This document summarizes and compares two high-gain antenna designs for 60 GHz wireless communication: 1) An aperture coupled patch antenna with a superstrate layer that increases the maximum measured gain to 14.6 dBi while maintaining broad radiation patterns. The superstrate size is critical for optimal performance. 2) A microstrip-fed stacked patch antenna with superstrate that achieves higher bandwidth but 1.3 dB lower maximum gain compared to the first design. Aperture coupling is found to be better for high-gain applications due to its ability to achieve higher gain with a consistent radiation pattern across the band.

1. 1422 IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 8, 2009
High-Efficient and High-Gain Superstrate Antenna
for 60-GHz Indoor Communication
Hamsakutty Vettikalladi, Olivier Lafond, and Mohammed Himdi
Abstract—A high-efficient and high-gain aperture coupled patch
antenna with superstrate at 60 GHz is studied and presented. It is
noted that adding superstrate will result in a significant effect on
the antenna performances, and the size of the superstrate is critical
for the optimum performance. The maximum measured gain of a
single antenna with superstrate is 14.6 dBi, which is higher than
that of a classical 2 2 array. It is found that the gain measured of
a single antenna with superstrate increases nearly 9 dB at 60 GHz
over its basic patch antenna. This superstrate antenna gives a very
high estimated efficiency of 76%. The 2:1 measured VSWR band-
width with superstrate is 6.8%. The radiation patterns are found to
be broadside all over the frequency band. Also, this letter explains
a comparison to another source of parasitic patch superstrate an-
tenna with normal microstrip coupling. It is found that aperture
coupling is better for high-gain antenna applications.
Index Terms—60 GHz, high efficiency, millimeter-wave antenna,
superstrate.
I. INTRODUCTION
ANTENNA engineers and scientists are more interested in
the 60-GHz frequency band for future broadband com-
mercial communications as this range is declared as unlicensed
all over the world [1], [2]. Millimeter-wave technology is one
solution to provide up to multi-Gb/s wireless connectivity for
short distances between electronic devices. The data rate is ex-
pected to be 40–100 times faster than today’s wireless LAN sys-
tems, transmitting an entire DVD’s data in roughly 15 s. The
frequency 60 GHz is ideally suited for personal area network
(PAN) applications. A 60-GHz link can replace various cables
used today in the office or in home, including gigabit Ethernet
(1000 Mb/s), USB 2.0 (480 Mb/s), or IEEE 1394 ( Mb/s).
Currently, the data rates of these connections have precluded
wireless links since they require so much bandwidth. While
other standards are evolving to address this market (802.11n and
UWB), 60 GHz is another viable candidate.
However, these new systems will need compact and high-effi-
ciency millimeter front-ends and antennas. For antennas, printed
solutions are always demanding for the researchers because of
their small size, weight, and ease of integration with active com-
ponents [3], [4]. It is reported that conventional antenna arrays
are used for high-gain applications, but in all these cases for
Manuscript received August 26, 2009; revised September 24, 2009 and Oc-
tober 14, 2009. First published January 15, 2010; current version published Jan-
uary 26, 2010.
The authors are with the Institute of Electronics and Telecommunication of
Rennes (IETR), University of Rennes1, Rennes 35042, France (e-mail: ham-
sakutty.vettikalladi@univ-rennes1.fr).
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.2010.2040570
Fig. 1. Cutting plane of aperture coupled antenna with superstrate, ground
plane size = 30 2 30 mm .
