2022 IEEE International Workshop on Electromagnetics: Applications and Student Innovation Competition (iWEM), Narashino,
Japan

Optimization of Axial Ratio Characteristics ofCircularly Polarized MACKEY

Michinori Yoneda
Department of Electrical andElectronic Engineering
Kanazawa Institute of Technology
Nonoiti, Isikawa, Japanb1812587@planet.kanazawa-it.ac.jp

Keito Yokoe
Department of Electrical andElectronic Engineering
Kanazawa Institute of Technology
Nonoiti, Isikawa, Japanb1995149@planet.kanazawa-it.ac.jp

Shigeru Makino
Department of Electrical andElectronic Engineering
Kanazawa Institute of Technology
Nonoiti, Isikawa, Japanmakino@neptune.kanazawa-it.ac.jpKenji Itoh
Department of Electrical andElectronic Engineering
Kanazawa Institute of Technology
Nonoiti, Isikawa, Japanitoh.kenji@neptune.kanazawa-it.ac.jp
Abstract—This research aimed to convert linear
convectional polarization to circular polarization using anunbalanced the metasurface-inspired antenna chip developedby the KIT EOE Laboratory (MACKEY). Moreover, we aimed
to achieve a Voltage Standing Wave Ratio (VSWR) of less than
three and axial ratio of less than 3 dB in free space and on metal
at 2.4–2.5 GHz. For this purpose, we proposed a circularly
polarized MACKEY C4 antenna with four grid plates. We
achieved our goal by examining the slit width and antenna
position.

were conducted to improve the axial ratio, using the slit widthand feeding element position.

Keywords—MACKEY, Circular Polarization, 2.45 GHz

I. INTRODUCTION(a)

Linear polarization MACKEY Ⅱ(b)Circular polarization MACKEY C4The metasurface-inspired antenna chip developed by theKIT EOE Laboratory (MACKEY) [1] was devised as a robust
antenna that is not affected by surrounding metals. In thisreport, we propose a new model, MACKEY type-C4(hereinafter referred to as "MACKEY C4"), based on
MACKEY II [2], which is a thinner version of MACKEY anduses an inverted L element for unbalanced power supply,
along with four grid plates to change the polarization fromconventional linear to circular.
II. PROPOSAL FOR MACKEY C4
Fig. 1 shows a model diagram of MACKEY II, whichradiates linearly polarized waves, and MACKEY C4, whichradiates circularly polarized waves. MACKEY C4 combines
MACKEY II orthogonally and feeds power with equal
amplitude and a phase difference of 90° to the two feed points
to radiate circularly polarized waves with an antenna size of
approximately λ/2 square. After orthogonalization, a gridplate is added to provide symmetry to the antenna plate. The
model in Fig. 1 shows the optimal design values considering
the slit width and feeding element position.
In this study, we aim to achieve a Voltage Standing Wave
Ratio (VSWR) of less than three and an axial ratio of less than
3 dB in the 2.4–2.5 GHz range, which is the bandwidth of WiFi 2 GHz, both in free space and on metal.
In the initial model of MACKEY C4, the axis-ratio
characteristic was more than 3 dB. Therefore, two studies
This work was supported by JST CREST (Grant Number
JPMJCR20Q1), Japan.

978-1-6654-3238-2/22/$31.00 ©2022 IEEE

Fig. 1. Model diagram of antenna

III. EXAMINING OF MACKEY C4
In this study, to investigate the possibility of circularpolarization by MACKEY, power feeding was performed
under ideal conditions of equal amplitude and a phasedifference of 90°. The analysis was performed using anelectromagnetic simulator (ANSYS, HFSS) based on thefinite-element method.
The effects of the slit width were examined by varying theslit width. Fig. 2 shows the change in the maximum value ofthe axial ratio and relative bandwidth of the VSWR when theslit width is varied. The axial ratio improved slightly as theslit width increased on the metal. The VSWR became
narrower as the slit width increased.

