IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 14, 2015 1573
A Compact Differential Filtering Quasi-Yagi
Antenna With High Frequency Selectivity and
Low Cross-Polarization Levels
JinShi, XuWu, Zhi NingChen, Fellow, IEEE, Xianming Qing, Member, IEEE,
Longlong Lin, Jianxin Chen, and Zhi-Hua Bao
Abstract—A compact differential filtering quasi-Yagi antenna
is proposed for high frequency selectivity and low cross-polariza-
tion. The proposed antenna is formed by inserting a double-sided
parallel-strip line (DSPSL) filterbetweenthedriverandthe
reflector of the quasi-Yagi antenna. This integration enables the
antenna to achieve both high frequency selectivity and compact
size. An antenna prototype exhibits a 10-dB return loss bandwidth
of 1.77–1.87 GHz, peak gain of 5.6 dBi, and maximum cross-po-
larization levels of
dB in E-/H-planes at 1.81 GHz.
The out-of-band suppression is enhanced by 14.4 and 11.8 dB at
1.67 and 1.97 GHz compared to the quasi-Yagi antenna itself,
respectively.
Index Terms—Compact, differential, double-sided parallel-strip
line (DSPSL), filtering antenna, low cross-polarization, quasi-Yagi
antenna.
I. INTRODUCTION
I
N MOST RF front-end systems, the antenna and filter are
two independent components which are usually designed
separately. A compact fil
tering antenna will definitely con-
tribute to the simplification and size reduction of the system
due to the increasing requirements of compact, low cost, and
low profile passive com
ponents.
There has been various filtering antennas reported whereas
most of them are single-ended [1]–[3]. The directly connecting
Manuscript received February 04, 2015; accepted March 01, 2015. Date of
publication March 16, 2015; date of current version August 06, 2015. This work
was supported in part by the National Natural Science Foundation of China
under Grants 61101002, 61471209, and 61271136; the Program for New Cen-
tury Excellent Talents in University under Grant NCET-11-0993; the Natural
Science Foundation of Jiangsu Province, China, under Grant BK 2012657; the
Six types of Talents Project of Jiangsu Province under Grant 2013-XXRJ-010;
the Open Research Program of the State Key Laboratory of Millimeter Waves,
China, under Grant K201415; and the Graduate Research and Innovation Plan
Project of the Universities of Jiangsu Province under Grants KYLX_1305 and
CXZZ13_0867.
J. Shi is with the School of Electronics and Information, Nantong University,
Nan Tong 226019, China, and also with the State Key Laboratory of Millimeter
Waves, Nan Jing 210096, China (e-mail: jinshi0601@hotmail.com).
X. Wu, L. Lin, J. Chen, and Z.-H. Bao are with the School of Electronics and
Information, Nantong University, Nan Tong 226019, China.
Z. N. Chen is with the Institute for Infocomm Research, A*STAR, Singapore
138632, Singapore, and also with the National University of Singapore, Sin-
gapore 117583, Singapore (e-mail: eleczn@nus.edu.sg; chenzn@i2r.a-star.edu.
sg).
X. Qing is with the Institute for Infocomm Research, A*STAR, Singapore
138632, Singapore (e-mail: qingxm@i2r.a-star.edu.sg).
Color versions of one or more of the figures in this letter are available online
at http://ieeexplore.ieee.org.
Digital Object Identifier 10.1109/LAWP.2015.2413054
of the filter and the antenna usually causes the impedance mis-
match and performance deterioration. Although the insertion of
an extra impedance transformer between the antenna and filter
alleviates this problem, it increases the system size and com-
plexity [1]. A codesign approach considering the antenna as
the last resonator of the filter has been proposed to reduce the
overall size [2], [3]. However, they are still larger than the an-
tennas alone.
On the other hand, differential filtering antennas [4], [5] have
attracted increasing attention because of better cross-polariza-
tion levels and convenient integration with differential circuits
and systems when compared with single-ended ones [6]. The
differential filtering antennas are realized by integrating either
a balanced filter with a quasi-Yagi antenna or a differential
coplanar strip line filter with a differential loop antenna in [4]
and [5]. However, such antennas still have a larger overall size
than the independent antennas themselves.
In this letter, a compact differential filtering quasi-Yagi an-
tenna is proposed. By inserting a double-sided parallel-strip line
(DSPSL) filter between the driver and the reflector, the proposed
filtering quasi-Yagi antenna achieves high frequency selectivity
and low cross-polarization levels without increasing the overall
size. In addition, the antenna maintains radiation performance
similar to that of the nonfiltering differential quasi-Yagi antenna.
Design procedures of the proposed differential filtering quasi-
Yagi antenna are given, and the performance is compared. The
proposed filtering antenna is numerically investigated through
Ansoft High Frequency Structure Simulation (HFSS) and ex-
perimentally validated.
II. A
NTENNA DESIGN
Fig. 1
exhibits the configuration of the proposed differen-
tial filtering quasi-Yagi antenna. It is fabricated on a double-
layer RO4003 C substrate (relative dielectric constant of 3.38,
loss
tangent of 0.0027, and thickness (
)of0.508mm)witha
prepreg layer (dielectric constant of 3.48, loss tangent of 0.003,
and thickness (
) of 0.2 mm) in between. The proposed antenna
is co
mposed of a driver, a director, a reflector, a DSPSL filter,
and a transition between the DSPSL and the feeding ports. The
driver as the main radiator is printed onto the top and bottom
laye
rs separately. The director that directs the antenna propaga-
tion toward the endfire direction is etched on the top layer. The
reflector, which is positioned on the middle layer, makes the an-
ten
na radiate forward and serves as the ground of the differential
microstrip line pair as well.
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