A reserch paper on absorber

1. R E S E A R C H A R T I C L E
Design and development of
low radar cross section antenna
using hybrid metamaterial
absorber
Atipriya Sharma1
| Ravi Panwar2
|
Rajesh Khanna1
1
Department of Electronics and Communication Engineering, Thapar
Institute of Engineering and Technology, Patiala, Punjab, India
2
Discipline of Electronics and Communication Engineering, Indian Institute
of Information Technology, Design and Manufacturing, Jabalpur, Madhya
Pradesh, India
Correspondence
Ravi Panwar, Discipline of Electronics and Communication Engineering,
Indian Institute of Information Technology, Design and Manufacturing,
Jabalpur 482005, Madhya Pradesh, India.
Email: rpanwar.iitr@gmail.com
Abstract
An efficient approach is presented in this article, to
reduce radar cross section (RCS) of a microstrip patch
antenna, without affecting other radiation characteristics
by the application of a novel hybrid metamaterial
(MM) structure. The microstrip antenna is designed to
operate at 4.2 GHz. Three different configurations of
MM structures (ie, CB_1, CB_2, and hybrid) with
splitted square and ring shaped two nonidentical MM
cells are designed and critically analyzed in the range of
2-18 GHz. A hybrid MM configuration is chosen for the
design and implementation of low RCS antenna due to
its exceptional performance as compared to CB_1 and
CB_2. The hybrid MM is organized in chessboard con-
figuration, comprises of splitted square and ring shaped
MM unit cell. The results show that proposed antenna
gives substantially out of band RCS reduction from 6 to
18 GHz and the proposed antenna has a lower RCS than
the reference antenna. Proposed antenna attains wide-
band bandwidth around 7.4 GHz (ranging 2.0-4.4 GHz,
7.8-9.1 GHz, and 14.3-18 GHz). The maximum reduc-
tion of −30.1 dBsm at 16.4 GHz is achieved in the
hybrid MM structure impinged microstrip patch antenna.
Finally, the fabrication and performance evaluation of
MM loaded antenna is carried out. Moreover, measured
results of the fabricated samples are closely matched with
simulated results, which prove the effectiveness of the
adopted approach for practical applications.
KEYWORDS
broadband, hybrid structure, metamaterial, microstrip antenna, radar
cross section reduction
1 | INTRODUCTION
Radar cross section reduction (RCS) has been extensively
studied by the researchers, for military tactics.1,2
Low observ-
able technology or stealth technology is one of the parts of mil-
itary tactics. Low observable technology concept is based on
making sensitive targets like airborne vehicles and naval ships
invisible to radar. In stealth technology, antenna plays the
dominant role, as it is a part of the communication system,
which transmits and receive electromagnetic (EM) wave.
Therefore, it is to say that the stealth property could be
reduced, because of the high RCS of an antenna. That
means, it is mandatory to reduce the RCS of an antenna.
