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VC 2013 Wiley Periodicals, Inc.
A COMPACT UWB CPW BANDPASS
FILTER WITH SHORT-ENDED H-SHAPED
RESONATOR AND CONTROLLABLE
NOTCHED BAND
Kai Wang, Sai Wai Wong, and Qing-Xin Chu
School of Electronic and Information Engineering, South China
University of Technology, Guangzhou, Guangdong, People’s
Republic of China
Received 13 November 2012
ABSTRACT: An ultra-wideband (UWB) bandpass filter (BPF) using the
hybrid microstrip and coplanar waveguide (CPW) structure is proposed
in this article. The BPF composes of CPW feed lines and H-shaped
microstrip resonator. By a CPW/microstrip back-to-back coupling
structure, the UWB BPF was realized with the passband covering the
entire UWB band (3.1–10.6 GHz). A narrow notched band achieved by
etching slots on the lower impedance part of the H-shaped resonator to
form an open circuit stub. At last, three U-slot DGSs are used to achieve
a good upper-stopband rejection. The measured results are in good
agreement with the simulated results. VC 2013 Wiley Periodicals, Inc.
Microwave Opt Technol Lett 55:1577–1581, 2013; View this article
online at wileyonlinelibrary.com. DOI 10.1002/mop.27663
Key words: coplanar waveguide; UWB bandpass filters; defected
ground structure; notched band; microstrip-line
1. INTRODUCTION
The U.S. Federal Communication Commission released the unli-
censed use of the ultra-wideband (UWB) (3.1–10.6 GHz) for
hand-held systems in 2002 [1]. Planar filters are an often-consid-
ered candidate for the UWB technology and have been studied
extensively in the past decade. As compared to microstrip struc-
ture, there is little work on hybrid microstrip and coplanar-
waveguide structure relatively. In [2], the authors present a
UWB bandpass filter (BPF) with hybrid microstrip feed line and
CPW resonator structure, and five modes allocated in the pass-
band appropriately by using the back-to-back coupled structure.
A broadside-coupled microstrip-coplanar waveguide (CPW)
structure was proposed in [3] with tightened coupling degree uti-
lized to design an alternative UWB filter with one, two, and
three sections. An UWB BPF was constituted only by CPW
structure [4] via cascading CPW lowpass and bandpass struc-
tures, and it achieved good performance, for example, sharp
skirt selectivity and good stopband rejection. A BPF with CPW
feed line and microstrip resonator was presented in [5], this
novel structure exhibits good in-band performance and a high
out-of-band rejection level.
On the other hand, to avoid unexpected signal interference
between the UWB system and the local-area network
Figure 1 (a) layout of CPW plane, (b) layout of microstrip plane, and
(c) Equivalent J-inverter network
DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 55, No. 7, July 2013 1577
applications, a notched band UWB BPF is required within the
defined UWB frequency spectrum as studied in [6–10]. In [6], a
notched band is simply created by embedding an asymmetric
shunt stub in the feed line, and the notched band can be change-
able by adjusting the size of stub. Multinarrow-notched bands
can be introduced by integrating slot lines on the bottom side of
the CPW BPF, which is shown in [7], and its notched band can
be control by changing the length of the slot lines. In [8], a dual
notch band is formed by embedding two open circuited stubs in
the form of defected microstrip structure.
In this article, we present an UWB BPF with hybrid CPW
feed line and microstrip resonator structure. The schematics are
shown in Figure 1 with marked dimensions. The short-ended H-
shaped microstrip resonator was studied in this article. A nar-
row-notched band achieved by etching slots on the lower imped-
ance part of the H-shaped resonator to form an open circuit
stub. At last, three U-slot defected ground structures (DGS) are
used to achieve a good stopband rejection. We found that the fil-
ter exhibits good in-band and out-of-band performance, includ-
ing a low insertion loss and a high out-of-band rejection level.
Simulation design for the filter is carried out on the electromag-
netic simulator ADS Momentum.
2. PROPOSED HYBRID BPF
Figure 1(b) shows the coupling structure of the hybrid CPW and
microstrip structure, and the equivalent J-inverter network is
shown in Figure 1(c). This hybrid structure results in building
up the UWB passband by virtue of the strong surface-to-surface
coupling structure.
