Plasmonics (2021) 16:2167–2177

https://doi.org/10.1007/s11468-021-01472-z

A Micro‑Sized Rhombus‑Shaped THz Antenna for High‑Speed

Short‑Range Wireless Communication Applications
Ch Murali Krishna1 · Sudipta Das2 · Anveshkumar Nella3 · Soufian Lakrit4 · Boddapati Taraka Phani Madhav5

Received: 6 April 2021 / Accepted: 3 June 2021 / Published online: 15 June 2021
© The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature 2021

Abstract
In this paper, a compact micro-sized rhombus-shaped wideband THz antenna is proposed. The radiating patch has been
modified by incorporating a rhombus-shaped gold metal-based element within the inscribed square-shaped slot on the
surface of the patch. The proposed monopole antenna is designed on a 45-μm-thick polyimide substrate material having a
dielectric constant of 4.3. The suggested compact antenna (300 × 300 µm2) offers high radiation efficiency and wide imped-
ance bandwidth. The designed wideband antenna shows 46.41% impedance bandwidth ranging from 0.445 to 0.714 THz.
The simulation results in terms of reflection coefficient, voltage standing wave ratio, gain, directivity, radiation efficiency,
radiation pattern, and surface current distribution are analyzed. The designed antenna offers − 10 dB impedance bandwidth
of 269 GHz (0.445–0.714 THz), the peak radiation efficiency of 97.3%, peak gain of 5.7 dB, maximum directivity of 6 dB,
and good impedance matching characteristics offering minimal VSWR of 1.1 and S ­ 11 parameter of − 26.4 dB within the
operating band. The suggested THz antenna would be an exemplary choice for future high-speed short-range indoor wire-
less communication, video rate imaging system, sensing, homeland defense system, biomedical imaging, security scanning,
detection of explosive, and material characterization in the THz regime.

Keywords Gold · Microstrip patch antenna · Slot · THz antenna · THz applications · Wideband

Introduction the researchers to examine an appropriate massive new

frequency band which is a terahertz (THz) electromagnetic
In recent years, the revolutionary growth of wireless spectrum that ranges from 0.1 to 10 THz with a wave-
technologies created the necessity of inexhaustible band- length of 0.03 to 3 mm [2, 3]. The THz frequency spec-
width to meet the demands of massive data traffic rate, trum (0.1–10 THz) has emerged as a very promising solu-
channel capacity, and interruption-free connectivity [1]. tion to fulfill the demands of secure high-speed wireless
These requirements have upraised a valid reason among communication applications by offering an increased data
transmission rate [4, 5]. The technologies to be operated
* Sudipta Das in the THz frequency band are acquiring an expeditious
sudipta.das1985@gmail.com development to support many high prospective applica-
1
tions like remote sensing [6], spectroscopic detection and
Research Scholar, Department of Electronics &
diagnostics [7], imaging system [8], material characteriza-
Communication Engineering, Indian Institute of Information
Technology, Design, and Manufacturing, Jabalpur, MP, India tion [9], viruses, chemical detection [10], explosive detec-
2 tion [11], medical diagnoses [12], and ultra-fast wireless
Department of Electronics & Communication Engineering,
IMPS College of Engineering & Technology, Malda, communication system [13]. The THz spectrum supports
West Bengal, India these widespread applications due to the numerous advan-
3
Department of Electronics & Communication Engineering, tages of the THz waves like the wider usable frequency
VIT Bhopal University, Bhopal, India band, higher spectral resolution, lower diffraction, and
4
Applied Mathematics and Information Systems Laboratory, better anti-interference performance as compared to mil-
EST of Nador, Mohammed First University, Oujda, Morocco limeter waves [14]. However, the prominent atmospheric
5
Department of Electronics and Communication Engineering, path loss has imposed a serious challenge for the com-
Koneru Lakshmaiah Education Foundation, Guntur, AP, mercialization of wireless communication systems in the
India

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2168 Plasmonics (2021) 16:2167–2177