Many ways have been reported to reduce RCS from the last
few years, such as frequency selective surfaces (FSS),3-5
arti-
ficial magnetic conductor (AMC),6-8
and electromagnetic
band-gap structures (EBG).8-10
Metamaterial (MMs) are arti-
ficial materials, which are engineered to possess unique EM
properties that are not found in naturally occurring mate-
rials.11,12
Shang et al introduced a low RCS microstrip patch
antenna.3
In this work, a remarkable reduction in RCS has
been achieved by replacing the ground plane of the reference
antenna with a complex ground plane, which consists of
FSS unit cells. In Reference 9, radar absorbing material has
been used to reduce the RCS of an antenna, which convert
EM wave into heat energy. Polarization conversion MM has
been employed to reduce the RCS of a patch antenna.13
RCSR has been achieved by using a chessboard like MM
surface, which consist of two unique unit cells of AMC.14
Microstrip resonators and uniplanar compact EBG structures
have been used to attain the in-band RCS reduction.15,16
Still
out of band reduction is not possible with the above dis-
cussed two methods. In Reference 10, EBG structures were
applied for RCSR, however, in this method during in band
RCSR gain loss is observed around 2 dB, which needs to be
improved. RCSR of an antenna has been obtained by a
square and octagonal ring shaped AMC structure in
Received: 22 March 2019
DOI: 10.1002/mop.31924
Microw Opt Technol Lett. 2019;61:2491–2499. wileyonlinelibrary.com/journal/mop © 2019 Wiley Periodicals, Inc. 2491

2. Reference 17. Jiang et al presented partially reflecting sur-
face antenna for in band and out of band RCSR in the range
of 8-17 GHz.18
Zhang et al proposed a left handed material
of hexagonal shape to reduce out of band RCSR of a micro-
strip antenna, without affecting the radiation properties of an
antenna.19
In this article, a low RCS microstrip patch antenna, with
unchanged gain impinged with a novel hybrid MM geometry
is developed. First, a reference antenna is designed, fabricated
and measured. Similarly, the same process is carried out with
hybrid MM impinged patch antenna. Finally, the simulated and
measured results of reference and hybrid patch antenna are
compared with each other. With the hybrid MM impinged
patch antenna remarkable RCSR is obtained due to the basic
principle of RCSR, that is, passive cancellation. The structure
of the paper is as follows. Section 2 shows the design of the
proposed absorber which consist of two parts. One is the design
of the unit cell and another is design of hybrid patch antenna.
Section 3 is devoted to critical analysis and simulated results of
hybrid patch antenna. Furthermore, fabrication and comparison
with measured data on hybrid patch antenna is discussed in
Section 4. Finally, a conclusion is drawn in Section 5.
2 | DESIGN OF MM INSPIRED
ANTENNA
2.1 | Design of MM unit cell
The front view of the unit cell of MM#1 and MM#2 is shown in
Figure 1A,B. MM#1 and MM#2 are made up of a conductor
backed by a grounded dielectric substrate. A 2.0 mm thick FR4
material (relative permittivity, εr = 4.3, and dielectric loss tan-
gent, tan δ = 0.025) has been chosen as a dielectric substrate
material. Table 1 presents the optimal design variables of the
proposed MM unit cells. MM#1 consists of a splitted square,
whereas MM#2 is made up of a splitted ring geometry. In
Figure 1, black color represents the copper layer, while the
white portion represents the dielectric substrate. One step
further, the surface current distribution of the MM#1 and
MM#2 is shown in Figure 2A,B, which shows that maximum
current flows at the edges of the inner square in MM#1 and with
MM#2 horizontal arms of split ring carry more current as com-
pared to the vertical arms. There are same and opposite current
directions are observed on the MM layer and the ground plane,
which generate the electric field and result in a magnetic flux
generation at the resonances. The similar effect has been
observed by Bakir et al.20
Computer Simulation Technology
(CST) Microwave Studio software has been used for the design,
optimization, and analysis of these structures. Along the x and
y directions, the periodic boundary conditions have been applied
and the Floquet port has been used to electrify incident wave in
the z direction. The phase reflection vs frequency graph of
MM#1 and MM#2 is shown in Figure 3A,B. The phase reflec-
tion of MM#1 and MM#2 is in the range of 180
30
has
been obtained in the range of 2-18 GHz. Therefore, a good
monostatic RCS reduction can be expected in this frequency
range. To justify this behavior, the chessboard structure and the
proposed hybrid structure with the same total dimension of
80 mm × 80 mm has been simulated.
2.2 | Design of reference and proposed
microstrip patch antennas
The configuration of the reference antenna with dimension
of 80 × 80 mm and the hybrid MM loaded antenna with
same dimension is shown in Figure 4A,B, respectively. MM
cells are distributed around the radiating patch to achieve the
low RCS of an antenna as depicted in Figure 4B. The operat-
ing frequency range of the reference antenna is 4.2 GHz.