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2022 IEEE International Workshop on Electromagnetics: Applications and Student Innovation Competition (iWEM), Narashino,Japan

The position of the power feed element was examined bymoving it from the center of the grid plate to the inside oroutside of the substrate. The width of the slit used in thisstudy was 9 mm. Fig. 3 shows the change in the maximum
value of the axial ratio and relative bandwidth of the VSWR
when the feeding element was moved. The axial ratios wereimproved by moving the feeding element at a certain distance.
The bandwidth of the VSWR did not change as the element
moved.
Fig. 4 shows the maximum value of the axial ratio and thechange in the specific bandwidth of the VSWR when thefeeding element position was optimized for each slit width.
Fig. 4 indicates that the axial ratios in free space and on metal
are less than 3 dB for each slit width, and the smaller the slitwidth, the wider is the specific bandwidth.

The VSWR and axial ratio in free space and on metal,
obtained by the analysis of the optimized MACKEY C4model in Fig. 1, are shown in Fig. 5; the radiation patterns
are shown in Fig. 6. As parameters during optimization, theslit width was 3 mm and the feed element was moved 2.5
mm inside the substrate.
Fig. 5 shows that the VSWR is less than three in therange of 2.36–2.5 GHz, both in free space and on metal,
which is wider than the target range of 2.4–2.5 GHz. The
axial ratio is less than 3 dB at all frequencies, indicating thatthe target has been achieved. Fig. 6 indicates that the crosspolarization along the x-axis, which is the frontal direction,is considerably smaller, and the realized gain of the mainpolarization is 5.61 in free space and 6.82 on the metal.

3579slit[mm]in_free_space on_metal

1110987654321Axial Ratio[dB]109876543210VSWR

relative band with of VSWR

109876543210

Axial Ratio[dB]109876543210

IV. ANALYSIS RESULTS FOR MACKEY C43579slit[mm]in_free_space on_metal

112.3

2.4
2.5
Frequency[GHz]in_free_space
on_metal1

relative band with of VSWR

Axial Ratio[dB]-3-2-10
Feeding element position[mm]in_free_space on_metal

109876543210-4357911slit[mm]in_free_space
on_metal

109876543210

relative band with of VSWR

Axial Ratio[dB]109876543210310 Z

00-10

LHCP_in_free_space
LHCP_on_metal-20

Y

RHCP_in_free_space
RHCP_on_metal

LHCP_in_free_space
LHCP_on_metal

X

RHCP_in_free_space
RHCP_on_metal

Fig. 6. Radiation pattern

V. CONCLUSION
This study presents a basic study of a new model forradiating circularly polarized waves from linearly polarizedwaves, an aspect that has been studied in the past. The targetof achieving a VSWR of less than three and an axial ratio ofless than 3 dB was accomplished by adjusting the slit widthand feeding element position in a model with a four-grid platestructure. In the future, we could investigate simpler ways tofeed power, such as using a single feeding point.

57911slit[mm]in_free_space in_free_space

Fig. 4. Change in the maximum values of the axial ratio and relative
bandwidth of the VSWR.

XZ Plane

X-10-20-3-2-1
01
Feeding element position[mm]in_free_space on_metal

Fig. 3. Change in the maximum value of the axial ratio and relative
bandwidth of the VSWR when the feeding element was moved.

2.4
2.5
2.6
Frequency[GHz]in_free_space
on_metal

XY Plane
10-4

2.3

Fig. 5. VSWR and axial ratio

Fig. 2. Change in the maximum value of the axial ratio and relative
bandwidth of the VSWR when the slit width was varied
109876543
2
10

2.6

REFERENCES
[1]

[2]

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T. Moroya, et al., “AMC-inspired small antenna MACKEY,”
IEICE. Trans. Commun., vol. J99-B, no. 9, pp. 786–794, September
2016.
K. Miyashita, S. Makino, and K. Itoh, “Feasibility study of an
unbalanced MACKEY type R with enhanced robustness on metal,” in
ISAP 2021, October 2021.