2012 IEEE Asia-Pacific Conference on Applied Electromagnetics (APACE 2012), December 11 - 13, 2012, Melaka, Malaysia

A Review of Substrate Integrated Waveguide (SIW)

Bandpass Filter Based on Different Method and
Design
Siti Sabariah Sabri, Badrul Hisham Ahmad and Abdul Rani Bin Othman
Centre for Telecommunication Research and Innovation (CeTRI), Department of Telecommunication Engineering
Faculty of Electronic and Computer Engineering, Universiti Teknikal Malaysia Melaka (UTeM)
Hang Tuah Jaya 76100, Melaka, Malaysia.
E-mail: sitisabariahsabri@gmail.com, badrulhisham@utem.edu.my, rani@utem.edu.my

Abstract— Substrate Integrated Waveguide (SIW) is an emerging no radiation and packaging problems. SIW components are a
technology of high-frequency integrated that appeared in recent good compromise between air-filled rectangular waveguide
years which provides an excellent platform in order to design and microstrip line.
millimeter wave circuits such as filters, resonators and antennae.
It offers advantages in terms of compact size and easy to Recent years, SIW technology was vastly explored to
integrate with the other planar circuit. The fabrication can be overcome the problems. Ke Wu [3] was introduced the
done by using standard printed circuit (PCB) where the cost of
substrate integrated circuit in 2003 which is the new concept
the manufacturing process will be reduced compared to the
conventional waveguide filter. This paper presents the review of for high-frequency electronics and optoelectronics. Other than
SIW bandpass filter for X-band applications for the past few SIW, Substrate Integrated Slab Waveguide (SISW) and
years that have operation frequency from 8.2–12.4 GHz. Most Substrate Integrated Non Radiating Dielectric (SINRD) guide
researchers focus on designing SIW bandpass filter rather than circuits also included in this concept. SIW structure is based
other filter because Chebychev filter response is easy to make on planar dielectric substrates with top and bottom layers
circuit synthesis. Different types of method have been introduced perforated with arrays of metalized via holes. Proved that,
in the SIW bandpass filter design and the performance of the SIW provides low-cost waveguide filter by using standard
filter design will be compared. printed circuit board (PCB) process [3-5]. In terms of size,
Keywords- Substrate Integrated Waveguide; bandpass filter;
SIW is more compact and easy to integrate with other
Chebychev; triangular cavities; symmetrical window; iris; contour microwave and millimeter-wave circuits in the same substrate
integral method compared to the conventional waveguide. Figure 1 shows the
structure of an SIW, which is consist of the top and bottom
I. INTRODUCTION metal planes of a substrate and two parallel arrays of via holes
Bandpass filter is the frequency selective which allows and also known as via fence in the substrate.
signals between two specific frequencies to pass and
discriminate against signals at other frequencies. The
rectangular waveguide filter is widely being used in
microwave and millimeter-wave such as in communications,
Electronic Warfare (EW), Automatic Test Equipment (ATE),
microwave subsystems and radar systems [1]. They are
required for high-power applications and preferred for
precision performance. At low signal levels, they are primarily
used at frequencies from 8 to more than 100 GHz. This
conventional waveguide filter also provides high Q factor,
high selectivity and low insertion loss [2]. In contrast, they are
difficult to integrate between planar and non-planar circuit. In
addition, it has a bulky size and expensive to manufacture.
Having the similarity between SIW structures and classical
rectangular waveguides, most of the planar (H-plane)
waveguide components have been implemented in SIW Figure 1. The basic structure of SIW
technology. This solution usually permits a substantial
reduction in size and in weight of components if compared to Via holes must be shorted to both metal planes to provide
classical waveguide. Moreover, losses of SIW components are vertical current paths, otherwise the propagation
lower than the corresponding microstrip devices and there are characteristics of SIW will be significantly degraded. Since

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 2012 IEEE Asia-Pacific Conference on Applied Electromagnetics (APACE 2012), December 11 - 13, 2012, Melaka, Malaysia

the vertical metal walls are replaced by via fences for the SIW the loss problem. As a result, the ratio d/p is considered to be
structures, propagating modes of SIW are very close to, but more critical than the pitch length because the post diameter
not exactly the same as, those of the rectangular waveguides and the pitch length are interrelated. Due to the synthesis, the
[6, 7]. This can be verified by checking the modal surface SIW can no longer be regarded as a normal homogeneous
current patterns. Only patterns with solely vertical current waveguide, and it is in fact an artificial periodic waveguide.
distributed on the side wall survive in SIWs. As the initial Therefore, the post diameter may significantly affect the return
dimensions of the simulation software, the size of the SIW loss of the waveguide section in view of its input port. Two
cavity is determined by the corresponding resonance design rules related to the post diameter and pitch that are used
frequency from [8]: to neglect the radiation loss formulated [8].

