Reconfigurable Dual-Band Filtering Power Divider With Ultra-Wide
Stopband Using Hybrid Microstrip/Square Defected Ground Structure
Zhen Tian, Yunbo Rao, Zhixian Deng, and Xun Luo
Center for Integrated Circuits, UESTC, Chengdu 611731, China
Abstract — In this paper, a reconfigurable dual-band filtering
power divider (FPD) with the wide tuning range and
ultra-wide stopband is proposed. The hybrid stepped-impedance
microstrip line/square defected ground structure (SIML/SDGS)
can introduce a lowpass response with an ultra-wide stopband.
Meanwhile, the coupled varactor-loaded tri-branch resonators
with SDGS are utilized to adjust the coupling coefficient for
improving passband bandwidth. To verify the aforementioned
mechanisms, a reconfigurable dual-band bandpass FPD is
developed with merits of the wide tuning range, high selectivity,
and ultra-wide stopband. The measured results exhibit that the
frequency tuning ranges of the proposed power divider are
57% and 41% for the dual-band, respectively. Meanwhile, the
harmonic suppression is up to 23.5 times of the lowest passband
center frequency (i.e., 0.85 GHz) with a rejection level higher
than 25 dB.
Keywords — Dual-band, filtering power divider (FPD),
hybrid microstrip/square defected ground structure (SDGS),
reconfigurable circuit, ultra-wide stopband.
I. INTRODUCTION
Continuous progress in modern wireless communication
systems during the last decades is driven by the steadily
increasing number of wireless devices and services. Filtering
power dividers (FPDs) find promising applications in
modern communication systems, since they afford two
functions of filtering and power dividing with reduced
loss, cost, and complexity. To solve the problem from the
electro-magnetic compatibility, a fixed FPD with wideband
harmonic suppression [1] is in great demand for multi-standard
systems. Meanwhile, the H-shape defected ground structure
(DGS) [2] is used for harmonic suppression. To meet
the requirement of multi-standard system, tunable passive
components [3]–[7] with the reduced circuit size and
flexible channel selection are proposed. However, as one
of the key elements of modern communication system,
the FPD with multiband, tunable operation, good isolation,
and ultra-wideband harmonic suppression remains great
challenges.
In this paper, the reconfigurable dual-band operation with
ultra-wideband harmonic suppression is introduced by the
hybrid microstrip/square defected ground structure (SDGS).
Compared with microstrip lines, such hybrid microstrip/SDGS
with enhanced impedance would not be limited by the
practical fabrication. Meanwhile, the coupling coefficient of
coupled microstrip will be improved with the SDGS. Pairs of
coupled varactor-loaded tri-branch resonators are introduced
for allocating two passbands and three tunable transmission
zeros. Then, a reconfigurable FPD is developed with measured
center frequencies of dual passbands at 0.85-1.53 GHz and
Varactor-
loaded
resonators
with SDGS
Harmonic suppression
Tunable & Filtering
Port 1
Port 2
Port 3
SIML/
SDGS
SIML/
SDGS
SIML/
SDGS
SIML/
SDGS
Varactor-
loaded
resonators
with SDGS
Loaded
open-stub
Loaded
open-stub
Enhancing
harmonic
suppression
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Fig. 1. (a) Configuration and (b) layout of the proposed FPD.
1.47-2.22 GHz, respectively, where its in-band isolation is
better than 19 dB. The harmonic suppression is up to 20 GHz
with the insertion loss higher than 25 dB. To the best of the
authors’ knowledge, the proposed FPD is the first experimental
demonstration of a reconfigurable dual-band bandpass FPD
with an ultra-wideband harmonic suppression.
II. SCHEMATIC AND OPERATION
Fig. 1(a) shows the configuration of the FPD, including
a Wilkinson-type power divider using two stages isolated
resisters, varactor-loaded coupled resonators, and additional
open-stubs. Corresponding to Fig. 1(a), the layout of the
proposed FPD is depicted in Fig. 1(b). To investigate the
mechanism of the proposed structure, the EM simulator IE3D,
ADS, and RT5880 dielectric substrate with ǫ
r
of 2.2 and a
thickness of 0.508 mm are used.
A. Filtering Operation
As shown in Fig. 2, the reconfigurable dual-band operation
of the FPD is introduced by the varactor-loaded coupled
tri-branch resonators with hybrid microstrip/SDGS. Such
978-1-7281-1309-8/19/$31.00 © 2019 IEEE 2019 IEEE/MTT-S International Microwave Symposium
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