Port City International University Journal, Vol-7(1+2):45-53
DESIGN AND PERFORMANCE ANALYSIS OF A SIX-ELEMENT MIMO
ANTENNA FOR UWB PORTABLE APPLICATIONS
*Swarup Chakraborty, Md. Mehedi Farhad
Department of Electrical and Electronic Engineering,
Port City International University, Bangladesh
ABSTRACT
A 6×6 multiple-input-multiple-output (MIMO) antenna is proposed for Ultra-Wide Band
(UWB) wireless applications. The proposed MIMO antenna is the combination of six single element
antennas. The single antenna consists of three slots (one sword-shaped and two rectangular shaped).
The slot is inserted to improve the reflection coefficient. The large bandwidth is achieved by designing
a defected ground structure. The six single antenna elements are placed symmetrically for the MIMO
arrangement. The MIMO antenna has a promising reflection coefficient result and 10 dB-impedance
bandwidths (greater than 6.5 GHz). The diversity performances of the MIMO antenna are evaluated by
the envelope correlation coefficient and diversity gain. Satisfactory outcomes are attained. Finally, the
various results analysis of the MIMO antenna in the vicinity of the human phantom hand are studied.
These performances of the MIMO antenna make the antenna more attractive for UWB portable
applications.
Keywords: UWB, MIMO, Portable applications, ECC, User impact.
INTRODUCTION
Multiple-input-multiple-output (MIMO) antenna are getting more popular because of their
capability to enhance multipath fading reduction (Zhang S et al., 2012). The MIMO antenna increases
the channel capacity by using a lot of antennas for transmitting and receiving data. Hence higher data
rates are attained in the MIMO antenna. Various MIMO antennas are available in the present world for
different applications.
Ultra-wideband (UWB) systems are alluring more devotion due to higher data rates and low
power levels for operation. Besides, the feature of the low power permits frequency reuse, as it does not
cause significant interference in neighboring devices. At present, there are lots of UWB antennas for
various applications like wireless, biomedical applications. A UWB antenna is proposed for biomedical
applications in (Chakraborty S, et al., 2018). The antenna consists of three different shaped slots and a
defected ground plane. The antenna works in three mode: off-body, on-body, and in-body mode. The
smaller size (17 mm×14 mm×1 mm) of the antenna makes it useable for different applications. The free
space or off-body operating frequency of the antenna is 4.0–10.5 GHz. A monopole UWB antenna for
the internet of things applications is projected in (Bekasiewicz A et al., 2016). A compact circular ring
antenna has been proposed in (Liu L et al., 2011) for UWB application. In this paper, the antenna is
used to design a six-element UWB MIMO antenna.
A lot of UWB MIMO antennas are proposed at present for different applications. A twoelement closely packed MIMO antenna has been reported in (Zhang S et al., 2012) for UWB dongle
applications. The operating band of the antenna is 3.1−5.15 GHz. A slot is designed between the
monopole and the ground plane enhanced the isolation at lower band and increases bandwidth. In (Ren
J et al., 2014), a compact size MIMO antenna is proposed for UWB applications. There are two single
*Corresponding Author: Swarup Chakraborty; Chakrabortyswarup.eee@gmail.com
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Swarup Chakraborty et al.
antenna elements where both elements are placed in a perpendicular direction for the MIMO
arrangement. The single antenna elements are the open L-shaped slot antenna. A two-element MIMO
antenna with high isolation between the antenna elements has projected in (Chandel R et al., 2016) for
UWB applications. A T-shaped stub has been extruded in the ground plane for higher isolation. The
operating band of the antenna is 2.9−20 GHz. A dual-band (WLAN and UWB) two element MIMO
antenna is proposed in (Mohammad S et al, 2013). The placement of the single antenna elements at four
different position (side by side, parallel, front to front and orthogonal) has been studied and orthogonal
position is found more suitable for the MIMO organization. In (Liu L et al., 2015), a MIMO of two
elements has been reported for portable UWB applications. The performances of the MIMO antenna in
device housing along with USB connector has been investigated. A perpendicularly placed two element
MIMO antenna is reported for band-notched UWB applications in (Kang Let al, 2015). Because of the
perpendicular placement of the antenna element, the isolation of the MIMO antenna is enhanced. For
mutual coupling reduction of a MIMO antenna, ref. (Debas T et al., 2018) propose a uni-polar
electromagnetic ban gap (EBG). A unipolar EBG of the size of 6.8×6.8 mm 2 is placed between antenna
elements for the improvement of the isolation. Again a 2×2 UWB MIMO antenna is proposed in (Luo
CM et al, 2015) where a T-shaped slot is inserted in the ground plane to increase isolation in the higher
frequency. A tree like structure is used to find high isolation (> 16 dB) between the antenna elements
in (Zhang S et al., 2009). The above-described works use a different technique to increase isolation. In
this communication, a MIMO antenna is proposed where higher isolation is found > 15dB without using
extra shape.
