International Conference on Trends in Electrical, Electronics and Power Engineering (ICTEEP'2012) July 15-16, 2012 Singapore
Design and Simulation of Edge-coupled
Stripline Band Pass Filter for Ka Band
Application
Hnin Yu Wai, Zaw Min Naing, Kyaw Soe Lwin and Hla Myo Tun

II. METHODOLOGY
Abstract— In this paper, band pass filter (BPF) development with
the assistance of the Richards-Kuroda Transformation method, on the
basis of the known Chebyshev-Lowpass Filter, is presented. This
suggested filter consists of four edge-coupled striplines. The filter is
operated at Ka-band downlink frequency segment of 19.7 GHz – 20.2
GHz for satellite application. The proposed circuit is simulated using
Roger 5870 substrate with dielectric constant of 2.33, substrate height
of 0.508 mm and thickness of 0.035 mm. The simulation results are
excellent and the filter is suitable for integration within various
microwave subsystems.
The design specification of the filter is shown in Table I.
The specification of dielectric material is obtained from
Rogers Corporation. It is shown in Table II.
The proposed filter is designed by following the five
steps. First step: Determining the order and type of
approximation functions to be used. Second step: Finding the
corresponding low-pass prototype. Third step: Transforming
the low-pass network into a bandpass configuration. Fourth
step: Scaling the bandpass configuration in both impedance
and frequency. Fifth step: Transforming the lumped circuit
element into distributed realization.
Keywords—Band Pass Filter, Chebyshev, Edge-coupled, Ka
Band, Stripline
I. INTRODUCTION
TABLE I
SPECIFICATIONS OF BAND PASS FILTER
Upper cut-off frequency
19.7 GHz
Lower cut-off frequency
20.2 GHz
3-dB Bandwidth
0.5 GHz
Passband ripple
0.5 dB
Attenuation at center frequency
≥ 30 dB
Stripline filters play an important role in many RF
applications. As technologies advances, more stringent
requirements of filters are required. One of the requirements is
the compactness of filters [1]–[2]. At very high frequencies,
the practical inductors and capacitors loses their intrinsic
characteristics. Also a limited range of component values are
available from the manufacturer [3]. Therefore for microwave
frequencies (>3GHz), passive filter is usually realized using
distributed circuit elements such as transmission line sections
[4].
Many works have been reported that use waveguides for
transmission line filter. However, waveguides systems are
bulky and expensive. Low-power and cheaper alternatives are
stripline and microstrip. These transmission lines are compact
[5]. Edge-coupled stripline is used instead of microstrip line as
stripline does not suffer from dispersion and its propagation
mode is pure TEM mode. Hence it is the preferred structured
for coupled-line filters [4].
Therefore, a third order chebyshev edge-coupled stripline
filter is designed in the research. The band pass filter is
simulated by using Ansoft Designer software.
TABLE II
SPECIFICATIONS OF DIELECTRIC MATERIAL FROM ROGERS CORPORATION
Dielectric Material Used
Roger 5870 from Rogers
Corporation
Dielectric Constant
2.33
Loss tanget, tanδ
0.0012
Substrate Height, h
0.508 mm
Copper Thickness, t
0.035mm
Metal Roughness
2.4e-3 mm
Hnin Yu Wai is with Department of Electronic Engineering, Mandalay
Technological University, Ministry of Science and Technology, Myanmar (email: powerlay@gmail.com).
Zaw Min Naing is with Technological University (Maubin), Myanmar (email: zawminnaing@pmail.ntu.edu.sg).
Kyaw Soe Lwin is with Department of Electronic Engineering, Mandalay
Technological University, Ministry of Science and Technology, Myanmar (email: kyawsoelwin007@gmail.com).
Hla Myo Tun is with Department of Electronic Engineering Department,
Mandalay Technological University, Ministry of Science and Technology,
Myanmar (e-mail: hmyotun@myanmar.com.mm).
Fig. 1 Characteristics for a chebyshev filter with 0.5dB ripple
97
International Conference on Trends in Electrical, Electronics and Power Engineering (ICTEEP'2012) July 15-16, 2012 Singapore
Since Cyebysh
hev filter has steeper initial descent into the
her filter typess, this type of filter
f
is chosen
n in
stoopband than oth
thiis research worrk. Order of fillter can be deteermined by using
thee attenuation ch
haracteristics shown
s
in Fig. 1 for a Chebysh
hev
filtter with 0.5dB
B ripple. Based
d on design speecification, thiirdordder filter is chosen using
g the proposeed edge-coup
pled
struucture.
TABL
LE III
LOW
O PASS PROTOTYP
PE ELEMENT VALU
UES
go
g1
g2
0.6
6986
1.0000
1.4
4029
0.7071
1.9841
1.5
5963
1.0967
1.5963
Order
1st
2nd
3rd
B
2f o2Cn R
R
RLn
L
2B
C
1.5963H
H
g3
1.096
67F
f = 0.159Hz
1.000
L3 0.002251pF
pF
0.00251p
225.41nH
C1
C2
0.00912nH L2
25.41nH
6.982pF
C3
50
f = 199.95 GHz
Fig. 4 BPF
F prototype for ddesigned frequenncy
1.5963H
C2
L1
50
To source
network
L3
L1
(5)
The frequency annd impedancee scaling off third-order
bandpasss filter with a cut-off freqquency of 19.995GHz with
3dB baandwidth of 500MHz and 550Ω impedancce rating for
both poorts is presentedd in Fig. 4 [6].
The element values
v
for the th
hird-order are taken from Taable
III of normalized values off 0.5dB equall ripple lowp
pass
proototype. The lo
owpass prototy
ype is presented
d in Fig. 2.
1
(4)
1
J1
J2
J3
J4
-90 degree
-90 degree
-90 degree
-90 deggree
Fig. 2 Third-ord
der low pass prottotype
λoo/4
A
After getting a lowpass filter prototyp
pe values, it is
traansformed into a bandpass design.
d
Althoug
gh, lowpass fillter
is transformed into
i
bandpass filter design,, the attenuation
banndwidth ratios remain the sam
me such that:
f
B
BW

