scispace - formally typeset
Search or ask a question
Journal ArticleDOI

A High-Efficiency Conformal Transmitarray Antenna Employing Dual-Layer Ultrathin Huygens Element

01 Feb 2021-IEEE Transactions on Antennas and Propagation (IEEE)-Vol. 69, Iss: 2, pp 848-858
TL;DR: In this paper, a high-efficiency conformal transmit array with ultrathin dual-layer Huygens element is developed, which consists of "I" shape patches for magnetic response and "T" shape stubs for electric response printed on two metal layers of a single substrate with only 0.5 mm thickness.
Abstract: A high-efficiency conformal transmitarray with ultrathin dual-layer Huygens element is developed. The element consists of “I” shape patches for magnetic response and “T” shape stubs for electric response printed on two metal layers of a single substrate with only 0.5 mm thickness ( $\lambda _{0}$ /60 at 10 GHz). By tuning the magnetic and electric responses, the transmitting phase of the element can be changed. Eight elements are designed to cover quantized 360° phase range with a maximal 1.67 dB loss. Then, the proposed elements are employed in a small conformal transmitarray design. To improve the antenna efficiency, the elements’ dimensions are calculated by considering the oblique incidence effects. Finally, a cylindrically conformal transmitarray with a larger aperture size is simulated, fabricated, and measured. It can achieve a measured gain of 20.6 dBi with a 47% aperture efficiency.

Summary (2 min read)

Introduction

  • By tuning the magnetic and electric responses, the transmitting phase of the element can be changed.
  • Significant research efforts have been devoted to reduce the thickness of the elements in order to reduce the entire profile of transmitarrays and/or make them attractive to conformal designs.
  • It should be noted that although using high dielectric substrate may be able to reduce the thickness of the array element, antenna efficiency will be significantly affected due to the losses and the total cost of the array will be increased.
  • In addition, there are some two-layer Huygens elements [29-30] that can introduce the electric and magnetic currents on two metal layers separately.
  • Compared with fully planar structures [27-28], this makes it more difficult to assemble a large surface.

A. Huygens Surface Theory

  • As shown in Fig. 1(a), when the incidence wave impinges on a Huygens surface, both the surface electric current Js and the magnetic current.
  • Ms would be induced, resulting in reflection and transmission waves which depend on the electric and magnetic current densities.
  • The Huygens surface can be analyzed from electric and magnetic sources separately, and the generated waves from two sources in z<0 and z>0 regions are shown in Fig. 1(b).
  • It can be seen from (15) and (16) that the electric and magnetic surface impedances are related to the transmitting phase.

B. Element Synthesis

  • The ‘I’ shape patches on the centre of top and bottom layers have exactly the same dimensions.
  • For many three-layer Huygens element, the metal traces on the first and third layers are used to generate a current loop to be equivalent to a magnetic dipole, while the trace in the middle layer is for introducing an electric dipole.
  • Then, the ‘T’ shape stubs will be designed to control the electric response.
  • It cannot be continuously changed when varying only one or two dimensions of the elements.

PROPERTIES OF HUYGENS ELEMENTS

  • Floquet ports with master–slave boundaries of 3D electromagnetic (EM) simulation software HFSS is used for the simulation.
  • Wz values would be tuned for magnetic response, while Sz and Gz are set as 2.3 mm and 1.7 mm, respectively, for simulation simplicity.
  • When one parameter is studied, the other two are kept unchanged as listed in Table Ⅱ. As shown in Fig. 3 (a), Zm curve moves to lower band as Wz increases, which provides a higher capacitance between ‘I’ shape patches of two adjacent elements.
  • As the developed elements use two metal layers to mimic a Huygens element and the substrate is lossy, small transmission loss is expected.
  • Small variations on the phase values are made to lower the loss.

TABLE Ⅲ DIMENSIONS OF ELEMENT 4 WITH DIFFERENT SUBSTRATE THICKNESS

  • This is due to the fact that the balanced condition between electric and magnetic responses is broken when the thickness of the substrate is reduced too much.
  • To verify the feasibility of the Huygens elements designed above, a small cylindrically conformal transmitarray is constructed with 10×11=110 elements, and its contour is provided in Fig.

PROPERTIES OF ELEMENT 1 UNDER DIFFERENT OBLIQUE INCIDENCE ANGLES

  • For elements in Zones 2-5, their dimensions are re-designed for each corresponding angle.
  • The unfolded transmitting surface was fabricated using standard PCB technology on low-cost Wangling F4B substrates (Dielectric Constant 3.55, tanδ = 0.0027).
  • For the measured results, the maximum gain is at 9.95 GHz with the value of 20.6 dBi, corresponding to a 47% antenna efficiency.
  • The measured cross-polarization levels for two planes are lower than -15 dB.

