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10.1109/LAWP.2014.2356599, IEEE Antennas and Wireless Propagation Letters
AWPL-05-14-0867-FINAL 1
A High-Gain Dual-Band EBG Resonator Antenna
with Circular Polarization
Basit Ali Zeb, Member, IEEE, Nasiha Nikolic, and Karu P. Esselle, Senior Member, IEEE
Abstract—A dual-band circularly polarized (CP) EBG res-
onator antenna (ERA) is presented. The antenna employs an
all-dielectric superstructure, which consists of two identical
unprinted dielectric slabs, and a dual-band corner-truncated
patch feed. A prototype antenna is fabricated and tested using
a superstructure made out of 3.175mm-thick Rogers TMM10
material. Measured peak gains are 16.1 dBic (LHCP) and
16.2 dBic (RHCP), measured radiation efficiencies are 93% and
91% and the boresight axial ratios are 1.9 dB and 1.5 dB, at
9.65 GHz and 11.75 GHz, respectively. This dual-band antenna
is easy to fabricate, making it suitable for high-gain low-cost CP
applications.
Index Terms—cavity resonator, circular polarization, dual-
band, electromagnetic band gap, Fabry-Perot cavity, high-gain,
partially reflecting surface, patch antenna, superstrate.
I. INT ROD UC TI ON
IN many advanced point-to-point links and satellite com-
munications systems, circular polarization (CP) is used to
minimize the polarization mismatch component of the link
budget by removing the need for alignment between the
transmitting and receiving antennas. The growing need of
frequency reuse and increase in telecommunication capacity
have stimulated the interest for multi-frequency operation.
Such systems often require planar high-gain antennas with
simple radiating apertures to reduce complexity and cost.
Amongst classical high-gain antennas such as horns and
reflectors, arrays offer attractive solutions due to their advan-
tages of planar shape and low profile. However, designing a
microstrip array becomes complex when both multi-frequency
operation and CP are required. Therefore, other planar high-
gain antennas with simple feed mechanisms are desirable.
In this paper, we investigate an electromagnetic band gap
(EBG) resonator antenna (ERA) based on an unprinted all-
dielectric superstructure for dual-band and CP operation.
ERAs, also known as Fabry-Perot cavity antennas, resonant
cavity antennas or 2D leaky-wave antennas, are a class of
planar antennas that offer promising directivity without resort-
ing to complex feed mechanisms [1]–[4]. Their superstrates
consist of partially but sufficiently reflecting superstructures
often formed using unprinted dielectric slabs [1], dielectric
rods [3] or 3D EBG structures such as woodpiles [5].
In recent years, a variety of dual-band and/or dual-polarized
ERAs have been designed [6]–[14]. Among them, ERAs based
on unprinted EBG superstructures are naturally appealing for
B.A. Zeb and K.P. Esselle are with the Department of Engineering,
Macquarie University, Sydney, New South Wales 2109, Australia e-mail:
bzeb@ieee.org; karu@ieee.org
N. Nikolic is with CSIRO, Computational Informatics, PO Box 76, Epping,
New South Wales 1710, Australia e-mail: Nasiha.Nikolic@csiro.au
Manuscript received xxx xx, 2014; revised xxx xx, xxxx.
dual-linear or circular polarization applications due to their
symmetry. Several techniques have been developed to design
CP-ERAs operating in a single frequency band: (1) a non-
polarizing superstructure placed on top of a CP feed [15]–
[17], (2) a self-polarizing superstructure to transform linearly
polarized (LP) feed radiation into CP radiation [18]–[20], and
(3) a freestanding and polarizing frequency-selective surface
(FSS) as the cover for a LP-ERA to convert its LP radiation to
CP radiation [21]. Apart from our recent work in [22], which
is limited to preliminary theoretical results only, no other dual-
band CP-ERAs have been reported in the literature, to the best
of authors’ knowledge.
This paper presents the detailed design and experimental
investigations of a dual-band CP-ERA. The objective was to
achieve good and almost equal directivity and good axial ratio
in both frequency bands. A dual-band CP feed was designed
to excite the cavity while a simple superstructure consisting
of two identical plain dielectric slabs [23] was employed
to achieve high gain. This configuration does not require
defect slabs with different thicknesses and/or permittivities
and results in simplicity and ease of fabrication. The antenna
and its superstructure were designed using CST Microwave
Studio (CST MWS) [24] and the design was verified through
prototype testing.
II. AN TE NNA CO NFI GU RATI ON
The configuration of the dual-band CP-ERA is shown in
Fig. 1. Its design has been inspired by previous all-dielectric
ERAs [1], [3], [5], [25] and its radiation mechanism can be
described in terms of defect modes as in [1], [3], [25] or using
the cavity resonance condition [2]. Its superstructure consists
of two identical unprinted dielectric slabs placed at height h
above a CP feed, which is on top of a PEC ground. Two corner-
truncated microstrip patches, one for each band, were designed
and integrated in the cavity. The two patches are connected to
the two input ports (Ports A and B) using microstrip feed
lines. When Port A is excited, the antenna radiates left-hand
circular polarization (LHCP) in the lower frequency band and
when Port B is excited the antenna radiates right-hand circular
polarization (RHCP) in the higher frequency band. Two open-
ended stubs are used to improve best input matching while
the corner truncations, c1and c2, are optimized to get the best
3-dB axial ratio (AR) in the two bands.
