A UWB-Specific Metasurface-Inspired MIMO Antenna with

Enhanced Isolation and Gain

Tejaswita Kumari

, Anupama Senapati

and Abu Nasar Ghazali

School of Electronics Engineering, Kalinga Institute of Industrial Technology, Patia, Bhubaneswar, 751024, Odisha, India

Keywords: DGS, High Isolation, Metasurface, UWB MIMO.

Abstract: This study presents a lightweight, compact Metasurface-inspired UWB-optimized MIMO antenna featuring

high isolation and substantial gain. The MIMO antenna design incorporates two identical patches arranged in

parallel to boost overall performance. To enhance impedance matching, a trapezoidal defected ground with

stepped features is employed. The antenna's feed, designed in a tapered shape, contributes to enhanced

impedance matching. A metasurface isolation system is implemented, utilizing a hexagonal-shaped unit cell

absorber, which is subsequently integrated into the middle of the defected ground. Metasurface achieves

significant isolation, up to 25 dB. The antenna abilities to provide a wide operating bandwidth of 1.96 GHz

to 13 GHz, suitable for UWB utilization, with a peak gain of 7.9 dBi at 7 GHz. A comparison with prior

literature demonstrates size optimization and enhanced isolation through the novel metasurface absorber. The

efficiency of the proposed antenna stands at 95.5%. Resonating at triple frequencies 5.2 GHz, 7.5 GHz, and

12.37 GHz, this MIMO metasurface antenna is well-suited for applications such as WPAN and WBAN.

1 INTRODUCTION

In the modern-day, ultrawideband antennas face

numerous difficulties including miniaturization, cost-

effectiveness, compactness, mechanical durability,

and the attainment of high-performance metrics such

as substantial gain, wider bandwidth to support

wireless security. Overcoming these hurdles to

develop a UWB antenna within a functional

bandwidth of 3.1 to 10.6 GHz {(FCC.,2002,

Balanis.,2016)} as specified by the FCC is a complex

endeavour. The constraints mentioned above

regarding UWB antennas can be addressed through

the application of fractal geometry. Fractal

geometry's characteristics like self-similarity with

space-filling render it a suitable choice for UWB

antenna (Bhatt et al.,2017, Tejaswita et al.,2024) For

UWB applications, incorporating a Koch fractal

structure around the outer edge of the octagonal patch

in a MIMO antenna improves its efficiency and

compactness in multiple important aspects. Since the

antenna's fractal structure extends its electrical length

without materially increasing its physical size, it can

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operate well at lower frequencies and still have a

small form factor. For UWB applications that need

wide frequency coverage, this functionality is

essential. Furthermore, many resonant frequencies

are supported by the self-similar patterns of fractal

structures, which improves bandwidth and makes it

possible for the antenna to effectively handle multiple

signals in various frequency bands. Additionally, the

Koch fractal's complex structure helps to realize

enhanced impedance matching throughout the UWB

band, which lowers return loss and increases

efficiency. as it contributes to improved antenna

performance. This assertion is supported by previous

studies conducted by numerous researchers (Werner

et al.,1999, J. Anguera et al.,2005, C. Borja et

al.,2003). To enhance reliability and address the

susceptibility to multipath fading inherent in

communication systems, the MIMO antenna system

has been integrated. This technology reduces

transmission errors and improves communication

range with data transfer rates. Ensuring ample

isolation among MIMO antenna elements presents a

notable obstacle when crafting compact antennas.

Kumari, T., Senapati, A. and Ghazali, A. N.

A UWB-Speciﬁc Metasurface-Inspired MIMO Antenna with Enhanced Isolation and Gain.

DOI: 10.5220/0013266200004646

Paper published under CC license (CC BY-NC-ND 4.0)

In Proceedings of the 1st International Conference on Cognitive & Cloud Computing (IC3Com 2024), pages 30-36

ISBN: 978-989-758-739-9

Nonetheless, various approaches are being pursued in

this direction, and implementations of MIMO

antennas are being explored in the existing literature,

as discussed below.

