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Optmization of SIW Band-pass Filter with the Wide and
Sharp Stop-band Using Space Mapping
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XU Juan
1
, LI Zhaolong
1,2
, CHEN Rushan
1**
5
(1. School of Electronic and Optical Engineering, Nanjing University of Science and Technology,
Nanjing, 210094;
2. State Key Lab of Millimeter Waves, Southeast University,Nanjing, 210096)
Foundations: Specialized Research Fund for the Doctoral Program of Higher Education(No: 20133219120004,
20123219110018)
Brief author introduction:XU Juan was born in Shandong. Her current research interests involve the intelligent
optimization algorithms, microwave/millimeter-wave passive circuits design and optimization
Correspondance author: LI Zhaolong is Associate Professor of Nanjing University of Science and Technology. His
current research interests involve integrated radar front-end design, antenna arrays, microwave/millimeter-wave
passive and active circuits design. E-mail: zhaolong.li@njust.edu.cn
Abstract: This work presents a wide and sharp stopband substrate integrated waveguide bandpass filter.
Non-physical cross-coupling provided by higher modes in the SIW cavities is used to generate the 10
finite transmission zeros for improved stopband performance. The design of SIW filters requires full
wave electromagnetic simulations and extensive optimization. If a full wave solver is used for
optimization, the design process is very time consuming. Using space mapping method, the
optimization goal is to shorten the design cycle by using a fast but less accurate simulator (coarse
model) to gain the information about the optimal parameters setting of the expensive but accurate 15
simulator (fine model). To obtain the optimal design for the fine model, the space mapping technique
compares the results of both models and modifies the parameters of fine model gradually. If the
misalignment between the fine and coarse models is not significant, the algorithm automatically
reduces the differences until the misalignment is reduced to acceptable limits. A fourth-order filter with
a passband of 12-12.5GHz is fabricated on a single layer Rogers RT/Duroid 5880 substrate. The return 20
loss is bigger than 17.4 dB in the pass band and the insertion loss is more than 40dB in the stop band.
The stopband is from 2 GHz to 11 GHz and 13.5 GHz to 17.3 GHz.
Key words: substrate integrated waveguide; band-pass filter; non-physical cross-coupling; space
mapping algorithm
25
0 Introduction
The microwave filter has two main forms: lumped element form and transmission line form.
And the transmission line filter includes waveguide, coaxial line, stripline and microstrip etc. .
Coaxial filter has good electromagnetic shielding performance, low loss and the advantages of
small size, but when the filter working in higher frequency the physical size is too small to be 30
practical; waveguide filter with low loss, high quality factor and high power capacity advantages,
but its disadvantage is large in size, not conductive to system miniaturization and integration; the
microstrip filter is the most common planar circuit, which has the advantages of small size, easy
processing, easy integrated with other circuit components, but its radiation loss is much bigger.
Substrate integrated waveguide (SIW) is a new waveguide structure, it inherits the advantages of 35
waveguide of low loss, high quality factor, high power capacity, but also a collection of microstrip
low profile, small size, easy to integrate with other planar circuit
[1-3]
.
The direct cascade SIW band-pass filter’s stopband characteristic is not ideal. In order to
improve the stopband performance, some designers presented the physical structure of the cross
coupling way to increase the transmission path
[4-7]
. The actual implementation of the cross or 40
bypass coupling is either physical or modal. In the case of physical cross coupling, a physically
element such as a coupling aperture in waveguide filters or fringing fields in planar filters is used.
This technique has the advantage that the coupling element is a physically identifiable and
adjustable element. However, the cross-coupled filters with physical coupling are not practical for