THz frequency regime. So, the designs of highly efficient

compact antennas are of earnest concern to compensate
for the high path loss energy at terahertz frequency [15].
The THz antennas are the most crucial element to radiate
and detect THz waves in THz wireless communication.
The quality of the terahertz system depends directly on
the performance (wide frequency band, miniaturization,
high efficiency, strong directivity, etc.) of the THz anten-
nas. Likewise, it is worthy to mention that the design
methodology of the THz antennas creates many new chal-
lenges to the researchers of the antenna community. In
the coming years, the design requirements of the terahertz
antennas will bring a revolution in the field of the printed
antenna technology. In recent years, some researchers have Fig. 1  3D view of the proposed THz monopole antenna
designed and suggested many new antenna structures for
terahertz frequency applications. In ref. [16], a photocon-
iv. To propose a new simple antenna configuration
ductive antenna offers a maximum gain of only 2.22 dBi.
In ref. [17], the reported metallic antenna is compact at
In this paper, a polyimide substrate-based rhombus-
THz operation but the complexity in the design process
shaped monopole microstrip antenna is proposed. Gold is
leads to limited production with higher implementation
employed as the conducting material for designing the patch
cost, and additionally, the structure is also difficult to
and ground plane of the proposed antenna configuration.
assemble with planar circuitry. Another choice of THz
In this design, the selection of gold as conducting material
antenna is the dielectric antenna [18]. However, it suf-
helps to improve the radiation efficiency and gain parameters
fers from the presence of a strong surface wave effect at
at terahertz frequency operation. The operating bandwidth of
the THz band which causes huge energy loss leading to
the proposed antenna is improved due to the configuration of
poor antenna efficiency. As an alternative, more innovative
the suggested patch in the presence of a partial rectangular
terahertz antennas are based on the implementations of
ground plane. The size of the suggested antenna is only 300
electromagnetic bandgap (EBG) [19], photonic bandgap
× 300 µm2 and provides impedance bandwidth of 46.41%
(PBG) crystal [20], and metamaterial structures (MTM)
(0.445 −0.714 THz) for S11 ≤ −10 dB. The peak gain, direc-
[21]. On the other hand, there has been growing inter-
tivity, and efficiency are found to be 5.7 dB, 6 dB, and
est in the design of THz antennas using graphene as con-
97.3%, respectively. So, the compact size, high efficiency,
ducting material [22–24]. In recent times, preference has
useful broad operating frequency band, acceptable gain,
been given to the utilization of microstrip technology for
and directivity are the advantages of the proposed rhombus-
designing THz antennas to be operated in the low fre-
shaped THz antenna. This proposed antenna is designed to
quency band of THz (0.1–1 THz). Several new microstrip
cover low loss transmission windows like 0.445–0.52 THz
antenna structures have been developed to support various
and 0.62–0.714 THz to support future high-speed short-
applications in the terahertz regime [25–31], but they are
range indoor wireless communication in the terahertz band.
having a larger physical dimension and limited operating
The proposed THz antenna also finds scientific applications
bandwidth. So, the challenge is to improve the operating
in video rate imaging systems, sensing, homeland defense
bandwidth of microstrip THz antennas while maintaining
system, biomedical imaging, and security scanning.
their miniaturized dimension.
The objective of this present work is to propose a novel
microstrip antenna that can address both the miniaturization Table 1  Intact dimensions of the proposed antenna
and narrow bandwidth issues at the lower-frequency band
Parameters Dimension Parameters Dimension
of terahertz wireless communication. The design goals of
the suggested antenna as compared to the other THz micro- Feedline length ­(Lf) 110 μm Feedline width ­(Wf) 30 μm
strip antennas [25–31] reported in the state of the art are as Patch length ­(Lp) 130 μm Patch width ­(Wp) 130 μm
follows: Substrate length 300 μm Substrate width 300 μm
­(Lsub) ­(Wsub)
i. To obtain the most miniaturized dimension while Substrate thickness 45 μm Ground length (­ Lg) 60 μm
working at the lowest operating frequency (h)
ii. To offer better operating bandwidth Square ring width 25 μm Rhombus dimension 60 μm
(G) (S)
iii. To offer better radiation efficiency

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Plasmonics (2021) 16:2167–2177 2169

Table 2  Material and simulation environment of the proposed THz antenna

Material Properties Simulation environment

Polyimide (substrate) Thickness (h) 45 μm, dielectric constant (εr) 4.3 and loss Software: HFSS v. 19
tangent (tan δ) 0.004 Excitation: lumped port
Boundary: radiation
Gold (conducting material) Thickness 2 μm, conductivity 4.1 ×107(S/m) Sweep type: discrete
Frequency sweep: 0.35 to 0.75 THz
Step size: 0.002 THz

