12 G to 20 G compact rectangle waveguide to circular waveguide mode convertor

12 G to 20 G compact rectangle waveguide to circular
waveguide mode convertor
Shitou Liu, Peng Zhao
School of Physical Electronics,
University of Electronic Science and Technology of China
Chengdu, China
[email protected]
Abstract—
— Rectangular waveguide to circular waveguide mode
converter is a critical components of a high-power microwave
test system. In certain frequency band, the traditional method of
round - rectangular waveguide mode converter can't satisfy the
performance requirements. In order to solve this problem, this
paper puts forward a kind of compact structure, and it has the
characteristic of small reflection coefficient, wide bandwidth,
waveform conversion efficiency high. Its center frequency is 16
GHz, the bandwidth of 8 GHz. Its relative bandwidth is 50%,and
VSWR is less than 1.1 in 12G-20G, and insertion loss is greater
than -0.02.
Keywords—converter; wide bandwidth; compact; small reflection
coefficient
I.
INTRODUCTION
Circular groove waveguide which has a large capacity of
dispersion, low power, low attenuation, large size, and the
advantages of simple processing, is very suitable for
microwave millimeter wave components. The current
laboratory commonly used microwave source are the TE10
rectangular waveguide mode. In order to put the energy input
from the rectangular waveguide to round shaped groove
waveguide, We must use the mode converter to make TE10
mode conversion of rectangle waveguide transmission to
circular groove waveguide mode TE11 mode[1]. Symmetrical
structure of the circular waveguide can lead to the existence of
polarization degenerate mode. When need single-mode work,
we don't usually use circular waveguide, we use the connector
to make TE11 mode into TE10 mode. So you can use of the
advantages of rectangular waveguide and circular waveguide,
let it serve us better. On the one hand, you need to complete
circular waveguide TE11 mode to TE10 rectangular
waveguide mode transformation, on the other hand to
complete the transition of the structure of the impedance
transformation[2].
In this paper, we adopt multistage transform structure but
only change the height to achieve a wide bandwidth, low
reflection, compact, easy processing and other features.
II. THE STRUCTURE DESIGN
Engineering of the common round - rectangular waveguide
mode converter has two kinds of structure forms. One is using
the method of cross section from the circular waveguide on
the circular waveguide section gradually transformed into
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rectangular waveguide cross-section, called deformation
gradually transition structure. This structure is shown in
Figure 1.
Fig. 1. The cross section of the gradient type converter structure
The converter structure is simple, but its geometry size is
longer, and the processing is difficult due to the existence
period of continuous change. The second is ladder transition
structure. We adopt the second structure. We adopt sections
with a certain length of truncated circular waveguide (ladder),
and this makes circular waveguide transition to rectangular
waveguide. This structure is shown in Figure 2.
Fig. 2. Stepwise circular - rectangular transition structure
The circular - rectangular transitional structure than before a
cross-section gradient type structure has the advantage of
compact structure, easy processing, and the reflection
coefficient is small. Truncated circular waveguide cutoff
wavelength and the difference between the paragraphs ladder
cross section jointly determine the characteristic impedance of
the converter. The initial design can be drawn from the
literature [3]. Size diagram is shown in Figure 3.
1392
$a1%
L1
$a2%
L2
Fig. 4. S11
$a3%
L3
L4
$a4%
$a%
Fig. 5. S21
&
b
(
&
b4
(
&
b3
(
&
b2
(
&
b1
(
&
2R
(
Fig. 3. Size marking figure
According to the actual requirements, the center frequency is
16 G, absolute bandwidth is 8 G, and within the band VSWR
is less than 1.1. VSWR is closer to 1, the higher transmission
efficiency. According to the theory, matching section length is
approximately a quarter wavelength, that is L1=L2=L3=L4 4.7mm. The difference between the width is about 1 mm, that
is (bi bi 1 ) / 2 1mm . This design according to some
actual requirements, a is 15.8 mm, b=7.9mm(bj140),
R=7.9mm.
The figure 4 shows that S11 is less than -37 dB form
12.4G to 20G and S11 is less than -30 dB form 12G to 12.4G.
VSWR is less than 1.1 is equivalent to S11 is less than -26 dB.
Therefore, our simulation results is far superior to the design
requirements. S21 is close to zero. We found that the
optimized L is larger than the initial value. This is due to the
changes brought by the ladder capacitance. The actual value of
bi basically accord with the theoretical value.
IV. CONCLUSION
Due to the actual needs of bandwidth are wide, reflection
coefficient is small, we chose the ladder transition structure.
Through theoretical calculation and software simulation
optimization, we finally got a waveguide mode converter
whose center frequency is 16 G, absolute bandwidth is 8 G
VSWR is less than 1.1 The results show that the design
method is feasible.
III. THE SIMULATION AND ANALYSIS
According to the initial size, we use the 3D simulation
software u-wave modeling. Through the optimized variables
LI and Bi , the simulation results meet the design
requirements. The optimized values of each parameter is as
follows:L1=7.19mm,L2=6.44mm,L3=5.72mm,L4=4.95mm,b1
=14.29mm,b2=12.51mm,b3=10.07mm,b4=8.28mm.
Reflection and transmission curve as are shown in the Figure4
and Figure5 below.
Acknowledgment
This work was supported by 702 office. The authors would
like to thank the Liu Chen for helping this work.
References
[1]
[2]
[3]
WK,QWHUQDWLRQDO&RQIHUHQFHRQ(OHFWURQLF3DFNDJLQJ7HFKQRORJ\
CHEN Dong2dong,SUN Yong2zhi,NIUBin,YANG Hong2sheng.
Optimized Design of Rectangle Waveguide to Circular Waveguide
Mode Convertor[J]. Chinese Journal of Electron Devices.Vol.29 No.2
Jun.2006:410-412.
LiSimin, ZHENG Keke, CAO Weiping. Study of improved circular
waveguide to rectangle waveguide mode convertor[J].ELECTRONIC
COMPONENTS AND MATERIALS. Vol.32 No.6 Jun.2013:61-64.
Luokun Liu, Guangxiang Sun.Round - Rectangular Transition Design[J].
Electronic scientific journal. Vol.14 No.16 Nov.1992:657-660.
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