978-1-6654-7962-2/22/$31.00 ©2022 IEEE

Single-Layered Reflectarray Antenna
with Branch Elements
Masayoshi Takao
Kanazawa Institute of Technology
7-1 Ogigaoka, Nonoichishi,
Ishikawa, 921-8501 Japanb1833012@planet.kanazawa-it.ac.jp

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

Shin-ichi Yamamoto
Mitsubishi Electric Corporation
5-1-1 Ofuna, Kamakura
Kanagawa, 247-0056 Japan
Yamamoto.Shinichi@dr.MitsubishiEle
ctric.co.jp

Yasuhiro Nishioka
Mitsubishi Electric Corporation
5-1-1 Ofuna, KamakuraKanagawa, 247-0056 Japan
Nishioka.Yasuhiro@bx.MitsubishiElect
ric.co.jp

Abstract—A reflectarray antenna (hereinafter referred to as"reflectarray") applies the reflection phase control function offrequency selective reflector to a plane reflector. Various beam
shapes can be formed by appropriately selecting the mirror
surface configuration and shape of the resonant elements. In thisstudy, the shape of the resonant elements of the reflectarray,
which changes the beam direction depending on thepolarization, is investigated.
Keywords—reflectarray antenna, polarization, grating lobe,element spacing, single layer antenna

I. INTRODUCTION
A reflectarray antenna [1] (hereinafter referred to as"reflectarray") has a plane reflector with resonant elements
periodically arranged at spacing d. It has been demonstrated
that a reflectarray with low-side-lobe and high-efficiency
characteristics can be designed using (1) for resonant element
spacing d, where the grating lobe does not propagate in the
dielectric material [2].

d1≤
λε r + sin θ(1)where λ is the wavelength corresponding to the maximum
frequency in the frequency band; εr is the dielectric constant;and θ is the maximum incident angle.
Using a resonant element spacing that satisfies condition(1), a reflectarray that changes the beam direction dependingon the polarization was investigated [3]. Consequently, itsatisfied all the requirements of the element; however, it led
to the issue of gain reduction owing to the multilayer structure.
Therefore, a single-layer element was considered to solve thisproblem [4]. The design difficulty of the element increased
significantly because the designable area of the polarization
was reduced by approximately half by the single-layeredstructure. Although independent phase control was achievedfor each polarization by changing the length of each of thethree line elements for one polarization, the phase change foreach polarization was approximately 270°, which could notcover the phase range of 360°.

Yusuke Kaimori
Kanazawa Institute of Technology
7-1 Ogigaoka, Nonoichishi,
Ishikawa, 921-8501 Japanb1714005@planet.kanazawa-it.ac.jp

In this study, we examined the resonant element shape of asingle layer. We demonstrated that by modifying the shape ofthe resonance element, we can achieve independent phase
control for each polarization while satisfying the 360°
reflection phase range for each polarization.
II. ELEMENT DESIGN
A. Element Requirements
In designing the elements, the frequency band was set to theKu band, as in a previous study [4]. Similarly, for the resonant
element spacing d, (1) was employed to prevent propagationof the grating lobes within the dielectric.
The requirements for the resonant elements to change thebeam direction according to the polarization are as follows.
(a) Phase-coverage range of 360° for each polarization.
(b) Independent phase control depending on polarization.
Therefore, we investigated a single-layer element thatsatisfies both of these above-mentioned conditions.
B. Model Design
The design model is illustrated in Fig. 1. The design
parameters of these elements are listed in table I, where λ0 is
the wavelength corresponding to the design frequency f0.
Furthermore, the thickness of the dielectric substrate was hA.
The element spacing d is denoted as PX and PY in the model
diagram for easy distinction of the directions. Essentially, d =PX = PY. Fig. 1 shows a top view of one of the cells in theelement model. The model consists of a dielectric layer,represented in green, on top of a metal plate, and a resonanceelement on top of the dielectric layer.
The order of change in the element shape is shown in Fig. 2,
using the element for H-polarization as an example. The
element length is extended, and the reflection phase ischanged in the order of ①–③ in Fig. 2. The same applies tothe element for V-polarization by replacing the element lengthℓB with ℓA for each step and rotating the entire element by 90°.
The resonance elements were designed to vary symmetricallywith respect to one cell to suppress the generation of crosspolarization components.

