Feasibility study of an unbalanced MACKEY type R
with enhanced robustness on metal
Keisuke Miyashita，Shigeru Makino，Kenji ItohKanazawa Institute of Technology
7-1 Ogigaoka, Nonoichishi
Ishikawa, 921-8501 Japanb1613494@planet.kanazawa-it.ac.jp

I. INTRODUCTION
An electrically small antenna named meta-surface-inspired
antenna chip developed by KIT EOE Laboratory (MACKEY)
basic-type (below: basic type), which is sufficiently robust to ametal object, is proposed [1]. In addition, MACKEY II isproposed as a reduced-thickness model of the basic type [2].
Fig. 1 shows a MACKEY II back-feed type, which isdesigned for the Wi-Fi 2.4 GHz band. The model has a threelayered structure comprising a grid plate, antenna plate, andmetal plate in descending order, with a dielectric filled in
between, as shown in Fig. 1. Impedance matching is performed
based on the grid width g and antenna length ℓ. Fig. 2 depicts
the measurement results of the VSWR characteristics in freespace and on metal. The measurement results in Fig. 2 show that
the MACKEY II back-feed type operates in both free space andmetal.
AMC
substrate

h=1.0mmεr=2.58tanδ=0.0014
εr=2.58tanδ=0.0014①②③68mm2.0mm

t=2.0mm

Antennasubstrate

Bird’s eye view

Feeding point
Side viewg=33.75mm

L=2×g + s=68mm

w=1mm

W=30mmg=33.75mm

L=2×g + s=68mmℓ=26mmFeeding points=0.5mm①Grid plate②Antenna plate③Metal plate
Metal plate
DielectricFig. 1. Model diagram of the MACKEY II back-feed type10987654321The basic type and MACKEY II are balanced types withdipole antennas as the feed elements, causing difficulties inconnecting them with unbalanced lines and chips. An
unbalanced MACKEY that can be easily connected to an
unbalanced system using an inverted L-shaped antenna as a feedelement, is proposed. In addition, the S-parameter measurement
method [3] is used in a balanced MACKEY because of its twoport feed, which increases the measurement time. On the other
hand, an unbalanced MACKEY has only one port and can bemeasured using a coaxial connector, shortening themeasurement time compared with the conventional S-parameter
method.
Fig. 3 shows the designed unbalanced MACKEY model.
The structure comprises a grid plate, antenna plate, and metal
plate, in descending order, similar to MACKEY II. Moreover, athrough-hole is provided to enable back feeding in the model torealize the inverted L-shaped antenna as a feed element. In thismodel, the AMC substrate thickness and antenna position werefixed at 2 mm and 1 mm, respectively. As the impedance
matched with the grid width g and antenna length ℓ, thethickness, length, and width of the model were 4 mm, 30 mm,and 69.3 mm, respectively. In terms of the model size, the results
were generally consistent with those of the balanced MACKEY
type.
Fig. 4 shows the measurement results of the VSWR
characteristics of the proposed model. The measurement resultsof MACKEY II back-feed type are also shown for comparison.
Fig. 4 indicates that the proposed unbalanced MACKEY
operates both in free space and on metal, similar to theconventional model. In addition, there is no significant
difference in the bandwidth compared to that of the balanced
type, which indicates that the robustness of the unbalanced
MACKEY to a metal object.
Antennasubstrate
AMCsubstrate

h=1.0mm①

εr=2.58tanδ=0.0014
εr=2.58tanδ=0.0014②③69.3mm

2.0mm

Keywords— MACKEY WiFi-2GHz, meta-surface-inspired
antenna, AMC substrate, unbalanced, robustness.

II. NOVEL UNBALANCED MACKEY WITH INVERTED L
ANTENNA AS FEED ELEMENT

t=2.0mm

Abstract— A meta-surface-inspired antenna chip developed byKIT EOE Laboratory (MACKEY), which operates not only in freespace but also on a metal plate, is proposed. In this study, anunbalanced MACKEY using an inverted L-shaped antenna as thefeed element is proposed. In addition, to improve thecharacteristics of unbalanced MACKEY on metals, an unbalanced
MACKEY type R is proposed with an optimized antenna width.

