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APUSNCURSINRSM.2017.8073155

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A Compact Microtrip Filtering Power Divider Made
Of Novel Coupled Resonators
Yifeng Chen, Xianling Liang, Weiren Zhu, Liang Liu, Junping Geng, Ronghong Jin, Maohua Zhu and Guanshen
Chenhu
Department of Electronic Engineering, Shanghai Jiao Tong University, Shanghai, China.
E-mail: liangxl@sjtu.edu.cn
Abstract—We present the design of a compact microstrip
filtering power dividers by utilizing the coupling between adjacent
resonators. For the purpose of effectively reducing the circuit area
and achieving a good isolation, four novel resonators are precisely
designed and arranged. Numerical simulation shows that a
filtering power with size as compact as 0.16 λg by 0.16 λg can
achieve a high isolation over 20 dB.
1
2
Input Port
Output Port
λ/4
3
Output Port
4
Isolation Port
Keywords—filtering power divider (FPD), microstrip, novel
resonator, compact structure.
3λ/4
I. INTRODUCTION
Fig. 1. Geometry structure of the typical 3 dB hybrid ring.
Port 1
With the development of modern wireless communication
systems, the miniaturization of RF front-end components is
highly demanded. Integrating multiple functionalities into one
component is an effective way to reduce the circuit area. A
power divider can split an input power into several parts, which
is frequently used in feeding networks in antenna array systems.
Meanwhile, an RF filter is also an essential component in
modern RF front-ends, which is used to filter out undesired
signals while pay little deterioration to useful signals. In many
systems, both the two components are indispensable. It is,
therefore, necessary to integrate them into one component for
size reduction and low loss.
In recent years, there were two design methods proposed to
meet the requirement. One method is to cascade the filtering
circuit with power dividers [1][2]. Another method is to replace
the quarter-wavelength transformers in Wilkinson power
dividers with bandpass filters [3][4]. Other than these two
methods, the couplings between adjacent resonators can also be
used for the integration of power dividers and filters [5]. By
replacing the quarter/three-quarters-wavelength-lines of the 3dB
hybrid ring with the coupling of resonators, the filtering power
divider (FPD) can be realized. Then, the circuit area can be
reduced significantly as the FPD is transformed into the
coupled-resonator network.
In this paper, to further reduce the circuit area, a coupledresonator network is used to design the FPD, which composed
of four novel resonators. The resonators are well placed for
achieving good isolation and filtering response. The FPD has a
size as compact as 0.16 λg× 0.16 λg and simulated isolation
higher than 20 dB within the whole passband.
II. FILTERING POWER DIVIDER DESIGN
Resonator 1
t1
Resonator 2
d21
l2
t2
w2
d31
d42
Port 2
t3
Resonator 3
Resonator 4
t4
d43
Port 3
50Ω
Fig. 2. Schematic layout of the proposed FPD.
2&3 and none for port 4. At the same time, port 2 and port 3 are
isolated each other. If port 4 is loaded by a 50 Ω resistor, the 3
dB hybrid ring can be regarded as a 3 dB power divider.
The schematic layout of the proposed FPD is shown in Fig.
2, which is composed of four resonators coupled with each other.
The magnetic resonance can be managed to be out-of-phase with
the electric resonance [5]. Therefore, the quarter-wavelengthlines and three-quarters-wavelength-lines in a 3 dB hybrid ring
can be mimicked by the electromagnetic coupling between
resonators. Particularly, the quarter-wavelength-line is achieved
by the electric couplings while the three-quarters-wavelengthline is realized by the magnetic coupling.
The typical structure of the 3 dB hybrid ring is shown in Fig.
1. The input power from port 1 divides evenly between ports
978-1-5386-3284-0/17/$31.00 ©2017 IEEE
2225
AP-S 2017
Figures 3(a) and 3(b) show the even and odd modes of the
proposed novel resonators, respectively. Since the resonant
frequency of the odd mode is much higher than that of the even
mode, the coupling between these two modes is negligibly weak.
It is seen that the even mode of the resonator is transformed from
the quarter-wavelength resonator shown in Fig. 3(c).
The geometric parameters of the proposed FPD are listed in
III. SIMULATION RESULTS
The simulated S-parameters are shown in Fig. 4. It is seen
that the simulated insertion losses |S21| and |S31| are
approximately 4 dB, which is caused by the filtering response of
the bandpass filter and the insertion loss of the 3 dB power
divider. Besides, the isolation between ports 2 and 3, |S32|, is
higher than 20 dB within the whole passband. However, as a
tradeoff of the excellent isolation performance, the bandwidth is
relatively narrow.
Table II compares the proposed FPD with other works. It is
seen that the proposed FPD owns not only the smallest size and
lowest insertion loss, but also a good in-band isolation as well.
(a)
(b)
TABLE II.
(c)
Fig. 3. (a) Even mode of the resonator, (b) Odd mode of the resonator
(c) Quarter-wavelength resonator.
COMPARISON BETWEEN THE PROPOSED FPD AND THE
OTHER WORKS
Insertion loss
(dB)
Isolation
(dB)
[2]
6.4
>15
0.49×0.38
[3]
6
>24
0.31×0.22
[5]
4.4
>30
0.19×0.19
This work
4
>20
0.16×0.16
Size (λg2)
IV. CONCLUSION
0
-10
Magnitude (dB)
In summary, we have presented a compact microstrip FPD
based on a coupled-resonator network consisting of four novel
identical resonators. Each resonator performs as a quarterwavelength-line in the 3 dB hybrid ring. These resonators are
precisely placed for achieving good isolation and filtering
responses. The proposed FPD has a compact size of 0.16 λg by
0.16 λg with simulated isolation over 20 dB at the frequencies of
interest. The insertion losses are approximately 4 dB including
the 3 dB loss from power divider within the whole passband.
S11
S21
S31
S32
-20
-30
-40
-50
ACKNOWLEDGMENT
-60
-70
0.50
0.75
1.00
1.25
1.50
1.75
This work was supported by the National Natural Science
Foundation (61671416, 61471240, 61571298 and 61571289)
2.00
Frequence (GHz)
REFERENCES
Fig. 4. S-parameters of the proposed FPD.
[1]
Table I. The substrate is Neltec NH9338 with a relative
dielectric constant of 3.38 and a thickness of 0.508 mm. The
widths of w2 and w1 are set to be 1.137 mm and 3.071 mm,
respectively, which are corresponding to the microstrip line
characteristic impedances of 50 Ω and 25 Ω. Due to the folded
line design, the proposed FPD only has a size of 27 mm × 27
mm, which equals to 0.16 λg × 0.16 λg (λg is the guided
wavelength at the center frequency of 1.2 GHz).
TABLE I.
[2]
[3]
[4]
DIMENSION OF THE PROPOSED FPD (ITEM: MM)
d21
d31
d42
d43
t1
t2
t3
t4
l1
l2
l3
0.49
0.6
0.6
0.35
6.8
6.8
6.5
6.8
15.5
11.5
5.5
[5]
2226
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Components Letters, vol. 24, no. 1, pp. 17-19, Jan. 2014.
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