, the space between accelerating electrode 3 and grid 9 i substantially field-free and electrons travel through this space at a constant horizontal velocity.
  • Balanced modulating potentials, /2e and /2e relative to cathode 3, are applied to deflection electrodes 6 and 7, respectively, by any source 11 of an input modulating electric signal. Consequently, a modulating voltage e is applied between deflecting electrodes 6 and 7 which deflects the electron beam transversely through the angle between broken lines 4' and 4".
  • Cathode 2 is maintained at a constant negative potential relative to accelerating electrode 3 by a conventional voltage supply 12.
  • the voltage between electrode 3 and cathode 2 determines a constant horizontal component of electron velocity in the electron beam between electrode 3 and grid 9.
  • the electrons have a vertical component of velocity that is proportional to the deflecting voltage between deflecting electrodes 5 and 7 at the instant when the electrons pass between the two deflecting electrodes.
  • Control electrode 5 is connected through a resistor 13 to a negative bias voltage supply 14, which biases control electrode 5 to a negative potential relative to cathode 2.
  • an alternating carrier voltage e provided by any suitable source 15, is supplied to control electrode 5 through a coupling capacitor 16.
  • the input signal e superimposed on the bias voltage provided by supply 14 is applied between control electrode 5 and cathode 2 for modulating the intensity of the electron beam within envelope 1.
  • the intensity of the electron beam is varied as a function of the input carrier signal a and the transverse deflection of the electron beam is varied as'a function of the input modulating signal e
  • Collector electrode 8 is connected through a load resister 17 to a voltage supply 18 which preferably maintains collector electrode '8 at a more positive potential than grid 9.
  • the modulating voltage e has zero amplitude. Then the electron beam within envelope 1 is undeflected and travels in a straight line between cathode 2 and grid 9 along the mean path represented by broken line 4. As the electrons pass through grid 9 they are quickly drawn into collector electrode 8 and produce a flow of electric current into the collector electrode through load resistor 17.
  • the intensity of the electron beam is modulated by the input carrier signal e
  • a relatively dense bunch of electrons passes through control electrode of the electron gun.
  • These electron bunches travel along the electron beam between electrode 3 and grid 9 at a velocity proportional to the square root of the voltage provided by supply 12.
  • each bunch of electron flows across the space between grid 9 and collector electrode 8 current flows into the collector electrode due to the positive charges induced thereon by the electrons flowing toward the collector electrode, which charges are neutralized as the electrons enter electrode 8. Therefore, provided that the transit time of electrons between grid 9 and electrode 8 is short compared to the period of the input carrier signal e each bunch of electrons in the electron beam causes a momen tary increase in the current flowing into collector 8 and the voltage drop across load resistor 17 contains an alternating component 2 that is substantially identical to the input carrier signal :2 delayed by the transit time of the electrons between control electrode 5 and collector electrode 8.
  • the frequency response of the tube is limited by the transit time of electrons traveling between grid 9 and control electrode 8. Therefore, a high frequency response can be obtained by providing a close spacing between collector electrode 8 and grid 9 and by providing a sufllcient voltage at the collector electrode to draw the electrons quickly into the collector electrode as they pass through grid 9.
  • the transit time is made to vary as a linear function of the instantaneous amplitude of the modulating voltage c This is desirable to avoid distortion.
  • Figs. 2 and 3 show a simple construction that may be employed for collector electrode 8 and drift-space shield 10.
  • the collector electrode is identified by the reference numeral 8
  • the shield is identified by the reference numeral 10'.
  • These two parts may be made from a single strip of metal folded to a U-shaped cross-section as is best shown in Fig. 3 and cut into two electrically separate parts 8' and 10 separated by a gap 20, as shown.
  • the gap 20 is cut along a segment of a parabola so that the right edge of part 10 corresponds in shape and position to grid 9 of Fig. 1 while the left end of part 8 corresponds in shape and position to electrode 8 of Fig. 1.
  • the two flat sides of the U-shaped strip are just far enough apart for the electron beam to pass between them. Since these two flat sides are close together and are electrically conductive external electric fields can penetrate only a short distance into the space between the two flat sides of the metal strip. Consequently, substantially all of the space between the two flat sides of part 10' is maintained at a substantially constant electric potential and electrons travel through this space at a substantially constant velocity.
  • the principal effect of electric fields penetrating a short distance into the space between the two flat sides of part 10 is that the effective electrical width of gap 20 is somewhat wider than its actual physical width. When the electrons reach gap 20 they are quickly drawn across the gap by the voltage gradient provided by maintaining part 8 positive with respect to part 10'.