The antenna isolation is only 12.5 dB. A compact

antenna featuring two elements was introduced in

(Zhao et al.,2017). In (Hussain et al.,2019), A 4-

elementMIMO antenna utilizing annular rings was

devised for cognitive radio applications. (Chandel et

al.,18) introduces a two-port antenna with tapered

feeding and dual stop-band attributes, engineered to

operate across the extensive frequency range of 2.9-

20 GHz. Isolation methods employing standard

ground stubs were applied, achieving isolation levels

below -22dB. In (Hussain et al.,19), a four-port

MIMO antenna with a pentagon shape was

developed, catering to various wireless applications

with reconfigurability as a key feature. Notably, no

specific isolation mechanism was reported, with

isolation primarily reliant on significant spacing

between the radiators, resulting in a large antenna

size. (Li, Zhenya et al.,2019) described a compact

Vivaldi-shaped antenna, employing stub techniques.

This work employed a novel design approach to

reduce mutual coupling. In (Iqbal et al.,2017), a two-

port antenna featuring F-shaped stubs was designed,

achieving isolation of only -20 dB However, due to

the large size of the patch, the overall dimensions of

the antenna were considerable. (Zhao et al.,2019)

presented a large-scale MIMO antenna measuring

120 x 60 mm, tailored for UWB applications. It is

clear from the literature analysis that achieving the

isolation in MIMO is very crucial, with the help of

metasurface we can overcome this drawback.

The paper's newness lies in its inventive

utilization of Koch fractal octagonal geometry and

Metasurface in the ground plane to devise an

ultrawideband MIMO antenna, which achieves

notable characteristics such as high isolation, gain,

miniaturization, compactness, wideband operation,

high efficiency, and three resonant frequencies. The

provided article encompasses an introduction in

Section 1, detailing the stepwise and optimized

outcomes, as well as the results and analysis depicted

in Section 2. The research conclusions are drawn in

sections 3, 4, and 5. With the aid of the ANSYS HFSS

v21.0 R1 software environment, the entire structural

design is completed (ANSYS., 2021).

ANTENNA

DESIGN APPROACH

& ANALYSIS

The suggested UWB antenna has been created by

cutting an octagonal shape's edge using a Koch

fractal. This suggested antenna combines antenna

technology with fractal geometries. Fractal geometry,

in general, is made up of repeated segments in

varying scales. In terms of length and size (D. Li et

al.,2012) derived by applying the following formula:

d ൌ

log ሺnሻ

log ሺRሻ

ሺ1ሻ

L ൌ H

ቀ

ቁ

୬

ሺ

ሻ

In the equation, where 'n' represents the number of

geometry segments, 'h' denotes the curve length, 'i'

stands for the iteration number, and 'r' signifies the

number of segments divided by each iteration.

Figure 1: Koch fractal Generation in the patch.

Figure 1. shows the design of the iteration in the

octagonal, the starting structure's length R is

represented by θ, which provides the fractal

geometry's convergence. When θ equals 45 degrees

and R equals 1.6 mm, these values define the edge

dimensions for the octagonal iterative subtraction

process in antenna.

The two-element antenna design undergoes

optimization and feature analysis using HFSS

software v.21. FR4 substrate, is selected for its

favorable attributes in providing wide bandwidth

followed by radiation characteristics for fundamental

design (Tasouji, N et al.,2013, Liu YY et al., 2016, Li

et al.,2018, Hussain et al.,2017, Ibrahim et al.,20 17).

Table 1 lists all of the optimized metasurface MIMO

antenna's variables.

Table 1: Optimized metasurface MIMO antenna's variables.