achieving high gain, arrays of large number of elements are
used, which not only increases the size of the antenna, but also
decreases the efficiency of it [5]–[7]. It has been reported that for
high gain, superstrate layer can be added at a particular height of
above the ground plane [8], [9]. Adding a superstrate will
increase the gain nearly 4 dB over a single parasitic patch [8]
and 5 dB in [9]. Here, authors are trying to develop a high-gain
and high-efficient antenna using superstrate by exploring dif-
ferent sources. In the first part of this letter, the authors present
an aperture coupled patch antenna with superstrate. It is found
that the dimension of the superstrate is critical for getting max-
imum gain and also for getting consistent radiation pattern all
over the frequency range of interest. Measured radiation pat-
terns and gain show that this antenna allows to obtain high gain
and high efficiency at 60 GHz. For a comparison, the second
part presents another radiating source, a microstrip-fed para-
sitic patch antenna with superstrate. Even though it increases
the bandwidth of the antenna, the gain is lower when compared
to the first case. The authors will explain that the radiation aper-
ture size and gain are linked to the type of source. In this case,
it is also observed that the size of the superstrate has significant
effect on the antenna performance.
II. APERTURE COUPLED SUPERSTRATE ANTENNA
Fig. 1 shows the side view of an aperture coupled patch an-
tenna with superstrate. The slot is optimized to 0.2 1 mm
for maximum coupling with a stub length of 0.75 mm. In order
to consider the easiness of implementation, we used a thick
ground plane of thickness mm. The antenna consists
of a patch with optimized dimension 1.3 1.3 mm on a sub-
strate RT Duroid 5880 of permittivity 2.2 and a loss tangent
with a thickness mm. Low-thick-
ness and low-permittivity substrate are used for reducing sur-
face waves. A dielectric superstrate is added above the aperture
coupled patch antenna. Here, we used only one layer to avoid
the technological manufacturing problems when many layers
are used at 60 GHz. The material used for the superstrate is
Roger substrate RT6006 with a relative permittivity of 7.5 at
1536-1225/$26.00 © 2010 IEEE

2. VETTIKALLADI et al.: HIGH-EFFICIENT AND HIGH-GAIN SUPERSTRATE ANTENNA FOR 60-GHz INDOOR COMMUNICATION 1423
Fig. 2. Variation of S11 and gain without superstrate and with var-
ious superstrate dimensions. Without superstrate — —; 1 :::::::::::::;
2 —–; 4 – – –; 6 – 1 – 1 –.
60 GHz. Theoretically, the thickness of superstrate must be
(0.456 mm), but here we took the thickness ( mm)
close to the theoretical thickness available in market for good
antenna performance. The distance between the superstrate and
ground plane is as per the theory [10]. A Rohacell foam
layer of permittivity 1.05 is sandwiched between base antenna
and superstrate.
Usually in all the known superstrate antennas, they used large
superstrates for improving the gain. However, our objective
is different. We want to use a small superstrate for obtaining
high stable gain and consistant radiation pattern all over the
frequency band of interest. To study the effect of superstrate
size “S” and hence to optimize, we considered four square sizes
( , and ). Simulations are done using CST
Microwave studio.
Fig. 2 shows the CST results of S11 and gain variations of
the slot coupled antenna without superstrate and with varying
superstrate size. It is observed that the S11 and gain vary with
various size of the superstrate. When there is no superstrate, the
antenna radiates at 60 GHz with a bandwidth of 3.7% over a
frequency range of 58.9 to 61.1 GHz with a maximum gain of
5.9 dBi. It is noted that with superstrate the gain is highest for
a superstrate size of . The 2:1 VSWR bandwidth is noted
to be – GHz i.e., 6.7% with a maximum gain
of 14.9 dBi. It is also noticed that the gain decreases when the
size of the superstrate is above or below . There is a gain en-
hancement of 9 dB with the superstrate. Fig. 3 shows the com-
parison of measured and simulated S11 and gain for the opti-
mized superstrate size of . Table I gives the comparison of
measured and simulated S11 and gain for the optimized super-
strate size. It is noted in S11 that there is a frequency band shift
of 2.8% (1.7 GHz) when a V-connector is used and a frequency
band shift of 1.5% when a V-band test fixture is used. These
frequency shifts are maybe due to the combined effect of con-
nectors and the inaccuracy of the distance between patch and
superstrate for the experimental prototype. Also, the gain mea-
sured and simulated are in good agreement, but with a frequency
shift as explained. The gain is measured using comparison tech-
nique with a standard horn of known gain.