ଶ ଶ (1) II. SIW BANDPASS FILTER

ܿ ߨ ߨ
݂ଵ଴ଵ ൌ ඨቆ ቇ ൅ቆ ቇ  The bandpass filter has been implemented in the microwave
ʹߨξߤ௥ ߝ௥ ‫ݓ‬௘௙௙ ݈௘௙௙ a receiver which is used to reject unwanted out-of-band
interference and establish sensitivity by defining the front-end
In the TE101 dominant mode, where weff and leff are the noise bandwidth. Meanwhile in microwave transmitter, they
equivalent width and length of the SIW cavity, they are reduce unwanted frequencies (spurii) and suppress transmitter
expressed by: noise at receive frequency. Besides the bandpass filter is also
used in various microwave multiplexers. Various methods
݀ଶ (2) have been implemented in designing the SIW bandpass filter.
‫ݓ‬௘௙௙ ൌ ‫ ݓ‬െ
ͲǤͻͷ‫݌‬
There are several designs of SIW bandpass filter for X-band
݀ ଶ (3) applications is being introduced by researchers in the past
݈௘௙௙ ൌ ݈ െ years based on a different method. Yu Lin Zhang developed
ͲǤͻͷ‫݌‬
the compact bandpass filter with SIW triangular cavities in
2005 [9]. The design filter was based on the coupling matrix
Where w and l are the real width and length of the SIW cavity.
synthesis method with center frequency of 2.4 GHz.
While d is the diameter and p the distance between adjacent
via hole as shown in Figure 2 below.

Figure 2. Diameter, d and pitch, p for via hole

Via holes form a major part of the SIW to realize the bilateral
edge walls, the miniaturization and large scale integration of
electronic devices place an interesting demand on multilayer
interconnect geometries. Via hole is one of the most important
discontinuities in multilayered circuits. The parameter of the
design the via hole are [3]: Figure 3. A typical view of an SIW triangle cavity structure [9]

ߣ௚ (4) Six-cavity filter was compacted to the shape of hexagon by

݀൏
ͷ adopting SIW triangle cavities. Design narrow bandpass filter
was based coupling coefficients of intercoupled resonators and
‫ ݌‬൑ ʹ݀ (5) external quality factors of the input and output resonators [10].
In order to control the overall insertion loss and ripple
The diameter, d of the holes, the spacing, p between the holes properties in a multipole filter, the external coupling must be
and the spacing, weff between two rows are the physical specified. The dimension of the triangle SIW cavity is the
parameters necessary for the design of the guide. The pitch, p same known as the equilateral triangle.
must be kept small to reduce the leakage loss between
adjacent posts. However, the post diameter is also subject to

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 2012 IEEE Asia-Pacific Conference on Applied Electromagnetics (APACE 2012), December 11 - 13, 2012, Melaka, Malaysia

Each extend doublet consists of a main doublet with an

additional resonator grown into one of the branches in which
the source and load are coupled to both branches of the
doublet in order to generate the two transmission zeros
required. The two consecutive building blocks are coupled by
an inverter between two non-resonating nodes (NRNs). The
extraction of a coupling matrix of a network that contains both
resonating nodes and NRNs is fundamentally identical to the
synthesis of standard coupled resonator filters. The
Figure 4. The six-equilateral (hexagon) -triangle SIW cavity [9] configuration of the filter as shown in Figure 6 and was
fabricated on a substrate with a thickness of 0.78 mm and
It is excited in the middle of each side, for instance a1, the dielectric constant 2.2. From the results in Figure 7, it shows
export signal from a2 is equal to that from a3 as shown in that the insertion loss is about 3.2 dB and the minimum return
Figure 3. The six-equilateral-triangle SIW-cavity filter is loss is greater than 18 dB.
arranged in the compacted hexagon shape as shown in Figure
4. This filter was fabricated by using substrate with dielectric
constant of 2.2 and thicknesses of 1 mm. Based on results in
Figure 5, it shows that the minimum insertion loss is less than
1.75 dB with a fractional bandwidth of 15.1% and the
stopband rejection is less than 33 dB at center frequency of
10.16 GHz.

