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Department of Electronics and Communication Engineering, Amrita Vishwa Vidyapeetham, Coimbatore, India
Abstract- A compact ring antenna with electromagnetic feed for 3G handsets at 2.1 GHz is proposed. The major
considerations of the conformal antenna design were the compact size so that it could be used for MIMO based mobile
applications. The EM feed strip effectively modifies impedance matching of 50Ω. Thus, the design and the development of
two antennas: conventional ring antenna and modified annular ring antenna is proposed. The conventional ring antenna with
outer radius 2.3642cm and inner radius 1.0642cm is observed to have a return loss of -27dB at 2.07GHz. The modified ring
antenna I with outer radius 2cm and inner radius 1.3cm with three notches at 0°, 180° and 270° is observed return loss of 36.86dB at 2.1GHz. The results were obtained by varying the length of EM feed strip.
Mobile communications often require small,
lightweight, low-profile, low-cost antennas. MIMO
technology has attracted attention in wireless
communications, because it offers significant increase
in data throughput and link range without additional
bandwidth or increases transmit power. It achieves
this goal by spreading the same total transmit power
over the antennas to achieve an array gain that
improves the spectral efficiency and to achieve a
diversity gain that improves the link reliability.
Because of these properties, MIMO is an important
part of modern wireless communication standards
such as Wi-Fi, 4G, 3GPP long term evolution,
Thus, making it easy for MIMO based applications.
In this paper, the design and analysis of annular ring
antenna system for communication system is done.
The EM simulation of selected configuration of ring
antenna systems and the performance is studied.
The proliferation of wireless communication systems
has promoted the development of miniaturized
antenna designs. In [1], the size of the resonant ring is
substantially smaller than that of the corresponding
patch and depends on the width of the microstrip
used. In general, the mean circumference of a ring
equals the guide wavelength of the microstrip used.
The circular ring antenna has a number of useful
features. The separation of resonant modes can be
controlled by the ratio of outer to inner radii.
The lower substrate layer consists of the microstrip
line. The feed line terminates in an open end
underneath the patch with an impedance matching of
50Ω. Duroid is used as the dielectric substrate whose
dielectric constant is 2.33.
The geometry of a ring microstrip antenna developed
with the coordinate system used is shown in Figure 1.
It comprises of three layers. The bottom layer is the
ground plane. The design consists of two substrate
layers. The upper substrate layer consists of ring
shaped conductor.
The design specifications of the ring antenna are
given below:
The disadvantage of the annular antenna is that it
suffers limitation in achieving required impedance
[2]. In our design the annular antenna with three
notches is proposed. The impedance can be improved
by adjusting the lengths of the notches [3]. The input
impedance of the annular antenna is dependent on the
width of the rings. For narrower rings the input
impedance is higher and difficult to achieve [4].
In this paper we are presenting modified ring antenna.
The main reason for choosing ring geometry over
other microstrip antenna geometries is that it occupies
the smallest physical area for operation at a given
frequency in the fundamental mode.
Resonant Frequency: 2.1GHz
Material used for ring conductor, trace and
ground plane: Copper
Material used for dielectric substrate:
Rogers RT
Duroid 5870
Substrate Permittivity: 2.33
Substrate Thickness: 0.159cm
Height of the trace: 0.108cm
Width of the trace: 0.126305228cm
Height of antenna: 0.005cm
Height of ground plane: 0.005cm
Length and width of substrate:17.4844cm
Proceedings of IRF International Conference, Bangalore 23rd March-2014, ISBN: 978-93-82702-68-9
Design and Analysis of EM Coupled Modified Ring Antenna for Mobile Applications
the patch. By introducing these notches, the current
on the patch and the field under the patch will take
the longer path around the notch from one edge to
another. Due to this the size of the antenna reduces or
the resonant frequency reduces [7].
The modified annular ring antenna has the increased
circumference by introducing a hair-pin bend in the
antenna structure. The notches will further make the
compactness by providing larger path for the current.
Due to the introduction of hair-pin bend, the
dominant mode will have the disturbing field
configuration in the inner side of the antenna. But by
satisfying the mode we could achieve the required
performance without compromising any space
The design procedure involves selection of outer and
inner radii of the ring antenna. The basic equation
relating the resonant frequency of the annular ring
antenna to its dimensions is given by,
Where, fnm is the resonant frequency of the
microstrip ring corresponding to the mode TMnm and
c is the velocity of light in free space, εr is the
relative dielectric constant of the substrate used and
Xnm is the root of characteristic equation describing
the modes of propagation.
