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Cold Analysis of Disc-Loaded Circular Waveguides for
Wideband Gyro-TWTs
Vishal [email protected]
Centre of Research in Microwave TubesDepartment of Electronics Engineering
Institute of Technology, Banaras Hindu UniversityVaranasi – 221 005
Applications of high power devices at millimeter wave frequency range
Radar (long-range and high resolution)Communication (high information density)Electronic warfareDirected energy weaponryMaterial processingWaste remediationOzone generationAtmospheric purification of admixtures like freons
that destroy ozone layer
Conventional Microwave Tubes
Increase of the operating frequency of conventional microwave tubesRF power output becomes limited due to
DC power dissipation RF losses Attainable electron current density Heat transfer (restricting the average power capability) Material breakdown (arcing) (restricting the peak power capability) Difficulty of fabricating tiny parts
Microwave Solid State Devices limited output power limited bandwidth low efficiency thermal considerations
Gyro-klystron, application in a linear accelerator
limited bandwidthcavity-type interaction structures
Gyro-travelling-wave tube (gyro-TWT) wider bandwidth
propagating waveguide interaction structure For the communication purposethere is need to broaden the bandwidth of a gyro-TWT
Unconventional high power microwave tubesoperable in the millimetre-wave frequency band for instance, gyro-devices
Controlling dispersion characteristics of the waveguide for wideband coalescence between the beam-mode and waveguide-mode dispersion characteristics
Method of broadbanding a gyro-TWT
i) by dielectric lining the metal wall of a circular waveguide
entails the risk of dielectric charging that results into heating if the dielectric is lossy
ii) by corrugation or metal disc loading a circular waveguide
optimisation of the corrugation or disc parameters brings about the desired shape of the structure dispersion for wide coalescence bandwidth for wideband device performance
Region I: disc-free region Lzrr D 0,0
Region II: disc-occupied region )(0, TLzrrr WD
)....,2,1,0(,/20 nLnIIn
)....,3,2,1(,/ mLmIIm
Propagating waves
Standing waves
Electromagnetic boundary conditions
LzEE
LzHHIII
IIz
Iz
0
0
Drr at
2122 ])([ In
In k
2122 ])([ IIm
IIm k
Relevant field intensitiesFor TE mode excitation)0( zE
10
10
00
0
)sin()exp(}{1
)sin()exp(}{
)(exp}{1
)(exp}{
m
IIm
IIm
IImII
m
II
m
IIm
IIm
IIm
IIz
In
n
In
InI
n
I
In
n
In
In
Iz
ztjrZAjE
ztjrZAH
ztjrJAjE
ztjrJAH
}{}{}{}{}{ 00000 rYrJrYrJrZ IImW
IImW
IIm
IIm
IIm
where
Field expressions Boundary conditions
Integrationwithin limitsof validity
Elimination of field constants
Dispersion relation
Multiplicationby )sin( zIIm
)1,(
0}{
}{1
}{
}{1
)()(
1det
0
0
0
022
mn
rZ
rJ
rZ
rJ
DIIm
DIn
IImD
IIm
DIn
In
In
IIm
Azimuthal interaction impedance An estimate of azimuthal electric field available for the interaction of RF with gyrating electrons in a gyro-TWT
tI
I
P
rErK 2
0
2
0,0,
2
}{}{
Pt Total power transmitted through the structure
000
220
01
00
10
1
010
20
20
212
22
0
2
0
02
02
10
0
0,
])/()[(
]1)[exp(
}{
}{1where
}{}{)(
}{}{
L
Lj
rJ
rZ
LR
rJrJRr
rJRkrK
I
III
DID
II
II
I
nD
InD
InnI
n
In
DII
I
Free-space intrinsic impedance
Dispersion Characteristics Interaction Impedance Characteristics
Dispersion Characteristics Interaction Impedance Characteristics
Region I: disc-free region Lzrr D 0,0
Region II: disc-occupied region )(0, TLzrrr WD
)....,2,1,0(,/20 nLnIIn
)....,3,2,1(),/( mTLmIIm
Propagating waves
Standing waves
Electromagnetic boundary conditions Drr at
LzTL
TLzEE
TLzHHII
I
IIz
Iz
)(0
)(0
)(0
2122 ])([ In
In k
2122 ])([ IIm
IIm k
)sin()cos()exp(
)](exp[)1(1
where
0}{}{}{}{det
0
0000
LjLLj
TLjM
rJrZrZrJM
IIm
In
IIm
IIm
IIIm
IIm
In
mIIm
In
nm
DInD
IImD
IImD
Innm
Dispersion Relation
Azimuthal Interaction Impedance
nD
InD
InnI
n
In
DII
I
rJrJRr
rJRkrK
}{}{)(
}{}{
20
20
212
22
0
2
0
02
02
10
0
0,
As special case results passes on to that of the circular waveguide loaded with infinitesimally thin discs
Validation of dispersion and interaction impedance characteristics of a disc-loaded circular waveguide, excited in the TE01 mode obtained by the
present analysis against HFSS
Validation of dispersion characteristics of a disc-loaded circular waveguide obtained by the present analysis against those due to Amari et al.
4.0/
1.0/
W
W
rL
rT
Dispersion and azimuthal interaction impedance characteristics of the disc-loaded circular waveguide typically for the TE01 mode,
taking disc hole radius as the parameter
Broken curves refer to circular waveguide loaded with infinitesimally thin discs
Dispersion and azimuthal interaction impedance characteristics of the disc-loaded circular waveguide typically for the TE01 mode,
taking disc periodicity as the parameter
5.0/
1.0/
WD
W
rr
rT
Broken curves refer to circular waveguide loaded with infinitesimally thin discs
5.0/
0.1/
WD
W
rr
rL
0.1// WW rTrL
Dispersion and azimuthal interaction impedance characteristics of the disc-loaded circular waveguide typically for the TE01 mode,
taking disc thickness as the parameter
Broken curve refers to circular waveguide loaded with infinitesimally thin discs
— Rigorous analysis of disc-loaded circular waveguide including all the harmonics and finite disc thickness was developed for its dispersion and azimuthal interaction impedance that is valid for all the azimuthally symmetric modes
— Effects of structure parameters, namely, disc-hole radius, periodicity and disc-thickness were studied
— Periodicity was identified as the most effective parameter for dispersion shaping and hence broadbanding a gyro-TWT
Conclusion