COMPARISON OF PROPOSED DESIGN WITH REFERENCED TRANSMITARRAYS

  • The slight beam tilt and the discrepancy on the realize gains can be mostly attributed to the fabrication inaccuracies in the 3D printed cylindrical frame that have effects on the curvature of the transmitting aperture.
  • Furthermore, there would be some alignment errors and the low-cost PCB board may have a varied dielectric constant from the datasheet.
  • The authors compare the results of the developed work with those of other transmitarrays with thin elements, as given in Table Ⅴ.
  • It can be seen that the proposed one has the thinnest structure while a very high aperture efficiency.

V. CONCLUSION

  • In order to meet the low profile demand on array elements for conformal transmitarray design, Huygens metasurface theory is employed in this work to achieve both ultra-thin array element and a high aperture efficiency.
  • The developed Huygens element consists of two metal layers with an entire thickness of 0.5 mm (λ0/60 at 10 GHz) and without any via.
  • By tuning magnetic and electric responses properly, eight elements are designed to cover quantized 360o phase range with a maximal 1.67 dB loss.
  • Based on those elements, a small conformal transmitarray is constructed, where, oblique incidence on the array aperture is considered to enhance the antenna’s performance.
  • Finally, a cylindrically conformal transmitarray with a larger aperture size is simulated and fabricated with a 20.6 dBi measured gain and a 47% aperture efficiency.

Did you find this useful? Give us your feedback

Figures (17)

Content maybe subject to copyright    Report

A High-Efficiency Conformal Transmitarray Antenna
Employing Dual-Layer Ultra-Thin Huygens Element
Li-Zhao Song, Student Member, IEEE, Pei-Yuan Qin, Senior Member, IEEE, and Y. Jay Guo, Fellow, IEEE
Abstract A high-efficiency conformal transmitarray with
ultra-thin dual-layer Huygens element is developed. The
element consists of ‘I’ shape patches for magnetic response and
‘T’ shape stubs for electric response printed on two metal layers
of a single substrate with only 0.5 mm thickness
0
/60 at 10
GHz). By tuning the magnetic and electric responses, the
transmitting phase of the element can be changed. Eight
elements are designed to cover quantized 360
o
phase range with
a maximal 1.67 dB loss. Then, the proposed elements are
employed in a small conformal transmitarray design. To
improve the antenna efficiency, the elements’ dimensions are
calculated by considering the oblique incidence effects. Finally,
a cylindrically conformal transmitarray with a larger aperture
size is simulated, fabricated and measured. It can achieve a
measured gain of 20.6 dBi with a 47% aperture efficiency.
Index TermsTransmitarrays, Huygens metasurface,
conformal antennas.
I. INTRODUCTION
Transmitarray antennas have been considered as
competitive candidates to serve long distance
communications for space and terrestrial wireless systems [1].
By leveraging the merits of lens antennas and microstrip
phased arrays, they can achieve high gains without using
complex and lossy feed networks and provide beam-steering
capabilities by properly adjusting the aperture phase
distribution [2-3].
The last two decades have witnessed substantial research
efforts in enhancing the performance of transmitarrays e.g.,
improving the gain bandwidth [4-7], achieving multi-band
operation [8-9], reducing the entire volume [10-14] and
realizing beam steering functionality [15-18]. Regarding the
abovementioned novel transmitarray prototypes, most of them
employed multi-layer array elements, i.e., at least three metal
layers printed on two dielectric substrates separated by air
gaps or dielectric materials. Generally, the total thickness of
the elements varies from 0.3 λ
0
1 λ
0
0
is the wavelength in
the free space). Significant research efforts have been devoted
to reduce the thickness of the elements in order to reduce the
entire profile of transmitarrays and/or make them attractive to
conformal designs.
In [6], a wideband transmitarray is developed using a
three-layer element with a thickness of 0.22 λ
0
. The peak
efficiency of the antenna is 40.7%. As reported in [10], a
three-layer metallic unit without air gap shows a low profile
of 1 mm (0.033 λ
0
) overall thickness and is employed for
transmitarray design with a 36% aperture efficiency. In [12],
a thin transmitarray with a more than 30% efficiency is
developed using three-metal-layer antenna elements with a
thickness of 1.6 mm (0.07 λ
0
at 13.5 GHz). Although the
thickness of the above transmitarray elements has been
considerably reduced, they are three-metal-layer structures.
Precise alignment and attachment of multilayers would be
very challenging and costly, especially at high frequencies.
This is one of the main reasons that many dual-layer
reflectarrays, i.e. one metal layer printed on a grounded
substrate, are developed [19-21]. However, only a few reports
on dual-layer transmitarray elements have been published. In
[22], a 1.5-mm-thick (0.1 λ
0
at 20 GHz) transmitarray element
is developed consisting of two modified Malta crosses printed
on two sides of a dielectric substrate with four vertical-plated
through vias. A 40% antenna efficiency is realized. In [13], a
thin planar lens antenna with an efficiency of about 26% is
presented using gradient metasurface elements. The element
consists of two metal layers printed on a single substrate with
a thickness of 3 mm (0.1 λ
0
at 10 GHz).
Another important motivation for using dual-layer ultra-
thin elements is for conformal antenna designs. Conformal
transmitarrays [23-25], which are developed to follow the
shapes of various mounting platforms, e.g., aircrafts and
unmanned aerial vehicles (UAV), have attracted much
attention due to their capabilities to meet aerodynamic
requirements. Considering the current manufacturing
technology, one of the most feasible methods to implement
conformal transmitarrays is to employ ultra-thin array
elements with a thickness of about 0.5 mm for the ease of
bending to make the antenna conformal. It should be noted
that direct ink printing technology can do metal printing on a
curved structure. However, to realize multi-layer metal
printing on curved surface is a very expensive and technically
difficult task, which may make conformal transmitarrays
unaffordable for many applications.
Regarding the aforementioned dual-layer array elements,
as their thickness is around 0.1 λ
0
, they are only suitable for
conformal transmitarrays operating at above 30 GHz
0
=10
Manuscript received July 31, 2019; revised April 22, 2020; accepted
July 19, 2020. This work was supported by the Australia Research
Council Discovery Program under Grant DE170101203 (Corresponding
author: Pei-Yuan Qin)
The authors are with the Global Big Data Technologies Centre
(GBDTC), University of Technology Sydney (UTS), Ultimo, NSW
2007, Australia. (pyqin1983@hotmail.com)

