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(IJCSIS) International Journal of Computer Science and Information Security,
Vol. 10, No. 3, March 2012
Step Tapered waveguide with cylindrical
waveguide
Harshukumar Khare, Prof. R.D. Patane
M.E (EXTC) Final year student Asst. Proffessor (EXTC)
TEC, Nerul, Navi-Mumbai TEC, Nerul, Navi-Mumbai
harshukhare@gmail.com rrpatne@yahoo.co.in
Abstract: Tapered Waveguide is a waveguide in which a the other standard values associated with circular waveguide
physical or electrical characteristic changes continuously with can be done relatively easily.
distance along the axis of the waveguide. Tapered waveguide A waveguide taper can always be built to have as low a
offer an excellent means of converting microwave mode sizes to mode conversion as is wanted in a certain frequency band
connect Microwave devices of different cross-sectional merely by making it long enough. However, an optimally
dimensions. This paper discusses the waveguide component for designed taper has the smallest possible length for a given
interconnecting rectangular and circular waveguide using step difference in diameters at its two ends for a specified
tapering. Model is designed for the frequency range from 2 to 4 unwanted mode level in a given frequency band. Tapered
GHz. Dominant Mode conversions ie from TE10 to TM11 is waveguide for matching impedance is nothing but a tapered
considered for tapering techniques. Step tapering is studied at waveguide in which only one mode is propagating. Power
different step sizes 4mm to 10 mm and analysis is done. All can only be converted into reflected waves, and it is this
simulations done with CST Microwave studio and S reflected power which is kept small in a properly designed
transmission line taper. If more than one mode is
parameters and E field parameters are analyzed. Simulation
propagating, power will be scattered not only into the
result shows that wave is properly propagated with no power
reflected wave but also into the other propagating modes. In
reflection and low power loss. fact , the power scattered into backward traveling waves is
Key words: Single & Double Step Tapering, Cylindrical quite small compared to the power scattered into forward
waveguide, CST, S parameter, E Field traveling waves, and only the latter need be considered in a
multimode waveguide taper. Therefore, the mode
conversion in the waveguide transition corresponds to the
I. INTRODUCTION reflection in transmission line taper.
A rectangular waveguide supports TM and TE modes A waveguide mode is a unique arrangement of the
but not TEM waves. A rectangular waveguide cannot electric and magnetic fields propagating in the z-direction
propagate below some certain frequency. This frequency is that satisfies all Maxwell equations and boundary conditions
called the cut-off frequency. imposed by the geometry of the conductors of the
Circular waveguides offer implementation advantages transmission system. Various waveguide modes are TEM,
over rectangular waveguide in that installation is much TE, TM and Hybrid modes. Dominant mode in Rectangular
simpler when forming runs for turns and offsets - waveguide is TE10 and in circular waveguide TE11. To
particularly when large radii are involved and the wind convert dominant mode in rectangular waveguide to
loading is less on a round cross-section, meaning towers do dominant mode in circular waveguide tapered waveguide is
not need to be as robust. Manufacturing is generally simpler, used. There are different types of tapering such as step
too, since only one dimension the radius needs to be tapering, conical tapering elliptical tapering, etc. Analysis
maintained. Applications where differential rotation is has been done using Step tapering with CST Microwave
required, like a rotary joint for a radar antenna, absolutely Studio.
require a circular cross-section, so even if rectangular
waveguide is used for the primary routing, a transition to II. DESIGN ASPECT
circular and then possibly back to rectangular is needed. The simulation was done by Transient solver of CST
Calculations for circular waveguide require the application Microwave Studio. The Cartesian coordinate system (x, y,
of Bessel functions, so working equations with a cheap and z) is used to model the 3D structure. Design & analysis
calculator is not going to happen. However, even
spreadsheets have Bessel function capability nowadays, so has been done with tapering and without tapering.
determining cutoff frequencies, field strengths, and any of
64 http://sites.google.com/site/ijcsis/
ISSN 1947-5500
(IJCSIS) International Journal of Computer Science and Information Security,
Vol. 10, No. 3, March 2012
A. Design without tapering
The rectangular brick is directly connected to circular
waveguide. Port of rectangular brick (Port 2) is excited and
the S parameters are obtained by Transient Solver. 3D
model of cylindrical waveguide and Rectangular Brick
Without tapering is shown in fig 1.
Fig 4 - 3D model of cylindrical waveguide and
Rectangular Brick with Step tapering
Simulated results for S parameters & E field are
calculated for different step sizes for sizes of 4 mm & 10mm
their S11 and S21 are shown in Fig 5.