The basic equation in [5], is used to compute the
stripline width is given by,
Suitable height of the stripline was computed in
order for the stripline to be of impedance 50Ω using
[6]. The stripline for EM coupling is introduced at
270° with respect to Figure 1 and Figure 4.Keeping
the height and width of the stripline constant the
length is varied for various results. Later on, steps are
taken to make it compact by introducing three
notches in a hair-pin bend antenna as shown in Figure
3. Dimensions of the ring antenna are changed alone.
The geometry of the newly designed antenna,
modified annular ring antenna is shown in Figure 4.
A. Conventional Ring Antenna (Figure 1)
As shown in Figure 1, the conventional ring antenna
of width 1.2cm has an outer radius and inner radius of
2.26682cm and 1.06682cm respectively. Whereas,
the ring antenna of width 1.3cm has an outer radius
and inner radius of
2.3642cm and 1.0642cm
respectively. This antenna is used for comparison
with the proposed modified ring antenna with three
In this design size reduction has been done by using
notches in a hair-pin bend structure. For compactness
of the antenna, notches have been introduced in the
radiating patch. Reduction of size can also be done by
introducing notches in the ground plane underneath
Proceedings of IRF International Conference, Bangalore 23rd March-2014, ISBN: 978-93-82702-68-9
Design and Analysis of EM Coupled Modified Ring Antenna for Mobile Applications
Results by varying the length of the stripline are also
shown in table I.
TABLE I: Varying the width of the conventional ring
antenna along with the length of the strip line.
B. Modified Ring Antenna (Figure 4):
The outer radius of the ring antenna is 2cm.
The inner radius of the ring antenna is 1.3cm.
The length of EM feed strip line is 8.8cm.
The dimension of notch 1 and 2 is 0.5cm×0.464cm.
The dimension of notch 3 is 0.5cm×0.097cm.
Figure 5 shows the E-plane and H-plane radiation
pattern of the antenna and the 3dB beamwidth is
formed at 60°, well suitable for MIMO applications.
The gain the antenna is found to be around 7dB in
both principle planes which shows that the radiation
pattern has excellent coverage in all specific
directions. The front to back ratio is found as -22dB
which is good for portable devices. From this
proposed study, it reveals that the antenna structure
maybe a better solution for making compact antenna
array systems for MIMO based wireless systems. The
scope for improving this structure for achieving
circular polarization is also in progress.
For further study, various parameters such as return
loss and resonant frequency have been noted with
variation in the length of the strip line.
By keeping the dimensions of 1st
and 2nd
notch with value
0.5cm×0.464 cm and 3rd
notch with value 0.5cm×0.097cm constant, the
length of the strip line has been changed accordingly
and its following results are shown in table 2.
Figure 4 shows the return loss characteristics of the
antenna with electromagnetic coupling, resonates at
2.1GHz.The characteristics show that, the bandwidth
of the antenna is limited to less than one percent and
it very narrow.
Table 2: Varying the length of the strip line by
keeping the dimensions of the notch constant.
The bandwidth can be increased by introducing
various other structural changes or by increasing the
height of the substrate With this design, a return loss
of -43.50dB is achieved at a resonant frequency of
Compared to the conventional ring antenna, there is a
reduction in size to 2cm and also better return loss is
achieved at exactly 2.1GHz, which is the required
resonant frequency.
Proceedings of IRF International Conference, Bangalore 23rd March-2014, ISBN: 978-93-82702-68-9
Design and Analysis of EM Coupled Modified Ring Antenna for Mobile Applications
From Table 2, Variation in resonant frequency and
return loss is observed with variation in the length of
stripline. The optimal result was got when the length
of the stripline is 8.8cm
This paper presents a modified ring antenna design
which is centered at frequency 2.1GHz for mobile
The gain has also been determined for each of these
proposed antennas. Notches were introduced in a
conventional ring antenna to improve the frequency,
return loss and gain. From modified ring antenna it
can be inferred that by changing the dimensions of
notch 1, notch 2, and notch 3 there is a change in the
resonant frequency and return loss.
Also by changing the length of the stripline , keeping
the dimensions of the other three notches constant
there is a change in return loss and frequency. With
these modifications, compactness is achieved when
compared to the conventional ring antenna.
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Proceedings of IRF International Conference, Bangalore 23rd March-2014, ISBN: 978-93-82702-68-9