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3632 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 60, NO. 8, AUGUST 2012
SIW-Based Array Antennas With Sequential Feedingfor X-Band Satellite Communication
Eun-Young Jung, Jae W. Lee, Member, IEEE, Taek K. Lee, Member, IEEE, and Woo-Kyung Lee, Member, IEEE
AbstractNovel phased array antennas suitable for X-bandsatellite communication are introduced and investigated forright-handed circular polarization (RHCP) in a multi-layeredfabrication. The primary function of the proposed antennas is totransmit high quality data obtained from satellites and the ground
station systems with the lowest amount of loss. For accuratedata transmission, the important parameters regarding antennaspecifications and electrical performance are the antenna gain andthe high-purity polarization. Hence, this paper describes novelprocedures for gain enhancements of the array antennas working
at X-band (from 8.0 to 8.5 GHz) with an RHCP characteristic,including a single element, 2 2 array, and 2 4 array withfour-way and eight-way power dividers, respectively. Taking into
consideration the long-distance communication between a satelliteand ground station, a substrate-integrated waveguide structurehas been proposed, in particular because it is known to have low
radiation loss and a low weight comparable to that of a microstrip,as well as low material loss similar to that of a metal-surroundedwaveguide.
Index TermsArray antenna, right-handed circular polariza-tion (RHCP), sequential feeding, substrate-integrated waveguide(SIW).
I. INTRODUCTION
AS INTEREST in satellite communication systems has
increased in modern satellite-related industries, it has
become more difficult to obtain cutting-edge technology
for payload and ground systems from other countries. Most
X-band satellite antennas are usually employed to undertake
the data transmission of high resolution captured and detected
images from a satellite to a ground station. In this paper, with
consideration given to the light weight, easy integration, and
low radiation loss requirements that are inherent in long-dis-
tance communication, a novel substrate-integrated waveguide
(SIW)-based array antenna as a preferred choice over the con-
ventional microstrip line has been proposed and analyzed with
several configurations. In particular, this proposed SIW-based
structure as a replacement for a microstrip line has been appliedfor many passive and active devices by researchers [1][4].
Manuscript received March 01, 2011; revised January 26, 2012; acceptedFebruary 15, 2012. Date of publication May 22, 2012; date of current ver-sion July 31, 2012. This work was supported in by the National Space Lab-oratory (NSL) Program through the Korea Science and Engineering Founda-tion funded by the Ministry of Education, Science and Technology under GrantS10801000159-08A0100-15910.
The authors are with the School of Electronics, Telecommunica-tion, and Computer Engineering, Korea Aerospace University, Goyang,Gyeonggi-do 412-791, Korea (e-mail: [email protected]; [email protected];[email protected]; [email protected]).
Color versions of one or more of the figures in this paper are available onlineat http://ieeexplore.ieee.org.
Digital Object Identifier 10.1109/TAP.2012.2201075
Fig. 1. Electricalcharacteristics of an SIW-basedsingle antenna. (a) Reflectioncoefficients. (b) RHCP gain and axial ratio.
As a candidate for possessing the necessary high power trans-
mission and low loss characteristics, SIW structures using via
arrays to replace the side walls show similar characteristics as
metallic rectangular waveguide encompassed by metals [5],
[6]. In order to properly verify the low radiation loss from an
SIW-based transmission line, the crosstalk problem between
two transmission lines has been treated with comparison data
in [6]. In order to increase the transmission efficiency between
satellite and ground system and enhance the antenna gain, the
design procedure, simulation, and measured data of SIW-based
2 2 and 2 4 array antennas have been introduced with a
single element operating at X-band from 8 to 8.5 GHz as shown
in Fig. 1. The electrical performances depicted in Fig. 1 show
the reflection coefficient, right-handed circular polarization
(RHCP) gain, and axial ratio bandwidths of a single antenna.
In a single structure shown in Fig. 1(a), to overcome problems
0018-926X/$31.00 2012 IEEE
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JUNG et al.: SIW-BASED ARRAY ANTENNAS WITH SEQUENTIAL FEEDING FOR X-BAND SATELLITE COMMUNICATION 3633
such as feeding loss, undesirable radiation, and reduced effi-
ciency caused by using a hybrid coupled and series microstrip
feeding structure, novel SIW-based and cavity-backed ring-slot
antenna unified with a SIW and coaxial feeding network having
low-loss and broadband impedance matching characteristics
has been proposed for RHCP generation. In order to improve
the narrow bandwidth in terms of axial ratio and enhance the
CP-gain, SIW-based 2 2 and 2 4 array antennas with a
sequential feeding scheme having a phase delay characteristic
and low radiation loss have been designed and investigated for
the application of X-band satellite communication antennas. In
Section II, the design of the 2 2 array antenna and four-way
power divider embedded into substrate are discussed. Also in
Section III, the detailed design procedure of the 2 4 array
antenna and eight-way power divider are dealt with, and the
electrical characteristics are discussed. Finally, in Section IV,
the effects of a sequential feeding scheme on the axial ratio
and a simple operating principle of the proposed phased array
are summarized, and this is followed by a brief conclusion in
Section V.