mm) for the ease of bending. Also, elements with vias are not
preferable for conformal designs. However, transmitarrays
working below 30 GHz are highly desired by many
applications, e.g., 5G systems and satellite systems.
Therefore, an ultra-thin element without any vias which can
be employed for conformal transmitarrays operating below 30
GHz is desperately needed. It should be noted that although
using high dielectric substrate may be able to reduce the
thickness of the array element, antenna efficiency will be
significantly affected due to the losses and the total cost of the
array will be increased. Another straightforward method is to
compress the total thickness of the multi-layer element.
However, this will reduce the antenna efficiency significantly
as the element loss is increased [25]. Actually, there is always
a tradeoff between the thickness of the array and its efficiency.
It can be found that the efficiency of the transmitarray is less
than 40% when the thickness of the element is about 0.1 λ
0
.
Therefore, a key challenge for conformal designs is to develop
ultra-thin array elements with a high transmitting efficiency.
In this paper, Huygens metasurface theory is employed to
develop an ultra-thin dual-layer element for high-efficiency
conformal transmitarrays. Huygens elements [26] can be used
for transmitarrays as they are capable of realizing non-
reflection and total transmission with sub-wavelength
thickness, making it be a good candidate to provide a high
efficiency and a low profile in transmitarray design. However,
most of the currently reported Huygens elements are multi-
layer structures. In [27], the element consists of three metal
layers using two vias to connect the first and the third layer to
create a current loop for magnetic response. The second layer
is for electric response. The total thickness is 3 mm at 10 GHz
(0.1 λ
0
at 10 GHz). The elements in [28] consist of three-layer
patterned metallic surfaces to mimic one electric dipole and
one magnetic dipole printed on two bonded substrates. The
thickness of the element is 0.4 mm (0.1 λ
0
at 77 GHz). In
addition, there are some two-layer Huygens elements [29-30]
that can introduce the electric and magnetic currents on two
metal layers separately. However, the main limitation is that
discrete printed circuit board tiles have to be made for each
array element and the boards are stacked into an array.
Compared with fully planar structures [27-28], this makes it
more difficult to assemble a large surface.
From the above discussions, one can conclude that
innovation is needed to develop dual-layer ultra-thin Huygens
elements for high-efficiency transmitarray antennas,
especially the conformal ones. In this paper, we developed a
two-layer Huygens element without any metallic vias first.
The element’s thickness h is 0.5 mm (λ
0
/60 at 10 GHz). It
consists of a pair of symmetrical ‘I’ shape patches on top and
bottom layers and double T’ shape strips located on the
margin of two layers to mimic a magnetic dipole and electric
dipole, respectively. Second, for transmitarray applications,
we design eight elements with different dimensions to cover a
quantized 360
o
phase range, and the highest element loss is
1.67 dB. Third, a cylindrically conformal transmitarray is
developed employing the developed Huygens elements. The
measured aperture efficiency is found to be 47%, which is
much higher than the conformal transmitarray previously
developed by the authors’ group [25] and other planar
transmitarrays with similar thickness. The element in [25] is a
triple-layer frequency-selective surface (FSS) structure and
the insertion loss is up to 3.6 dB when its thickness is about
λ
0
/25 at 25 GHz. To the authors’ best knowledge, the
developed conformal transmitarray is the first one with a high
antenna efficiency and the thinnest aperture.
(a)
(b) (c)
Fig. 1 Huygens surface: (a) Field sketch with macro-perspective;
(b) Fields generated by E-current and M-current separately; (c)
Equivalent circuit model.
The rest of this paper is organized as follows. In Section
II, a detailed element design procedure is developed based on
Huygens surface theory. A cylindrically conformal
transmitarray based on the proposed element is simulated and
analyzed in Section III. As a verification, a prototype is
fabricated and measured in Section IV. The paper concludes
in Section V.
II. HUYGENS ELEMENT DESIGN
A. Huygens Surface Theory
As shown in Fig. 1(a), when the incidence wave impinges
on a Huygens surface, both the surface electric current Js and
the magnetic current Ms would be induced, resulting in
reflection and transmission waves which depend on the
electric and magnetic current densities. Once E-current and
M-current are excited, each of them can be taken as a source
to generate electromagnetic fields on both sides of the surface.
The Huygens surface can be analyzed from electric and

