WO1997038437A1 - Resonant cavity for attenuating electromagnetic standing waves in a waveguide - Google Patents

Resonant cavity for attenuating electromagnetic standing waves in a waveguide Download PDF

Info

Publication number
WO1997038437A1
WO1997038437A1 PCT/US1997/005775 US9705775W WO9738437A1 WO 1997038437 A1 WO1997038437 A1 WO 1997038437A1 US 9705775 W US9705775 W US 9705775W WO 9738437 A1 WO9738437 A1 WO 9738437A1
Authority
WO
WIPO (PCT)
Prior art keywords
waveguide
cavity
standing wave
iris
resonant cavity
Prior art date
Application number
PCT/US1997/005775
Other languages
French (fr)
Inventor
Edward L. Wright
George Caryotakis
William R. Fowkes
Robert M. Phillips
Original Assignee
The Board Of Trustees Of The Leland Stanford Junior University
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by The Board Of Trustees Of The Leland Stanford Junior University filed Critical The Board Of Trustees Of The Leland Stanford Junior University
Publication of WO1997038437A1 publication Critical patent/WO1997038437A1/en

Links

Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J23/00—Details of transit-time tubes of the types covered by group H01J25/00
    • H01J23/36—Coupling devices having distributed capacitance and inductance, structurally associated with the tube, for introducing or removing wave energy
    • H01J23/54—Filtering devices preventing unwanted frequencies or modes to be coupled to, or out of, the interaction circuit; Prevention of high frequency leakage in the environment