Now, we look into the H-shaped resonator, it can be seen as
a short-ended step impedance resonator, which is depicted in
Figure 2(a). It consists of a low impedance line section in the
middle section and four identical high impedance short-circuited
line sections on the two sides, and the individual high imped-
ance of one side can be described as two parallel short-ended
stubs. A–A0 in Figure 2(a) is the symmetric plane and the char-
acteristic of the high impedances of the resonator are defined as
Z1, and the low impedances are defined as Z2, h1 and h2 is the
corresponding electrical length. R ¼ Z2/Z1 is defined as the im-
pedance ratio of low and high impedance lines.
Figure 2(b) shows the condition under the odd mode excita-
tion, the symmetric plane is short-circuit. We can easily obtain
the input admittance Yino
Yino ¼ �j 2Y1 tan h2 þ Y2 tan h1
tan h1 tan h2
Y1 and Y2 are corresponding input admittances of Z1 and Z2.
Figure 2(c) shows the condition under the even mode excita-
tion, the symmetric plane is open circuit. Herein, the input ad-
mittance Yine is given below.
Yine ¼ �j 2Y1 cot h2 � Y2 tan h1
tan h1 cot h2
Figure 2 (a) H-shaped resonator structure, (b) odd mode, and (c)
even mode
Figure 3 (a) Normalized resonant frequencies, (b) layout of gradual
changes in feed line. (c) Circuit block diagram. (d) Simulation of the
proposed structure. [Color figure can be viewed in the online issue,
which is available at wileyonlinelibrary.com]
1578 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 55, No. 7, July 2013 DOI 10.1002/mop
Under the resonance condition, the input admittance Yino and
Yine are equal to zero, so the resonance frequency depends on h1
and h2.
If 2h1 ¼ h2 ¼ h, three resonance frequencies can be
obtained.
hðfs1Þ ¼ 2 arctan
ffiffiffiffiffiffiffiffiffiffiffiffi
R
Rþ 1
r
;
hðfs2Þ ¼ 2 arctan
ffiffiffiffiffiffiffiffiffiffiffiffiffiffi
4Rþ 1p ;
hðfs3Þ¼ 2p� 2 arctan
ffiffiffiffiffiffiffiffiffiffiffiffiffiffi
4Rþ 1p ;
hðfs4Þ ¼ 2p� 2 arctan
ffiffiffiffiffiffiffiffiffiffiffiffiffiffi
R
Rþ 1 ;
r
hðfs5Þ ¼ 2p
Obviously, only the first resonance frequency h(fs1) is in the
desired passband as shown in Figure 3(a), and the other four res-
onance frequencies are out of band at the value of R ¼ 0.35. In
this novel coupling structure, two modes are achieved by the
strong coupling [9, 10] between the CPW and the microstrip
line. Whereas, the other two modes are achieved by the tapered
feed line, which is shown in Figure 3(b). The sections from the
short-ended microstrip line to tapered feed line are quarter-
wavelength (at 6.85 GHz), these two sections can be modeled as
K-inverter. As a result, the network in Figure 1(c) should be
modified as Figure 3(c). Another four modes are achieved by
two J-inverters and two K-inverters. The simulation of the pro-
posed UWB BPF with tapered feed line is depicted in
Figure 3(d).
3. A NOTCHED BAND AND THREE U-SLOT DGSS
To generate notch band, an embedded open circuit stub is real-
ized in the low impedance part of the H-shaped resonator, which
is shown in Figure 4(a). The stub is kg/4 in length at corre-
sponding center frequency to stop signal interference between
UWB system and systems.
The length of the open circuit stub is defined as L, and the
gap which is shown in Figure 4(a) is defined as W. Figure 4(b)
displays the insertion loss with the fixed W ¼ 0.2 mm and vari-
able L, and the notched band position moves to the low fre-
quency due to increase of L, so the notched band can be con-
trolled by altering the length of the stub. Actually, the
controlled frequency ranges from 5 to 7 GHz. In this article, we
chose L ¼ 8.85 mm which made the center frequency of the
notched band designed at 6 GHz. With fixed L ¼ 8.85 and vari-
able W, increasing the gap (W) widens the bandwidth of the
notched band and vice versa as demonstrated in Figure 4(c). It
should be noted that the center frequency of the notched band
slightly shifted to lower frequency when the gap was increased
(W), this may be caused by increasing the loading effect of the
quarter-wavelength of the open stub.