magnetic sources separately, and the generated waves from
two sources in z<0 and z>0 regions are shown in Fig. 1(b).
For a single E-current surface, it would satisfy the
boundary conditions:
󰇟
󰇛
󰇜
󰇛
󰇜󰇠  (1)
󰇟
󰇛
󰇜
󰇛
󰇜󰇠

󰇛 󰇜 (2)
where E
e
and H
e
denote the electric and magnetic field
intensities generated from E-current, respectively. E
te
is the
tangential part of E
e
, and Z
e
represents surface electric
impedance. By inserting the fields generated from J
s
, as
denoted in Fig. 1(b), into equation (1) and (2), we can get


 (3)
󰇛


󰇜

󰇛󰇜
(4)
The tangential electric field on the surface is:

󰇛 󰇜



(5)
where

and

are the fields generated by J
s
in z<0 region,
while

and

are the ones in z>0 region, and
refers to
the incident field which exists in the whole area. Then, we
can derive

󰇛


󰇜


(6)




 (7)
where denotes the wave impedance in free space. For a
single M-current surface, it would satisfy the following
boundary conditions:

󰇟
󰇛
󰇜
󰇛
󰇜
󰇠

󰇛
󰇜
(8)
󰇟
󰇛
󰇜
󰇛
󰇜󰇠  (9)
where E
m
and H
m
denote the electric and magnetic field
intensities generated from M-current, respectively. H
tm
is the
tangential part of H
m
, and Z
m
represents surface magnetic
impedance. With similar derivation process to the E-current
surface, we can obtain


 (10)
Finally, for a complete Huygens surface with both E-current
and M-current, as shown in Fig. 1(a), we denote reflection
and transmission coefficients as R and T, respectively, as
given in [29, 31]. Then one obtains
󰇛



󰇜





 (11)
󰇛




󰇜





 (12)
After doing transformation of equation (11)-(12), we get


 (13)



 (14)
(a)
(b)
Fig. 2 Developed two-layer Huygens element model: (a) 3D
structure; (b) top and bottom layers.
Therefore, the Huygens surface is capable to realize non-
reflection and full-transmission with variable transmission
phase
, referred as 
, as long as it satisfies

󰇛
󰇜
 (15)
 󰇡
󰇢 (16)
It can be seen from (15) and (16) that the electric and
magnetic surface impedances are related to the transmitting
phase. In another word, for each specific transmitting phase,
there are corresponding surface impedances. In the next sub-
section, we will develop Huygens elements for specified
transmitting phases. As indicated in [32-33], the whole
Huygens surface can be equivalent to be a circuit model as
shown in Fig. 1(c), and Z
e
and Z
m
can be defined by Z matrix
from microwave network theory:



 (17)

