US3634790A - Parasitic mode suppressor - Google Patents

Parasitic mode suppressor Download PDF

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Publication number
US3634790A
US3634790A US23332A US3634790DA US3634790A US 3634790 A US3634790 A US 3634790A US 23332 A US23332 A US 23332A US 3634790D A US3634790D A US 3634790DA US 3634790 A US3634790 A US 3634790A
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Prior art keywords
mode
cavity
ring
coaxial
parasitic
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Expired - Lifetime
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US23332A
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English (en)
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Max Turteltaub
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Thales SA
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Thomson CSF SA
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
    • H01P7/00—Resonators of the waveguide type
    • H01P7/04—Coaxial resonators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
    • H01P1/00—Auxiliary devices
    • H01P1/16—Auxiliary devices for mode selection, e.g. mode suppression or mode promotion; for mode conversion
    • H01P1/162—Auxiliary devices for mode selection, e.g. mode suppression or mode promotion; for mode conversion absorbing spurious or unwanted modes of propagation

Definitions

  • the present invention relates to improvements in devices for suppressing parasitic modes in the ultrahigh frequency field and to cavities and electron tubes equipped with such devices.
  • the invention relates more particularly to the elimination of parasitic modes within cavities used as the input or output circuits of electron tubes.
  • the tuning circuits are then replaced by resonance cavities formed by terminated sections of waveguides or coaxial lines: termination is generally effected at one 'end by a short-circuiting piston which can move along the longitudinal axis of the cavity and whose distance from the. other end which is substantially equal to an odd number of quarter wavelengths, makes it possible to adjust the tuning as a function of the operating frequency.
  • the TEM mode is the one which is used, this mode being the dominant mode in this kind of circuit and having furthermore the advantage that it enables wideband transmission to be effected since there is no cutoff frequency.
  • the frequency of the TEM mode is equal to the resonance frequency of a parasitic mode of higher order, for example the TE or TM,,,, modes, where the indices m and n designate whole numbers.
  • the increase in losses, due to interference between the dominant mode and the parasitic mode drastically reduces the output power from the associated transmitter or oscillator and thus gives rise to gaps in the range of usable frequencies.
  • Filters of the kind currently employed in prior art systems for the elimination of undesired modes comprise conductive plates located perpendicularly to the lines of force of the electric field of the desired mode.
  • a series of coaxial cylindrical plates are used in a circular waveguide for transmitting the TM, modes in which the electric field is radial, and eliminating the TE modes.
  • these plates have to have a substantial length in relation to the operating wavelength, and also their presence inside the waveguide conflicts with the operation of the tuning piston.
  • attempts have been made to eliminate the T5,, mode by inserting in the coaxial cavity constituted by the electrodes of an electron tube, a ring of material having poor conductivity.
  • this ring is fixed permanently at the time of construction of the tube and, while its operation may be satisfactory for a given frequency, if any attempt to vary this frequency is made, its efficiency tails off rapidly.
  • a device for suppressing parasitic TE modes in a coaxial or cylindrical cavity comprising a generally ring-shaped structure of an electrically conductive and resistive material, coaxial with said cavity, and having apertures whose plane intersects the magnetic lines of forces of the mode to be suppressed and means for displacing said structure along said cavity.
  • FIG. 1 is an electron tube, a tuning cavity of which is equipped with the device in accordance with the invention
  • FIGS. 2, 3 and 4 indicate the configuration of the electric and magnetic fields of the TEM wave in a coaxial cavity tuned to three-fourths of the wavelength
  • FIGS. 5 and 6 show the configuration of the electric and magnetic fields of the TE mode, in the same cavity
  • FIG. 7 shows the graphs indicating the resonance frequencies common to the TEM and TE, modes as a function of the tuning of the cavity
  • FIGS. 8 and 9 show schematic sections of a preferred embodiment of the invention.
  • FIGS. 10 and 11 show schematic sections of another embodiment of the invention.
  • FIGS. 12 and 13 show schematic sections of still another embodiment of the invention.
  • FIG. 14 shows a simplified section of a tuning cavity showing the relative dispositions of the suppressor ring, the shortcircuiting piston, and their respective control elements.
  • FIG. 1 illustrates, schematically and in section, a tube 10 with a cathode 11, a grid 12 and an anode 13, the tube being connected to operate as an amplifier.
  • the input circuits and output circuits are respectively formed by coaxial cavities I4 and 15.
  • the grid-plate tuning cavity 15 is shown by way of nonlimitative example as folded around the cathode-grid cavity 14, which is a conventional arrangement in transmitter tubes for operation in the 1,000 MHz./sec. band.
  • the cavity 15 is thus formed by a conductor 16, terminated by the face 17 which is aligned with the grid 12, and by a conductor 18 terminated by the front face 19 of the cavity.
  • the input voltage is applied to the tube 10 by means of a capacitive probe 20 which penetrates into the gridcathode cavity 14 through an opening 21.
  • the output voltage is picked up by means of a capacitive probe 22 which penetrates into the grid-anode cavity through an opening 23 and is connected to the load (not shown).
  • These two cavities is generally tuned to an odd number of quarter wavelengths by means of respective short-circuiting pistons 24 and 26 of annular form which can be moved axially by means of respective control rods 25 and 27.
  • the mica capacitors 28 and 29, respectively inserted in the cathode and plate conductors, are intended to isolate the DC components of the cathode and anode currents.
  • the dominant mode in this kind of cavity is the TEM mode, shown in cross section in FIG. 2 and in longitudinal section in FIG. 3.
  • the full line arrows represent the electric field and the dotted arrows the magnetic field.
  • the tuning of the cavity will be assumed to be set at 3M4, A being the operating wavelength.
  • the effect of the terminal wall 19 will be disregarded.