Apparently, the out of band performance has unwanted pass-
band, so slot-shaped DGSs on microstrip line [11] are used to
provide a good stopband property. The layout and simulated S-
parameters of the three cascading U-slot DGSs is showed in Fig-
ures 5(a) and 5(b), respectively. Obviously, three transmission
zeros are generated in the stopband that are created by the three
slot lines, and the three transmission zeros allocated from left to
right in Figure 5(b) correspond to the three slot lines which are
shown in Figure 5(a) from left to right. The simulation of the
proposed structure with three U-slot DGSs is shown in Figure
5(c) with fixed L ¼ 8.85 mm and W ¼ 0.2 mm. In comparison
between Figures 3(d) and (c), three transmission zeros were gen-
erated by three U-slot DGSs and a good upper-stopband-band
rejection is achieved.
3. IMPLEMENTATION AND EXPERIMENTAL RESULTS
According to the earlier analysis, the proposed UWB BPF is
designed, simulated, and fabricated. The final dimensions of the
UWB BPF is shown in Table 1, and the dimensions of the open
circuit stub is shown in Figure 4(a), and fixed L ¼ 8.85 mm and
W ¼ 0.2 mm, and the three U-slot DGSs dimensions are marked
in Figure 5(a).
The filter was fabricated on a substrate with a relative dielec-
tric constant of 2.55 and thickness of 0.8 mm, and the photo-
graph of fabricated UWB BPF is shown in Figures 6(a) and
6(b). Figure 6(c) provides a comparison of the simulated and
measured characteristics of the filter, and a good agreement is
observed over the passband. The measured insertion loss of the
filter is better than 0.7 dB, and the return loss is greater than 15
Figure 4 (a) Layout of etch slots on H-shaped resonator. (b) Simula-
tion results of rejection characteristics with fixed W ¼ 0.2 mm and vari-
able L. (C) Simulation results of rejection characteristics with fixed L ¼
8.85 and variable W. [Color figure can be viewed in the online issue,
which is available at wileyonlinelibrary.com]
DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 55, No. 7, July 2013 1579
dB. The notch band is well located at 6 GHz with 17 dB attenu-
ation in measurement. The upper stopband is beyond 15 dB
from 11 to 16.5 GHz. The novel hybrid structure with H-shaped
resonator is implemented for UWB BPF, and it is suitable to
apply in UWB communication systems.
4. CONCLUSION
A novel UWB BPF with hybrid CPW and microstrip structure is
proposed and implemented. The H-shaped resonator has been
discussed, a narrow notched band has been realized by embed-
ding an open circuit stub, and three U-slot DGSs were used to
achieve a good stopband rejection. The fabricated UWB BPF
has a wide passband of 2.9–10.9 GHz, and insertion loss is bet-
ter than 0.7 dB. The notch band is well located at 6 GHz with
17 dB attenuation in measurement. The upper stopband is
beyond 15 dB from 11 to 16.5 GHz.
ACKNOWLEDGMENT
This work is supported by the National Natural Science Foundation
of China (61101017) and the Fundamental Research Funds for the
Central Universities (2012ZM0024).
REFERENCES
1. Revision of Part 15 of the Commission’s Rules Regarding Ultra-
Wide-band Transmission System, FCC ET-Docket 98–153,
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TABLE 1 Dimensions of Proposed UWB Filter Shown in
Figure 1 (unit: mm)
W1 W2 W3 W4 W5 W6 W7
0.2 5.4 0.7 3.48 6.2 2.1 0.7
L1 L2 L3 S1 R r
3.3 2.75 12 5.8 0.6 0.6
Figure 6 (a) CPW plane of fabricated filter, (b) microstrip plane of
fabricated filter, and (c) results of measured and simulated. [Color figure
can be viewed in the online issue, which is available at
wileyonlinelibrary.com]
Figure 5 (a) Layout of H-shaped resonator with three U-slot DGSs.