󰇛


󰇜 (18)
B. Element Synthesis
The schematics of the developed Huygens element is
given in Fig. 2. It consists of two metallization layers printed
on two sides of a 0.5-mm-thick substrate (Dielectric Constant
3.55, tanδ = 0.0027). The substrate thickness is selected as 0.5
mm in this work in order to make it bendable. The ‘I’ shape
patches on the centre of top and bottom layers have exactly
the same dimensions. Besides, one pair of two ‘T’ shape stubs
are printed on each side of the substrate but at different
positions. The distance between ‘T’ stubs and the edge of the
cell is 0.8 mm. The period of the unit cell P is 8.5 mm.
For many three-layer Huygens element, the metal traces
on the first and third layers are used to generate a current loop
to be equivalent to a magnetic dipole, while the trace in the
middle layer is for introducing an electric dipole. For our
developed element, only two metal layers are used and the
substrate is significantly thinner. When a x-polarized wave
impinges on the element, the ‘I’ shape patches on top and
bottom layers produce currents with opposite directions,
thereby generating a current loop, which can be equivalent to
a magnetic dipole. This will be verified in the current
distribution shown in the next sub-section. Two pairs of ‘T’
shape stubs will produce currents along x-axis with the same
direction, thereby introducing an electric dipole. These ‘T’
shape stubs will not affect the magnetic response, while the ‘I’
shape patches have influence on the electric response.
Therefore, the ‘I’ shape patches will be designed first. Then,
the ‘T’ shape stubs will be designed to control the electric
response.
The magnetic response related to the magnetic surface
impedance Z
m
can be adjusted by changing the capacitive or
inductive properties of the ‘I’ shape patches, which are related
to the patch dimensions W
z
, G
z
and S
z
. The electric response
related to the electric surface impedance Z
e
can be
manipulated by varying the values of L
c
, W
c
and W
p
. In some
cases where large capacitance between the two ‘T’ shape stubs
is needed, e.g., the element is illuminated under large oblique
incidence angles which would be discussed in Section Ⅲ, the
interdigital parasitic strips with length L
d
will be adopted for
each pair, as shown in the inset of Fig. 2(b). For an x-polarized
incident wave, the transmitting phase of the Huygens element
can be varied by changing the element’s dimensions.
However, it cannot be continuously changed when varying
only one or two dimensions of the elements. An optimization
on the element’s entire dimensions would be needed to
achieve a continuous phase change, which may make the
design of transmitarrays very complicated. Instead, quantized
phase distribution is employed. In this work, eight elements
are designed to achieve a 3-bit quantized phase distribution.
The detailed phase points and corresponding Z
m
and Z
e
values
calculated from (15) and (16) are listed in Table Ⅰ.
As discussed in the last paragraph, the dimensions of the
‘I’ shape patches of the element will be determined first for
the magnetic response. At this step, only the ‘I’ shape patches
are modelled on the element and simulated without the two
‘T’ shape stubs. Then the two ‘T’ shape stubs are added to the
element and the model is simulated for electric response.
TABLE I
HUYGENS PROPERTIES FROM THEORETICAL CALCULATION WITH
QUANTIZED 360
O
PHASE COVER
Element No.
Phase
Im(Z
e
)/kΩ
Im(Z
m
)/kΩ
1
-15
o
-1.43
0.1
2
-60
o
-0.33
0.44
3
-105
o
-0.14
0.98
4
-150
o
-0.05
2.81
5
-195
o
0.02
-5.72
6
-240
o
0.11
-1.31
7
-285
o
0.25
-0.58
8
-330
o
0.7
-0.2
TABLE
PROPERTIES OF HUYGENS ELEMENTS
Element
No.
Im(Z
e
)
/kΩ
Im(Z
m
)
/kΩ


Wz
/mm
Wc
/mm
Lc
/mm
1
-2.3
0.13
-14
o
3.6
1.3
0.1
2
-0.35
0.17
-41
o
3.8
1.6
0.1
3
-0.12
0.64
-100
o
4.1
/
/
4
-0.04
1.6
-153
o
4.19
1.2
0.6
5
-0.02
-0.44
-187
o
4.2
1.2
0.37
6
0.1
-1.1
-241
o
4.25
1.5
0.4
7
0.22
-0.52
-284
o
4.3
1.62
0.4
8
0.94
-0.25
-330
o
4.4
1.62
0.35
Floquet ports with masterslave boundaries of 3D
electromagnetic (EM) simulation software HFSS is used for
the simulation. In this work, W
z
values would be tuned for
magnetic response, while S
z
and G
z
are set as 2.3 mm and 1.7
mm, respectively, for simulation simplicity. Moreover, L
c
and
W
c
are varied for tuning electric response with W
p
=0.2 mm.
The dimensions, transmitting phases and magnitudes for the
eight elements are given in Table Ⅱ.
Fig. 3 shows the parametric studies on W
z
, L
c
and W
c
based
on element 1. When one parameter is studied, the other two
are kept unchanged as listed in Table . As shown in Fig. 3
(a), Z
m
curve moves to lower band as W
z
increases, which
provides a higher capacitance between ‘I’ shape patches of
two adjacent elements. Besides, as seen in Fig. 3 (b) and (c),
the Z
e
curve shifts left as W
c
increases, and it has the same
changing trend when L
c
is decreased. This means Z
e
would
move to lower band when the capacitance between two ‘T’
shape stubs of each element increases. Furthermore, as seen
in Fig. 4, L
c
has almost no effect on the magnetic response at
the desired frequency 10 GHz for a changing range between
0.05 mm and 0.65 mm. W
c
is found to have little influence on
the magnetic response either, which is not shown here due to
the space limit. This is the reason why magnetic and electric
responses can be designed independently.