This study was supported by JSPS (20K04491).

389

10.2° when the H-polarization was changed by 360°.
Similarly, Fig. 4 shows that the phase change of the Vpolarization was 396° when the V-polarization was copolarized. In this case, the phase change of the H-polarization
was 8.51° when the V-polarization changed by 360°.

ℓA2

ℓB1

ℓA3

ℓA1/2

As shown above, a phase range of 360° was covered foreach polarization. The phase change of the orthogonal
polarization to the co-polarization was sufficiently small (lessthan 11°) to enable independent phase control for eachpolarization. Therefore, the proposed element shape satisfies
both conditions (a) and (b) for changing the beam direction
depending on the polarization.

ℓB3
ℓB2

PX

Reflection Phase [deg]H-polPY
Fig. 1. Element modelDESIGN PARAMETERS OF ELEMENTBandKuThickness hA

0.127λ0Dielectric constant εr

2.59

tanδ

0.0028Angle of incidence [deg]25Element spacing PX , PY0.394 λ0Line width w

①-300
①-400

②③-500-600
0.10.20.30.40.5B10.004 λ0〜0.354 λ0

Element length ℓA2 , ℓ

B20〜0.007 λ0

Element length ℓA3 , ℓB30〜0.173 λ00.6

0.7

0.8

0.9

10.9

1

Element length, ℓB [lambda]
Fig. 3. Reflection phase characteristic of H-polarization

0.004 λ0A1 , ℓℓB1-200

H-pol

Element length ℓ②0-100

0Reflection Phase [deg]TABLE I.

V-pol100③ ℓB30-100-200-300①-400②③-500-600
0ℓB2V-pol100

0.1

0.2

0.3

0.4

0.5

0.6

0.70.8Element length, ℓA [lambda]
Fig. 4. Reflection phase characteristic of V-polarization

Fig. 2. Variation of element shape

III. ANALYSIS RESULT

IV. CONCLUSION

Electromagnetic field analysis was performed for theproposed element geometry using ANSYS HFSS. We definedℓA = ℓA1 + 4ℓA2 + 4ℓA3 and ℓB = ℓB1 + 4ℓB2 + 4ℓB3 for the totalelement length ℓA and ℓB. For each of the V- and Hpolarizations, the total element length of the polarization
orthogonal to the main polarization (hereinafter referred to as
orthogonal polarization) was fixed at the maximum value ℓ =1.08λ0, and the total element length of the co-polarization ℓ
was varied in the range 0.004λ0 to 1.08λ0. The reflection phasecharacteristics of the H-polarization and V-polarization are
shown in Figs. 3 and 4, respectively. Areas ①–③, which are
divided by dotted lines in the graphs, correspond to thechanges in the element shape shown in Fig. 2. The blue areasin the graphs indicate the areas where the phase of the mainpolarization changes by 360°. Fig. 3 shows that when the Hpolarization is co-polarized, the phase change of the Hpolarization is 411°. The phase shift of the V-polarization was

This study demonstrated independent phase control and
360° phase region coverage for both polarizations by thearrangement of the branch elements. We plan to employ these
proposed elements to build a prototype reflectarray andperform measurements to verify the array utility.
REFERENCES
[1]
[2]
[3]

[4]

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J. Huang, J.A.Encinar, “Reflectarray Antennas,” Wiley, New Jersey,
2007.
Y. Fuji, et al., “High-efficiency and Low-side-lobe Reflectarray
Antenna,” ISAP, December, 2014.
M. Fukaya, R. Obata, S. Makino, H. Nakajima, M. Takikawa, “A Dualpolarized Stacked Reflectarray Antenna with Changing Beamdirection,” AP-S, July, 2020.
S. Takino, S. Shigemitsu, Y. Kaimori, S. Makino, “A Dual-polarized
Single Layer Reflectarray Antenna with changing beam-direction,”
IEICE Technical Report A･P2021-138, January, 2022 (in Japanese).