The channel capacity and reliability of the communication system can be improved by
increasing antenna elements. A two- and four-element MIMO antennas are designed in (Toktas A et
al., 2015) for UWB applications. The single antennas are position in an orthogonal direction to prepare
the MIMO antenna. The rotationally symmetric fashion is used to place the single antenna elements for
the MIMO organization in the 4x4 element MIMO antenna. Again, two- and four-elements MIMO
antennas are reported in (Huang H et al, 2015) with similar types of fashion used to place the antenna
elements in the respective MIMO antennas. A four-element MIMO antenna is proposed in (Zhu J et al.,
2015) for operating in 3−12 GHz and higher isolation is found in the overall frequency band. Another
four element MIMO antenna has been projected in (Srivastava G et al, 2015 for portable wireless
applications. A UWB slot antenna is used as single element for the MIMO organization. A doublesided 4×4 MIMO antenna is reported in (Ali WA. et al., 2015). The orthogonally placed two elements
are placed on front side of the substrate while the other two elements in similar style are positioned in
the backside of the substrate. This antenna arrangement increases the isolation. For further enhanced
isolation, a decoupling structure is placed between the antenna elements.
In this communication, a 6×6 UWB MIMO antenna is proposed to operate in (4−10.5 GHz) for
wireless applications. A UWB single antenna is designed at an initial stage. The single antenna has one
sword-shaped and two rectangular-shaped slots. The slots are inserted to find better impedance
matching. The rectangular slot is etched in the ground plane for finding defected ground structure
(DGS). The DGS improved the bandwidth tremendously. To generate the MIMO antenna, six single
antennas are placed in symmetrical way. Better isolation is achieved among the antenna elements. The
diversity performances of the MIMO antenna are analyzed be envelope correlation coefficient (ECC)
and diversity gain (DG). Both ECC and DG are in acceptable limits. Moreover, the human hand effects
on the MIMO antenna are studied by the various result analysis. Those results prepare the antenna more
feasible for portable UWB portable applications.
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Six-Element Mimo Antenna
The arrangement of the paper is as follows: the single antenna design and performance analysis
are discussed in the first section. The second section is populated by design, result analysis of the MIMO
antenna and user impacts on the MIMO antenna.
(a)
(b)
Fig. 01. The overall view of the single antenna (a) Front view and (b) Back View
Fig. 02 The Effects of Slots in S11
Fig. 03 The Effects of DGS in bandwidth
MATERIALS AND METHOD
Design of the Single Antenna
Fig. 01 shows the antenna’s overall structure. The radiating element of the antenna is a
microstrip patch. The FR4 (dielectric constant = 4.4) is used as a substrate and Copper is used as a
radiating patch and ground. The antenna has three different shaped slots. At first, the rectangular patch
is used as a radiating element of the antenna. Fig. 02 shows the result of the S11 of the patch antenna.
The S11 is found is less than −25 dB and 10-dB impedance bandwidth is achieved at 5.5 GHz. Then a
sword-shaped slot (S1) is added in the patch. The reflection coefficient after adding slot S1 is shown in
Fig. 02. The minimum S11 is found −30 dB at 9.0 GHz and 10-dB impedance bandwidth is attained
more than 6.5 GHz. Then, a rectangular slot (S2) is etched on the patch which is positioned on the right
side of the S1. The S11 is improved by inserting the S2 as shown in Fig. 02. Finally, another rectangular
slot (S3) is inserted which is situated on the left side of the S1. Fig.02 displays S11 of the final design
antenna. The minimum S11 is achieved less than −50 dB.
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Swarup Chakraborty et al.
Fig. 04. Simulated S11 of the single Antenna Fig. 05. Simulated Efficiencies and Gain of
the single antenna
Fig. 06. Overall design of the MIMO antenna
The defected ground technique is used to increase the 10-dB impedance bandwidth. To achieve
a DGS, a rectangular slot is designed in the ground plane. Fig. 03 shows the results of the reflection
coefficient at full ground and defected ground. From Fig. 03, it is evident that at the full ground the 10dB impedance bandwidth is only 1.0 GHz. But the 10-dB impedance bandwidth is achieved more 6.5
GHz after DGS So, 10-dB impedance bandwidth is increased at DGS.
Performance Analysis of the Single Antenna
To simulate the designed antenna, CST microwave studio is used. Fig. 04 shows the S11 of the
antenna. The minimum S11 is found less than −64 dB. 10-dB impedance is found more than 6.5 GHz.
Fig. 05 displays efficiency of the antenna. Both radiation and total efficiencies are found more than
60%. The total efficiency is comparatively lower than the radiation efficiency. The reason is that the
loss of the input is included in the total efficiency.
