US3684913A - Coupled cavity slow wave circuit for microwave tubes - Google Patents

Coupled cavity slow wave circuit for microwave tubes Download PDF

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Publication number
US3684913A
US3684913A US69198A US3684913DA US3684913A US 3684913 A US3684913 A US 3684913A US 69198 A US69198 A US 69198A US 3684913D A US3684913D A US 3684913DA US 3684913 A US3684913 A US 3684913A
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Prior art keywords
cavity
slow wave
circuit
mode
passband
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Expired - Lifetime
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US69198A
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English (en)
Inventor
Bertram G James
Ward A Harman
John A Ruetz
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Varian Medical Systems Inc
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Varian Associates Inc
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    • 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
    • H01J23/16—Circuit elements, having distributed capacitance and inductance, structurally associated with the tube and interacting with the discharge
    • H01J23/24—Slow-wave structures, e.g. delay systems

Definitions

  • FIG. 3 6- PLANES INVENTORS BERTRAM 6. JAMES WARD A. vHARM/ ⁇ N JOHN A.
  • Another feature of the present invention is the same as any one or more of the preceding features wherein the beam is cumulatively electromagnetically interacted with the wave energy in the circuitjn the region of 1.01r to 2.011- radians of phase shift per cavity of the coupledcavity slow wave circuit, whereby the interaction impedance of the circuit is substantially increased.
  • FIG. 1 is a schematic diagram, partly in block diagram form, partly in line diagram form, and partly in sectional view, depicting the prior art microwave tube,
  • FIG. 2 is a perspective schematic line diagram of one of the coupled cavities of the prior art slow wave circuit of FIG. 1,
  • FIG. 3 is a schematic enlarged cross-sectional view of an alternative embodiment of that portion of the struc ture of FIG. 1 delineated by line 3-3 and employing features of the present invention
  • FIG. 4 is a schematic perspective line diagram depicting one of the coupled cavities of the circuit of FIG.
  • FIG. 5 is an 10-13 diagram depicting the passbands for the cavity mode, slot mode, and coalesced cavity and slotmode circuits
  • FIG. 7 is a plot of interaction gap impedance versus normalized phase shift per cavity depicting the characteristics for the coalesced mode circuit of the present invention and for the staggered and staggered coalesced mode circuits of the prior art, and
  • FIG. 8 is a plot of power output in kilowatts versus frequency in GHZ depicting the output characteristics of a traveling wave tube employing. features of the present invention.
  • the prior art tube 1 includes an electron gun 2 disposed to project a beam of electrons 3 over an elongated beam path to a collector electrode 4 for collecting and dissipating the energy of the beam.
  • a coupled cavity slow wave'circuit 5 is disposed along the beam path 3 for cumulative electromagnetic interaction with the beam.
  • the circuit is arranged for operation in the phase shift per cavity portion of the w-B diagram such that between 1.011 and 2.01r phase shift occurs between successive interaction gaps of the circuit.
  • the circuit is operated in the second spatial harmonic of the (0-3 diagram for amplification of wave energy coupled onto the circuit 5 via an input coupling means such as an input coupling iris 6.
  • Wave energy cumulatively interacts with the beam to produce an amplified output wave which is coupled from the downstream end of the circuit via an output iris 7 to a waveguide 8 communicating with a load, such as an antenna, not shown.
  • the prior art coupled cavity slow wave circuit includes a longitudinal array of cavity resonators 9 coupled together via the intermediary of an array of coupling slots 11, which are staggered along the circuit in opposite end walls of each of the cavities. More specifically, coupling slots 11 alternate from one side of the beam to the other as the wave energy propagates through the circuit in the mean direction of the beam. This will hereinafter be referred to as a staggered" coupled cavity circuit, as shown in FIG. 2.
  • the prior art staggered coupled cavity slow wave circuit 5 has an (-3 diagram as shown in FIG. by curves 12 and 13.
  • Curve 12 represents the -13 diagram for the first or low frequency passband of the cavity mode and curve 13 of the (0-3 diagram represents the higher passband or the slot mode of the staggered coupled cavity circuit 5.
  • This prior art circuit has been coalesced, in the prior art, by properly dimensioning the cavities 9 and by tuning the resonant frequency of the slots 11 to a frequency substantially below the upper passband edge of the cavity mode.
  • the resultant coalesced mode circuit has an 00-3 diagram as shown by curves 14 and 15 of FIG. 5.
  • the cold bandwidth for the coalesced mode staggered slot circuit is substantially increased as compared with the circuit before the modes are coalesced.
  • the interaction impedance of the uncoalesced staggered slot circuit increases to very high impedances for phase shifts per cavity between 1.61r and 2.01r radians, whereas the impedance for the coalesced mode staggered slot circuit levels out at a relatively high value.. p
  • the beam velocity must be arranged for interaction generally below 1.51r radians of phase shift per cavity or else interaction is obtained due to the high interaction impedance, near the 2.01r radians of phase shift per cavity, causing the tube to enter into oscillation.
  • Coupled cavity slow wave circuit 19 is substantially the same as that of FIG. 1 with the exception that the coupling slots 21 are arranged with their geometric centers in substantial axial alignment with a line which is parallel to the beam axisand disposed to one side of the beam axis 3.