A. Superstructure for Dual-Band Operation
To design an efficient dual-band CP-ERA, the superstructure
performance is evaluated first using the guidelines presented
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This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI
10.1109/LAWP.2014.2356599, IEEE Antennas and Wireless Propagation Letters
AWPL-05-14-0867-FINAL 2
Fig. 1. Dual-band circularly polarized ERA and its CP feed. Its Superstruc-
ture Model (SM) and the Defect-Cavity Model (DCM), which is obtained by
removing the ground plane and adding the image dielectric slabs, are also
shown.
in [23] for linearly polarized dual-band ERAs. Here, a su-
perstructure made out of two 3.175mm-thick TMM10 slabs
(ϵr= 9.2±0.23 and tanδ=0.0022) is considered. It is
characterized using the two unit-cell models, Superstructure
Model (SM) [26], [27] and Defect-Cavity Model (DCM) [1],
[6], [11]. Its unit cell SM (shown in Fig. 1) is used to compute
the magnitude and phase ϕsup of its reflection-coefficient,
ΓSM . The inter-slab cavity acts as a localized defect that
leads to the locally-inverted reflection phase profile shown in
Fig. 2, when h1is tuned to make the superstructure resonate
at a pre-determined frequency (fres =10 GHz here). Fig. 2
shows that the ϕsup is equal to the ideal value (ϕideal) at fres
(10 GHz) and at two other frequencies which are f1(9.7 GHz)
and f2(11.8 GHz). However, at fr es the whole superstructure
resonates and becomes transparent. In other words, |ΓSM |is
not large enough to make the main cavity resonate at this
frequency.
Hence, antenna directivity enhancement is possible only at
two frequency bands around f1=9.7 GHz and f2=11.8 GHz
when a suitable antenna feeds the cavity. Since |ΓDC M |curve
in Fig. 2 has nulls at f1,f2as well as fres, it can be
used to tune the antenna operating frequencies to f1and f2.
Simultaneous use of SM and DCM adds confidence to the
design process.
B. Design of the Dual-Band CP-ERA
The dual-band CP-ERA, shown in Fig. 1, has been designed
by truncating the superstructure area and employing a dual-
band CP feed as its excitation source. The substrate for
the two patches is 0.787mm-thick Rogers RT/Duroid 5880
material (ϵr=2.2 and tanδ=0.0004). The parameters
hand h1are adjusted to 12.1 mm and 13.6 mm, to tune
the antenna operating frequencies to f1=9.65 GHz and
f2=11.75 GHz. The use of higher-permittivity superstructure
slabs ensures strong reflectivity (and higher peak directivity),
but the superstructure area was optimized to achieve good and
8 9 10 11 12 13
−60
−50
−40
−30
−20
−10
0
Reflection Magnitude (dB)
Frequency (GHz)
8 9 10 11 12 13
0
100
200
300
Reflection Phase (deg)
|ΓSM|
|ΓDCM|
φideal
φsup
f2
fres
f1
Fig. 2. Reflection magnitude and phase of the superstructure. ΓSM and
ΓDCM are calculated with unit-cell periodic boundary conditions and a
normally incident wave at Port 1. h= 12.1mm and h1= 13.6mm. ϕideal
is the ideal superstructure phase that is required to make the main cavity
resonate at any given frequency.
Fig. 3. Photographs of the dual-band CP-ERA. The superstructure is made
out of two 3.175mm-thick TMM10 slabs. The feed line bends provide physical
separation between the two input ports to accommodate feed connectors. h=
12.1mm and h1= 13.6mm. Antenna area is 110 ×110 mm2.
almost equal directivity in each frequency band. The optimum
lateral dimensions are 110 ×110 mm2(i.e., 3.6λ0×3.6λ0
at 10 GHz). The dual-band CP feed was also optimized for
best matching and good quality CP (AR≈1.6 at 9.65 GHz and
AR≈1.9 at 11.75 GHz). Its final dimensions are: a1= 9.6mm,
a2= 7.7mm, c1= 1.45 mm and c2= 1.3mm.
III. MEASUREMENTS AND RES ULTS
A fabricated prototype of the dual-band CP-ERA is shown
in Fig. 3. The superstructure parameters are given in Sec-
tion II-A. A 1mm-thick aluminum plate is used to support
the feed antenna substrate and connector assembly. A small
1mm spacing between the two patches is chosen to keep them
close to the geometrical center of the cavity, and hence to
reduce asymmetry in the radiation patterns of the resulting
ERA. Testing was carried out by feeding one port while the
other port is terminated with a 50Ω load. As shown in Fig. 4,
the two input ports are well-matched and sufficiently isolated
in each frequency band. Note that the measured results agree
very well with the predicted results.
1536-1225 (c) 2013 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See
http://www.ieee.org/publications_standards/publications/rights/index.html for more information.