Figure 7. Simulated and measured results of highly-selective SIW BPF [11]

The next researcher applied the contour integral

method in order to design SIW bandpass filter. In 2010 [15],
Shahvirdi was this method to design four pole Chebychev X-
Figure 5 . Measured and simulated scattering parameters of the six-triangle
band dual inductive post SIW filter based upon the
SIW-cavity [9] discretization of the boundary of the structure as shown in
Figure 8. It needs less memory than full wave method. For
decreasing the computation time, circular vias replaced by
In 2009 [11], highly selective six-pole elliptic SIW square ones. The centers of these square vias are the same as
bandpass filter was produced by Shen which is consist of two the circulars [16].
planar SIW extend doublets. The modular design approach
based on cascading small building blocks is adopted to reduce
the effect of manufacturing tolerance on the performance of
the elliptic and the pseudoelliptic filter [12-14].

Figure 8. Schematic of the dual inductive post integrated waveguide filter

[15]

This contour integral method, the boundary of the structure is

discretized and the two dimensional wave equations are
transformed into an integral equation around the periphery of
the circuit. The advantages of the dual inductive post is that
the post diameter can be selected arbitrarily and also all the
Figure 6. Coupling and routing schemes for two cascaded building blocks post diameters can be chosen equally [17, 18]. A four pole X-
using NRNs and configuration of SIW six-pole elliptic filter [11] band Chebychev dual inductive post waveguide filer designed
for terrestrial broadcasting which use RT/Duroid 5870 with

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 2012 IEEE Asia-Pacific Conference on Applied Electromagnetics (APACE 2012), December 11 - 13, 2012, Melaka, Malaysia

dielectric constant of 2.33 and a thickness of 0.7874 mm. The This filter design, composed ofo three SIW cavities which are
simulated time per frequency using the contour integral coupled to microstrip line and a coupling structure. It can
method with circular vias was 8.2 secondss and with square change effective cavity dimennsions and hence the resonant
vias was 0.71 seconds while this simulatiion time was 2.9 frequency. This structure can also make zeros in cavity
seconds per frequency point in HFSS sim mulation. This is response. The coupling structuure including coupling via and
shown that the memory needed by the contoour integral is less circular disks can act as an open-circuited
o line and will be
than the memory require by HFSS. The maximumm insertion shorted at its resonance. It has a very sharp slope in both cut-
loss is the pass band is 1.5 dB and the returnn loss is better than off frequencies compared to otther three poles filter since they
13 dB as shown in Figure 9. provide a steep cut-off frequenncy. Besides, it also reduces the
effects of higher order modes of cavities. In the Figure 12, at
the center frequency of 10.26 GHz
G with a fractional bandwidth
of 4%, obtained the insertion looss of 3.7 dB.

Figure 9. S11 and S21 of a dual inductive post filter analyzed by the contour
integral method and Ansoft HFSS [115]

Faezah proposed the X-band SIW bandppass filter based on Figure 12 . Measured and simulated response of the bandpass filter using SIW
cavities coupled to a microstrip line in 2010 [19]. This method resonattors [19]
suitable for multilayer structures that may allso can be used as
a tunable filter by tuning SIW cavity. The three-pole The recent development off SIW bandpass filter in 2011 is
narrowband SIW filters was designed based on cavity the design of X-band symm metrical window. Xiong Zou
coupling method as shown in Figure 10 and a 11. The idea suggests the transforming bandpassb filter to equivalent
comes from short-circuited stub filters [20].. Each SIW cavity conventional rectangular waveeguide bandpass filter [21]. The
is directly excited by the 50 microstrip line in two layer equivalent-circuit model is deeveloped to simplify the design
configurations which provides a good narrrowband response approach for symmetrical winndow based on SIW techniques
for filter. The coupling structure can makee transfer function as shown in Figure 12. Thee structure composed by five
zeros and hence gets better decay steepness in
i the stop band. cavities. The common form ms of discontinuities used in
waveguide circuits which is a metallic
m partition also known as
iris in order to extend partially across the waveguide in a plane
perpendicular to axis [22]. Thee higher-mode fields for iris are
set up when a wave is inciddent, so total field satisfies the
proper boundary conditions. A dominate-mode wave is
reflected from the iris and some s of the incident power is
transmitted through the openingg.