BWc
fc
Secction 1
Section 2
Section 3
Section 4
(1)
Whhere, BW = baandwidth at the required valuee of attenuation
n
BW
Wc = 3dB bandwith of bandpaass filter
t
pass
The actual transformation
from lowpaass to bandp
connfiguration is accomplished
d by resonatin
ng each lowp
pass
eleement with an element of th
he opposite ty
ype and the saame
vallue. All shunt elements
e
of low
wpass prototyp
pe circuit beco
ome
parrallel-resonant circuits, and
d all series elements
e
beco
ome
serries-resonant circuit.
c
The co
orresponding transformation
t
n of
low
wpass network
k into bandpasss configuratio
on for third-order
Chhevbyshev filteer is shown in Fig.
F 3.
1
1.5963H1.5963F
F
L1
C1
1.0967H
f = 0.159Hz
0
Ricchard’s transfo
formatioand Kuuroda’s identitties are used
to accom
mplish the connversion from tthe lumped annd distributed
circuit designs. The eexplanation off Richard’s traansformation
An equivalent
and Kuuroda’s identitiies are in [2], [4] and [5]. A
circuit model for 3rdd order edge-ccoupled transm
mission lines
with oppen circuit att 2 ends and each section of coupled
striplinee are shown in Fig. 5.
Eaach section of coupled stripline conntains three
parametters: S, W, andd d. Two stripllines of width W are in the
parallell- or edge-couupled configurration with a separation S
and d iss the diameterr or height of tthe substrate. The coupled
line struucture supportts two quasi-T
TEM modes, i.e., the even
mode annd the odd moode. The three parameters aree determined
from thhe odd and eveen mode impeddance (Zoo & Z
Zoe) of each
coupledd line. Zoo andd Zoe are in tuurn depends onn the gain of
the corrresponding adm
mittance invertter J.
1.5963H 1.5963F
L3
L2
Fig. 5 3rd order edge-couppled stripline filtter
1.0967F
C2
C3
1
Fig
g. 3 Low pass to band pass transfformation
med filter iss then frequency-scaled and
a
The transform
im
mpedance-scaled
d using the following formu
ulas. For paralllelressonant branchees,
Cn
2RB
RB
L
2f o2 Ln
C
(2)
(3)
J1 
1 
Z
Zo 2 g1
(6)
Jn 
1

2Zo g n1 g n
(7)
J N 1 
andd, for the seriees-resonant braanches,
98
1
Zo

2 g N g N 1
(8)
International Conference on Trends in Electrical, Electronics and Power Engineering (ICTEEP'2012) July 15-16, 2012 Singapore
f 2  f1
fo
 Z o (1  JZ
J o  ( JZ o ) 2 )
10)
(1
Z ooo  Z o (1  JZ
J o  ( JZ o ) )
(11)