Bird’s eye view

Feeding point

VSWR

Side view
L=2×g + s=69.3mm

w=1mm

g=34.4mm g=34.4mm

in_free_space
on_metalℓ=29.9mm

L=2×g + s=69.3mm

Feeding points=0.5mm

22.1

2.2

2.3

2.4

2.5

2.6

2.7

2.8

2.93

Frequency[GHz]Fig. 2. VSWR characteristics of the MACKEY II back-feed typeIn this study, an unbalanced MACKEY that can be connected to devices
in unbalanced systems, and an unbalanced MACKEY type R with improved
characteristics on metal.

①Grid plate②Antenna plate
Copper③Metal plate

NPC-F260A

Fig. 3. Model diagram of the unbalanced MACKEY II

1098
7654
32
1

VSWR

VSWR

10987654
3
21

back-feed_air
back-feed_metal
unbalanced_air
unbalanced_metal

2

2.1

2.2

2.3

2.4

2.5

2.6

2.7

2.8

2.9

23

in_free_space

Fig. 4. VSWR characteristics of the two models.

3

on_metalFig. 6. VSWR characteristics of the unbalanced MACKEY type R

III. IMPROVING THE ROBUSTNESS OF UNBALANCED MACKEY
In Section 2, the unbalanced MACKEY as an antenna withrobustness on metal, which works both in free space and on
metal, is demonstrated. However, because of a frequency shift
in metals compared with that in free space, it does not fully
satisfy the Wi-Fi 2.4 GHz bandwidth on metal in themeasurement results. A previous study reported that the effecton metal could be reduced by varying the vertical length of theantenna, with the grid vertical width remaining fixed in the basic
type [4]. Therefore, a similar experiment was conducted tofurther enhance the robustness of MACKEY on metal.
In this study, the grid vertical width gw was fixed at 30 mm,
and the antenna vertical length W was increased from 30 mm to50 mm in increments of 2 mm. The operating bandwidth wascalculated for each antenna width, and the antenna width withthe widest operating bandwidth was investigated. The operatingbandwidth is defined as the relative bandwidth on metal minus
the frequency shift between free air and metal, and wider theoperating bandwidth, wider the bandwidth that can be used bothin free space and on metal.
Fig. 5 shows the operating bandwidth of the unbalanced
type; although it increased with an increase in W, it decreases
slightly after increasing to a certain level. In addition, it can beseen from the figure that the antenna width W, which has thewidest operating bandwidth, is 40 mm.
Fig. 6 shows the analysis results of the VSWR characteristics
at W = 40 mm, which show only a negligible frequency shift in
free space or on metal. However, it does not fully satisfy the WiFi 2.4 GHz band owing to the overall narrower bandwidth.
Fig. 7 shows the analysis results of radiation patterns for W= 50 mm, which show that the radiation is sufficient, both in freespace and on metal.
Operating bandwidth[%]2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9Frequency[GHz]Frequency[GHz]

4
3.8
3.6
3.4
3.2
3
2.8
2.6
2.4
2.2210X2.45GHzX
1000-10-10-20YZ-20ZYX
Theta_in_free_space
Theta_on_metal

Fig. 6. Radiation pattern of the unbalanced MACKEY type R

IV. CONCLUSION
In this paper, an unbalanced MACKEY, which can be easily
connected to unbalanced devices by using an inverted L antennaas the feed element, and an unbalanced MACKEY type R, which
has enhanced robustness on metal, are proposed.
The proposed unbalanced MACKEY with an inverted Lantenna as the feed element performs comparably with thebalanced-type conventional model , and works both in free spaceand on metal.
In addition, the proposed unbalanced MACKEY type R is an
improved version of the unbalanced MACKEY, with betterrobustness against metal owing to the varying antenna verticallengths. In the model, the antenna vertical lengths varied from30 mm to 50 mm, and the operating bandwidth was the highest
for W = 40 mm. The unbalanced MACKEY type R designedwith W = 40 mm showed only a negligible frequency shift in
free space and on metal, and was comparable to the conventionalmodel in terms of radiation pattern and gain.
ACKNOWLEDGMENT
This work was supported by JST CREST Grant Number
JPMJCR20Q1, Japan.
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50

[3]

[4]

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