FIGURE 1 Front view of the proposed unit cell (A) MM#1, (B) MM#2. MM, metamaterial
TABLE 1 Optimal design variables of the proposed MM unit cells
Parameter Value (mm) Parameter Value(mm)
A 9.5 N 0.4
D 0.8 O 2.5
I 1.3 Q 9.2
Abbreviation: MM, metamaterial.
2492 SHARMA ET AL.

3. FIGURE 2 Surface current of unit cell (A) MM#1, (B) MM#2. MM, metamaterial [Color figure can be viewed at wileyonlinelibrary.com]
FIGURE 3 Frequency dependent phase reflection (A) MM#1, (B) MM#2. MM, metamaterial
FIGURE 4 Configurations of (A) reference antenna, (B) hybrid MM loaded antenna, (C) side view of the hybrid MM loaded antenna structure.
MM, metamaterial

4. The side view of the hybrid MM loaded antenna is shown in
Figure 4C. The design parameters of reference and MM
impinged antennas are described in Table 2.
CB_1 and CB_2 configurations are also simulated to know
the effect of the structure on the monostatic RCS. However,
CB_1 and CB_2 surfaces differ in shape of the unit cell and
arrangement of unit cells, as shown in the Figure 5A,B, while the
other design parameters of CB_1 and CB_2 are same with hybrid
antenna. Figure 5C illustrates the design of the hybrid MM struc-
ture. CB_1, CB_2, and hybrid configurations are compared with
respect to bandwidth, resonant frequency, and monostatic RCS
value as depicted in Table 3. At the resonant frequencies, a phase
shift has been observed because of MM structure, which leads to
reduction of RCS. Compared to the hybrid structure, CB_1 and
CB_2 are showing high RCS as manifested in Figure 6.
3 | CRITICAL ANALYSIS AND
SIMULATED RESULTS
For an extensive study, the scattering and radiation properties
of the reference antenna and the hybrid structure have been
simulated. A comparison of simulated RC-frequency spectra’s
of reference antenna and proposed antenna is shown in
Figure 7A. It has been observed that the peak RC value of the
reference antenna is −28.5 dB at 4.2 GHz, while the peak RC
value of the proposed antenna is −19.6 dB at 4.19 GHz. The
difference between both resonant frequencies is 0.01%, which
is an acceptable value. Using the hybrid MM structure, out of
band RCS reduction is possible. To validate this, monostatic
reduction vs frequency graph of reference antenna and pro-
posed antenna is shown in Figure 7B. A noticeable out of band
RCS reduction is achieved with maximum RCSR value of
−30.1 dBsm at 16.4 GHz as clear from Figure 7B. The com-
parison of xoz (E plane) and yoz (H plane) of the radiation pat-
terns in terms of gain of reference and proposed antennas are
plotted in Figure 8A,B. It can be observed that in both anten-
nas, the change in gain value is almost negligible. Means, the
radiation properties of an antenna is not degraded by the appli-
cation of hybrid structure. Meanwhile, the parametric studies
TABLE 2 Design parameter of proposed antennas
Parameter Value (mm) Parameter Value(mm)
P 80 G 5.0
W 15.6 V 4.5
T 4.0 U 6.5
H 2.5 Y 9.75
FIGURE 5 Configurations of (A) CB_1, (B) CB_2, and (C) hybrid MM geometry. MM, metamaterial
TABLE 3 Comparison of RCS characteristics of CB_1, CB_2, and
hybrid geometries
Configuration
Bandwidth
(GHz)
Resonant
frequency
(GHz)
Monostatic RCS
value (dBsm)
CB_1 5.9 4.0 and 8.7 −13.3 and −16.6
CB_2 3.1 4.0 and 17.0 −12.2 and −13.3
Hybrid 7.4 4.0, 8.7, 16.4,
and 17.7
−13.3, −16.9,
−30.1, and −23.3
Abbreviation: RCS, radar cross section.
2494 SHARMA ET AL.

5. are also performed on the hybrid structure to examine the effect
of parameters on the monostatic RCS characteristics.