Definitions

  • This invention relates to the damping of unwanted standing waves in a waveguide circuit, and, more particularly, to the damping of unwanted modes that can oscillate in an extended interaction output circuit of a high power klystron when the klystron is coupling energy to a narrow band device such as a mode transducer.
  • a klystron is a type of electron beam microwave amplifier.
  • a klystron comprises a number of cavities divided into essentially three sections: an input section, a buncher section, and an output circuit.
  • An electron beam sent through the klystron is velocity modulated by an input RF signal that is provided to the input section.
  • the buncher section the faster electrons gradually overtake the slower electrons, resulting in electron beam bunching.
  • the traveling electron bunches represent an RF current .
  • the RF current induces electromagnetic oscillations in the output circuit of the klystron as the bunched beam passes through the output circuit, and the electromagnetic energy is extracted from the output circuit as an electromagnetic wave.
  • the development of high powered klystrons has necessitated the use of extended interaction output circuits.
  • the risk of unwanted oscillations is increased when the klystron output is directed into a narrow band device such as a mode transducer, pulse compressor, or half-wave window. These devices typically present a high reflection coefficient to frequencies outside the narrow frequency range for which the device was designed. The reflected waves propagate back to the klystron where they are amplified and returned to the narrow band device. The trapped waves quickly overwhelm the desired signal. The result is a powerful standing wave between the klystron and narrow band device oscillating at an undesired frequency.
  • a narrow band device such as a mode transducer, pulse compressor, or half-wave window.
  • the coupling is provided by an iris cut into the side of the waveguide at the location of an antinode of the standing wave.
  • the cavity is resonant at the unwanted frequency.
  • the lossy material can be stainless steel or other metals and may be coated on the inside with lossy coatings, e.g. iron particles.
  • the lossy material can dissipate energy through resistive effects or magnetic hysteresis effects or both.
  • the Q 0 of the cavity and the Q e of the iris are equal. The Q's are made as low as possible without causing excessive attenuation of the desired frequency.
  • the resonant cavity can be made cubic, spherical, cylindrical or any other shape.
  • the oscillating standing wave couples energy into the resonant cavity through the iris. This energy is dissipated in the walls of the cavity, thereby attenuating the standing wave.
  • Fig. 1 is a top view of the present invention used in conjunction with a klystron. A graph of the standing wave electric field pattern is included.
  • Fig. 2 is a graph of attenuation vs. frequency for two resonant cavities with different values of Q 0 ⁇
  • Fig. 1 A preferred embodiment of the invention is shown in Fig. 1.
  • the present invention is used to attenuate the unwanted oscillations that can occur in a klystron output circuit 2.
  • the output 2 feeds into a pair of rectangular waveguides 4 which join at a coupler to form a single rectangular waveguide 6.
  • the waves propagate to a narrow band device 8.
  • narrow band device 8 is a TE]_o to TEoi mode transducer.
  • the mode transducer 8 is tuned to the desired operating frequency 0 of the klystron and so only these frequencies pass through the transducer 8. All other frequencies are reflected back to the klystron output circuit 2.
  • the present invention can be used in any situation where undesired frequencies establish a standing wave pattern in a waveguide. Since counter propagating waves comprise a standing wave, the present invention can be used in any situation where undesired frequencies are preferentially 0 reflected.
  • the reflected wave sets up a standing wave pattern in the waveguide.
  • the amplitude of the standing wave electric field with respect to position along the length of waveguide 6 is 5 shown in a graph 10.
  • a resonant cavity 12 is coupled to the waveguide 6 through an iris 14 which is located at a maximum in the standing wave electric field pattern (an antinode) .
  • the positions of the antinodes are indicated in Fig. 1 as dashed lines 16. Typically, the antinodes will be an odd 0 number of quarter wavelengths from narrow band device 8.
  • the resonant cavity 12 is resonant at the frequency of the undesired standing waves. Energy from the standing wave enters the resonant cavity 12 through the iris 14.
  • the energy- is then dissipated in the walls of the cavity 12 , which are 5 made of a lossy material.
  • the present invention can prevent the klystron from oscillating at an unwanted frequency.
  • the resonant cavity 12 can be any shape.
  • the cavity 12 is a pillbox shape.
  • the design and construction of resonant cavities is well known in the art.
  • the material of the resonant cavity 12 can be lossy through surface current losses or through magnetic hysteresis losses or a combination of both. 400 series stainless steel, for example, is lossy through both mechanisms.
  • the lossy material may also comprise, for example, kovar or monel .
  • the Qo of the cavity 12 will depend upon the loss characteristics of the material of which the cavity 12 is made. Lossier materials will lower the Q Q - A stainless steel cavity, for example, may have a Q D of approximately 300-350 at approximately 10 GHz .
  • the use of lossy surface coatings such as flame sprayed iron filings can also be used to achieve a desired Q 0 . Such techniques are well known in the art.
  • the Qo of the cavity 12 and the Q e of the iris 14 are made equal in order to provide the most effective coupling between the resonant cavity 12 and the unwanted standing wave in the waveguide 6.
  • Circular and rectangular irises 14 are the most commonly used in the art, but the iris 14 can be any shape.
  • the Qo of the cavity 12 and the Q e of the iris 14 are made as low as possible without attenuating the desired signal.
  • Fig. 2 illustrates the mechanism that places a lower limit on the Q's of the cavity 12 and iris 14.
  • FI is the unwanted frequency to which the cavity 12 is tuned, hence the peak of the attenuation curve is located at FI.
  • F2 is the desired signal frequency.
  • Attenuation curve 18 corresponds to a relatively large cavity/iris Q.
  • the attenuation curve broadens and the cavity 12 will absorb energy at the desired signal frequency, F2, which is, of course, undesirable. It will be obvious to one skilled in the art how to adjust the Q 0 of the cavity 12 and Q e of the iris 14 to achieve the optimum attenuation of unwanted frequencies while leaving desired frequencies relatively unaffected.
  • two or more resonant cavities 12 can be used, each individually tuned and located to produce damping at a chosen frequency.
  • cavities 12 can be used together to attenuate the same unwanted frequency.
  • identical cavities 12 and irises 14 can be placed at separate antinodes .