Figure 10. Bandpass filter by using SIW ressonator [19]

Figure 12. Circuit of symmeetrical window SIW filter [21]

The iris and reflections teermination are considered as

impedance or reactance term minating transmission line. The
five stages Chebychev bandpass filter with 0.01 dB ripple we
obtained at a frequency of 10 GHz. The iris waveguide filter
Figure 11. Manufactured filter [resonator], a) First layyer (microstrip track),
b) Second layer (SIW cavities) [199]
has a sharp skirt characteristic.. The symmetrical window SIW

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 2012 IEEE Asia-Pacific Conference on Applied Electromagnetics (APACE 2012), December 11 - 13, 2012, Melaka, Malaysia

filter is designed with a 3 dB bandwidth of 5% from 9.77- (PCB) which has contributed to the low cost of manufacturing
10.27 GHz as shown in Figure 13. The insertion loss is about process. In other hand, all the results show slightly different
1.4 dB and for return loss is more than 20 dB. between simulations and measurements. This happens, due to
the dielectric constant shift and dielectric loss increase in high
frequency. The diameter and pitch of via holes also cause to
this problem.

TABLE I. Comparison of different method and design of SIW Bandpass filter

Filter/
[9] 2005 [11] 2009 [15] 2010 [19] 2010 [21] 2011
Year

Coupling Coupling Coupling Symmetri

Method Contour
(Triangular (Cascadin (Multilayer cal
and design integral
cavities) g blocks) structures) windows

fo (GHz) 10.61 8.90 10.40 10.06 10.00

Figure 13. Results for the symmetrical window SIW bandpass filter [21]
Fractional
bandwidth, 15.1 1.5 - 4 5
III. DISCUSSION FBW (%)
Insertion
The review and analysis among the available reported loss, IL 1.75 3.20 1.50 3.80 1.40
(dB)
bandpass filter at X-band using SIW technology for the past Return
few years has been done. The comparison and performance of loss, RL >10 >18 >13 >10 >20
the different method and design of every each design were (dB)
Stopband
presented in Table 1. The different methods are being used in rejection >33 >60 >30 >62 >35
order to design SIW bandpass filter. Three of the filter design (dB)
using the coupling matrix method but different in terms of Size (mm2) 20×20 48×89 13×78 24×70 18×88
design such as triangular cavities, cascading blocks and
multilayer structures. Other methods such as contour integral Dielectric
2.40 2.20 2.33 2.20 2.20
and symmetrical windows also have been introduced constant, r
previously. Different number of poles has been design of each
Microstrip Microstrip Microstrip
filter. Transition -
tapered tapered
-
tapered

Each filter design has its own advantages. For triangular Number of
6 6 4 3 5
cavities, it did mention that the narrow bandpass filter is based poles

on coupling coefficients of inter coupled resonators and Manufactu

ring PCB PCB PCB PCB PCB
external quality factors of input and output resonator. Next by process
using cascading blocks, it reduced the effects manufacturing
tolerance on the performance of elliptic and pseudo elliptic
filters. The contour integral method is easily programmed and CONCLUSION
since the boundary of the circuit is only discretised. Besides, The different methods of designing SIW bandpass filter at
this method needs less memory compared to the full-wave X-band applications have been reviewed. The entire filter
analyzer. By using the coupling method for multilayer shows good performance in terms of insertion loss and return
structures, it provided the frequency tuning for SIW exact loss. Besides, the size of the filters designed is small and
design while the symmetrical window method shows high- compact as well easy to integrate to others planar circuit. The
selectivity. fabrication process is done by using PCB which is beneficial
to the low-cost manufacturing process.
The symmetrical window method shows better
performance compared to other method. From observation, the
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