International Journal of Engineering Trends and Technology (IJETT) - Volume4Issue4- April 2013
Design of 20 dB Bethe-hole Waveguide Coupler
Mehul P Vanvi#1, Ved Vyas Dwivedi*2, Jaymin K Bhalani#3
#
*
Communication System Engineering, Charusat University
At & Po:Changa-388421, Dist-Anand,India
C U Shah College of Engineering & Technology
Wadhvan-363030, Dist-Surendranagar, India
Abstract: Design of a X-band WR-90 based 20 dB Bethe-hole
Waveguide Coupler is chosen as main coupler Operating at
9GHz frequency. Theoretical design of this coupler has been
done to find out the aperture position, radius of hole and
Directivity. Theoretical results are verified with simulation
result. ANSOFT’s High Frequency Structure Simulation(HFSS)
has been used for simulation. Results of simulation and the
theoretical results are compared in this paper. Calculated results
and simulation results are in close approximation. Although the
Directivity is more sensitive function of frequency this
comparison helps in fabrication of the coupler.
Keywords: C-coupling coefficient, D- directivity.
I. INTRODUCTION
A directional coupler of four-port passive device
commonly used for coupling a known fraction of the
microwave power to a port( coupled port) in the auxiliary line
while flowing from the input port to the output port in the
main line. The remaining port is an ideally isolated port and
matched terminated. Bethe-hole coupler is one of the type of
Waveguide directional coupler in which two waveguide
coupled together through one hole in common broad wall as
shown in fig (1).
C  20 log
A
dB
A10
(1)
D  20log
A10
dB
A10
(2)


A10  
1
1
E10 J dv 
H10 Mdv


P10
P10
Where, A10 and A10 is the amplitude of forward and reverse
travelling wave is
jwA 
0 m  2  s  2
 s 
2 s

 2  sin
 2 2 cos 2
0  e sin

P10 
a
Z10 
a  a
a 
(3)
A10  

1
1
E10 J dv 
H10 Mdv

P10
P10 
jwA 
0 m  2  s  2
 s 
2 s


sin

sin
 2 2 cos 2
 0 e

2 
P10 
a
Z10 
a  a
a 
(4)
Where P10= a*b /z10 normalized power constant Note from
(4&5)that the amplitude of the wave exited towards port 4 ()

is generally different from that excited toward port 3( A10 ) so
Figure (1) Bethe-hole Coupler
II. DESIGN
We have considered bethe-hole coupler of S aperture
couple two parallel waveguides. Here in Design used WR-90
type waveguide which is used for X-band application. An
aperture excites forward and reverse travelling waves with
different amplitudes.The structure of bethe-hole coupler is
symmetric with respect to all four ports. Basic definition of
coupling and directivity giving by the following formula,
ISSN: 2231-5381

we can cancel the power delivered to port 4 by setting A10 =0.
If we assume that the aperture is round, then gives the
polarizabilities as
e 
2r03
and
3
m 
4r03
, where r0
3
is the radius of the aperture. Then from (4) we obtain the
following condition to find the position of aperture s,
http://www.ijettjournal.org
Page 676
International Journal of Engineering Trends and Technology (IJETT) - Volume4Issue4- April 2013
sin
0
s
2