It is seen from Fig 5 that for step size 4 mm plots the
sufficient amount of power is reflected back which shows
that taper is not properly coupled and for step size 10 mm it
is seen that no power is reflected back hence source is safe
Fig 1 - 3D model of cylindrical waveguide and
in this case.
Rectangular Brick Without tapering
S11 plot gives that around 2.1 GHz S11 goes upto 19 Step size 4mm Step Size 10mm
dBas shown in Fig 2 which is not a desirable case as huge S11 S11
amount of power is reflected back to the source damaging
the network analyzer.
S21 S21
Fig 2 - S11 plot
S21 plot is shown in fig. 3 which indicates that no
sufficient output is coupled to the output port as it is
approaching to 0dB i.e. no power is coupled from port 1 to
port 2 and vice versa.
Fig-5– S11 & S21 for Step size 4mm & 10 mm
E Field distribution in single step tapered and cylindrical
waveguide is shown in Fig. 6.
Fig 3 - S21 plot
B. Design with tapering
i) Single Step tapering
The 3D model of single step tapering is shown in Fig 4.
Fig-6 E Field distribution in single step tapering
65 http://sites.google.com/site/ijcsis/
ISSN 1947-5500
(IJCSIS) International Journal of Computer Science and Information Security,
Vol. 10, No. 3, March 2012
ep
ii) Double Ste Tapering III. ION
RESULT & CONCLUSI
The schematic of double ste tapering is s
c ep shown in Fig 7 T
The total sim mulation proce ne
ess was don by CST
which two step of 10 mm are used.
in w ps e Micr hat
rowave Studio. It is infer th Tapering b between two
waveeguides is go ood possible solution to c connect two
wave ed lent
eguides. Tapere waveguide offer an excell means of
verting microw
conv zes
wave mode siz to connect microwave
ces
devic of different cross-sectio ons. Properly
onal dimensio
e single stepping with 10 mm s size with
wave is guided in s g step
no r waveguide. Im
reflection in w mpedance matching is the
or h
mino problem with double step.
EDGMENT
ACKNOWLE
The e Dr.
T authors are grateful to D R.C Sethi, HOD,EXTC
TEC and Prof. Mrs. Jyothi Digge, PG coordinator,
e g
Fig 7 - Double Step Tapering EXT eir ort ble
TC,TEC for the great suppo and valuab guidance.
y
They would also like to ackno p
owledged help & support
21 tion are shown
Their S11, S2 plots and E field distribut n ived from Dr. Abhay Deshpande, Scientist,
recei
Figs . m
in F 8, 9 &10. In double step tapering from Fig 8 & 9 it t SAMMEER,IIT-B.
ows
sho that imped g urs.
dance matching problem occu Due to this s
ve ed om l
wav is not guide properly fro cylindrical waveguide to o
tangular waveg
rect guide.
NCES
REFERN
[1] Chen Huaibi, Hua Yuanzhong, L Yuzheng, Ton Dechun, Ding
C ang Lin ng
Xiaodong Departm
X ing
ment of Engineeri physics, Tsing ghua University,
Beijing 100084, B
B BACKWARD TR VE
RAVELING WAV ELECTRON
LINAC, 1998 IEE
L EE
[2] J Petillo, W. Krueger, A. M
J. Mondelli, “Frequ uency Domain
D
Determination of the Waveguide Lo SSCL Drift Tube
oaded Q for the S
Linac” IEEE Particle accelerator con
L nference 1993.
[3] M ulla wi
Muralidhar Yeddu , Sami Tantaw , SLAC, Menlo Park, “Analysis
o a Compact Circ
of cular TE0,1 - Rec Waveguide Mode
ctangular TE0,2 W
pering
Fig 8 - S11 plot for double step tap Converter”, Proce
C 07, ,
eedings of PAC0 Albuquerque, New Mexico,
USA, 2007,pp-587
U 7-589
[4] L.
L Solymar, “Spur rious mode gener orm
ration in nonunifo waveguide,”
IRE Transactions on Microwave Th
I heory and Techniq ques, vol. MTT-
7,
7 pp. 379–383, 19 959.
[5] Dr. c,” F 0
D R.C.Sethi etc Design of RF structure for 10 MeV,10 KW,
I tron linac.
Industrial RF elect
[6] P. va,
P K. Jana, Purushottam Shrivastav Nita. S. Kulka arni, “Design of
M er
Microwave Couple for 10 MeV Ele ectrons LINAC”
Fig 9 - S21 plot for double step tap
pering
Fig 10 - E F ion step
Field Distributi in Double s tapering
66 http://sites.google.com/site/ijcsis/
ISSN 1947-5500
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