Geometrical Configuration of the Proposed The major geometrical parameters of the proposed
Terahertz Antenna antenna are illustrated in Table 1. The design and simulation
studies are performed using EM simulation HFSS software.
The proposed design of the monopole wideband tera- The fabrication and practical testing of the THz antenna
hertz antenna labeled with design parameters is shown in are quite difficult as well as challenging due to its very com-
Fig. 1. The proposed structure is obtained by inscribing a pact dimensions and with the available resources. However,
square-shaped slot in the radiating patch and adjoining a techniques like PCB etching [32], nano-lithography [33], and
rhombus-shaped metallic structure within it. On the other micro-machining [34] are used for the THz antenna fabrica-
hand, a rectangular partial ground plane is employed in tion. The PCB etching process is a method to remove unwanted
the design of this wideband terahertz antenna. This pro- material from the conducting layers. However, it requires accu-
jected antenna is designed on a polyimide substrate of a rate and high-precision etching modules. The nano-lithography
thickness (h) 45 μm, dielectric constant (εr) of 4.3, and is a technique used to print or etch microscopic-level struc-
loss tangent (tan δ) of 0.004. The selected polyimide tures. The technique micro-machining is also used to shape or
substrate provides mechanical support to the designed design or to etch materials in the micro scale levels.
antenna. The gold material with a thickness of 2 μm is In this paper, the proposed THz antennas have been ana-
used for designing the suggested structures of the patch lyzed and simulated results are presented with detailed dis-
(top layer) and ground plane (bottom layer) of the pro- cussion in the next sections.
posed terahertz antenna. The gold-based radiating patch The material properties, simulating environment, and
with an area of 130 × 130 μm2 is mounted on the polyim- boundary conditions for the proposed antenna design are
ide substrate of dimensions 300 μm × 300 μm. A micro- presented in Table 2.
strip line of width 30 μm has been utilized to feed power An R-L-C equivalent model for the proposed THz mono-
to the projected antenna through a 50-Ω SMA connector, pole antenna is shown in Fig. 2. This model is obtained from
which ensures maximum transfer of the input power to the equivalent model discussions presented in the literature
the antenna for providing effective radiations. [35–37].Where,

Fig. 2  Equivalent model of the proposed antenna

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2170 Plasmonics (2021) 16:2167–2177

�� �
𝜔𝜇0 �2
𝜔 𝜇0 𝜀S − k0 2 sin2 𝜃tg
� √
Z1 = j � × tan
� √ �2 (1)
2 2
𝜔 𝜇0 𝜀S − k0 sin 𝜃

𝜀reff + 0.3 ( Wh + 0.264)

( )
1 1 1 1
= + + (2) ΔL = 0.412h × ( (6)
Zin Z g Zm Z 1 𝜀reff − 0.258 ( Wh + 0.8)
)

The gold impedance is represented by Zg, the equivalent where

impedance of polyimide surface is Z1, tg is the thickness of C = light velocity in free space,
polyimide substrate, 𝜀s is the permittivity of substrate mate- fr = resonant frequency,
rial, K0 is the free space wave number, θ is the incidence angle, 𝜀r = substrate permittivity,
and free space intrinsic impedance ( Z0) is 377Ω. Reflectance h = substrate thickness,
efficiency (r) is defined as r = {Zin} − Z0∕ {Zin} + Z0. W = patch width,
ΔL = extended length due to fringing fields.
Design Procedures of the Proposed Antenna Initially, for the design of the proposed antenna, a reso-
and Its Performance Evaluation nant frequency of 0.475 THz is taken into consideration as it
supports high-speed THz communication systems. So, for a
The conventional patch antenna can be designed from the frequency of 0.475 THz the patch width (W) and length (L)
dimensions by following the design equations as presented are coming out to be 0.194 mm and 0.13 mm, respectively.
below [38]. Initially, the width (W) of radiating patch can However, it is known that the antenna length has a control on
be computed from Eq. (3). resonant frequency and width has a control on bandwidth. In
( )√ order to have compact dimensions for the required patch, a
C 2
W= (3) square structure is considered with calculated dimensions at
2fr 𝜀r + 1
the resonant 0.475 THz. Finally, the patch length and width
Radiating patch length (L) is calculated from the design are considered as 0.13 mm.
Eq. (4). The radiating patch of the antenna is square-shaped and has
a surface area of 16,900 μm2 (130 μm × 130 μm) correspond-
L= �
1
� − 2ΔL ing to the resonant frequency of 0.475 THz and a polyimide
√ √
2fr 𝜀0 𝜇0 𝜀reff (4) substrate having a dielectric constant of 4.3 and loss tangent
of 0.004. At THz frequencies, usually, the metals with lower
Effective dielectric constant (𝜀reff ) is given by Eq. (5). conductivities are not preferred for the design of the conduct-
ing surfaces of the antenna as the field penetration increases
into the lower conductive metals which degrade the radiation
( ) ( )
𝜀r + 1 𝜀r − 1 [ h ]−1∕2
𝜀reff = + 12 + 1 (5)
2 2 w

The extended length due to fringing fields is given by

Eq. (6).