Z ooe
2
Retuurn loss measuurement is usedd to evaluate thhe impedance
match oof a filter. A
As the match bbetween the ccharacteristic
impedannce of the ttransmission lline and the terminating
impedannce improves,, the reflectedd wave becom
mes smaller.
Therefoore, the reflectiion coefficientt in “(8)” decrreases. When
a perfeect match exissts, there is nno reflected w
wave and the
reflectioon coefficient is zero. If thhe reflection ccoefficient is
equal too 1, a perfect m
mismatch exissts. Thus, the nnormal range
of valuues for the maagnitude of thhe reflection ccoefficient is
betweenn zero and one.
Inserrtion loss (S21) is the differeence in dB pow
wer between
the signnals at the filterr input and outtput [7].
(9)
III. SIMULATION RESULTS
The B
BPF circuit is simulated withh Ansoft Desiggner Student
Versionn 2.2 software iin order to preddict the perform
mance of the
filter. F
Few parameterrs in the circuiit are analyzedd and have a
good reelationship to the microwavve theory. An optimization
process has been intrroduced alongg the simulatioon procedure
focusingg on the filteer dimension in order to iimprove the
responsse of the filter.
The configurationss of the softtware for Ka--band edgecoupledd stripline filterr are shown in Fig.8. The sofftware results
of odd and even m
mode impedannces for each section are
presenteed in Fig.9. T
The software rresults are neaarly identical
with thee calculated ressults. The simuulated responsee of insertion
loss (S221) and return looss (S11) is shoown in Fig.10.
F
Fig. 6 Characteristic curve of od
dd and even mod
de design data fo
or
edge-coupleed striplines
Fig. 7 Ph
hotograph of edg
ge-coupled stripline BPF
From the charracteristic curv
ve in Fig.6, thee parameters W,
W S
andd d for each section are obtained.
o
For section
s
1 and 4;
S/bb=0.2, W/b=0.7. Therefore, b=d=h=0.508m
b
mm, W=0.355m
mm
andd s=0.1mm. For
F Section 2 and
a 3; S/b = 0.8, W/b = 0.75.
Thherefore, s= 0.4
4064mm and W = 0.381mm. The photograaph
of edge-coupled stripline band pass
p filter is sh
hown in Fig.7.
The two paraameters (inserttion loss and return loss) are
mance of filter.. A
cruucial to analyzze to obtain a good perform
good filter will be high return
n loss and sm
mall insertion loss
nd. Return loss (S11) is a ratio
r
of refleccted
rippple in passban
pow
wer to inciden
nt power at th
he test port of
o a filter and
d is
exppressed in deciibels (dB).
 Pr


S11  10 log reflected
 Pincident 
Fig. 8 Connfiguration for ffilter specificatioons
(1
12)
The ratio of the reflected wave to the incident wavee is
known as the refflection coefficcient and is sim
mply a measuree of
thee quality of thee match betweeen the transmisssion line and the
terrminating impeedances.

Vreflected
Vincident
S111  10 log
(13)
(14)
Fig. 9 Softwaree results of odd aand even impedaances
99
International Conference on Trends in Electrical, Electronics and Power Engineering (ICTEEP'2012) July 15-16, 2012 Singapore
frequencies, lumped element filter is converted into distributed
stripline filter by using Richard’s transformation and Kuroda’s
identities. The filter is simulated with Ansoft Designer
software to predict the performance of filter. The simulated
insertion loss is less than 0.01dB in the desired passband and
the simulated return loss is greater than 50 dB at center
frequency. All simulated results are nearly identical with the
calculated results and also they are good agreement to the
design specifications.
ACKNOWLEDGMENT
The author is greatly indebted to her parents and all of her
teachers who have taught her during the whole life. The author
also would like to thank Dr. Chaw Myat Nwe, Associate
Professor at Electronic Engineering Department, Mandalay
Technological University, for her suggestions and comments
in doing this research.
Fig. 10 Simulated insertion loss and return loss
REFERENCES
The simulated insertion loss is less than 0.01 dB in
passband. Also the response is flat and uniform over the entire
pass-band. In addition, the simulated response has the
attenuation of more than 50 dB at 19.95 GHz. For S11 of 50
dB, reflection coefficient is 0.00001 which is nearly equal to
0 and a perfect match exists. Therefore, all simulated results
are nearly identical to the design specifications.
The simulated group delay for the designed filter is depicted
in Fig.11. It is clear from the result that the group delay
reaches a peak value close to the cut-off point. Moreover, the
simulated group delay has a very low peak-to-peak variation
of less than 3ns across the passband of the filter. Therefore,
the designed filter shows attractive characteristics for BPF
applications.
[1]
[2]
[3]
[4]
[5]
[6]
[7]
Fig. 11 Simulated group delay result
IV. CONCLUSION
This paper describes a procedure for designing edgecoupled stripline band pass filter. It also rejects image signal
appearing at the frequency range between 19.7GHz to
20.2GHz. Third-order edge-coupled stripline filter is used in
order to realize these objectives. Since the practical inductors
and capacitors loses their intrinsic characteristics at high
100
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