Fig. 3. Variation of S11 and gain with a superstrate dimension of 2 . Simula-
tion ——; measured with V coaxial mounting connector – – 0; measured with
V test fixture 0 0 0 0.
TABLE I
COMPARISON BETWEEN SIMULATED AND MEASURED RESULTS OF APERTURE
COUPLED SUPERSTRATE ANTENNA
For calculating the efficiency, we compared the measured
gain with the simulated directivity. The measured and simulated
E-plane radiation patterns are shown in Fig. 4 for the optimized
superstrate dimension. It is clear from Fig. 3 that the measured
S11 and gain are shifted; the measured gain is maximum be-
tween 57 to 59 GHz, and simulated gain is from 59 to 61 GHz.
Hence, the radiation patterns are plotted by taking into account
this frequency shifting (i.e., radiation pattern plotted is 60 GHz
simulation and 58 GHz measurement, and so on). It is noted
that the radiation patterns are found to be broad and in good
agreement with measurements, and there is a cross-polar level
of less than dB at all frequencies. The radiation patterns are
verified to be the same in all the frequencies in the band of in-
terest. The measured half-power beamwidth is found to be 23
at 58 GHz. Also verified by simulation is that the back radia-
tion in this case is below dB, as compared to the antenna
without superstrate ( dB).
The measured and simulated H-plane radiation patterns are
shown in Fig. 5 for the optimized superstrate dimension. The
radiation patterns are also plotted by taking into account the
shifting as explained in E-plane radiation pattern. It is noted
that the radiation patterns are found to be broad and in good
agreement with measurements, and there is a cross-polar level
of less than dB at all frequencies. The measured half-power
beamwidth is found to be 22 at 58 GHz.
When the superstrate size is higher than , the broad nature
of the pattern disappeared at 60 GHz. Fig. 6 shows the simulated
(60 GHz) and measured (58 GHz) H-plane radiation patterns of
the antenna with a superstrate dimension of . It is noted that
the radiation patterns change from broad side to sectorial/null

3. 1424 IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 8, 2009
Fig. 4. Measured and simulated E-plane radiation patterns of super-
strate antenna. 57 GHz—measured —–2—; 59 GHz—simulated– – – –;
58 GHz—measured —-+—-; 60 GHz—simulated —–; 59 GHz—measured
——; 61 GHz—simulated ::::::::::::.
Fig. 5. Measured and simulated H-plane radiation patterns of superstrate
antenna. 57 GHz—measured —-2—; 59 GHz—simulated– – – –; 58 GHz—mea-
sured —– +—; 60 GHz—simulated —–; 59 GHz—measured —- —-;
61 GHz—simulated ::::::::::::::.
at 60 GHz, which is also useful for some other applications. It
concludes that the dimension of the superstrate is critical for the
optimum performance of the antenna. This is the case for other
frequencies in the band and also is the same in E-plane. To con-
clude, the dimension of the superstrate is very important in order
to get the consistent radiation pattern for all the frequency band,
and it is found to be in this case. This is the main difference
from the already-developed superstrate antennas published in
the literature.
III. MICROSTRIP-FED PARASITIC PATCH ANTENNA WITH
SUPERSTRATE
Here, the authors explain a comparison with another source.
Fig. 7 shows the side view of the microstrip-fed stacked patch
antenna with superstrate. It consists of a lower patch with an op-
timized dimension of 1.63 1.6 mm on a substrate RT Duroid
5880 ( mm). The upper patch with an op-
timized dimension of 1.63 1.63 mm is printed on the lower
Fig. 6. Measured and simulated H-plane radiation pattern for a superstrate di-
mension of 6 . Co-simulated ——; Co-measured —; Cross-simulated —-+—-;
Cross-measured —-2—.