(a)
(b)
(c)
Fig. 3 Parametric studies for element 1: (a) Simulated Z
m
with
different W
z
; (b) Simulated Z
e
with different W
c
; (c) Simulated Z
e
with different L
c
Fig. 4 Simulated Z
m
with different L
c
.
Fig. 5 Simulated S_
21
and |S_
11
| for element 1.
Fig. 6 Simulated S parameter of element 4 with different substrate
thickness values.
By using the above parametric studies, an iterative method
is employed to obtain other elements’ dimensions at 10 GHz.
First, the Z matrix of an initial element model is simulated
under periodic boundary condition, and the values of Z
m
and
Z
e
can be obtained based on (17)-(18). Then, the dimensions
are further adjusted to make Z
m
and Z
e
close to the required

Citations
More filters
Journal ArticleDOI
TL;DR: In this article, a wideband dual-layer Huygens unit cell based on offset electric dipole pair (OEDP) was proposed, which avoided the unbalanced resonant frequencies between the two polarizabilities, thereby achieving wideband transmission.
Abstract: A wideband dual-layer Huygens’ unit cell based on offset electric dipole pair (OEDP) is proposed. Different from traditional designs with a combination of electric and magnetic polarizabilities, the proposed Huygens’ unit cell exclusively employs electric polarizabilities. By doing so, it practically avoids the unbalanced resonant frequencies between the two polarizabilities, thereby achieving wideband transmission. Based on the proposed unit cell, a wideband and high-gain multibeam array antenna is developed. First, a Rotman lens is designed by using a substrate-integrated waveguide (SIW) technology. Then a parallel-fed slot antenna array is connected to the Rotman lens to generate multiple beams. Without using a series-fed slot antenna array, the multibeam array antenna based on Rotman lens can operate within a relatively wide bandwidth (28–32 GHz). Second, a wideband dual-layer Huygens’ metasurface is developed that serves as a superstrate of the multibeam array antenna for increasing the antenna gain further. A wideband and high-gain multibeam array antenna is finally realized, which is comprised of a Rotman lens, a parallel-fed slot antenna array, and a Huygens’ metasurface. To verify the performance of this design, a prototype is fabricated and its measured results are compared to the simulated counterparts.

40 citations

Journal ArticleDOI
TL;DR: In this paper, a 2D Ruze lens-inspired antenna with an elliptical cylindrical shape was designed for a wide-angle multibeam radiation in this communication, where multiple feeds can be placed on the middle horizontal plane to realize multiple beams.
Abstract: A transmitarray antenna with an elliptical cylindrical shape is presented for a wide-angle multibeam radiation in this communication. The transmitarray has a cylindrical radiating aperture with an elliptical cross-section, namely, elliptical cylindrical shape. Multiple feeds can be placed on the middle horizontal plane to realize multiple beams. Inspired by a 2-D Ruze lens, the antenna shape and the phase compensation are jointly designed according to the desired maximal beam direction. Innovative methods including a feed refocusing analysis and a virtual focal length are utilized to achieve the phase compensation across the 3-D aperture for multiple beam radiations with a small scanning loss. In order to validate the proposed antenna, a prototype operating in the millimeter-wave (mm-wave) $E$ -band has been designed, fabricated, and measured. By changing the position of the feeding gain horn along the refocusing arc, the main beam of antenna can be scanned in 11 directions. The measured peak boresight realized gain is 27 dBi at 70.5 GHz and a beam coverage of ±43° with a less than 2.7 dB scanning loss is obtained.

23 citations

Journal ArticleDOI
Han-Yu Xie1, Bian Wu1, Yue-Lin Wang1, Chi Fan1, Jianzhong Chen1, Tao Su1 
TL;DR: In this paper, a wideband fourth-order filtering antenna consisting of two substrate integrated waveguide (SIW) dual-mode cavities is presented, where the coupling matrix theory is adopted to guide the design of the filtering antenna, and the generation principle of these two RNs can be explained by cross coupling.
Abstract: A wideband fourth-order filtering antenna consists of two substrate integrated waveguide (SIW) dual-mode cavities is presented in this letter. The first SIW cavity creates two resonant nodes and one radiation null (RN) located on the upper stopband. The second SIW cavity integrated with a slot cannot only achieve radiation function but also realize dual-mode resonance, which can produce another lower out-of-band RN. These two RNs can be controlled to improve frequency selectivity and design flexibility. The coupling matrix theory is adopted to guide the design of the filtering antenna, and the generation principle of these two RNs can be explained by cross coupling. Finally, such a filtering antenna operating at the center frequency of 5.4 GHz with a fractional bandwidth of 7.64% and a maximum gain of 5.3 dBi is fabricated and measured.

