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Design of the Compact Dual-Band
Bandpass Filter With High Isolation for
GPS/WLAN Applications
IEEE MICROWAVE AND WIRELESS COMPONENTS
LETTERS, VOL. 19, NO. 12, DECEMBER 2009
Yu-Chi Chang, Chia-Hsiung Kao, Min-Hang Weng and
Ru-Yuan Yang
Adviser : Hon Kuan
Reporter : Yi-Hsin Su
Student ID : M98L0210
Date : 2010/3/2
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Outline




Introduction
Design Procedure
Fabrication And Measure Results
Conclusion
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Introduction
 Recently, the development of multi-service mobile wireless
communication systems has become attractive for commercial products
especially in the combination of global position system (GPS) and
wireless local area network (WLAN), global system for mobile
communications (GSM)and GPS or GSM and WLAN.
 Most of the reported dual-band BPFs only provide the dual passband
performance in a single-service system, especially in WLAN with IEEE
802.11 a/b standard.
 This paper develop a very simple structure to realize a compact and
high performance dual-band BPF with a high isolation loss of 55 dB
between the two passbands of GPS/WLAN and a wide upper stopband.
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Design Procedure
Practical layout of the designed dual-band BPF.
 The schematic of the dual-band
BPF basically consisting of two
asymmetric SIRs and a pair of I/O
ports.
 This dual-band BPF is designed
and fabricated on Duroid 5880
substrate having a thickness of
0.787 mm, a dielectric constant of
2.2, and a loss tangent of 0.0009.
 the structural parameters:
L1=15.02mm,L2=4.45mm,L3=15.5
3mm,L4=15.02mm,L5=0.29mm,L6
=9.16mm,W1=0.2mm,W2=0.2mm,
W3=3.7mm,S1=0.5mm,S2=0.1mm
,S3=1.18mm,S4=0.1mm,S5=1.96m
m
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Design Procedure
Schematic of the asymmetric SIR.
 The proposed asymmetric SIR with one step
discontinuity is different from the conventional SIR
with two step discontinuities.
 The asymmetric SIRs are composed of a highimpedance section(Z1=1/Y1) and a low-impedance
section(Z2=1/Y2).
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Design Procedure
 The impedance ratio R is defined as R=Z2/Z1,θt is defined as
the total wavelength of the asymmetric SIR.
 It is known that the resonance conditions of the proposed
asymmetric SIR is determined when Yin=0.
 The length ratio (α) of asymmetric SIR is also varied to
adjust the higher order resonant modes over a wide
frequency range.
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Design Procedure
 That normalized ratios of the second
resonant frequency(f1) to the fundamental
resonant frequency(f0) for an asymmetric
SIR with R=0.25,0.45,0.65 and 1.
 Some higher order resonant modes are
very close to the fundamental resonant
mode; thus it is possible to shift different
resonant modes to form a dual-band
performance
 The length ratio α can be explicitly
determined as 0.625 for obtaining the
dual-band response when considering the
Normalized ratios of the second resonant frequency to the
asymmetric SIR with R=0.25
fundamental resonant frequency for an asymmetry SIR with
R=0.25,0.45.0.65 and 1.
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Design Procedure
 The 3-dB fractional bandwidths
(FBW) of the two passband are set
as FBW1 of 6% for the first
passband and FBW2 of 4% for the
second passband with the same
passband ripple of 0.01 dB.
 From the filter specifications, the
lumped circuit element values of the
low-pass prototype filter are found
to be g0=1,g1=1.3782,g2=1.2693,
j1=-0.2492, and j2=0.9772.
Mij is the coupling coefficient that
M23= FBW*j2/g2, M14= FBW*j1/g1
and M12= M34 =FBW*(g1g2)1/2.
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Design Procedure
(a)
(b)
Coupling coefficient of (a) M23, (b) M12 and m34for first passband
and second passband simultaneously.
 The coupling coefficients that are calculated. The coupled spacing can be
tuned to satisfy the coupling degree between the adjacent resonators
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Fabrication And Measure Results
 The two passbands of the fabricated
dual-band BPF in detail. The
measured results have a return loss
greater than 30 dB, an insertion loss
less than 0.9 dB, and a FBW of 6%
for 1.575 GHz, and the measured
results have a return loss greater
than 20 dB, an insertion loss less
than 1.1 dB, and a FBW of 3.8%
for 2.4 GHz.
 It is also clearly found that the
isolation level is around 55 dB
between the two passbands and the
upper stopband is from 2.7 to 5.3
(a) Simulated and measured frequency responses of the fabricated
GHz at the average attenuation
dualband BPF and (b) two passbands in detail.] (Insert is the
photograph).
level of 38 dB.
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Conclusion





A novel compact dual-band BPF at 1.575 and 2.4 GHz using two
asymmetric SIRs with low loss, wide stopband and high isolation .
The two passbands can be properly tuned by controlling the resonant modes
of the proposed asymmetric SIR, which are discussed as functions of the
impedance ratio and physical length ratio.
The circuit size is reduced greatly about 60%compared with the dual-band
BPF using the conventional SIRs with the same specifications .
The isolation is greater than 55 dB, introducing a high isolation between the
two passbands.
The average attenuation level of 38 dB is obtained to achieve a wide upper
stopband from 2.7 to 5.3 GHz .
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