  • the open end of the coaxial waveguide illustrated corresponds to a voltage antinode where the electric field is maximum and the magnetic field minimum. The same condition is produced in the transverse plane 32 at a distance M2 from the open end.
  • the end terminated by the short-circuiting piston 26 corresponds, conversely, to a voltage minimum and a current maximum; the same condition exists in the transverse plane 30, at a distance M4 from the open end.
  • the wall 19 which closes off the cavity behaves substantially as a shunt capacitor across the open end of FIG. 3: the field is modified in the manner shown in FIG. 4 and thus axially acts on the electrons in transit between the grid 12 and the plate 13.
  • the parasitic mode most frequently encountered in a coaxial cavity is the TE, mode, this'being the mode having the lowest cutoff frequency which may exist in this kind of cavity.
  • TE modes are likely to be permanently present in a coaxial line, given certain conditions, a particularly annoying situation occurs when there is resonance common to the TEM and TE modes at certain operating frequencies and tuning states of the cavity.
  • the configuration of the TE mode is illuminated in cross section and in longitudinal section in FIGS. 5 and 6, where the full line arrows represent the electric field and the dotted arrows the magnetic field.
  • FIG. 7 shows the number of common resonance conditions which exist between the TEM mode and the TE mode as a function of the tuning of the cavity and the operating frequency.
  • the full line curves relate to the TEM mode.
  • the dotted graphs relate to the TE, mode.
  • FIG. 8 and 9 respectively illustrate in transverse and longitudinal section, a preferred embodiment of the invention.
  • the device 33 in accordance with the invention consists of a ring, made up of two elements, one external ring 34, shown in greater detail in FIGS. 10 and 11, and one internal ring 35,
  • FIGS. 12 and 13 These two rings are fixed to one another and made of a material which, whilst conductive, has a high resistance to high-frequency currents.
  • the ring 35 carries a series of concentric slots 36, six in the case illustrated, the length of which is substantially in the order of magnitude of the guided TE mode half wave. Actually, it is generally more expedient to make these slots somewhat shorter in order to take account of the capacitive effect of the walls, as described hereinafter.
  • the ring 35 contains three holes which serve to attach insulating control rods 38 (see FIG. 14).
  • the outer diameter of the ring 34 is slightly smaller than the internal diameter of the wall 18 so that the ring 33 slides inside the cavity 15 without touching the wall 18.
  • the lateral part of the ring 34 in the form of a cylinder, contains a series of substantially circular holes 39 having diameters substantially in the order of one tenth of the wavelength.
  • insulating plugs 40 of Teflon for example, are inserted, one of which has been shown in the withdrawn position in FIG. 9.
  • the plugs are designed to prevent any contact between the ring 33 and the wall 18 of the cavity, to center it mechanically therein, and to insulate it electrically.
  • the lines of force of the magnetic field shown in FIGS. 2, 3 and 4 are parallel both to the flat surface of the ring 35 and to the cylindrical surface 41 of the ring 34.
  • the TEM wave is not attenuated.
  • the distribution of the fields is different: the magnetic field of the TE wave has a component in the direction of propagation of the wave, i.e. normal to the surface of the ring 35, as FIG. 6 shows.
  • FIG. 5 shows that a similar effect is obtained by the ring 34 whose lateral wall, containing the slots 39, is substantially normal to the lines of force of the magnetic field at its two maxima represented by the two points of convergence of the field in FIG. 5.
  • the slots 36 are slightly shorter than half the wavelength of the parasitic TE mode.
  • the fundamental frequency of the TE mode of which can be calculated or measured it is easy to determine the wavelength of the slots 36 and therefore the number of slots which can be cut in the ring 35.
  • the capacitive effect of the walls is substantially increased so that these slots must be shorter still than the half wavelength in order to give rise to the same resonance phenomena.
  • they can be given the form of circular orifices having a diameter in the order of one tenth of the wavelength.
  • the above reasoning shows the importance of placing the ring 33 in a zone corresponding to the maximum in the magnetic field associated with the TE mode. If the operating frequency is varied, so that the tuning of the cavity is modified too, the position of this maximum will vary as well and theoretically the position of the device 33 ought to be modified too.
  • This adjustment can be effected by means of one of the rods 38 illustrated in longitudinal section in FIGv 14.
  • the rod 38 assembled to the ring 33 by means of the holes 37, is of an insulating material and slides with no friction through the corresponding openings formed in the short-circuiting piston, the latter being operated in all cases by the control rods 27.
  • the displacement of the ring 33 by the rods 38 thus makes it possible to find the optimum position for producing maximum attenuation of the parasitic mode.
  • the operating frequency can be varied by an amount in the order of 50 MI-Iz./sec. without any necessity for readjustment of the ring 33.
  • ferromagnetic alloys such as ferronickel alloys, kovar, and so on
  • components of nickel-plated copper have been used with advantage, this system producing both the desired skin effect and a satisfactory thermal gradient.
  • the following data relate to the tuning cavity of a tube operating at frequencies in the order of 460860 MHz./sec. i.e. in the bands 4 and 5.
  • the coaxial cavity was defined by two diameters 142 mm. and mm.; a ring 33 was used in which the rim 34 had a maximum diameter of 141.4 mm. and the rim 35 an internal diameter of mm.
  • Each of the six resonance slots had a length in the order of l 18 mm. and a width of 12 mm.
  • the TE mode pulled in at a plate current of 500 ma. without the mode suppressor.
  • an anode current of 5 a. could be obtained.
  • a device 33 may be used quite both for the elimination of higher order TE modes, such as TE TE etc. in a coaxial cavity, or for the ture of an electrically conductive and resistive material. coaxial with said cavity and having apertures whose plane intersects the magnetic lines of forces of the mode to be suppressed and means for displacing said structure along said cavity, in which the ratio of the major dimension of said apertures to the half wavelength of the mode which is to be suppressed, is such that said apertures are resonant for this mode.
  • a cavity resonator comprising a device as claimed in claim I.