Landscapes

  • Control Of Motors That Do Not Use Commutators (AREA)

Abstract

A resonant cavity (12) made of a lossy material is coupled to a waveguide (6) through an iris (14). The cavity (12) can be made of stainless steel or have a coating of lossy material on an inside surface thereof. Moreover, the cavity (12) is resonant at a frequency (F1) of the undesired standing wave inside waveguide (6). The iris (14) is located at an electric field antinode (16) of the standing wave. For optimum coupling between the waveguide (6) and cavity (12), the quality factor (Qo) of the cavity (12) is made equal to the quality factor (Qe) of the iris (14) such that standing wave energy at unwanted frequency (F1) is absorbed in cavity (12). Multiple frequencies of the standing wave may be eliminated by locating identical cavities (12) at different antinodes (16) along the waveguide (6). This invention is useful with an extended interaction klystron output circuit (2) coupled by the waveguide (6) to a node convertor (8).

Description

Resonant Cavity for Attenuating Electromagnetic Standing Waves in a Waveguide.
RELATED APPLICATIONS This application claims priority from U.S. provisional patent application 60/014,957 filed 8 April 1996, which is hereby incorporated by reference.
FIELD OF THE INVENTION This invention relates to the damping of unwanted standing waves in a waveguide circuit, and, more particularly, to the damping of unwanted modes that can oscillate in an extended interaction output circuit of a high power klystron when the klystron is coupling energy to a narrow band device such as a mode transducer.
BACKGROUND OF THE INVENTION
A klystron is a type of electron beam microwave amplifier. A klystron comprises a number of cavities divided into essentially three sections: an input section, a buncher section, and an output circuit. An electron beam sent through the klystron is velocity modulated by an input RF signal that is provided to the input section. In the buncher section, the faster electrons gradually overtake the slower electrons, resulting in electron beam bunching. The traveling electron bunches represent an RF current . The RF current induces electromagnetic oscillations in the output circuit of the klystron as the bunched beam passes through the output circuit, and the electromagnetic energy is extracted from the output circuit as an electromagnetic wave. The development of high powered klystrons has necessitated the use of extended interaction output circuits. Conventional single gap output circuits will suffer breakdown at high power levels (100 MW) and long pulse widths (1.5 μs) due to high surface electric fields . The use of extended interaction output circuits provides a means of reducing these fields by dividing among several gaps the voltage necessary to extract energy from the electron beam. As power levels increase, the output circuit must be made longer with more gaps. Longer output circuits have an increased susceptibility to resonating at undesired frequencies, diverting energy from the desired frequency and possibly causing damage. Often, more than one unwanted frequency is generated.
The risk of unwanted oscillations is increased when the klystron output is directed into a narrow band device such as a mode transducer, pulse compressor, or half-wave window. These devices typically present a high reflection coefficient to frequencies outside the narrow frequency range for which the device was designed. The reflected waves propagate back to the klystron where they are amplified and returned to the narrow band device. The trapped waves quickly overwhelm the desired signal. The result is a powerful standing wave between the klystron and narrow band device oscillating at an undesired frequency.
What is needed is a simple means by which the undesired oscillations can be damped that does not attenuate the desired signal.
OBJECTS AND ADVANTAGES OF THE INVENTION
Accordingly, it is an object of the present invention to provide a means for attenuating the undesired standing waves that can result when a klystron with an extended interaction output circuit is connected to a narrow band device. More generally, it is an object of the present invention to provide a means for attenuating undesired standing waves in a waveguide.
It is a further object of the present invention to provide standing wave attenuation with a simple, inexpensive apparatus .
SUMMARY OF THE INVENTION These objects and advantages are attained by coupling a resonant cavity made of a lossy material to the side of a waveguide. The coupling is provided by an iris cut into the side of the waveguide at the location of an antinode of the standing wave. The cavity is resonant at the unwanted frequency. The lossy material can be stainless steel or other metals and may be coated on the inside with lossy coatings, e.g. iron particles. The lossy material can dissipate energy through resistive effects or magnetic hysteresis effects or both. The Q0 of the cavity and the Qe of the iris are equal. The Q's are made as low as possible without causing excessive attenuation of the desired frequency.
The resonant cavity can be made cubic, spherical, cylindrical or any other shape.
The oscillating standing wave couples energy into the resonant cavity through the iris. This energy is dissipated in the walls of the cavity, thereby attenuating the standing wave.