  • the coupling slots 21 are dimensioned to have a resonance frequency substantially at the upper band edge frequency of the cavity mode, as indicated by line 12 of FIG. 5.
  • the in-line coupled cavity slow wave circuit is coalesced to provide coalesced w-B curves, as shown by curves 14 and 15 of FIG. 5.
  • the coalesced mode in-line slot circuit has a normalized frequency versus phase shift characteristic as indicated by the family of curves identified by numeral 22 in FIG. 6.
  • the coalesced mode in-line circuit 19 of FIG. 3 and 4 has an interaction impedance versus phase shift per cavity identified by the family of curves 24 of FIG. 7. This family of curves is to be distinguished from the family of curves for the coalesced staggered circuit of FIGS.
  • the beam voltage may be swept through the Zn operating point without encountering instability in the tube and without causing backward wave oscillations.
  • the circuit of FIGS. 3 and 4 may be operated in the phase shift per cavity region between 1.511 and 1.81:- radians without encountering instability. This allows the period of the circuit to be substantially increased for a given operating frequency, thereby permitting higher interaction gap impedance for the circuit, alternatively by trading off wall thickness for interaction gap impedance, the thermal capacity of the circuit can be substantially increased over the prior art staggered circuit of FIGS. 1 and 2.
  • the coalesced in-line circuit of FIGS. 3 and 4 can be made to operate at a normalized phase shift per cavity between 1.61-r and 1.811 radians per cavity. This represents approximately a 25 percent greater period length for the coalesced in-line circuit as compared with the coalesced mode staggered circuit. This extra length can either be put into cavity height for increasing the interaction impedance or it can be used to increase the wall thickness between cavities 9. For example, with an initial wall thickness representing 25 percent of the period and a cavity height of percent, a 25 percent increase in period permits the same cavity height to be used with double the wall thickness between cavities 9. This essentially doubles the power handling capability of the circuit.
  • the total gap interaction impedance V /2P of a couf pled cavity circuit is determined principally by the cavity R/Q and the slope of the phase curve.
  • the interaction impedance is always relatively high in regions where the circuit group velocity is low.
  • the effective beam interaction impedance also depends upon the gap coupling coefficient so that a figure of merit for coupled cavity circuits becomes (R/Q)(M/Bp)
  • FIG. 7 shows the total gap interaction impedance of the family of circuits presented in FIG. 6. All circuits have been calculated for R/Q 50.
  • the impedances obtained with the staggered circuit configuration of FIGS. 1 and 2 are contained between the limits of curves (A) and (B).
  • the coalesced inline circuit tends to produce higher impedance at low values of Bp because of the low group velocity associated with the circuit under these conditions.
  • Measured impedance data has been found to agree well with calculated equivalent circuit data except for predicting the zero interaction impedance which is experimentally observed at the Zn point in the case of the coalesced in-line circuit.
  • FIG. 8 shows a plot of the power output as a function of the frequency. The maximum power measured was 8.4 kilowatts cw with a 1 db bandwidth of 2 percent and a saturated gain of 34.7 db.
  • This tube was constructed with no beam current modulating electrode. Also no wave attenuative material was added to the circuit. Measured insertion loss of the circuit section was approximately 1 db.
  • Beam power was applied to the tube by varying the beam voltage from zero to the operating voltage.
  • the beam voltage was varied through the 211 point to search for band edge instabilities. No instabilities were observed.
  • the elimination of the need for additional circuit loss greatly simplified the fabrication techniques, particularly at the extremely small circuit size associated with millimeter waves.
  • the coupled cavity in-line circuit of FIGS. 3 and 5 has been described as used for forward wave interaction in a traveling wave tube operating with a phase shift per period between 1.511- and 1.81; radians per cavity, it may also be used to advantage as the output circuit for a hybrid tube utilizing a succession of klyst'ron buncher cavities followed by the in-line coupled cavity circuit of FIGS. 3 and 4 as the output circuit.
  • a microwave tube means for pro ecting a beam 10 jacent-ones of said cavity resonator having common end walls, an array of wave energy coupling slot means disposed in the common end walls of said cavity resonators for wave energy coupling together the array of cavity resonators to define a slow wave circuit haw ing a cavity mode passband of frequencies associated with the coupled cavities and a slot mode passband of frequencies centered at a higher frequency than the cavity mode passband and associated with the array of slots, the improvement wherein, said slots in opposite end walls of said coupled cavities are disposed with their centers on one side of said beam path and are dimensioned relative to the dimensions of said cavity resonator to have a resonant frequency at substantially the upper band edge frequency of the cavity mode to coalesce the high frequency band edge of the cavity mode and the low frequency band edge of the slot mode for increasing the width of the operating passband of the tube employing said slow wave circuit.
  • said coupled cavity slow wave circuit means is a backward wave circuit for the fundamental space harmonic.
  • the method of claim 4 including the step of, positioning the centers of said coupling slots in opposite end walls of each of said coupled cavities to fall substantially in a plane defined by the axis of the beam and the geometric centers of the coupling slots.
  • the method of claim 4 including the step of, positioning the coupling slots in opposite end walls of each of the coupled cavities to lie substantially in a straight line generally parallel to the beam axis.