Figure 9 shows the frequency dependent monostatic
RCS characteristics of hybrid structure whose range is from
2 to 18 GHz. The study has been carried out to know the
effect of the gap between Inner Square and outer square (d),
which is illustrated in Figure 9A. The value of “d” varies
from 0.4 to 1.2 mm with step size of 0.2 mm. Before
0.8 mm, the value of RCS reducing, but after 0.8 mm the
value of RCS increases, therefore, the optimal value of “d”
is 0.8 mm. In this study, the value of “d” is varied from 0.4
to 1.2 mm. In Figure 9B, the inner radius (i) of the split ring
is varied from 1.1 to 1.5 mm. As mentioned earlier, the split
ring is the responsible for the high frequency RCS reduction,
the value of the inner circle radius increasing the peak shifts
toward the upside almost at 16 GHz. The optimal value of
the inner circle is 1.3 mm. Identically, the outer radius (o) of
the split ring is differed from 2.3 to 2.7 mm, as illustrated in
Figure 9C. The resonant frequency shifts toward the lower
side of the spectrum, when the outer radius increases, which
also results in wideband response. The optimal value of the
outer radius of split ring is 2.3 mm. To investigate the effect
of the gap between split ends (n), the value of n has been
varied from 0.2 to 0.8 mm with 0.2 step size as shown in
Figure 9D. In the first case, the value of n is equal to zero
means that there is no gap between circle and square. For
FIGURE 6 Comparison of proposed MM geometries (ie, CB_1,
CB_2, and hybrid) in terms of their monostatic RCS. MM,
metamaterial; RCS, radar cross section [Color figure can be viewed at
wileyonlinelibrary.com]
FIGURE 7 Comparison of reference and proposed antennas (A) RC characteristics and (B) RCS characteristics. RCS, radar cross section [Color
figure can be viewed at wileyonlinelibrary.com]
FIGURE 8 Radiation pattern of reference and proposed antenna (A) E plane, (B) H plane [Color figure can be viewed at wileyonlinelibrary.com]
SHARMA ET AL. 2495

6. FIGURE 9 Effect of design variables (A) gap between inner square and outer square, (B) inner circle radius, (C) outer circle radius, and (D) gap
between split ends [Color figure can be viewed at wileyonlinelibrary.com]
FIGURE 10 Fabricated sample of reference and proposed antennas (A) top view and (B) bottom view [Color figure can be viewed at
wileyonlinelibrary.com]
FIGURE 11 Frequency dependent measured and simulated RC characteristics of (A) reference, (B) proposed antennas [Color figure can be
viewed at wileyonlinelibrary.com]

7. every value of “n,” completely different response is obtained,
due to changes in the value of capacitance leading to a change
in the gap.
4 | FABRICATION AND
COMPARISION WITH
MEASURED DATA
The reference and the hybrid antennas were fabricated using
printed circuit board technology to validate the theoretical
results. Figure 10A,B illustrates the images of the fabricated
samples of the reference and proposed antennas. The perfor-
mance evaluation of the fabricated antennas has been carried
out using microwave measurement setup, which consist of a
broadband horn antenna (1-18 GHz) and a vector network
analyzer (VNA Keysight made, Model No. E5063A). To
estimate the similarity and dissimilarity between the mea-
sured and simulated S-parameter of the reference and hybrid
antennas, the comparison has been reported in Figure 11A,
B. Table 4 illustrates the comparison between primary and
proposed antennas in terms of simulated and measured
results. It has been observed that the measured peak RC
value of the reference antenna is −22.0 dB at 4.1 GHz, while
the peak measured RC value of the proposed antenna is
−24.6 dB at 4.2 GHz.
