2022 International Workshop on Antenna Technology (iWAT)

A Method for Reducing the Size of MACKEY II
Antenna Using Slits
Kota Hakamata
Kanazawa Institute of Technology
7-1 Ogigaoka, Nonoichishi,
Ishikawa, 921-8501 Japanb1714005@planet.kanazawa-it.ac.jp

Kleisuke Miyashita
Kanazawa Institute of Technology
7-1 Ogigaoka, Nonoichishi,
Ishikawa, 921-8501 Japanb1613494@planet.kanazawa-it.ac.jp

Shigeru Makino
Kanazawa Institute of Technology
7-1 Ogigaoka, Nonoichishi,
Ishikawa, 921-8501 Japanmakino@neptune.kanazawa-it.ac.jp

Kenji ItohKanazawa Institute of Technology
7-1 Ogigaoka, Nonoichishi,Ishikawa, 921-8501 Japanitoh.kenji@neptune.kanazawa-it.ac.jp
10Abstract— A metasurface-inspired antenna chip developed
by KIT EOE Laboratory (MACKEY), which operates in freespace and on a metal plate, was investigated in this study. We
proposed a method for reducing the size of MACKEY II in the920 MHz band to the size of a credit card.

98VSWR

7Keywords— MACKEY, RFID 920 MHz, metasurface inspired
antenna, artificial magnetic conductor substrate

I. INTRODUCTION

t=2.0mmFig. 1 shows the MACKEY II back feed type model
designed for the radio frequency identification (RFID) bandof 920 MHz. The model is a three-layer structure consisting ofan antenna plate, a grid plate, and a metal plate in descendingorder, with a dielectric material separating them. Impedance
matching was performed based on the grid width ℊ andantenna length ℓ. Fig. 2 shows the measurement results of thevoltage standing wave ratio (VSWR) characteristics in a freespace and on a metal plate. The measurement results in Fig. 2demonstrate that the MACKEY II back feed type antennaoperates both in free space and on a metal plate.

tt=1.0mm

ε=2.58tanδ=0.0014
ε=2.58tanδ=0.0014①Antenna
substrate
AMC substrate②③Feeding point=97.85mm =97.85mm①Grid plate

w=1mm

L=2× + s=196.2mm
W=50mms=0.5mm6543

An electrically small antenna, known as MACKEY basictype, which is sufficiently robust to interact with metalobjects, has been developed [1]. In addition, a model with
reduced thickness, MACKEY II has been proposed [2].

h=1.0mm

leito Yokoe
Kanazawa Institute of Technology
7-1 Ogigaoka, Nonoichishi,Ishikawa, 921-8501 Japanb1995149@planet.kanazawa-it.ac.jp

In free space

210.88 0.89

On metal
0.90.91 0.92 0.93 0.94 0.95 0.96

Frequency[GHz]Fig. 2. VSWR characteristics of the MACKEY II antenna.

II. PROPOSED MINIATURIZED MACKEY II ANTENNA
Fig. 3 shows the current distribution on the grid substrate.
The MACKEY radiates radio waves from the edge of thelattice plate, where the current flows strongly [1]. In theconventional MACKEY antenna, the length L of the grid plateedge is λ/2 and depends on the designed frequency. Thus, thebase length L of the 920 MHz band MACKEY II is 200 mm,
which is large. We reduced this length by introducing slits
along the length of the grid plate to ensure a current path of
λ/2 or more, even with a shorter physical length.
Fig. 4 shows the principle of miniaturization. By
introducing slits along the long sides of the grid plate, thecurrent path (blue lines in Fig. 4) was extended in ameandering pattern. This ensured electrical securing of thecurrent path of λ/2 or more, even with a reduced physicallength. The MACKEY II design with the proposed structureis designated as MACKEY II type H.

ℓ=69mm②Antenna plate

L=2× + s=196.2mm

Feeding pointCopper
NPC-F260A③Metal plate
Fig. 1. Model diagram of the MACKEY II antenna

978-1-6654-9449-6/22/$31.00 ©2022 IEEE

Fig. 3. Current distribution on the grid substrate at 920 MHz.

231

2022 International Workshop on Antenna Technology (iWAT)

L＜ λ/2

Cut N slits in thegrid plate.