Design

Parameters

Value

(mm)

Design

Parameters

Value

(mm)

Ls 35 d 10

Ws 35 e 7.6

a 5 f 5

b 13.7 g1 35

g3 3.06 g5 23

g4 9.4 c 27.5

A UWB-Speciﬁc Metasurface-Inspired MIMO Antenna with Enhanced Isolation and Gain

Figure 2: MIMO antenna with dimension (a) Patch with

dimension (b) Ground with dimension metasurface

Figure 2. shows the (a) Patch with dimension and (b)

Ground with dimension metasurface. There are many

antennas reported which show the metasurface helps

to improve the characteristics of the antenna (Li et

al.,2023, Kumar et al.,2022, Pandey et al.,2024,

Wang et al.,2023, Saxena et al.,2023). Using a

metasurface in the ground plane coupled with a two-

element Koch fractal antenna MIMO configuration

greatly improves isolation and gain for the UWB

spectrum via several methods. By forming bandgaps

that stop surface currents from propagating, the

metasurface improves isolation and minimizes

interference by suppressing surface waves also

reducing mutual coupling. Furthermore, by reflecting

electromagnetic waves with an in-phase reflection

coefficient, metasurfaces function as artificial

magnetic conductors. This optimizes the radiation

pattern and total gain by concentrating more power in

the desired direction. Over the UWB spectrum, the

metasurface ensures clean operation by suppressing

unsuitable modes and harmonics. By lowering ohmic

losses and back radiation, it also increases radiation

efficiency by turning a larger percentage of input

power into usable radiated power Optimizing

performance over the UWB range is possible because

of the metasurface's precise control over

electromagnetic wave propagation, which enables

customized radiation patterns. Because of this

integration, the design is efficient and compact, which

is crucial for current UWB applications that have

limited space. Moreover, metasurfaces' frequency-

selective qualities optimize antenna efficiency in

particular UWB bands, improving isolation and gain

where it's most needed. All these elements work

together to create a small, high-performance, and

efficient UWB MIMO antenna system. The entire

design process is described in the initial phase, with

the following unit cell of the metasurface that will be

designed and examined in the following section.

2.1 Unit Cell Development

On a FR-4 substrate, a hexagonal unit cell is

fabricated with the required dimensions as shown in

Figure 3, with a total size of 2 mm × 2 mm.

Figure 3: metasurface unit cell (a) hexagonal unit cell with

dimension (b) unit cell under boundary condition (c)

deployed metasurface unit cell S parameter.

In Figure 3 (a) a unit cell is shown with dimensions

here a =, b =2 mm, c = 2 mm, and (b) a unit cell under

the boundary condition. here a Floquet port is used

to examine the unit cell and master-slave is used in

the unit cell boundary. hexagonal unit cell's S-

parameter analysis is in Figure 3 (c). As can be seen

from the graph, S11 is continuously below -10 dB,

and the unit cell shows effective absorption within the

target range of 3.88-12.37 GHz. Additionally, the

proposed antenna's ground plane has this unit cell

arrayed repetitively across it. An analysis of the

recommended antenna is shown on Figure 4. Figure 4

(a) depicts an individual antenna with a Koch fractal

at the lower half of it. The antenna with a Koch fractal

in its upper half is seen in Figure 4 (b). The two-

element MIMO antenna is displayed in Figure 4 (c);

the MIMO antenna combined with a metasurface is

displayed in Figure 4 (d).

IC3Com 2024 - International Conference on Cognitive & Cloud Computing

Figure 4: Step-wise evaluation of the MIMO antenna.

3 RESULTS

3.1 Gain and Efficiency

The peak gain Two-element meta surface UWB

MIMO antenna of 7.9 dBi at 7 GHz is in Figure 5 (a).

and followed by Figure 5 (b) is the overall efficiency

of the 2-element MIMO antenna 95.5%.

3.2 S-Parameter

Figure 5 (c) shows a Simulated S11-parameter of

novel UWB two-element MIMO Koch fractal

antenna with a metasurface. suggested antenna

achieves three resonant frequencies 5.2 GHz, 7.5

GHz, 12.37 GHz, and a wide bandwidth of 1.96 GHz

to 13 GHz. The isolation between the two antenna is

also very good below 25 dB for the entire bandwidth.

3.3 CCL / TARC

Figure 5 (d). shows Channel capacity loss (CCL) and

the TRAC of the MIMO antenna. Ideally, the CCL

value is 0 and the practical value is between 0 to 0.4.