To measure the radiation pattern in terms of the gain of
the fabricated sample, a signal generator with a transmitter
broadband horn antenna (15 dB gain) has been used on one
end of the anechoic chamber. The antenna under test was
placed on the other end of the anechoic chamber, connected
to the VNA. Sigma generator has been set to provide the sig-
nal of 4.2 GHz and power level 0 dBm, on the other side
VNA marker was also positioned at 4.2 GHz (resonating fre-
quency). The measurement has been performed using a soft-
ware, which controls the antenna rotator and also plots the
data from VNA in polar plot form. A comparison between
measured and simulated radiation pattern of reference and
proposed antennas at E Plane and H plane is illustrated in
Figure 12A-D. The maximum radiation of proposed and ref-
erence antennas is toward the front side of the structure, and
also the backward radiation is quite less, as shown in
Figure 12A-D. The measured data are marginally varied as a
result of the fabrication tolerance and the loss due to the sub-
miniature version A connector. The comparison of the pro-
posed structure with relevant reported works is presented in
TABLE 4 Comparison between simulated and measured results of primary and proposed antenna
Antenna
Simulated resonant
frequency (GHz)
Simulated RC
value (dB)
Measured resonant
frequency (GHz) Measured RC value (dB)
Primary antenna 4.2 −28.5 4.1 −22.0
Proposed antenna 4.19 −19.6 4.2 −24.6
FIGURE 12 Radiation pattern of reference antenna (A) E plane, (B) H plane and proposed antenna (C) E plane, (D) H plane [Color figure can
be viewed at wileyonlinelibrary.com]
SHARMA ET AL. 2497

8. Table 5. One can notice that the proposed structure has a
low profile, simple geometry, and unchanged radiation prop-
erties as compared to other reported works.14,21-26
The RCS
properties of the proposed structure are in quite good agree-
ment with other reported works.
5 | CONCLUSION
In this article, broadband RCSR of an antenna has been
achieved by using hybrid configuration consists of the two
unique structures. Split ring and split square have been selected
as the unit cells, the other two configurations of hybrid struc-
ture are also simulated to examine the effect of prototype over
the monostatic RCS of an antenna. Finally, the optimal sample
has been fabricated and measured. The simulated results shows
that the proposed antenna operates at 4.2 GHz, and more than
−10 dBsm RCSR has been achieved from 2.0 to 4.1 GHz, 8.0
to 9.1 GHz, and 14.4 to 18 GHz, without affecting the radia-
tion characteristics of an antenna. A critical analysis of the pro-
posed antenna has been carried out to study the effect of
design variables over the monostatic RCS characteristics of an
antenna. A good agreement has been observed between simu-
lated and measured data, which shows the value of the struc-
ture for distinct practical applications.
CONFLICT OF INTEREST
This is to certify that the Investigator has no conflict of inter-
est in executing the project, whatsoever.
ORCID
Ravi Panwar https://orcid.org/0000-0002-9015-0891
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RCSR
band (GHz)
Peak RCSR
(dBsm)
Radiation
property
Proposed Square microstrip
patch antenna
Hybrid MM Hybrid structure 7.5-18 −30.1 Unchanged
14 Rectangle patch Jerusalem crosses
and square patches
Chessboard AMC structure 8-20 −31.9 Changed
21 Slot antenna Split square shape patches Orthogonal arranged chessboard
polarization-dependent
AMC structure
4.2-6 −19 Changed
22 Slot antenna Square patch Metasurface structure 4.9-7.18 −30 Changed
23 Slot antenna Rectangular patch Metasurface structure 6-14 −24 Changed
24 Square microstrip
patch antenna
Shared aperture metasurface Polarization conversion
metasurface structure
9-17 −43 Changed
25 Slot antenna Horizontal and vertical
strip based patch
Metasurface structure 9-19 −27 Changed
26 Slot antenna Orthogonal arranged
stair shape patches
Metasurface structure 3.5-7 −30.9 Changed
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How to cite this article: Sharma A, Panwar R,
Khanna R. Design and development of low radar
cross section antenna using hybrid metamaterial
absorber. Microw Opt Technol Lett. 2019;61:
2491–2499. https://doi.org/10.1002/mop.31924
SHARMA ET AL. 2499