DESCRIPTION OF THE FIGURES
Fig. 1 is a top view of the present invention used in conjunction with a klystron. A graph of the standing wave electric field pattern is included.
Fig. 2 is a graph of attenuation vs. frequency for two resonant cavities with different values of Q0■
DETAILED DESCRIPTION A preferred embodiment of the invention is shown in Fig. 1. Here, the present invention is used to attenuate the unwanted oscillations that can occur in a klystron output circuit 2. ? The output 2 feeds into a pair of rectangular waveguides 4 which join at a coupler to form a single rectangular waveguide 6. The waves propagate to a narrow band device 8. In Fig. 1 narrow band device 8 is a TE]_o to TEoi mode transducer. The mode transducer 8 is tuned to the desired operating frequency 0 of the klystron and so only these frequencies pass through the transducer 8. All other frequencies are reflected back to the klystron output circuit 2. Other narrow frequency band devices such as pulse compressors or half wave windows will similarly reflect frequencies outside their designed range of 5 operation. The present invention can be used in any situation where undesired frequencies establish a standing wave pattern in a waveguide. Since counter propagating waves comprise a standing wave, the present invention can be used in any situation where undesired frequencies are preferentially 0 reflected.
The reflected wave sets up a standing wave pattern in the waveguide. The amplitude of the standing wave electric field with respect to position along the length of waveguide 6 is 5 shown in a graph 10. A resonant cavity 12 is coupled to the waveguide 6 through an iris 14 which is located at a maximum in the standing wave electric field pattern (an antinode) . The positions of the antinodes are indicated in Fig. 1 as dashed lines 16. Typically, the antinodes will be an odd 0 number of quarter wavelengths from narrow band device 8. The resonant cavity 12 is resonant at the frequency of the undesired standing waves. Energy from the standing wave enters the resonant cavity 12 through the iris 14. The energy- is then dissipated in the walls of the cavity 12 , which are 5 made of a lossy material. When used between a klystron 2 and a narrow band device 8, the present invention can prevent the klystron from oscillating at an unwanted frequency.
The resonant cavity 12 can be any shape. In the embodiment of Fig. 1 the cavity 12 is a pillbox shape. The design and construction of resonant cavities is well known in the art.
The material of the resonant cavity 12 can be lossy through surface current losses or through magnetic hysteresis losses or a combination of both. 400 series stainless steel, for example, is lossy through both mechanisms. The lossy material may also comprise, for example, kovar or monel .
The Qo of the cavity 12 will depend upon the loss characteristics of the material of which the cavity 12 is made. Lossier materials will lower the QQ- A stainless steel cavity, for example, may have a QD of approximately 300-350 at approximately 10 GHz . The use of lossy surface coatings such as flame sprayed iron filings can also be used to achieve a desired Q0. Such techniques are well known in the art.
The Qo of the cavity 12 and the Qe of the iris 14 are made equal in order to provide the most effective coupling between the resonant cavity 12 and the unwanted standing wave in the waveguide 6. Circular and rectangular irises 14 are the most commonly used in the art, but the iris 14 can be any shape.
The Qo of the cavity 12 and the Qe of the iris 14 are made as low as possible without attenuating the desired signal. The lower the Qs of the cavity 12 and iris 14, the less precise the position and construction of the cavity 12 and iris 14 needs to be. Fig. 2 illustrates the mechanism that places a lower limit on the Q's of the cavity 12 and iris 14. FI is the unwanted frequency to which the cavity 12 is tuned, hence the peak of the attenuation curve is located at FI. F2 is the desired signal frequency. Attenuation curve 18 corresponds to a relatively large cavity/iris Q. If the cavity/iris Q is lowered, as shown by the curve 20, then the attenuation curve broadens and the cavity 12 will absorb energy at the desired signal frequency, F2, which is, of course, undesirable. It will be obvious to one skilled in the art how to adjust the Q0 of the cavity 12 and Qe of the iris 14 to achieve the optimum attenuation of unwanted frequencies while leaving desired frequencies relatively unaffected.
It will be obvious to one skilled in the art that the present invention can be applied to circular waveguides and rectangular waveguides .
It is understood that if two or more unwanted frequencies exist, two or more resonant cavities 12 can be used, each individually tuned and located to produce damping at a chosen frequency.
It is also understood that two or more cavities 12 can be used together to attenuate the same unwanted frequency. In this case, identical cavities 12 and irises 14 can be placed at separate antinodes .
It will be clear to one skilled in the art that the above embodiment may be altered in many ways without departing from the scope of the invention. Accordingly, the scope of the invention should be determined by the following claims and their legal equivalents .