This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI
10.1109/LAWP.2014.2356599, IEEE Antennas and Wireless Propagation Letters
AWPL-05-14-0867-FINAL 3
9 10 11 12 13
−50
−40
−30
−20
−10
0
Frequency (GHz)
Magnitude (dB)
Computed S21
Measured S21
Computed S11
Measured S11
Computed S22
Measured S22
Fig. 4. Input reflection coefficients and coupling between the ports of the
dual-band CP-ERA.
The radiation patterns of the dual-band CP-ERA, measured
in the CSIRO far-field range, are shown in Fig. 5. Asymmetry
in the xz-plane (ϕ= 0◦cut) at 11.75 GHz is due to the off-
centered feed placement. Nevertheless, the side lobes remain
fairly low and the measurements agree well with the computed
results.
The ERA gain was measured in the spherical near-field
range of the Australian Antenna Measurement Facility using
the gain comparison method with a standard gain horn as
the reference antenna. The results are shown in Fig. 6. The
best axial ratios in the two bands are 1.9 dB and 1.5 dB at
9.65 GHz and 11.7 GHz, respectively. The peak measured
gains are 16.1 dBic (LHCP) and 16.2 dBic (RHCP) while the
measured radiation efficiencies are 93% and 91% at the same
two frequencies.
Overall, these measured results confirm the ability of the
superstructure to support both the LHCP and RHCP of the
CP feed leading to a dual-band CP-ERA with respective
polarizations. The CP-ERA gives good impedance matching
and axial ratio in each frequency band.
IV. DISCUSSION
Apart from the superstructure, peak gains of the CP-ERA
depend on the quality of the CP feed. The CP feed was initially
designed without the superstructure and it required slight tun-
ing when placed inside the cavity. Without the superstructure,
the best |S11|and |S22 |values are –23 dB and –30 dB in
the lower and higher band, respectively. They are −21 dB
and –26 dB, respectively, when placed inside the cavity. No
significant de-tuning of the CP feed was noted due to the
superstructure loading. This observation is contrary to the case
of dual-band ERAs (or any ERAs) with printed superstructures
where the feed must be designed with the superstructure to
avoid significant mismatch and de-tuning. The side-by-side
placement of the two patches resulted in relatively stronger
mutual coupling particularly in the higher frequency band.
Mutual coupling can be decreased by increasing the spacing
between the two patches at the expense of making the feed off-
centered thus resulting in more asymmetrical radiation patterns
−90 −60 −30 0 30 60 90
−30
−25
−20
−15
−10
−5
0
Angle (deg)
Normalized Pattern (dB)
Computed
Measured
(a) 9.65 GHz, xz-plane (ϕ= 00)
−90 −60 −30 0 30 60 90
−30
−25
−20
−15
−10
−5
0
Angle (deg)
Normalized Pattern (dB)
Computed
Measured
(b) 9.65 GHz, yz-plane (ϕ= 900)
−90 −60 −30 0 30 60 90
−30
−25
−20
−15
−10
−5
0
Angle (deg)
Normalized Pattern (dB)
Computed
Measured
(c) 11.75 GHz, xz-plane (ϕ= 00)
−90 −60 −30 0 30 60 90
−30
−25
−20
−15
−10
−5
0
Angle (deg)
Normalized Pattern (dB)
Computed
Measured
(d) 11.75 GHz, yz-plane (ϕ= 900)
Fig. 5. Radiation patterns of the dual-band CP-ERA.
and higher side-lobe levels. The bandwidth in each band may
be increased by replacing the simple CP feed with a wideband
CP feed such as a sequentially rotated patch array.
1536-1225 (c) 2013 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See
http://www.ieee.org/publications_standards/publications/rights/index.html for more information.
This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI
10.1109/LAWP.2014.2356599, IEEE Antennas and Wireless Propagation Letters
AWPL-05-14-0867-FINAL 4
8.5 9 9.5 10 10.5 11 11.5 12 12.5
0
3
6
9
12
15
18
21
Freq(GHz)
Peak Value (dB)
Meas. Directivity
Meas. Gain
Axial Ratio
Fig. 6. Peak gain, directivity and axial ratio of the dual-band CP-ERA.
V. CONCLUSION
This paper presents the design and experimental results of
a high-gain dual-band circularly polarized ERA for the first
time. The antenna exploits the symmetry of its superstructure,
made out of two unprinted identical dielectric slabs, and less-
directive LHCP and RHCP radiations of a dual-band CP feed.
The measurements of a prototype confirms that the ERA has
a peak gain of 16.2 dBic, good LHCP (best measured axial
ratio of 1.9 dB) in one frequency band and good RHCP
(best measured axial ratio of 1.5 dB) in the other band. A
trade-off between the quality of the radiation patterns and
mutual coupling between ports was made with the off-centered
placement of the two patches inside the cavity. For best
radiation patterns, they should ideally be placed close to the
geometrical center of the cavity.
ACKNOWLEDGMENT
This work is supported by the Australian Government under
the Australia-India Strategic Research Fund and the Australian
Research Council (ARC).
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