Proceedings of 2nd International Symposium for Color Science and Art 2020-2021

Analysis of Radiation Characteristics of Optically Transparent
Antenna Using Transparent Conductive Thin Film
Fukuro Koshiji, Yuri Yamada, Yoji Yasuda, Katsumi Yamada, Takayuki Uchida
Tokyo Polytechnic Univ., 1583 Iiyama, Atsugi, Kanagawa 243-0297, Japan

ABSTRACTIn this study, the radiation efficiency of the antenna
with respect to the thickness and conductivity of thetransparent conductive film was investigated. As a result,it was found that the thickness of the transparent
conductive film had a significant effect on the radiation
efficiency of the antenna, and the radiation efficiency ofmore than 68 % was obtained for a monopole antennausing an ITO transparent conductive film with a thicknessof 300 nm.

Antennaelement

Zℓ

Feed pointdtw
gGroundconductor

XYdFig. 1 Antenna configuration

1. INTRODUCTION
In recent years, research and development on theInternet of Things (IoT) and the 5th generation (5G) mobile
communication system have been attracting attention [1].
Antennas are indispensable and one of the mostimportant components in these wireless systems. Inparticular, since array antennas are used in 5G systems to
improve communication characteristics, it is a challenge toinstall a large number of antennas while maintaining
aesthetics so as not to impair the design.
If the antennas could be made of optically transparent
conductive materials, the placement and design of theantennas would be more flexible, and these antennas
could be placed on the surface of optical displays, windowpanes, and even product covers and housings withoutcompromising their appearance.
For antennas which use transparent conductive films, itis essential to have both good optical transparency andelectrical characteristics, but there are not many studies
on antenna performance such as radiation efficiency withrespect to film thickness and conductivity [2].
By forming a very thin metal mesh layer on thetransparent dielectric material, the radiation efficiency of
the antenna can be ensured, but the optical transmittanceis reduced.
In this study, the radiation efficiency of a monopole
antenna using a transparent conductive film with respect
to the film thickness and conductivity is investigated.

width d = 80 mm, and feed point spacing g = 0.5 mm. The
thickness t of the transparent conductive film is from 100nm to 18 μm. The antenna shown in the Fig. 1 resonates ataround 3.3 GHz (the element length is about a quarterwavelength).
3. RADIATION EFFICIENCY
Figure 2 shows the relationship between conductivity
and radiation efficiency for transparent conductive films
with thicknesses from t = 100 nm to 18 μm, obtained byelectromagnetic field analyses.
Table 1 shows the skin depth and the radiation
efficiency at film thicknesses of 100 nm, 1 μm, and 18 μmin Fig. 2.
As can be seen from the Fig. 2 and Table 1, theradiation efficiency of more than 90 % can be obtained
when the film thickness is about the same as the skindepth.
It can be seen that as the conductivity of the transparent
conductive film decreases, the skin depth also becomesdeeper, and the radiation efficiency decreases
significantly when the film thickness is thin.
4. CHARACTERISTICS OF ANTENNA MADE ON AN
EXPERIMENTAL BASIS
Figure 3 shows a prototyped monopole antenna using a
300 nm-thick of Indium Tin Oxide (ITO) transparent
conductive film (sheet resistance of 5 Ω, conductivity of 6.7× 105 S/m, average transmittance of visible light 80 %) asthe radiating element on a 0.7 mm glass plate.

2. ANTENNA CONFIGURATION
Figure 1 shows the configuration of the monopole
antenna investigated in this study, with the radiating
element length ℓ = 20 mm, width w = 1 mm, ground plane

23

Radiation efficiency η [%]Proceedings of 2nd International Symposium for Color Science and Art 2020-2021

1008060t = 18 µmt = 10 µmt = 5 µmt = 1 µmt = 0.5 µmt = 0.1 µm

402005.8×103

5.8×104

5.8×105

5.8×106

Conductivity σ [S/m]

5.8×107

Fig.2 Relationship between conductivity and radiation efficiency for several film thickness
Table 1 Radiation efficiency for several film thickness
Conductivity
σ [S/m]
5.8 ×107
5.8 ×106
5.8 ×105
5.8 ×104
5.8 ×103

Antennaelement(ITO 300 nm)
FeedpointRadiation efficiency η [%]t = 18 μm
t = 1.0 μm
t = 0.1 μm
99.9
99.5
92.9
99.4
93.1
67.1
96.4
67.2
17.9
76.8
15.1
0.8
28.7
0.6
0.20

Unit: mm

S11 [dB]

5Skin depthδ [μm]
1.15
3.64
11.5
36.4
115

Simulated
Measured-5-1020-15-20

0.5
Groundconductor-25

Fig.3 A prototyped antenna
made on an experimental basis

1234

Frequency [GHz]5Fig.4 S11 characteristics obtained
from measurement and simulation
Table 2 Radiation efficiency of the prototyped antenna
made on an experimental basis

Figure 4 shows the reflection characteristics S11 of theprototyped antenna shown in Fig. 3. As shown in the Fig. 4,
it can be that the antenna resonates around 3 GHz andoperates as an antenna.
Table 2 shows the results of the radiation efficiency ofthe prototype antenna measured by Wheeler method. As
can be seen from the table, the radiation efficiencies of
68 % and 73 % obtained from measurement andelectromagnetic field analysis, respectively.
The result show that it is possible to achieve both an
optical transmittance of more than 80 % and a radiation
efficiency of about 70 %, which can be used as anantenna.

using an ITO transparent conductive film with a thicknessof 300 nm. In addition, it was shown that the antenna canbe flexibly implemented without compromising the design
and aesthetics of the object on which it is mounted, as wellas the design and arrangement of the antenna itself.

5. CONCLUSIONSIn this study, the radiation efficiency of the antenna withrespect to the thickness and conductivity of thetransparent conductive film was investigated. As a result,it was found that the thickness of the transparent
conductive film had a significant effect on the radiation
efficiency of the antenna, and the radiation efficiency ofmore than 68 % was obtained for a monopole antenna

6. REFERENCES[1] Jeffrey G. Andrews, et al., “What Will 5G Be?”, IEEE
Journal on Selected Areas in Communications, Vol. 32,
No. 6, pp.1065-1082, June 2014.
[2] R. B. Green et al., “Optically transparent antennas andfilters: A smart city concept to alleviate infrastructureand network capacity challenges,” IEEE Antennas
Propagation Magazine, vol. 61, no. 3, pp.37-47, June
2019.

Radiation efficiency η24

Simulated [%]Measured [%]73.0

68.0