IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 63, NO. 12, DECEMBER 2015 4013
Wideband Balanced Network with High Isolation
Using Double-Sided Parallel-Strip Line
Wenjie Feng, Member, IEEE, Chaoying Zhao, Wenquan Che,SeniorMember,IE
EE, and Quan Xue, Fellow, IEEE
Abstract—A new wideband balanced power dividing/combining
network with high isolation is proposed in this paper. The differen-
tial/common mode equivalent circuits of the balanced network can
be easily reduced based on the matrix transformation. Two double-
sided parallel-strip line (DSPSL) 180
phase inverters loaded with
four isolation resistors are used to realize high isolation for the
power division output ports. A planar wideband balanced network
with bandwidth 52.7% of (1.68–2.84 GHz,
dB) for the differential mode and high isolation for the differen-
tial/common mode is designed and fabricated. The measured re-
sults show good agreement with the theoretical expectations.
Index Terms—Wideband, balanced network, double-sided par-
allel-strip line (DSPSL), differential/common mode.
I. INTRODUCTION
RF
and microwave circuit and system is becoming a
more complicated, more function space, balanced
circuits with wideband common-mode rejection capability, and
high immunity to the environmental noise are imperatively
needed to suppress the electromagnetic mutual interference
among the interconnection, and nodes of different dielectric
layer circuits in communication system [1]. In the past few
years, different balanced filters, balanced driven antennas,
balanced amplifiers with high performance are illustrated in
[2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14],
[15], [16].
In addition, former in-phase and out-of-phase power
dividing/combining networks were mainly focused on
single-ended components [17]–[20]. Balanced power di-
viding/combining networks without single-ended networks are
also highly required in balanced networks [1]. In [21], [22], two
balanced networks with high isolation are introduced, however,
the bandwidths of the differential mode power division is less
than 30% (
dB). In our former works,
Manuscript received June 19, 2015; revised October 12, 2015; accepted Oc-
tober 23, 2015. Date of publication November 12, 2015; date of current version
December 02, 2015. This work was supported by the 2012 Distinguished Young
Scientist awarded by the National Natural Science Foundation Committee of
China(61225001), Natural Science Foundation of China(61401206, 61571231)
and Jiangsu Province(BK20140791), and the 2014 Zijin Intelligent Programof
NanjingUniversityofScience and Technology.
Wenjie Feng, Chaoying Zhao, Wenquan Che are with the Depart-
ment of Communication Engineering, Nanjing University of Science and
Technology, 210094 Nanjing, China (e-mail: fengwenjie1985@163.com,
zhaochaoying1992@163.com, yeeren_che@163.com).
Quan Xue is with the State Key Laboratory of Millimeter Waves, Depart-
ment of Electronic Engineering, and CityU Shenzhen Research Institute, City
University of Hong Kong, China (e-mail: eeqxue@cityu.edu.hk).
Color versions of one or more of the figures in this paper are available online
at http://ieeexplore.ieee.org.
Digital Object Identifier 10.1109/TMTT.2015.2495357
two new wideband in/out-of-phase balanced networks with
wideband common mode suppression are proposed in [23].
The main advantages of the two balanced networks are the
wideband for the differential mode power division (bandwidth
over 50%,
dB), and wideband common
mode suppression (bandwidth over 100%,
dB).
However, due to the fact that there are no isolation resistors for
the two networks, the isolation
of the differen-
tial/common mode power division cannot be deduced from the
equations of the standard matrix [21], so the isolation results
are not as good as the ideal mixed-mode
-parameters.
The double-sided parallel-strip line (DSPSL), as one kind of
balanced transmission lines, is quite useful and convenient for
the balanced microwave components designs. DSPSL has im-
portant advantages of easy realization of low and high charac-
teristic impedance, simple circuit structures of wideband tran-
sitions [24], [25]. Using these advantages, some novel double-
sided parallel-strip line (DSPSL) passive/active circuits are il-
lustrated in [26], [27], [28]. In this paper, a new wideband bal-
anced power dividing/combining network with high isolation
and wideband power division for the differential mode is pro-
posed, and the circuit is shown as Fig. 1. When the differential
mode is excited in the balanced input Port 1 (Port
), an equal
in-phase power division can be realized in the balanced output
Ports 2, 3 (Ports 2
,3); and when the common mode is excited
in the balanced input Port 1 (Port 1
), a bandstop transmission
characteristic can be realized due to the two transmission lines
for the balanced network. The circuit and structure of
the balanced network is simulated with Ansoft Designer v3.0
and Ansoft HFSS v.11.0, and constructed on the dielectric sub-
strate Rogers5880 with
mm, and
.
II. S
YNTHESIS DESIGN OF THE BALANCED POWER
DIVIDING/COMBINING NETWORKS
A. Mixed-Mod e Scattering Matrix of Six-Port Balanced
Network
As discussed in [21], [22], [23], the mixed-mode scattering
matrix
of a six-port balanced power dividing/combining
network can be defined as
(1)
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