  • the frequency response of the tube depends only upon the transit time of the electrons across the electrical width of gap 20 which comprises the physical width of the gap plus some additional width due to the slight penetration of electric fields into the space between the two parallel flat sides of parts 10' and 8'.
  • this end of the U-shaped metal strip can be closed by an insert 21, as shown, or by simply pressing the two sides of the U-shaped structure together at this end.
  • collector electrode 8" has substantially the same exterior shape as collector electrode 8' of Fig. 2 but in the construction illustrated in Fig. 4 the collector electrode is made from one solid piece of metal and has no hollow interior space. 7 Therefore, the electrons strike the collector electrode immediately upon crossing the gap between the parts and 8" and there can be no widening of the gap due to the penetration of electric fields into the collector electrode.
  • the shield 10" may be substantially identical to part 10' shown in Figs. 2 and 3 but, if desired, the two flat sides of part 10" may be somewhat further apart than the two flat sides of part 10 to provide more space for the passage of the electron beam.
  • a plurality of parallel wires are welded or otherwise attached transversely across the right end of part 10" extending between the two flat parallel sides and forming a grid 9" close to but slightly separated from collector electrode 8".
  • Grid 9" corresponds to grid 9 of Fig. 1.
  • the grid reduces the penetration of electric fields into the space between the two flat parallel sides of part 10" and thus makes the effective electrical width of the gap between parts 10" and 8" more nearly equal to the physical width of the gap. This increases the frequency response of the tube and makes possible the use of the apparatus with higher carrier frequencies.
  • the transit time modulators herein described can be used for a considerable variety of purposes.
  • the size of the tube and the magnitude of the voltage supplied by supply 12 are made such that the transit time along path 4 differs from the transit time along 4 by one period of the carrier signal e then a full 360 degrees of phase modulation is easily obtained responsive to a modulating voltage e of moderate amplitude.
  • the output means essentially the gap between grid 9 and collector electrode 8 or its equivalent
  • the instantaneous phase shift can be made linearly proportional to the instantaneous amplitude of the modulating voltage, thereby providing modulation of exceptionally low distortion which is difiicult to obtain by other methods.
  • the modulating voltage e has a sawtooth waveform providing successive 360 degree phase shifts separated by relatively short flyback intervals low-distortion frequency translation can be achieved without resort to the heterodyne principle.
  • electrostatic deflection electrodes 6 and 7 can be replaced with magnetic deflection means in a manner similar to the common use of magnetic deflection in television picture tubes.
  • magnetic deflection is employed a slight reshaping of the collector electrode 8 and grid 9 may be desirable due to the wellknown diflferences between the electron ballistics of electrostatic and magnetic deflection.
  • corrections will generally not be large and in practical cases will often be negligible.
  • a transit time modulator comprising an evacuated envelope, an electron gun for producing an electron beam within said envelope, said gun including a cathode, a control electrode, and an accelerating electrode, means for supplying a first variable voltage between said control electrode and said cathode for varying the intensity of said beam, a collector electrode disposed in slanting relation to said beam, deflection means for producing a variable transverse deflection of said beam to move said beam along the slant of said collector electrode, and shielding means for maintaining a substantially field-free space through which the electrons of said beam travel at substantially constant velocity between said deflecting means and said collector electrode, said shielding means comprising a folded metal strip having a substantially U- shaped cross section.
  • An electron tube comprising within an evacuated envelope the combination of an electron gun operable to produce an intensity modulated electron beam, a conductive shield having two parallel flat sides disposed on opposite sides of said beam, and a collector electrode for receiving said beam, said colector electrode and said shielding means being separated by a gap having the shape of a segment of a parabola, said gap being disposed in slanting relation to said beam.

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US675103A 1957-07-30 1957-07-30 Transit time modulator Expired - Lifetime US2866115A (en)

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Application Number Priority Date Filing Date Title
BE568458D BE568458A (en(2012)) 1957-07-30
US675103A US2866115A (en) 1957-07-30 1957-07-30 Transit time modulator

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2071382A (en) * 1937-02-23 Electron discharge device
US2290587A (en) * 1939-03-14 1942-07-21 Rca Corp Phase modulator
US2401740A (en) * 1941-05-28 1946-06-11 Rca Corp Electron discharge device
US2519443A (en) * 1947-11-04 1950-08-22 Hartford Nat Bank & Trust Co Mixing or detector circuit arrangement

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2071382A (en) * 1937-02-23 Electron discharge device
US2290587A (en) * 1939-03-14 1942-07-21 Rca Corp Phase modulator
US2401740A (en) * 1941-05-28 1946-06-11 Rca Corp Electron discharge device
US2519443A (en) * 1947-11-04 1950-08-22 Hartford Nat Bank & Trust Co Mixing or detector circuit arrangement

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BE568458A (en(2012))

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