13 citations

Journal ArticleDOI
TL;DR: In this article , the authors overview the recent advances in conformal transmitarrays for UAV-based wireless communications, introducing new design methodologies and highlighting new opportunities to be exploited.
Abstract: Unmanned aerial vehicles (UAVs) aided wireless communications promise to provide high-speed cost-effective wireless connectivity without needing fixed infrastructure coverage. They are a key technology enabler for sixth generation (6G) wireless networks, where a three-dimensional coverage including space, aero and terrestrial networks are to be deployed to guarantee seamless service continuity and reliability. Owing to the aerodynamic requirements, it is highly desirable to employ conformal antennas that can follow the shapes of the UAVs to reduce the extra drag and fuel consumption. To enable hundred giga-bits-per-second (Gb/s) data rates and massive connectivity for 6G networks, conformal antenna arrays featured with high gains and beam scanning/multiple beams are demanded for millimeter-wave and higher-frequency-range communications. However, new challenges exist in designing and implementing high-gain conformal arrays for UAV platforms. In this article, we overview the recent advances in conformal transmitarrays for UAV-based wireless communications, introducing new design methodologies and high-lighting new opportunities to be exploited.

8 citations

Journal ArticleDOI
TL;DR: In this article , an amplitude and phase independently adjustable transmitarray aperture with a thin profile and low cost to fabrication characteristics is proposed, and a transmitarray antenna (TA) featuring the high gain and low sidelobe level (SLL) is realized based on it.
Abstract: This article introduces an amplitude and phase independently adjustable transmitarray aperture with a thin profile and low cost to fabrication characteristics, and a transmitarray antenna (TA) featuring the high gain and low sidelobe level (SLL) is realized based on it. The TA is made up of a standard feed horn and a transmitarray aperture, each of which comprises a three-layer metasurface that is well-designed to tune the transmitted phase and amplitude on its own. As a result, the transmitarray aperture can cover the 360° phase range required for phase compensation while also realizing the amplitude distribution calculated by the Taylor design, contributing to the low SLLs. The advantage of independently controlling the amplitude and phase not only enables the proposed TA to be easy to realize and less cost on optimization but also improves the performance of high gain and low SLLs with a low profile and easy fabrication. Theoretical analyses and simulations are carried out, and a prototype is fabricated and measured. At 10 GHz, the measured peak gain is 21.16 dBi, with SLLs of −31.21 and −29.93 dB in the H- and E-planes, respectively. As a result, the tight agreements between measurement and simulation validate the design concept.

6 citations

References
More filters
Journal ArticleDOI
TL;DR: Huygens' principle is applied to develop designer surfaces that provide extreme control of electromagnetic wave fronts across electrically thin layers to find a wide range of applications over the entire electromagnetic spectrum including single-surface lenses, polarization controlling devices, stealth technologies, and perfect absorbers.
Abstract: Huygens' principle is a well-known concept in electromagnetics that dates back to 1690. Here, it is applied to develop designer surfaces that provide extreme control of electromagnetic wave fronts across electrically thin layers. These reflectionless surfaces, referred to as metamaterial Huygens' surfaces, provide new beam shaping, steering, and focusing capabilities. The metamaterial Huygens' surfaces are realized with two-dimensional arrays of polarizable particles that provide both electric and magnetic polarization currents to generate prescribed wave fronts. A straightforward design methodology is demonstrated and applied to develop a beam-refracting surface and a Gaussian-to-Bessel beam transformer. Metamaterial Huygens' surfaces could find a wide range of applications over the entire electromagnetic spectrum including single-surface lenses, polarization controlling devices, stealth technologies, and perfect absorbers.

1,418 citations


"A High-Efficiency Conformal Transmi..." refers background in this paper

  • ...In addition, there are some two-layer Huygens elements [29], [30] that can introduce the electric and magnetic currents on two metal layers separately....

    [...]

Journal ArticleDOI
TL;DR: In this article, the basic physics and applications of planar metamaterials, often called metasurfaces, which are composed of optically thin and densely packed planar arrays of resonant or nearly resonant subwavelength elements, are reviewed.

1,047 citations


"A High-Efficiency Conformal Transmi..." refers background in this paper

  • ...Huygens elements [26] can be used for transmitarrays as they are capable of realizing nonreflection and total transmission with subwavelength thickness, making it be a good candidate to provide a high efficiency and a low profile in transmitarray design....

    [...]

  • ...The phase interval between maximum electric and magnetic magnitude responses is 90 ◦ , which satisfy nonreflection Huygens element requirement [26], [34]....

    [...]

