Development of an Ultra Compact Dual Band Antenna on a One Cubic
Centimeter (1 cm3) Surface
Symeon Nikolaou*(l), Photos Vryonides(l), Dimitrios E. Anagnostou(2) and
Muhannad AI-Tarifi(2)
(2)
(1) Department ofEE, Frederick University Cyprus, Nicosia, 1036, Cyprus.
South Dakota School of Mines and Technology, Rapid City, SD 57701-3995, U.S.A.
[email protected]
Abstract: This paper discusses the development of a dual, broadband antenna,
designed to be used for a compact sensor with total size no more than one cubic
centimeter (1 cm3). The antenna specifications require more than 100 MHz
bandwidth at 2.4 GHz and more than 1 GHz bandwidth at frequencies higher than
6 GHz. The 2.4 GHz radiation is used for the downlink, control data reception,
and the wideband radiation is used to support the high data rate transmission to
the sensor reader (uplink). A novel folded dual monopole antenna is presented
that meets the sensor requirements. It is printed on two faces of a one cubic
centimeter box. On one side a "fat" monopole is implemented successfully for the
wideband operation and on an adjacent side a folded monopole operates
effectively at 2.4 GHz. Both monopoles use the same, common feed line. The
sensor IC is embedded inside the 1 cm3 cube.
I.
Introduction
As the use of wireless sensors is spread in every-day life there is a constant need
for customized antennas to meet very specific radiation or communication
requirements. Many of the constraints are associated with the size limitations.
Especially when the required antenna operates in relatively low frequency, or
when broadband operation is needed the size reduction can be a challenging task
for antenna designers. Recent fabrication techniques and novel materials [1] have
allowed the implementation of folded [2] or conformal [3] non planar antennas.
Such antennas are used for RFID or sensor applications [4]. In several cases the
implementation of wideband conformal antennas results in relatively large
antennas [5]. The antenna proposed in this paper is designed on two IOmm x
IOmm boards of Rogers R04003, which form a ninety degrees angle. On one face
a folded monopole in meander shape radiates at 2.4 GHz and on the adjacent face
another printed monopole radiates starting at 6 GHz in a bandwidth that exceeds
the one GHz specification. The dual broadband antenna performs satisfactory in
both bands and at the same time its size fits on the surface of a one cubic
centimeter box as a result of an ultra compact design.
II.
Antenna Design
The proposed antenna was designed on two IOmm x 10 mm, 0.78 mm thick
Rogers R04003 material (Er=3.38, tan8=0.0027). The two substrates form a
ninety degrees angle and are mechanically connected as can be seen in figs. 1 and
2. An IC is embedded inside the resulted 1 cm3 cube. The antenna is microstrip-
978-1-4244-3647-7/09/$25.00 ©2009 IEEE
fed. The feed line has width 1.5 mm and length 2 mm and is terminated with a
two-step wider metal segment. The smaller patch has dimensions 0.5 mm by 3.5
mm and the larger one 4.5 mm by 6 mm (fig. 3). From the lower left corner of the
larger patch a longitudinal linear segment with length S1=3 .25 mm and width
W=l mm, extends up to the edge of the substrate. In the perpendicular side the
linear segment is connected to a meander-shaped, folded metal stripe. The sizes of
the linear segments are summarized in Table I. The ground patch (shown in fig. 3)
on the bottom side of the substrate, has dimensions 10 mm by 4 mm and it has a
smaller rectangle notch with dimensions 1.5 mm by 6.2 mm. The design
schematic is presented in figs. 2 and 3.
III. Discussion of Simulated Results
For simulation and optimization of the antenna design, Ansoft HFSS [6] was
used. The simulated return loss for the proposed conformal antenna is presented
in fig. 4. It demonstrates two different radiating bands, a narrowband at 2.4 GHz
and bandwidth about 200 MHz, and a second one, starting at 6 GHz and
bandwidth wider that 1 GHz. Both operating frequencies outperform the
bandwidth requirements set for the sensor. The fat monopole on x-y plane in
combination with the notched ground plane result in the broadband behavior of
the above 6 GHz radiation while the folded meander-shaped monopole is
responsible for the downlink communication frequency around 2.4 GHz.
Generally the longer the meander-shaped monopole is, the lower the
corresponding resonance appears. The linear segment necessary for the 2.4 GHz
resonance which cannot physically fit in the planar 10mm x 10mm planar
substrate can be easily implemented on the compact, proposed conformal
structure.