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US23332A 1969-03-28 1970-03-27 Parasitic mode suppressor Expired - Lifetime US3634790A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
FR6909363A FR2038783A5 (es) 1969-03-28 1969-03-28

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US3634790A true US3634790A (en) 1972-01-11

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US (1) US3634790A (es)
JP (1) JPS5246073B1 (es)
AT (1) AT300139B (es)
DE (1) DE2014545A1 (es)
FR (1) FR2038783A5 (es)
GB (1) GB1294746A (es)
SE (1) SE361109B (es)
YU (1) YU33681B (es)

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3758880A (en) * 1971-07-16 1973-09-11 Licentia Gmbh Waveguide mode coupler for separating waves of useful mode from waves of higher mode
US3995241A (en) * 1974-06-28 1976-11-30 Thomson-Csf Device for attenuating very short parasitic waves in electronic tubes with coaxial, cylindrical electrodes
US4017760A (en) * 1975-01-14 1977-04-12 Thomson-Csf Parasitic oscillation suppressor for electronic tubes
US4174492A (en) * 1976-07-19 1979-11-13 Siemens Aktiengesellschaft Device for attenuating cavity interference waves in a high-frequency electron tube
US4398121A (en) * 1981-02-05 1983-08-09 Varian Associates, Inc. Mode suppression means for gyrotron cavities
US4851788A (en) * 1988-06-01 1989-07-25 Varian Associates, Inc. Mode suppressors for whispering gallery gyrotron
EP0339374A1 (en) * 1988-04-25 1989-11-02 Matsushita Electronics Corporation A magnetron
US4926145A (en) * 1988-12-16 1990-05-15 Flam & Russell, Inc. Radial power combiner/divider with mode suppression
US6558137B2 (en) * 2000-12-01 2003-05-06 Tecumseh Products Company Reciprocating piston compressor having improved noise attenuation
US20080238231A1 (en) * 2007-03-30 2008-10-02 Carter Daniel L Mounting Device and Method For Positioning A Motor Within An Image Forming Apparatus