IV. ANALYSIS RESULTS AND DISCUSSIONS

Fig. 4. Miniaturization principle

III. CONSIDERATIONS FOR MINIATURIZATION
Fig. 5 shows the model diagram of the MACKEY II type
H antenna. In this study, the substrate length L and height W
were fixed at 80 mm and 50 mm, respectively, as the expected
size is that of a card. The relationship between the base length
L and the design parameters is expressed in (1).
L=2*tg+4*ℊm+s(1)In Eq. (1), L was fixed at 80 mm, and the dielectric length(tg) was obtained by determining the metal length (ℊm) and slit
width (s). The lowest resonant frequency for the conventional
type H was 880 MHz for ℊm≈10mm [3]. However, since theantenna design is done at 920 MHz, we thought it would bepossible to design the antenna with a larger slit width s and slit
spacing width hg. Therefore, we analyzed two patterns fromthe conventional type H, one in which only s is increased andthe other in which only hg is increased.
Fig. 6 shows the relationship between ℊm and theresonant frequency. The black lines represent the conventional
type H (hg=4.0mm and s=0.5mm), the red lines represent thecase where only s is increased from the conventional type H(hg=4.0mm and s=1.8mm) and the green lines represent thecase where only hg is increased from the conventional type H(hg=4.7mm and s=0.5mm). As expected, increasing s and hg
shifted the resonance frequency toward the high-frequency
side. Also, the lowest resonant frequency is at ℊm≈10mm for
all three models.
t=2.0mmX①h=1.0mm

ZY②
Feeding point③Side view

Bird's-eye view
L=80mmFeeding pointt=2.0mm

htg

w=1mm

W=50mm

L=2× + s=80mm

The analyzed MACKEY II type H with larger s or hg andconventional MACKEY II type H are compared in thissection. Type H is analyzed according to the specifications
indicated by the blue circle in Fig. 6. Fig. 7 shows the designed
type H model with L × W = 80 × 50 mm, and the model volume
is reduced to approximately 40% of that of the MACKEY II.
Table I shows the parameters for ℊm, ℓ and ℊ. The sum of thecurrent paths of the grid plate is approximately 170 mm, whichis almost equal to that of the length of MACKEY II, as shownin Fig. 1. Since the stacking structure of type H is identical tothat of MACKEY II, the feed is supplied at the back of themodel via mounted holes. The VSWR characteristics andspecific bandwidth in free space are shown in Fig. 8 and Table
II, and those on metal are shown in Fig. 9 and Table III,respectively. The black lines represent the conventional type
H (hg=4.0mm and s=0.5mm), the red lines represent the casewhere only s is increased from the conventional type H(hg=4.0mm and s=1.8mm) and the green lines represent thecase where only hg is increased from the conventional type H(hg=4.7mm and s=0.5mm). Bandwidths for all three models
were generally consistent. However, the shift on the metal wasslightly smaller only when s was increased. The radiation
patterns and gains are shown in Fig. 10 and Table IV,
respectively. The black lines represent the conventional type
H (hg=4.0mm and s=0.5mm), the red lines represent the casewhere only s is increased from the conventional type H(hg=4.0mm and s=1.8mm) and the green lines represent thecase where only hg is increased from the conventional type H(hg=4.7mm and s=0.5mm). The radiation patterns appear at
the frequency where the VSWR is the lowest. The type H witha larger s or hg has a higher gain than the conventional type
H. The frequency response of the radiation efficiency is shownin Fig. 11. The black lines represent the conventional type H(hg=4.0mm and s=0.5mm), the red lines represent the casewhere only s is increased from the conventional type H(hg=4.0mm and s=1.8mm) and the green lines represent thecase where only hg is increased from the conventional type H(hg=4.7mm and s=0.5mm). The type H with a larger s or hg
has a higher radiation efficiency than the conventional type H.
Based on this result, s and hg must be further increased toobtain high gain with the type H. In other words, MACKEY
needs to be made even larger.

