Feasibility Study on Circularly Polarized MACKEY
Michinori Yoneda(1), Keito Yokoe(1), Shigeru Makino(1), Kenji Itoh(1)(1)Kanazawa Institute of Technology,7-1 Ogigaoka, Nonoichishi, Ishikawa, Japan(b1812587@planet.kanazawa-it.ac.jp)
Abstract—A metasurface-inspired antenna chip (MACKEY),
which was developed in the KIT EOE laboratory and operates infree space and on a metal plate, was investigated. In this study,
we devised a MACKEY by varying the polarization fromconventional linear to circular.

I. INTRODUCTION
The metasurface-inspired antenna chip (MACKEY),
developed by the KIT EOE Laboratory)[1], is a robust antennathat is not affected by the surrounding metal. In this paper, wepropose a new model, MACKEY C-type (hereinafter referredto as "C-type"), by varying the polarization from conventional
linear to circular. The C-type is a square with a side length ofλ/2. The C-type is based on MACKEY II [2], which is athinner version of MACKEY, with an unbalanced feed using
an inverted L-shaped element.

In this study, we aim to achieve a voltage standing waveratio (VSWR) of less than 3 and an axial ratio characteristic ofless than 3 dB in both free space and on metal in the frequency
band of 2.4–2.5 GHz, which is the operating band of 2 GHz
Wi-Fi.

gggsL

ww=1

(1) Grid plate(2) Antenna plate(3) metal plate(b) Model diagram of C-type (circular polarization)
Fig. 1. Model diagram of antenna.

III. ANALYSIS OF C-TYPE
In this study, to investigate the possibility of circularpolarization by using MACKEY, power feeding was conductedunder ideal conditions of equal amplitudes and a 90° phasedifference. The analysis was performed by using the finite
element method on an electromagnetic field simulator (AnsysHFSS).Fig. 2 shows the VSWR and axial ratio characteristics
in free space and on the metal, achieved by the C-type analysis.
Fig. 2 indicates that the VSWR in free space and on metal andthe axial ratio characteristics in free space achieve the target;
however, the axial ratio characteristics on the metal are morethan 3 dB in the band around 2.5 GHz, indicating that thetarget is not achieved.

VSWR109876543212.3

2.4

2.5

2.6

Frequency[GHz]in_free_space on_metal(a) Model diagram of MACKEY II (linear polarization)

L=81.6

ll=28

s=9

10
9876543210

Axial Ratio[dB]

II. PROPOSAL FOR C-TYPE
Fig. 1 shows the model diagram of MACKEY II and the Ctype. MACKEY II, which radiates linearly polarized waves, isplaced orthogonally, and circularly polarized waves areradiated with a size of approximately λ/2 square by feedingpowers of equal amplitudes and a phase difference of 90° to thetwo feeding points. After orthogonalization, a grid plate isadded to provide symmetry to the antenna substrate. The
design values are optimized by considering the slit width andantenna position.

g=36.3

2.3

2.4

2.5

2.6

Frequency[GHz]in_free_space on_metal

Fig. 2. Characteristics of VSWR and axial ratioin free space and on metal.

10
987
6543
2
101098765432
1

VSWR

Two parasitic elements were added to the antenna plate toimprove the axial ratio by increasing the symmetry of theantenna structure. The addition of the parasitic elements wasterminated at a resistance of 50 Ω. The model diagram ispresented in Fig. 3. The VSWR and axial ratio characteristics
in free space and on the metal are depicted in Fig. 4. As shownin Fig. 4, the axial ratio characteristic improves to a value
close to 0 dB at all frequencies. In addition, the VSWR andaxial ratio characteristics in both the free space and on themetal meet the target.

2.3

2.4

2.5

2.6

Frequency[GHz]MeasureAnalysis

gs=4

Ls2.52.6

AnalysisAnalysis

Frequency[GHz]MeasureAnalysis(b) Characteristics of VSWR and axial ratio
on metalFig. 5. Characteristics of VSWR and axial ratioin free space and on metal.

ww=1g

MeasureAxial Ratio[dB]

Frequency[GHz]MeasureFeeding
point

2.4

Characteristics of VSWR and axial ratioin free10
space
10
9988
7
7
6
6
5
54
4
3
3
2
2
1
0
1
2.3 2.4 2.5 2.6
2.3 2.4 2.5 2.6

L=76.2ll=27

2.3

Frequency[GHz]

(a)

VSWRg

g=36.1

Axial Ratio[dB]

IV. CONSIDERATION OF PARASITIC ELEMENTS

Parasiticelements(1) Grid plate (2) Antenna plate (3) metal plate
Fig. 3. Model diagram of C-type with the two additional
parasitic elements.

VSWR

2.3

2.4

2.5

2.6

Frequency[GHz]in_free_space on_metal

Axial Ratio[dB]

1098
765
4
32
10

10
98
765
4
3
21

2.3

2.4

2.5

2.6

Gain in front
MeasureAnalysis
direction[dBi]in_free_space
4.04
4.90
on_metal
4.67
6.01
Fig. 6. Radiation pattern and frontal gain at 2.45 GHz.

Frequency[GHz]in_free_space on_metal

Fig. 4. Characteristics of VSWR and axial ratioin free space and on metal.

V. COMPARISON OF ANALYZED AND MEASURED VALUES FOR
C-TYPE
Measurements were performed using the model displayedin Fig. 3. The VSWR and axial ratio characteristics in freespace and on the metal are shown in Fig. 5, and the radiation
pattern and frontal gain at 2.45 GHz are presented in Fig. 6. Fig.
5 shows that the measured VSWR is slightly higher than theanalytical value for both the free space and metal. In case ofthe widening of the VSWR, Fig. 6 shows that the gain in thefrontal direction is lower than the analytical value, indicatingthat the loss of the antenna is larger and that of the reflectedwave is smaller. The reason for the higher axial ratio
characteristics is that the antenna shifts slightly from the front
at the time of measurement. As shown in Fig. 6, the gain ofcross-polarization increases when the angle is shifted slightly
from the front. Because the axial ratio depends on the level ofdifference between the gain of the main polarization and crosspolarization, the axial ratio characteristics may have becomelarger owing to the effect of this cross-polarization.

VI. CONCLUSION
In this paper, we present a feasibility study of a new model
for radiating circularly polarized waves based on thepreviously studied linearly polarized waves. We achieved a
VSWR of less than 3 and an axial ratio characteristic of lessthan 3 dB at 2.4–2.5 GHz. In the future, we will further
improve the characteristics of the system and study how tosimplify the feed power, for example, by using only one
feeding point.
Acknowledgment
This work was supported by JST CREST Grant Number
JPMJCR20Q1, Japan.
REFERENCES[1]

T.Moroya, et al., “AMC-inspired small antenna MACKEY,”
IEICE. Trans. Commun., vol. J99-B, no. 9, pp. 786–794, September
2016.
[2]
K. Miyashita. et al., “Feasibility study of an unbalanced MACKEY
type R with enhanced robustness on metal,” in ISAP 2021, October 2021.