Fig. 7. Cutting plane of stacked patch antenna with superstrate.
side of a parasitic substrate RT Duroid 5880 (
mm). The distance between the lower patch and the upper
patch is optimized as mm for a resonance at 60 GHz
for a larger bandwidth and gain. This antenna is then loaded with
superstrate.
The material used for the superstrate is Roger substrate
RT6006 ( at 60 GHz, mm). The dimension
of the superstrate and the height from the ground plane are
optimized [11]. We found that the maximum gain, with losses,
obtained is 13.6 dBi, even though a bandwidth of 59–66 GHz
(11.7%) is achieved for an optimized superstrate dimension of
'` with an optimized height of [11] from the
ground plane. The radiation patterns are found to be broad and
are explained in [11].
Fig. 8 shows the simulated comparison of return loss and
gain with the microstrip-fed parasitic patch superstrate antenna
and the aperture coupled superstrate antenna. Table II shows the
comparison of gain and optimized superstrate size in both cases.
It is noted that the stacked patch antenna improves the band-
width by 3 GHz (5%) compared to the aperture coupled patch
antenna. However, the gain decreases by 1.3 dB. We can also
note that the dimension of the superstrate is different for the two
cases in order to get the maximum gain and also for getting con-
sistent pattern all over the frequency band of interest. Also from
Table II, by using aperture coupling antenna with a superstrate
dimension of , we obtained the same gain and beamwidth
as that of the microstrip-fed antenna, but here the gain obtained

4. VETTIKALLADI et al.: HIGH-EFFICIENT AND HIGH-GAIN SUPERSTRATE ANTENNA FOR 60-GHz INDOOR COMMUNICATION 1425
Fig. 8. Comparison of return loss and gain with aperture coupling (——-) and
microstrip fed parasitic patch coupling (—-+—-).
Fig. 9. Gain pattern for a microstrip-fed parasitic patch superstrate with a
superstrate size = 2 , for different frequencies in the band.
is not the optimized value. We got the optimized gain at a su-
perstrate size of . However, the radiation patterns are broad
for both the sizes, but using microstrip-fed stacked patch an-
tenna, the optimized superstrate size is for getting max-
imum gain and broad pattern. It is considered as the limitation
of size in this case. If we change the dimension to , then the
radiation patterns are not broadsided as shown in Fig. 9. The
pattern changes from broadside to null for different frequencies
in the band. Here, the small superstrate size compared to slot
coupling case is due to the presence of the parasitic patch that
disturbs the field in the cavity .
IV. CONCLUSION
A comparison of 60-GHz aperture coupled superstrate an-
tenna and microstrip-fed stacked superstrate antenna are studied
and discussed. It is found by measurement that with superstrate
we can improve the gain up to 14.6 dBi by using aperture cou-
pling with an estimated efficiency of 76%. This result is very
good and is higher than that of a classical 2 2 array on RT
Duroid substrate with a gain of 12 dBi and an efficiency of 60%
TABLE II
SIMULATED COMPARISON OF SUPERSTRATE ANTENNA WITH DIFFERENT
SOURCE COUPLING AT 60 GHZ, INCLUDING ALL LOSSES
[7]. We also improved the S11 bandwidth by adding a para-
sitic layer to a microstrip-fed stacked superstrate antenna. Even
though parasitic layer improves the S11 bandwidth by 3 GHz
(5%), it decreases the gain to 13.6 dBi as compared to aperture
coupling. The inconvenience of this design at 60 GHz, in manu-
facturing this prototype, is to maintain the different layers with
good air thickness, and, also, the parasitic layer is so flexible
because of thin substrate. The detailed effects of the superstrate
size in both the cases are studied and presented. This parameter
is critical to achieve a flat gain in the considering bandwidth.
In conclusion, for high-gain and high-efficient antenna applica-
tions, and also for the ease of implementation, aperture coupling
with limited superstrate is better compared to the other source
used in this study.
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