Fig. 05 illustrates the gain of the antenna. The Fig. shows the maximum gain at different
frequencies at different theta and phi.
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Six-Element Mimo Antenna
Fig. 07. Reflection coefficient of the different
elements of the MIMO antenna
(a)
(b)
Fig. 08. Isolations of the MIMO antenna
(c)
Fig. 09. Radiation pattern at xz-plane of A1 (a) 4 GHz (b) 7 GHz (c) 9.66 GHz
Fig. 10. Efficiencies and Gain of the MIMO
antenna
Fig. 11. ECC of the MIMO antenna
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Swarup Chakraborty et al.
MIMO Antenna Design
Fig. 06 shows the overall view of the MIMO antenna. The MIMO antenna consists of six single
antenna elements. The single elements are placed in a symmetrical fashion. The elements are denoted
as A1, A2, A3, A4, A5, A6. At first, three single elements are placed side by side along the x-axis at
distance of 18 mm. Then, a copy of this antenna’s topology is positioned side by side along the y-axis
at distance of 12 mm. The total size of the MIMO antenna is 70×42 mm 2.
RESULTS AND DISCUSSION
The Fig. 07 shows the S11 of every element of the MIMO antenna. The bandwidths of the
elements are similar and found more than 6.5 GHz. The minimum reflection co-efficient is achieved
less than -60 dB for every antenna element.
Fig. 12. DG of the MIMO antenna
Fig. 13. MIMO antenna with the human
phantom hand
Fig. 14. Reflection coefficient of the MIMO Fig. 15. Efficiencies of the MIMO antenna
antenna with the human phantom hand
with the human phantom hand
The Fig. 08 displays the isolation of the MIMO antenna. Every isolation is attained less than
−15 dB. A maximum of 43 dB isolation is found between A1 and A4.
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Six-Element Mimo Antenna
The Fig. 09 displays the radiation pattern of the single element A1 at different frequencies. It
is noted that the radiation patterns of the other element are similar to the that of A1. Cross-pol
suppression is found more than 15 dB in every frequency. The co-pol gain is increased when frequency
increases. The maximum co-pol gain at 9.66 GHz is 3.12 dBi theta = 163°.
The Fig. 10 displays the maximum gain vs frequency of the MIMO antenna. The maximum
gain is achieved is greater than 4 dBi at 9.66 GHz. It is noted that the maximum gain is achieved at
different theta at different frequencies.
The Fig. 10 shows the radiation efficiency of the MIMO antenna. Radiation efficiency of every
antenna element is attained more than 60%. The total efficiency of the MIMO antenna is found more
than 50 %.
The Fig. 11 shows the ECC performances of the MIMO antenna. The ECC evaluates how much
one single antenna element works independently. The standard value of ECC is less than 0.5. ECC
parameters of the MIMO are less 0.1 in the region of interest.
The Fig. 12 shows the DG of the MIMO antenna. DG provides information about the reduction
of transmission power without a performance loss when a diversity scheme is introduced. For MIMO
operation, the diversity gain of the antenna should be around 10 dB. The DG parameters of the MIMO
antenna are about 10 dB in the overall frequency band. The results of the ECC and DG show a promising
diversity performance of the antenna.
To find the workability of the MIMO antenna in the portable device applications, the analysis
of the result of the antenna in the vicinity with the human phantom hand is necessary. For this purpose,
the MIMO antenna is simulated with a human phantom hand. Fig. 13 shows the MIMO antenna with a
human hand model.
Fig 14 exhibits the reflection coefficient of the MIMO antenna at the on-body environment.
The 10-dB impedance bandwidths of the antenna elements except A2 and A3 are similar to free space
bandwidth. The impedance bandwidths of the A2 and A3 is slightly reduced.
The Fig 15 shows the total and radiation efficiencies of the MIMO antenna at the on-body
environment. Both efficiencies are reduced at on-body environment because the human body is a lossy
element.
Conclusion
A UWB MIMO antenna for the UWB portable applications is proposed in this journal. Initially
a UWB single antenna is designed to operate in a 4−10.5 GHz frequency band. The single antenna
contains three slots and a DGS. One of the slots is sword-shaped and other slots are rectangular shaped.
The slots are designed to find better impedance matching of the single antenna. The DGS is used to
enlarge the 10-dB impedance bandwidth. The six single antenna elements are placed in a symmetrical
style to organize the MIMO antenna. The MIMO antenna shows promising impedance matching and
10-dB impedance bandwidth. The diversity performances of the MIMO antenna studied by the ECC
and diversity gain result are satisfactory in the overall frequency range. By considering the abovediscussed results, the MIMO antenna is more feasible for UWB applications.
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Swarup Chakraborty et al.
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Six-Element Mimo Antenna
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