(b) Simulation of three cascading U-slot DGSs. (c) Simulation of the
proposed structure with DGSs. [Color figure can be viewed in the online
issue, which is available at wileyonlinelibrary.com]
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6. S.W. Wong and L. Zhu, Ultra-wide bandpass filters with sharpened
roll-off skirts, extended upper-stopband, and controllable notch-
band, Microwave Opt Technol Lett 50 (2008), 2958–2961.
7. B.Y. Yao, Y.G. Zhou, and Q.S. Cao, A UWB bandpass filter with
multi notched bands using microstrip/coplanar waveguide, In: 8th
international symposium on antenna, propagation and EM theory,
2008, pp. 637–640.
8. H. Shaman and J.-S. Hong, Ultra-wideband (UWB) microstrip
bandpass filter with narrow notched band, In: 38th European
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9. J. Gao, L. Zhu, M. Menzel, and F. B€ogelsack, Short-circuited
CPW multiple-mode resonator for Ultra-wideband (UWB) band-
pass filter, IEEE Microwave Wireless Compon Lett 16 (2006),
124–126.
10. H. Wang and L. Zhu, Ultra-wideband bandpass filter using back-
to-back microstrip-to-CPW transition structure, Electron Lett 41
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11. D.-J. Woo, T.-K. Lee, J.-W. Lee, and W.-K. Choi, Novel U-slot
and V-slot DGSs for bandstop filter with improved Q factor, IEEE
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VC 2013 Wiley Periodicals, Inc.
A LOW-POWER TECHNIQUE TO BOOST
THE OUTPUT AMPLITUDE OF MULTI
GIGAHERTZ PUSH-PUSH LC VCOS
Reza Molavi,1,2 Shahriar Mirabbasi,1
and Hormoz Djahanshahi2
1 Department of Electrical and Computer Engineering, University of
British Columbia, Vancouver, BC, Canada; Corresponding author:
reza@ece.ubc.ca
2 PMC Sierra, Burnaby, BC, Canada
Received 23 November 2012
ABSTRACT: A design technique to increase the output amplitude and
hence the output power of push-push LC-based voltage-controlled
oscillators (LC VCOs) is presented that relies on LC resonance boosting
of the second harmonic. Measurement results are in good agreement
with the results predicted from the analysis. Using the proposed
technique, a low-power push-push LC VCO is designed and
implemented in 90-nm CMOS. Based on the measurement results, the
VCO has a frequency tuning range of 23%, from 20.1 to 24.8 GHz. It
exhibits up to 8 dB improvement in its output power at the middle of the
frequency band compared to a traditional push-push VCO. VC 2013
Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:1581–1584,
2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/
mop.27599
Key words: high-frequency oscillator; LC oscillator; push-push voltage-
controlled oscillator; accumulation-mode MOS varactor
1. INTRODUCTION
Push-push voltage-controlled oscillator (VCO) is a well-known cir-
cuit architecture that offers higher oscillation frequencies than con-
ventional fundamental-mode oscillators. In this architecture, the
concept of harmonic amplification is used to constructively add the
even-order harmonics of the oscillator’s fundamental frequency.
Typically, the second-harmonic component is weak, hence a con-
siderable amount of power is required to amplify it to an accepta-
ble level. A recent work combines the outputs of two quadrature-
coupled push-push LC VCOs to generate differential outputs with
a two-fold increase in amplitude at the expense of doubling the
power consumption as compared to a fundamental-mode VCO [1].
Different techniques have been used to extract the second
harmonic from a fundamental-mode VCO [1–3]. These techni-
ques are largely based on taking the second harmonic from a
common-mode node of the VCO, for example, drain of the tail
current source or a tap to the power supply path, and then use
power-hungry amplifiers to bring this weak second-harmonic
signal to a satisfactory level. In this work, relying on an inherent
characteristic of an LC VCO, we create an extra resonance at
the second harmonic to increase the desired output amplitude,
while reducing the total power consumption of the push-push
VCO.
2. ANALYSIS
Consider the LC tank of a differential VCO with a center-tapped
inductor, as shown in Figure 1. In this differential structure, the
fundamental oscillation frequency of the tank (f0) appears as
two voltage components in opposite phases at nodes A and B.
On