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US69198A 1970-09-03 1970-09-03 Coupled cavity slow wave circuit for microwave tubes Expired - Lifetime US3684913A (en)

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US (1) US3684913A (cs)
CA (1) CA956386A (cs)
DE (1) DE2138799A1 (cs)
FR (1) FR2105208B1 (cs)
GB (1) GB1362832A (cs)
IL (1) IL37339A (cs)
NL (1) NL7111795A (cs)

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3011480A1 (de) * 1979-03-26 1980-10-09 Varian Associates Verzoegerungsleitung fuer wanderfeldroehren
FR2510815A1 (fr) * 1981-07-29 1983-02-04 Varian Associates Circuit en echelle pour tube a ondes progressives
US4619041A (en) * 1982-10-06 1986-10-28 English Electric Valve Company Limited Method for manufacturing coupled cavity travelling wave tubes
US5932971A (en) * 1997-06-05 1999-08-03 Hughes Electronics Corp Optimally designed traveling wave tube for operation backed off from saturation
US6313710B1 (en) * 1999-05-20 2001-11-06 Liming Chen Interaction structure with integral coupling and bunching section
US6417622B2 (en) 1999-01-14 2002-07-09 Northrop Grumman Corporation Broadband, inverted slot mode, coupled cavity circuit
US6593695B2 (en) 1999-01-14 2003-07-15 Northrop Grumman Corp. Broadband, inverted slot mode, coupled cavity circuit
US7898193B2 (en) 2008-06-04 2011-03-01 Far-Tech, Inc. Slot resonance coupled standing wave linear particle accelerator
CN105513925A (zh) * 2015-12-08 2016-04-20 中国电子科技集团公司第十二研究所 一种消除折叠波导慢波结构第一止带的方法
CN111129679A (zh) * 2020-01-13 2020-05-08 成都理工大学 慢波匹配电路、金丝键合慢波匹配结构及其仿真设计方法