ℓ=40mm①h=1.0mm②Antenna plate③Metal plate

NPC-F260A

prepreg

CopperFeeding point
Side view

Bird's-eye view

L=80mm

L=2× + sh

1000
990
980
970
960
950
940
930
920
910
900
890
880
870

W=50mmFig. 5. Model diagram of the type H antenna

Resonant frequency [MHz]ZY③s①Grid plate

X②

w=1mm

L ≒ λ/2ℓFeeding points①Grid plate

Copper②Antenna plate③Metal plate

prepreg

NPC-F260A

Fig. 7. Type H analysis model
TABLE I.
4.5

5.5

6.5

7.58.5hg=4.0mm
s=0.5mm

9.5 10.5 11.5 12.5 13.5 14.5 15.5

Metal width
hg=4.0mm_s=0.5mm[mm]

hg=4.0_s=1.8mm

DESIGN PARAMETERS

hg=4.7_s=0.5mm

Fig. 6. Relationship between gm and resonant frequency at L = 80 m232

hg=4.0mm
s=1.8mmhg=4.7mm
s=0.5mm

[mm]

13.65

9.509.90ℓ [mm]

41.1

39.3

39.7[mm]

39.75

39.1039.75

2022 International Workshop on Antenna Technology (iWAT)TABLE IV.

10987654321Analysis

COMPARISON OF GAINS

hg=4.0mm
s=0.5mmhg=4.0mm
s=1.8mm

In free space On metal

0.90.91hg=4.0mm_s=0.5mm

0.92
0.93
Frequency[GHz]hg=4.0mm_s=1.8mm

Radiation Efficiency

VSWR

Gain [dBi]0.94hg=4.7mm_s=0.5mm

-1.58

-0.23

10.9
0.8
0.7
0.60.5
0.4
0.3
0.2
0.1
0.86 0.88

hg=4.0mm_s=0.5mmBANDWIDTHS OF TYPE H IN FREE SPACE

Fractional bandwidth [%] hg=4.0mm(VSWR≦3)
s=0.5mm

Analysis0.613

hg=4.0mm
s=1.8mmhg=4.7mm
s=0.5mm

0.637

0.646

On metal In free space On metal

-1.25

-0.05

-1.20

0.9 0.92 0.94 0.96 0.98
Frequency[GHz]Fig. 8. VSWR characteristics of type H in free space
TABLE II.

In free spacehg=4.7mm
s=0.5mmhg=4.0mm_s=1.8mm

0.37

1

hg=4.7mm_s=0.5mm

Fig. 11. Frequency characteristics of the radiative efficiency of Type H

V. CONCLUSION
In this study, a MACKEY II type H antenna wasproposed to reduce the length of MACKEY II. In type H, thecurrent path was extended by introducing slits on the grid
substrate, which is the radiating element. From theevaluation of the MACKEY II type H structure, two models
with larger slit width s or slit spacing width hg from theconventional MACKEY II H model were examined. Type H
with larger spacing width hg and slit width s has a higher
gain than the conventional type H, although the bandwidth is
not much different. Furthermore, to make MACKEY
wideband and high-gain, the antenna size must be increased.

VSWR

10987654321

ACKNOWLEDGMENT

0.90.91
0.92
0.93
Frequency[GHz]hg=4.0mm_s=0.5mm

hg=4.0mm_s=1.8mm

0.94This work was supported by JST CREST, Japan (Grant
Number JPMJCR20Qa).

hg=4.7mm_s=0.5mm

PEFERENCES

Fig. 9. VSWR characteristics of type H on metal
TABLE III.

[1]

BANDWIDTHS OF TYPE H ON METAL

Fractional bandwidth [%] hg=4.0mm(VSWR≦3)
s=0.5mm

Analysishg=4.0mms=1.8mm

hg=4.7mm
s=0.5mm0.423

0.4110.432

XY plane
XZ plane
In free space 10 Z
10 XXZY

50-5-10-15-20Y

50-5-10-15-20

[2]

[3]X

hg=4.0mm_s=0.5mm

hg=4.0mm_s=1.8mm

XY plane

hg=4.7mm_s=0.5mm

10 X
50-5-10-15-20On metalY

XZ plane
10 Z

50-5-10-15-20

X

Fig. 10. Radiation Patterns of Type H

233

T. Moroya et al., “AMC inspired small antenna MACKEY,” IEICE
Trans. Commun., vol. J99-B, no. 9, pp. 786–794, 2016.
K. Miyashita et al., “MACKEY II with reduced thickness by using anew structure,” in Proc. IEEE International Symposium on Antennasand Propagation and North American Radio Science MeetingAPS2020, Jul. 2020, pp. 599–600, 2020..
K. Hakamata et al., “Development of MACKEY II type H miniaturizedusing slits,” in 2021 International Conference on Emerging
Technologies for Communications, Dec. 2021, P3-1