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2456653A (en) * 1942-12-10 1948-12-21 Sperry Corp Seal for high-frequency transmission lines
US2593234A (en) * 1945-05-12 1952-04-15 Bell Telephone Labor Inc Cavity resonator
US2605459A (en) * 1943-10-23 1952-07-29 Jackson H Cook Monitoring apparatus for radio pulse transmission systems
US2710945A (en) * 1947-09-26 1955-06-14 Bell Telephone Labor Inc Mode suppression in resonant cavities
US3087089A (en) * 1957-10-26 1963-04-23 Telefunken Gmbh Line to travelling wave tube coupling
US3475707A (en) * 1966-12-21 1969-10-28 Varian Associates Porous intermediate layer for affixing lossy coatings to r.f. tube circuits
US3502934A (en) * 1967-09-15 1970-03-24 Varian Associates High frequency electron discharge devices having improved mode suppression means for cavities with re-entrant drift tubes

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2456653A (en) * 1942-12-10 1948-12-21 Sperry Corp Seal for high-frequency transmission lines
US2605459A (en) * 1943-10-23 1952-07-29 Jackson H Cook Monitoring apparatus for radio pulse transmission systems
US2593234A (en) * 1945-05-12 1952-04-15 Bell Telephone Labor Inc Cavity resonator
US2710945A (en) * 1947-09-26 1955-06-14 Bell Telephone Labor Inc Mode suppression in resonant cavities
US3087089A (en) * 1957-10-26 1963-04-23 Telefunken Gmbh Line to travelling wave tube coupling
US3475707A (en) * 1966-12-21 1969-10-28 Varian Associates Porous intermediate layer for affixing lossy coatings to r.f. tube circuits
US3502934A (en) * 1967-09-15 1970-03-24 Varian Associates High frequency electron discharge devices having improved mode suppression means for cavities with re-entrant drift tubes

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
Harvard, Very High Frequency Techniques Vol. II, Staff of Radio Research Lab. Harvard U., McGraw Hill 1947, pp. 911 914. *

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3758880A (en) * 1971-07-16 1973-09-11 Licentia Gmbh Waveguide mode coupler for separating waves of useful mode from waves of higher mode
US3995241A (en) * 1974-06-28 1976-11-30 Thomson-Csf Device for attenuating very short parasitic waves in electronic tubes with coaxial, cylindrical electrodes
US4017760A (en) * 1975-01-14 1977-04-12 Thomson-Csf Parasitic oscillation suppressor for electronic tubes
US4174492A (en) * 1976-07-19 1979-11-13 Siemens Aktiengesellschaft Device for attenuating cavity interference waves in a high-frequency electron tube
US4398121A (en) * 1981-02-05 1983-08-09 Varian Associates, Inc. Mode suppression means for gyrotron cavities
EP0339374A1 (en) * 1988-04-25 1989-11-02 Matsushita Electronics Corporation A magnetron
US5021713A (en) * 1988-04-25 1991-06-04 Matsushita Electronics Corporation Magnetron
US4851788A (en) * 1988-06-01 1989-07-25 Varian Associates, Inc. Mode suppressors for whispering gallery gyrotron
US4926145A (en) * 1988-12-16 1990-05-15 Flam & Russell, Inc. Radial power combiner/divider with mode suppression
US6558137B2 (en) * 2000-12-01 2003-05-06 Tecumseh Products Company Reciprocating piston compressor having improved noise attenuation
US20080238231A1 (en) * 2007-03-30 2008-10-02 Carter Daniel L Mounting Device and Method For Positioning A Motor Within An Image Forming Apparatus
US7837168B2 (en) * 2007-03-30 2010-11-23 Lexmark International, Inc. Mounting device and method for positioning a motor within an image forming apparatus

Also Published As

Publication number Publication date
DE2014545A1 (de) 1970-10-01
YU75270A (en) 1977-06-30
AT300139B (de) 1972-07-10
SE361109B (es) 1973-10-15
FR2038783A5 (es) 1971-01-08
JPS5246073B1 (es) 1977-11-21
GB1294746A (en) 1972-11-01
YU33681B (en) 1977-12-31

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