Journal ArticleDOI
TL;DR: In this article, a subwavelength reconfigurable Huygens' metasurface realized by loading it with controllable active elements is presented, which offers unprecedented potentials for real-time, fast, and sophisticated electromagnetic wave manipulation such as dynamic holography, focusing, beam shaping/steering, imaging, and active emission control.
Abstract: Metasurfaces enable a new paradigm to control electromagnetic waves by manipulating subwavelength artificial structures within just a fraction of wavelength. Despite the rapid growth, simultaneously achieving low-dimensionality, high transmission efficiency, real-time continuous reconfigurability, and a wide variety of reprogrammable functions is still very challenging, forcing researchers to realize just one or few of the aforementioned features in one design. This study reports a subwavelength reconfigurable Huygens' metasurface realized by loading it with controllable active elements. The proposed design provides a unified solution to the aforementioned challenges of real-time local reconfigurability of efficient Huygens' metasurfaces. As one exemplary demonstration, a reconfigurable metalens at the microwave frequencies is experimentally realized, which, to the best of the knowledge, demonstrates for the first time that multiple and complex focal spots can be controlled simultaneously at distinct spatial positions and reprogrammable in any desired fashion, with fast response time and high efficiency. The presented active Huygens' metalens may offer unprecedented potentials for real-time, fast, and sophisticated electromagnetic wave manipulation such as dynamic holography, focusing, beam shaping/steering, imaging, and active emission control.

443 citations

Journal ArticleDOI
TL;DR: In this article, the equivalence principle is applied to the design of Huygens metasurfaces, which are planar arrays of balanced electric and magnetic polarizable particles (meta-atoms) of subwavelength size.
Abstract: We review the current trends in the design of Huygens’ metasurfaces (HMSs), which are planar arrays of balanced electric and magnetic polarizable particles (meta-atoms) of subwavelength size. We focus on schemes that follow the equivalence principle, as these can be rigorously incorporated into Maxwell’s equations, leading to design specifications in the form of (electric and magnetic) surface-impedance distributions. The advantages of this approach with respect to the more common phase-shift stipulation approach are highlighted and discussed. We present a (microscopic) methodology to associate a general meta-atom configuration with an equivalent surface impedance, and derive metasurface (macroscopic) design procedures for various beam forming applications. The methods and concepts developed in the paper provide the basic tools for understanding and designing scalar, passive, and lossless HMSs, and we indicate possible extensions applicable to more complex structures.

314 citations


"A High-Efficiency Conformal Transmi..." refers background in this paper

  • ...It is known that the performance of Huygens surface is sensitive to the incidence angle [32]....

    [...]

  • ...As indicated in [32] and [33], the whole Huygens surface can be equivalent to be a circuit model, as shown...

    [...]

Journal ArticleDOI
TL;DR: In this paper, the authors designed and fabricated two separate transmit arrays that operate at 77 GHz, one as a quarter-wave plate that transforms a linearly polarized incident wave into a circularly polarized transmitted wave.
Abstract: Two separate transmitarrays that operate at 77 GHz are designed and fabricated. The first transmitarray acts as a quarter-wave plate that transforms a linearly polarized incident wave into a circularly polarized transmitted wave. The second transmitarray acts as both a quarter-wave plate and a beam refracting surface to provide polarization and wavefront control. When the second transmittarray is illuminated with a normally incident, linearly polarized beam, the transmitted field is efficiently refracted to 45 °, and the polarization is converted to circular. The half-power bandwidth was measured to be 17%, and the axial ratio of the transmitted field remained below 2.5 dB over the entire bandwidth. Both designs have a subwavelength thickness of 0.4 mm (λ°/9.7). The developed structures are fabricated with low-cost printed-circuit-board processes on flexible substrates. The transmitarrays are realized by cascading three patterned metallic surfaces (sheet admittances) to achieve complete phase control, while maintaining high transmission. Polarization conversion is accomplished with anisotropic sheets that independently control the field polarized along the two orthogonal axes. The structures are analyzed with both circuit- and fields-based approaches.

305 citations


"A High-Efficiency Conformal Transmi..." refers background in this paper

  • ...The losses are found to be comparable with those three-layer Huygens elements [28]....

    [...]

  • ...structures [27], [28], this makes it more difficult to assemble a large surface....

    [...]

  • ...The elements in [28] consist of three-layer patterned metallic surfaces to mimic one electric dipole and one magnetic dipole printed on two bonded substrates....

    [...]

Frequently Asked Questions (1)
Q1. What are the contributions mentioned in the paper "A high-efficiency conformal transmitarray antenna employing dual-layer ultra-thin huygens element" ?

In this paper, a dual-layer Huygens element was used for conformal transmit array design, where the oblique incidence on the array aperture was considered to enhance the antenna performance.