II. SIW-BASED 2 2 ARRAY ANTENNA
A. Four-Way Power Divider in the Bottom Layer
In order to design the 2 2 array antenna using a single
element shown in Fig. 1, it was necessary to design a power
divider providing equal amplitude at each output port in the
2 2 array. For radiation efficiency and easy fabrication in
multi-layers, the SIW-based four-way equal power divider was
designed and measured as a replacement for the microstrip
structures [7][10]. Fig. 2 depicts the configuration and elec-
trical performances of the four-way power divider embedded
into substrate. In general, the operating frequency of the pro-
posed four-way power divider is dependent on the separated
distance parameter, fd, between the central feeding point
and the extended guiding via. Hence, the center frequency,
8.25 GHz within 88.5 GHz, results in the determination of
optimum parameter value, fd equal to 8.2 mm.
As estimated from the data shown in Fig. 2(b), it is guaran-
teed that the simulated bandwidth of the reflection coefficients
amounts to 2.5 GHz ranging from 7.0 to 9.5 GHz, covering all
the required impedance bandwidth from 8.0 to 8.5 GHz.
B. 2 2 Array Antenna in the Top Layer
By increasing the number of single antennas shown in Fig. 1and incorporating the array antenna with the four-way power
divider shown in Fig. 2 in a double layer, a novel SIW-based
2 2 array antenna has been designed as shown in Fig. 3, and
the parameter values have been optimized for the best electrical
performances.
While four radiating elements and 90 phase-delay lines with
a progressive phase shift for sequential feeding are aligned in
the top layer, the SIW-embedded four-way power divider and
additional phase-delay lines occupy the bottom layer. For an
equal ground effect between the grounds of the two layers and
signal transitions between the two layers, ground vias and the
RF signal via transition for signal transmission without loss, as
shown in Fig. 3, are employed, respectively. The overall res-
onant frequency of the 2 2 array antenna shown in Fig. 3(a)
Fig. 2. SIW-based four-way equal power divider. (a) Structure of four-waypower divider. (b) Characteristic of -parameter.
is determined by controlling the radius R1 of the circular patch
with the cavity under the patch antenna as follows [11]:
(1)
(2)
(3)
where CF and K11 refer to the correction factor and thefirst root
of the first-kind differentiated Bessel function of TM11 mode,
respectively. The constant, , and parameter, , are the speed
of light and the radius of the circular patch, respectively.
As mentioned previously, oneof the requirements of the2 2
array antenna for satellite communication is the generation of
the RHCP characteristic. This RHCP/left-handed circular polar-
ization (LHCP) generation is usually dependent on the location
of theshorting via inside the circular patch and therotation angle
of the shorting via [12], [13]. As important parameters for
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3634 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 60, NO. 8, AUGUST 2012
Fig. 3. Structure of SIW-based 2 2 array antenna. (a) Radiating antennas inthe top layer. (b) Power divider in the bottom layer.
impedance matching, the parameters, gr and gw, can be modeled
as asymmetrical inductive diaphragms changing the inductance
and leading to the satisfaction of the matching condition at the
input port [14]. The final optimized parameter values are sum-
marized in Table I for the best performances.
In Table I, parameters and
are essential for the sequential feeding to generate a pro-
gressive phase shift in the top and bottom layers. In the config-
uration depicted in Fig. 3(a) and (b), are
set to be equal to for easy fabrication, and
the difference between the nearest phase-delay lines has been
determined to be equal to 9.56 mm accounting for the
90 phase shift. Contrary to a single antenna, the separated dis-
tance of the nearest radiating slot antenna plays an important
TABLE ISIMULATED DESIGN PARAMETERS AND VALUES OF 2 2 ARRAY ANTENNA
Fig. 4. Simulated and measured reflection coefficients of 2 2 array antenna.
role in determining the number and magnitude of sidelobes and
the mainlobe level, which affects the overall radiation pattern
and total gain. In general, it is well known that the optimized
separated distance between the radiating elements is dependent
on the alignment of the array structure and the main beam di-
rection. In this paper, the minimum separated distance between
radiating elements has been set up to be optimized as by
applying the rule of thumb of [15][17]. The em-
ployed substrate for the fabricated 2 2 array antenna in Fig. 3
is an RT/Duroid 5880 having a relative dielectric constant of 2.2
and a thickness of 1.57 mm. For a perfect ground connection
between the two layers, several ground vias have been adopted.