2
2 2
a
4  k0 a
2  02  a 2 
(5)
Design a Bethe-hole coupler of type shown in figure(1) for Xband waveguide WR-90 operating at 9Ghz,with a coupling of 20 dB.
We have the following constant,a = 2.286cm, b =1.016cm, 0 =c / f =
3.333cm, k0= 2π / 0 = 1.886cm-1, β= 2π / λg = 1.29cm-1,Z10 = k0ή0 /
β = 550.9 ohm, P10= a*b / Z10=4.215 ×10-3 cm2/ohm,
Then (5) can be used to find the aperture position s, from (1) get
aperture radius and for directivity equation (2) is used. For solving all
these equation we get s=0.969cm, r0=0.415cm and directivity
D= -62.95dB.
III.
SIMULATION
Using the above result simulation model has been created
in ANSOFT’s HFSS-11. Waveguide WR-90 of 0.127cm wall
thickness is chosen as main waveguide. Coupler has been
designed for operating frequency of 9GHz over a 7-11GHz
band. The common wall of main waveguide and auxiliary
waveguide is also chosen as 0.127cm.
The structure has been simulated in HFSS by using driven
model. Figure (2) shows the HFSS model of simulation. In
this model we have taken WR-90 waveguide with Inside
dimensions 2.286×1.016 cm and Outside dimensions
2.540×1.270cm. In which outside waveguide are taken as
copper material and inside boxes are taken as vacuum. Also a
hole in the center of the waveguide is take as vacuum
material. The length of guide is in multiple of 0 . So for better
result we get 5 time multiple of 0 .so we take 16.65cm the
length of waveguide. Which have four wave port with two
excitation mode in this design.
Figure(3) E-field pattern
Here in below figure result is shown. Where,S31 is
coupling coefficient and S41 is directivity. By Observing that
coupling varies by less than 1dB over the band. The
directivity is very large (>60dB)at the design frequency, but
decreases 5-10 dB at the band edges.
Figure (4) S-parameter result of coupler in HFSS
IV.
COMPARISON
In this case the radius of hole is taken same as calculated.
The simulated results of HFSS is close to designed value.
Table 1 shows the comparison of coupling coefficient and
directivity of coupler with HFSS and calculated at 9GHz.
Figure (2) HFSS model of coupler
Also far field pattern of the E-filed is shown in figure(3)
where we can see vector pattern for loss of some E-field.
ISSN: 2231-5381
http://www.ijettjournal.org
Page 677
International Journal of Engineering Trends and Technology (IJETT) - Volume4Issue4- April 2013
CODE
Coupling
coefficient
Directivity
HFSS
-25.69dB
-64.33dB
Calculated
-21.62dB
-62.95dB
REFERENCES
[1]
[2]
[3]
Table 1: Comparative values of coupling coefficient and directivity at
9GHz.
[4]
[5]
CONCLUSION
X-band 20dB Bethe-hole waveguide coupler is designed.
Result of design calculation and simulation are closely
matching. The theoretical calculations helped in engineering
drawing of this coupler is ready and it is in the process of
fabrication.
V.
[6]
[7]
[8]
ACKNOWLEDGMENT
The author is thankful to Dr. Niraj Shah, and Prof. Brijesh
Shah, for their support and encouragement during the research
Endeavour. We would like to thank V. T. Patel Department of
Electronics and Communication, CHARUSAT University,
India, for cooperation in the research work.
ISSN: 2231-5381
[9]
Yashwant D. Wanmode, Deodatta Baxy, and Purushottam
Shrivastava.”Design Of 10 dB S-Band Multihole Waveguide Coupler.”
Pulse High Power Microwave Section, Raja Ramanna Center for
Advanced Technology, INDORE,INDIA.
D. M. Pozar, Microwave Engineering, 2nd Ed., Ch 7, pp. 368-374, John
& Wiley & Sons, Canada,1998
R.E.Collin,Foundations for Microwave Engineering, Ch 6, pp. 413-419,
McGraw-Hill, Singapore, 1966
Amin M.Abbosh and Marek E. Bialkowski. “Design of Compact
Directional Couplers for UWB Applications.” IEEE Transaction on
Microwave Theory and Techniques , Vol. 55, No. 2, February 2007
J.Y.Shao,S.C.Huang and Y.H.Pang. “Wilkinson power divider
incorporating quasi-elliptic filters for improved out of band rejection.”
Electronics Letters , Vol.47 , No. 23, November 2011
C.G.Montgometry,R.H.Dicke and E.M.Purcell,“Principal of Microwave
Circuits” MIT Radiation Laboratory Series, vol.8, McGraw-Hill,
N.Y.,1948
Special Issue on Electromagnetics-Based Optimization of Microwave
Components and Circuits, IEEE Trans. Microwave Theory Tech., Vol.
52, Jan. 2004
Devid H Whittum. “Single-Hole Directional Coupler for W-Band”
ARDB Technical Note 119.
Microwave encyclopedia, Retrieved 22 July,2010 from World Wide
Web:
http://www.microwaves101.com/encyclopedia/coupled_line_couplers.cf
m
http://www.ijettjournal.org
Page 678