Claims

What is claimed is : 1 . An apparatus for attenuating an electromagnetic standing wave of a predetermined f requency in a waveguide , said apparatus compri s ing a resonant cavity coupled to said waveguide through an iris located in a wall o f said waveguide at a position along the waveguide corresponding to an antinode of said electromagnetic s tanding wave , wherein said resonant cavi ty i s resonant at said predetermined frequency, said resonant cavity is made of a substantially lossy material , and a QQ of said resonant cavity and a Qe of said iris are substantially equal .
2. The apparatus of claim 1 wherein said electromagnetic standing wave oscillates at said predetermined frequency between an output circuit of a klystron and a device with a substantially high reflection coefficient.
3 . The apparatus of claim 2 wherein said output circuit is an extended interaction output circuit .
4 . The apparatus of claim 1 wherein said lossy material is selected from the group consisting of stainless steel , kovar and monel .
5 . A method for for attenuating an electromagnetic standing wave of a predetermined frequency in a waveguide , said method compris ing coupl ing a resonant cavi ty to said waveguide through an iris located in a wal l of said waveguide at a position along the waveguide corresponding to an antinode of said electromagnetic standing wave , wherein said resonant cavity is adapted to resonate at said predetermined frequency , said resonant cavity is made of a substantial ly lossy material at the predetermined frequency, and a QG of said resonant cavity and a Qe of said iris are substantially equal.
6. The method of claim 1 wherein said electromagnetic standing wave oscillates at said predetermined frequency between an output circuit of a klystron and a device with a substantially high reflection coefficient.
PCT/US1997/005775 1996-04-08 1997-04-08 Resonant cavity for attenuating electromagnetic standing waves in a waveguide WO1997038437A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US1495796P 1996-04-08 1996-04-08
US60/014,957 1996-04-08

Publications (1)

Publication Number Publication Date
WO1997038437A1 true WO1997038437A1 (en) 1997-10-16

Family

ID=21768774

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/US1997/005775 WO1997038437A1 (en) 1996-04-08 1997-04-08 Resonant cavity for attenuating electromagnetic standing waves in a waveguide

Country Status (1)

Country Link
WO (1) WO1997038437A1 (en)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2392004A (en) * 2002-05-13 2004-02-18 New Japan Radio Co Ltd Magnetron device
WO2010129657A1 (en) * 2009-05-05 2010-11-11 Varian Medical Systems, Inc. Multiple output cavities in sheet beam klystron
US10064119B2 (en) 2016-12-27 2018-08-28 Google Llc Attenuation device in transmitter system