Under the criterion that the reflection coefficient must be less
than dB, it is observed from Fig. 4 that the measured andsimulated results show wide input impedance bandwidths cov-
ering 1.1 GHz from 7.74 to 8.84 GHz and 1.3 GHz from 7.4 to
8.7 GHz, respectively. As important electrical characteristics,
the RHCP gain and axial ratio of the proposed antenna have
been investigated by using simulations and measurements, as
shown in Fig. 5. There is a discrepancy, which appears as a fre-
quency shift in the data, due to the tolerance error in the manu-
facturing process of the radius of the radiating circular elements.
Fig. 6 delineates simultaneously the RHCP and LHCP gains
in - and -planes at 8.3 and 8.4 GHz of the 2 2 array an-
tenna. It is expected that the cross-polarization level describing
the relative ratio of RHCP (Co-pol.) to LHCP is above 15 dB in
the mainbeam direction of from Fig. 6. This indicates
that the proper position and the optimized rotating angle of
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JUNG et al.: SIW-BASED ARRAY ANTENNAS WITH SEQUENTIAL FEEDING FOR X-BAND SATELLITE COMMUNICATION 3635
Fig. 5. RHCP gain and axial ratio result of 2 2 array antenna.
Fig. 6. Measured radiation patterns of 2 2 array antenna. (a) 8.3 GHz (plane, plane). (b) 8.4 GHz ( plane, plane).
shorting via in the radiating elements have been attained and a
reasonable solution has been confirmed.
Fig. 7. -parameter characteristics of eight-way equal power divider.
III. SIW-BASED 2 4 ARRAY ANTENNA
A. Eight-Way Power Divider in the Bottom Layer
As the next step to increase the antenna gain and improve
RHCP purity, a 2 4 array antenna with a novel eight-way
power divider was designed and investigated. The power divider
was installed in the bottom layer fed by the input source in the
overall antenna structure. By selecting the optimum value of the
parameter, fd, to resonate at the operating frequency of 9.3 mm,
the SIW-embedded eight-way power divider satisfying equal di-
vision at all output ports was designed, fabricated, and measured
for comparison. Fig. 7 shows the simulated -parameter char-
acteristics of the eight-way power divider.
B. 2 4 Array Antenna in the Top Layer
With the high data rate required in X-band satellite commu-
nication and the extending 2 2 array antenna taken into con-
sideration, a novel 2 4 array antenna has been proposed to
improve RHCP gain and enhance the CP-purity with an opti-
mized sequential feeding scheme. In a similar configuration to
the 2 2 array antenna described in Section II, the proposed
2 4 array antenna has eight radiating elements in the top layer
[shown in Fig. 8(a)], an eight-way power divider, and phase-
delay lines in the bottom layer [in Fig. 8(b)]. In order to main-
tain the electrical performance, the parameters R1 (slot radius)
and ad (the separate distance) have been newly optimized while
the other parameters are nearly the same as those of the 2 2array antenna.
For sequential feeding which protects the electric field from
being canceled in the opposite elements, the eight elements have
been divided into four groups, namely A, B, C, and D, as shown
in Fig. 9(a) and (b), and each group is fed by a 90 phase-de-
layed line and equal magnitude. However, the feeding signals of
the two elements inside each group are provided by equal phase
and equal amplitude. For example, the total lengths of the delay
lines of the two elements in group A are equal to each other, as
in . At this time, and
are not equal to and , respectively. In a similar way,
the total phase-delay line of one radiating element in group B is
which is equal to the sum of and . The
total difference of the phase-delay line between groups A and B
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3636 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 60, NO. 8, AUGUST 2012
Fig. 8. Structure of SIW-based 2 4 array antenna. (a) Top layer. (b) Bottomlayer. (c) Fabricated 2 4 array antenna.
can be calculated as , which
results in the phase difference of 90 . Fig. 8(c) shows the fabri-
cated 2 4 array antenna which measures 141 mm (length) by
109 mm (width). In terms of the reflection coefficients, Fig. 9
depicts a good agreement between the simulated and measured
data covering the required bandwidth from 8 to 8.45 GHz under
the criterion of less than dB. Fig. 10 shows the measured
and simulated data of RHCP gains and axial ratio of the 2 4
array antenna. From Fig. 10, it is seen that the peak gains of
Fig. 9. Simulated and measured reflection coefficients of 2 4 array antenna.