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3205398A (en) * 1960-04-18 1965-09-07 Matthew A Allen Long-slot coupled wave propagating circuit
US3221204A (en) * 1961-11-20 1965-11-30 Hughes Aircraft Co Traveling-wave tube with trap means for preventing oscillation at unwanted frequencies
US3297906A (en) * 1963-05-29 1967-01-10 Varian Associates High frequency electron discharge device of the traveling wave type having an interconnected cell slow wave circuit with improved slot coupling
US3471738A (en) * 1966-01-26 1969-10-07 Thomson Varian Periodic slow wave structure
US3504308A (en) * 1965-09-29 1970-03-31 Siemens Ag Traveling wave amplifier tube of the higher power type with a delay line of spaced structural configuration

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3205398A (en) * 1960-04-18 1965-09-07 Matthew A Allen Long-slot coupled wave propagating circuit
US3221204A (en) * 1961-11-20 1965-11-30 Hughes Aircraft Co Traveling-wave tube with trap means for preventing oscillation at unwanted frequencies
US3297906A (en) * 1963-05-29 1967-01-10 Varian Associates High frequency electron discharge device of the traveling wave type having an interconnected cell slow wave circuit with improved slot coupling
US3504308A (en) * 1965-09-29 1970-03-31 Siemens Ag Traveling wave amplifier tube of the higher power type with a delay line of spaced structural configuration
US3471738A (en) * 1966-01-26 1969-10-07 Thomson Varian Periodic slow wave structure

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
Power Travelling Wave Tubes by Gittins, Copyright 1965, pages 67 77 *

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3011480A1 (de) * 1979-03-26 1980-10-09 Varian Associates Verzoegerungsleitung fuer wanderfeldroehren
FR2510815A1 (fr) * 1981-07-29 1983-02-04 Varian Associates Circuit en echelle pour tube a ondes progressives
US4619041A (en) * 1982-10-06 1986-10-28 English Electric Valve Company Limited Method for manufacturing coupled cavity travelling wave tubes
US5932971A (en) * 1997-06-05 1999-08-03 Hughes Electronics Corp Optimally designed traveling wave tube for operation backed off from saturation
US6417622B2 (en) 1999-01-14 2002-07-09 Northrop Grumman Corporation Broadband, inverted slot mode, coupled cavity circuit
US6593695B2 (en) 1999-01-14 2003-07-15 Northrop Grumman Corp. Broadband, inverted slot mode, coupled cavity circuit
US6313710B1 (en) * 1999-05-20 2001-11-06 Liming Chen Interaction structure with integral coupling and bunching section
US7898193B2 (en) 2008-06-04 2011-03-01 Far-Tech, Inc. Slot resonance coupled standing wave linear particle accelerator
CN105513925A (zh) * 2015-12-08 2016-04-20 中国电子科技集团公司第十二研究所 一种消除折叠波导慢波结构第一止带的方法
CN111129679A (zh) * 2020-01-13 2020-05-08 成都理工大学 慢波匹配电路、金丝键合慢波匹配结构及其仿真设计方法
CN111129679B (zh) * 2020-01-13 2024-06-11 成都理工大学 微波电路中金丝键合慢波匹配结构的设计制作方法

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Publication number Publication date
FR2105208B1 (cs) 1975-12-12
GB1362832A (en) 1974-08-07
DE2138799A1 (de) 1972-03-09
IL37339A (en) 1974-10-22
NL7111795A (cs) 1972-03-07
FR2105208A1 (cs) 1972-04-28
IL37339A0 (en) 1971-10-20
CA956386A (en) 1974-10-15

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