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2644889A (en) * 1950-02-14 1953-07-07 Polytechnic Res And Dev Compan Mode suppressor for external cavity klystron oscillators
US2869085A (en) * 1954-01-19 1959-01-13 Raytheon Mfg Co Selective absorbers
US3353123A (en) * 1965-09-01 1967-11-14 Gen Electric Microwave filter comprising absorbing structures for removing suprious wave energy
US5469024A (en) * 1994-01-21 1995-11-21 Litton Systems, Inc. Leaky wall filter for use in extended interaction klystron

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2644889A (en) * 1950-02-14 1953-07-07 Polytechnic Res And Dev Compan Mode suppressor for external cavity klystron oscillators
US2869085A (en) * 1954-01-19 1959-01-13 Raytheon Mfg Co Selective absorbers
US3353123A (en) * 1965-09-01 1967-11-14 Gen Electric Microwave filter comprising absorbing structures for removing suprious wave energy
US5469024A (en) * 1994-01-21 1995-11-21 Litton Systems, Inc. Leaky wall filter for use in extended interaction klystron

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2392004A (en) * 2002-05-13 2004-02-18 New Japan Radio Co Ltd Magnetron device
GB2392004B (en) * 2002-05-13 2006-01-18 New Japan Radio Co Ltd Magnetron device
WO2010129657A1 (en) * 2009-05-05 2010-11-11 Varian Medical Systems, Inc. Multiple output cavities in sheet beam klystron
US8975816B2 (en) 2009-05-05 2015-03-10 Varian Medical Systems, Inc. Multiple output cavities in sheet beam klystron
US10064119B2 (en) 2016-12-27 2018-08-28 Google Llc Attenuation device in transmitter system

Similar Documents

Publication Publication Date Title
US2476034A (en) Conformal grating resonant cavity
US5477107A (en) Linear-beam cavity circuits with non-resonant RF loss slabs
WO1997038437A1 (en) Resonant cavity for attenuating electromagnetic standing waves in a waveguide
CA1139444A (en) Traveling wave tube with non-reciprocal attenuating adjunct
US3600711A (en) Coaxial filter having harmonic reflective and absorptive means
US2625605A (en) Resonator
RU2714508C1 (en) Miniature multi-beam klystron
WO1989012906A1 (en) Coupled cavity circuit with increased iris resonant frequency
US3909754A (en) Waveguide bandstop filter
US3324338A (en) Traveling-wave tube with oscillation preventing and gain shaping means including an elongated lossy ceramic element
US4053810A (en) Lossless traveling wave booster tube
JPH03502272A (en) Mode converter for microwave energy transfer circuit
US4258286A (en) Coupled cavity type traveling wave tube
JPH0729697A (en) High-order resonance mode suppressor
US3354346A (en) Traveling-wave tube having loss-filled, capacitively-coupled cavities coupled to the interaction cells of the slowwave structure
US3889149A (en) Liquid cooled attenuator
JP4224264B2 (en) Cavity coupled traveling wave tube
IL35442A (en) Mode suppresion means for a clover-leaf slow wave circuit
US3428922A (en) Mode trap band-pass filters
McCabe et al. Survey of high-power microwave filters
JP4252274B2 (en) Magnetron
Tomiyasu On spurious outputs from high-power pulsed microwave tubes and their control
JP2922933B2 (en) Magnetron
Johnson Interference Emission Filtering in High Power Microwave Transmitters
JP3099883B2 (en) Higher mode attenuation antenna

Legal Events

Date Code Title Description
AK Designated states

Kind code of ref document: A1

Designated state(s): CN JP

AL Designated countries for regional patents

Kind code of ref document: A1

Designated state(s): AT BE CH DE DK ES FI FR GB GR IE IT LU MC NL PT SE

121 Ep: the epo has been informed by wipo that ep was designated in this application
DFPE Request for preliminary examination filed prior to expiration of 19th month from priority date (pct application filed before 20040101)
WA Withdrawal of international application
NENP Non-entry into the national phase

Ref country code: JP

Ref document number: 97536433

Format of ref document f/p: F