Fig. 10. RHCP gain and axial ratio results of 2 4 array antenna.
RHCP in simulation and measured data are 15.2 and 14.6 dBic
at 8.3 and 8.4 GHz, respectively, which represents a 100 MHz
frequency deviation between the two results. However, the de-
viation is small enough to be neglected because of the 1-dB tol-
erance. Meanwhile, it is observed from Fig. 10 that the simu-
lated axial ratio bandwidthcovers 600 MHz from 7.9 to 8.5 GHz
under the criterion of 3 dB, and the measured results reach
550 MHz from 8.1 to 8.65 GHz. The radiation patterns de-
scribed in Fig. 11 show that the beam patterns of the -plane
are sharper than those of the -plane. This phenomenon is due
to the number of array elements in the -plane being longer
than that of the array elements in the -plane.
In Table II, the electrical performances of the proposed three
antennas focused on the SIW-based structure are listed for easy
comparison. As expected, it is seen that the increase of antenna
elements and the employment of sequential feeding result in the
high gain and wide bandwidth with high CP-purity.
IV. EFFECTS OF SEQUENTIAL FEEDING SCHEME
In general, it is well known that the sequential feeding scheme
previously applied in the 2 2 and 2 4 array antenna is useful,
with respect to feeding, for an equal amplitude and a progressive
phase shift between the nearest radiating elements at the output
ports. This feeding scheme leads to an enhancement of axial
ratio bandwidth in the CP-generation of an array antenna and
an improvement of CP-purity [18][20].
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JUNG et al.: SIW-BASED ARRAY ANTENNAS WITH SEQUENTIAL FEEDING FOR X-BAND SATELLITE COMMUNICATION 3637
Fig. 11. Measured radiation patterns of 2 4 array antenna. (a) 8.3 GHz (plane, plane). (b) 8.4 GHz ( plane, plane).
TABLE IISUMMARY OF MEASURED ELECTRICAL CHARACTERISTICS OF DESIGNED AND
FABRICATED SIW-BASED ANTENNAS
In this paper, a 90 phase delay line has been employed for
sequential feeding. As a simple principle of high-purity CP-gen-
eration in the proposed SIW-based array antenna, each compo-
nent of the generated electric fields in each radiating element
Fig. 12. Example of the generated E-field direction for 2 2 array antenna.
Fig. 13. Radiation pattern variations of array antenna according to sequentialfeeding. (a) 2 2 array antenna. (b) 2 4 array antenna.
fed from the power divider has considerable importance in the
overalloperationas shown in Fig. 12. If elementsNo. 1, 2, 3, and
4 are fed by an equal amplitude and equal phase reference, the
electric fields at the opposite position will be cancelled out like
the E1s of No. 1 and No. 3 and E1s of No.2 and No. 4. However,
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3638 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 60, NO. 8, AUGUST 2012
Fig. 14. Axial ratio variations of array antenna accordingto sequential feeding.(a) 2 2 array antenna. (b) 2 4 array antenna.
this problem can be overcomeby feeding each element with pro-
gressively different phases. Depending on the phase difference
in each element, the electric field E1 generated at No. 1 will be
combined with the electric field E4 generated at No.4 of a 90
phase delayed. From the entire structure shown in Fig. 12, it
is confirmed that all the generated electric fields at an instance
have the same direction by the generation of E1 at No. 1, E4 at
No. 2, E3 at No. 3, and E2 at No. 4. Because of the feeding of
equal phases, field cancellation can be properly avoided.
In order to check the effects of the sequential feeding scheme
on the 2 2 and 2 4 array antenna, the variation of radiation
patterns and axial ratios with/without the phase delay lines have
been simulated and evaluated. In the case with/without phasedelay line, which is shown in Figs. 13(a) and (b), it is observed
that there is a null point due to the field cancellation at the di-
rection of , and a similar phenomenon occurs in both the
2 2 and 2 4 array antennas. In addition, a sequential feeding
scheme affects the axial ratio characteristic as well as the radi-
ation patterns in the array antennas. Hence, Fig. 14 depicts the
axial ratio characteristics before and after a sequential feeding
and phase-delay lines are applied in the case of 2 2 and 2 4
array antennas. It is seen from Fig. 14 that the electrical perfor-
mance with respect to axial ratio without phase delay lines be-
comes about 10 dB worse than those with phase delay lines. The
reason is thought to be the field cancellation generated from the
radiating elements located at the opposite sides when the phase
delay line is not employed.