The proposed antenna CCL value is up to the mark.

Figure 5: (a) Simulated Peak Gain with and without

metasurface and (b) Efficiency of Two-element meta

surface UWB MIMO antenna. (c) S parameter of the

MIMO antenna with and without meta surface and S21

graph for isolation. (d) Simulated CCL and TARC of Two-

element meta surface UWB MIMO antenna.

3.4 Radiation Pattern

Figure 6 shows the generated radiation patterns for

metasurface MIMO antenna. The E-plane followed

by H-plane patterns are shown for resonant

frequencies of 5.2 GHz, 7.5 GHz, and 12.37 GHz.

A UWB-Speciﬁc Metasurface-Inspired MIMO Antenna with Enhanced Isolation and Gain

Figure 6: S parameter Simulated Radiation Pattern at the

resonant frequency 5.2 GHz, 7.5GHz, and 12.37 GHz of

metasurface MIMO antenna.

3.5 Surface Current Distribution

Figure 7. depicts the two-element meta surface

antenna’s current distribution at resonance

frequencies (a) 5.2 GHz, (b) 7.5 GHz, and (c) 12.37

GHz. From the Figure, it is evident that the Meta

surface unicell absorbed the radiation very well.

Figure 7: Current Distribution of Two-element meta surface

UWB MIMO antenna at (a) 5.2 GHz, (b) 7.5 GHz, and (c)

12.37 GHz.

4 ANALYSIS IN RELATION

Table 2: shows the analysis relation with another MIMO

antenna and the suggested antenna.

Ref.

No.

Dimension

(mm)

Isolation

(dB)

Bandwidth

Liu

YY,2016

44×44

less than

15.5

2.95-10.8

GHz

Li, 2018

30×30

less than

2.8-19.2

GHz

Hussain,

2017

60×120

less than

1.77- 2.51

GHz

Ibrahi

2017

6cm

×5cm

10-18

3-10.6

GHz

Li, 2023

60×60 30

3.66-16.61

GHz

Kuma

2022

45×45 20

4.5-16.4

GHz

Pandey,

2024

32×48 27

1.87-13.82

GHz

Wan

, 2023 68×68 20 2.14-14.95

Saxena,

2023

29×23 20

6.75-14.6

GHz

35×35 25

1.96 - 13

GHz.

[SW= suggested Work]

5 CONCLUSION

In light of Metasurface inspiration, a Koch fractal

octagonal MIMO antenna is presented in this research

for Ultrawideband (UWB) frequency range

applications. The suggested antenna can be made

smaller and more compact for UWB operations by

utilizing a Koch fractal structure around the octagonal

patch's edges. Additionally, a two-element Koch

fractal antenna MIMO configuration is coupled with

a Metasurface in ground plane to expand antenna

properties like isolation and gain. With this setup, the

1.96 - 13 GHz UWB spectrum is achieved. This

antenna is a viable choice for UWB applications

because of its very low ECC (Envelope Correlation

Coefficient) of 0.3, peak gain of 8 dBi, isolation

below 25 dB, and adequate transmission coefficients.

Due to its affordable substrate and advantageous

antenna properties, in terms of important performance

IC3Com 2024 - International Conference on Cognitive & Cloud Computing

metrics, the UWB-specific Metasurface-inspired

MIMO antenna performs significantly better than

current alternatives for WPAN and WBAN

applications. Due to mutual coupling and surface

wave suppression by the metasurface, it obtains a

reduced Envelope Correlation Coefficient (ECC).

Better signal diversity and reliability are the outcome

of this. In addition, the antenna has a larger peak gain,

which concentrates more energy in the desired

direction and improves signal coverage and intensity.

Maintaining high data speeds is dependent on its

remarkable isolation, which guarantees little

interference and crosstalk between antenna elements.

The metasurface also shows minimum signal leakage

by reducing transmission coefficients. These

advantages make it ideal for high-performance,

reliable communication in WPAN and WBAN

environments.

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