Simulated radiation patterns for the proposed antenna at 2.4 GHz and 6 GHz,
which are the frequencies that characterize the two bands, are presented in figs. 5
and 6. Fig 5a presents the E plane (y-z) patterns, where 8=00 corresponds to z-axis
and 8=900 corresponds to the y-axis at 2.4 GHz. The H plane (x-z) plot is depicted
in fig. 5b, where 8=00 is the z-axis and 8=900 is the x-axis. E and H planes naming
is consistent with the anticipated naming in the case that the fat monopole (on x-y
plane) was the only radiating antenna. Fig. 6 shows the plots for both co and cross
polarization (Etheta and Ephi) on E and H planes, at f=6 GHz. The non-planar shape
of the antenna results in the distorted, non-omni-directional pattern in H plane (xz). As can be seen in all radiation patterns the radiation is not linear. In all cases
both Etheta and Ephi are significant therefore none can be ignored. The apparent
advantage is that the presented antenna will be operating adequately regardless
the incident wave polarization.
IV.
Conclusion
An ultra compact dual band antenna that fits on the surface of a one cubic
centimeter box has been introduced. The antenna is intended to be integrated with
a compact sensor with full duplex communication capability. There are two bands
of operation, a narrowband at 2.4 GHz for the downlink and a wideband starting
at 6 GHz with bandwidth higher that one GHz for the uplink. Despite the strict
size restrictions and the demanding bandwidth requirements the proposed
antennas operates well in both ranges and presents nearly omni-directional
patterns.
References:
[1] D.C. Thompson, O.Tantot, H. Jallageas, G.E. Ponchak, M.M. Tentzeris, J. Papapolymerou,
"Characterization of liquid crystal polymer (LCP) material and transmission lines on LCP
substrates from 30 to 110 GHz", IEEE Transactions on Microwave Theory and Techniques,
vol. 52, no.4, pp. 1343-1352, April 2004
[2] G. Ruvio, M.L.Ammann,Microwaves,"From L-shaped planar monopoles to a novel folded
antenna with wide bandwidth" Antennas and Propagation, lEE Proceedings of Antenas. and
Propagation. Vol. 153,pp.456 - 460
[3] R.L. Li, G.DeJean,M.M. Tentzeris, J.Laskar,"Integrable miniaturized folded antennas for
RFID applications". Procs. of the 2004 IEEE-APS Symposium, pp.1431 - 1434, Monterey
CA, June 2004
[4] S. Nikolaou, D.E. Anagnostou, "Conformal antenna on LCP for sensor applications." Procs.
of the 2008 IEEE-APS Symposium,pp.I-4, San Diego, CA, July 2008
[5] S. Nikolaou, G.E. Ponchak, J.Papapolymerou, M.M. Tentzeris, "Conformal double
exponentially tapered slot antenna (DETSA) on LCP for UWB applications", IEEE Trans.
Antennas Propag., vol. 54, issue 6, pp.1663 - 1669, Jun. 2006.
[6] Ansoft High Frequency Structure Simulator (HFSS). Ver. 10 Ansoft Corporation
Table I: Dual band antenna dimensions
81
82
83
3.25 mm
9.50mm
7.00mm
84
85
86
W2
Fig. 1: Cubic Centimeter Sensor
8.50 mm
5.10 mm
3.00mm
1.00 mm
O.78mm
Fig. 2: Antenna Structure
4.5
-
Return loss
1
1
m-10
I
I
I
~
4
-15
I
I
I
I
1
1
--~--
I
I
I
I
I
T - --1- - -
r
1
1
1
1
I
I
I
I
I
I
I
I
1
1
1
1
1
1
1
1
I
3
4
5
6
Frequency (GHz)
Fig. 4: Return Loss SII
180
180
b)
270
Fig. 5a: y-z plane at 2.4 GHz
270
Fig. 5b: x-z plane at 2.4 GHz
180
180
270
Fig. 6a: y-z plane at 6 GHz
I
--~--T--~---f-----
2
a)
1
I
I
I
-1---
-20
Fig. 3: Antenna Schematic (mm)
1
-~--+--~---
:2-
en
1
--J---...J--
-5
270
Fig. 6b: x-z plane at 6 GHz
1
8