V. CONCLUSION
In this paper,a single element and two types of novel array an-
tennas focused on the SIW-based design have been suggested,
designed, and investigated in terms of electrical performances.
In particular, in order to minimize the radiation loss for long-
distance communication, novel SIW-based array antennas have
been employed and sequential feeding has been adopted for anenhancement of RHCP characteristics. As a systematical design
procedure of the SIW-based array antenna, a single element op-
erating at X-band ranging from 8.0 to 8.5 GHz, a 2 2 array an-
tenna with doublelayersincluding a four-way power divider,and
2 4 array antennas with different sequential phase progression
have been designed, fabricated, and measured for verification
between simulation and measured results, and an improvement
in electrical performance has been obtained, particularly with
respect to reflection coefficient bandwidth, antenna gain, and
axial ratio bandwidth. In addition, it is ensured from the data
that the proposed novel structure could be particularly useful
for a small satellite with limitations regarding weight and size.
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Eun-Young Jung received the B.S. and M.S.degrees in electronics, telecommunications, andcomputer engineering from Korea Aerospace Uni-versity, Goyang, Korea, in 2009 and 2011.
Her research interests include UWB antennadesign and array antenna design for satellitecommunication.
Jae W. Lee (S92M98) received the B.S. degreein electronic engineering from Hanyang University,Seoul, Korea, in 1992, and the M.S. and Ph.D. de-grees in electrical engineering (with an emphasis inelectromagnetics) from the Korea Advanced Instituteof Science and Technology (KAIST), Taejon, Korea,1994, and 1998, respectively.
From 1998 to 2004, he was a Senior Member inthe Advanced Radio Technology Department, Radioand Broadcasting Research Laboratory, Electronicsand Telecommunications Research Institute (ETRI),
Taejon, Korea. He later joined the School of Electronics, Telecommunicationsand Computer Engineering, Korea Aerospace University, Goyang, Korea,where he is currently an Associate Professor. From January 2011 to January2012, he was a Visiting Scholar with Clemson University, SC. His researchinterests include high power amplifier design, computational electromagnetics,electromagnetic interference/electromagnetic compatibility analysis on printed
circuit board, and component design in microwave and millimeter-wave.
Taek K. Lee (S83M90) was born in Gyeongbuk,Korea, on January 11, 1958. He received the B.S.degree in electronic engineering from Korea Uni-versity, Seoul, Korea, in 1983, and the M.S. andPh.D. degrees in electrical engineering from theKorea Advanced Institute of Science and Tech-nology (KAIST), Seoul, Korea, in 1985 and 1990,respectively.
From May 1990 to April 1991, he was a Post-doctoral Fellow with The University of Texas atAustin (under a grant from the Korea Science and
Engineering Foundation). From August 1991 to February 1992, he was withKAIST. In March 1992, he joined the faculty of Korea Aerospace University,Goyang, Korea, where he is currently a Professor with the School of Elec-tronics, Telecommunication, and Computer Engineering. From July 2001 toJuly 2002, he was an Associate Visiting Research Professor with the Universityof Illinois at UrbanaChampaign. His research interests include computationalelectromagnetics, antennas, analysis and design of microwave passive circuits,and geophysical scattering.
Woo-Kyung Lee (S94M00) received the B.Sc.and M.Sc. degrees from the Korea Advanced In-stitute of Science and Technology (KAIST), Seoul,
Korea, in 1990 and 1994, and the Ph.D. degree fromthe University College London, United Kingdom, in2000, all in electrical engineering.
From 1999 to 2002, he worked as a ResearchProfessor at SaTReC, KAIST, and was involvedin developing communication and antenna systemsfor small satellite systems. From 2003 to 2004, heworked at Samsung Advanced Institute of Tech-
nology for UWB, antenna, communication system researches. In 2004, hejoined the Electrical Engineering and Avionics Department, Korea AerospaceUniversity, Seoul, Korea, where he currently works as an Associate Professor.His research interests are in the area of communication and radar systemdesign, spaceborne antenna development, image processing, and electroniccounter measure and electronic counter counter measure techniques.
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