Fig. 3  Square slot–loaded dual band THz antenna Fig. 4  Reflection coefficient ­(S11) characteristics of dual band antenna

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Plasmonics (2021) 16:2167–2177 2171

Fig. 5  Geometry of the proposed gold-based wideband THz antenna

Fig. 7  VSWR comparisons of the dual and wideband antenna

efficiency of the THz antennas. In this work, the metal used
to build the designed antenna is gold (Au). The main reason
behind the selection of gold as a conducting material is to in the gain and radiation efficiency parameters. The simulated
obtain higher radiation efficiency as it has very high conduc- results and analysis of these two design cases are discussed in
tivity and less ohmic losses. The gold is resistant to chemi- the next subsections.
cal reaction, and also the higher value of gold’s extinction
coefficient indicates higher absorption in the THz frequen-
cies. Further, the structure of the conventional antenna has Effect of the Incorporated Square‑Shaped Slot
been modified to meet the proposed design objectives such in the Patch and Employment of Rectangular Partial
as improvements in resonance characteristics, gain, and effi- Ground Plane in the Antenna Design (Dual Band
ciency. At first, the geometry of the patch is modified by Antenna)
inserting a square-shaped slot in the patch and by employing
a partial rectangular ground plane in the design. This struc- In this section, the results and structure of the THz antenna
ture offers dual band resonance behavior. Finally, a rhombus- designed using the incorporation of square-shaped slot in
shaped metallic structure is merged inside the square slot to the radiating patch with the presence of a rectangular par-
form the modified patch to enhance the impedance bandwidth tial ground plane are presented. This THz antenna model is
of the designed antenna. The combinations of the proposed shown in Fig. 3. The presented structure has been designed
patch (rhombus-shaped metallic structure incorporated within and simulated using the HFSS (high-frequency structure
the square slot) and partial rectangular ground plane offer simulator) tool. In this structure, the upper conducting layer
wideband resonance characteristics as well as enhancement on the substrate acts as a source and the other side of the

Fig. 6  Reflection coefficient characteristics of dual and wideband Fig. 8  Gain versus frequency characteristics of dual- and wide-band
antenna antenna

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Table 3  Comparison of the characteristics parameters of dual- and wide-band antenna

Design Operating bands −10 dB impedance Fractional Maximum Maximum Maximum Radiation
bandwidth (THz) bandwidth ­S11 (dB) gain (dB) directivity efficiency
(%) (dB) (%)

Square slot–loaded antenna Dual 0.407–0.533 THz 26.80 −17 5.4 5.7 92.5–97
0.622–0.703 THz 12.22 −15.7
Proposed antenna Wide 0.445–0.714 THz 47.23 −26.4 5.7 6.0 93.8–97.3

substrate is a partial conducting material, which acts as a impedance matching, reflection coefficient and enhances
perfect reflected ground plane. The top layer (patch) and bot- −10 dB impedance bandwidth. Furthermore, compared to
tom layer (ground plane) of the designed antenna are made the presented dual band antenna, improvements in gain
of gold material having a thickness of 2 μm. The selection and radiation efficiency are also observed due to the pro-
of substrate material with proper dielectric constant (εr) and posed antenna configuration. The geometry of the proposed
thickness of the substrate ­(hs) has an impact on the charac- wide band THz antenna is depicted in Fig. 5. The proposed
teristics and dimension of the antenna. In this design, the structure is composed of a microstrip line–fed modified
material preferred for a dielectric layer is polyimide hav- patch and a rectangular partial ground plane as suggested
ing the dielectric constant of 4.3 and loss tangent of 0.004. in Fig. 5. Here in Fig. 6, ­S11 parameters versus frequency
The overall dimension of the proposed antenna is 300 μm are plotted to compare the performance of the developed
× 300 μm × 45 μm. The antenna resonance characteristics THz antenna structures (dual-band antenna and wideband
change due to the presence of a square-shaped slot with an antenna). As observed from Fig. 6, the resonance behavior
optimized dimension of 80 μm × 80 μm and a partial ground of the antenna is greatly influenced due to the inclusion
plane structure. The designed antenna with this suggested of a rhombus-shaped radiating element within the square
configuration offers dual band resonance characteristics with slot. The proposed antenna shows dual-band resonance
enhanced bandwidths. with wide impedance bandwidth covering the entire band
The performance of the square slot–loaded antenna is defined from 0.445 to 0.714 THz. The VSWR parameter of the
in terms of its resonance characteristic parameter. The reflection designed antennas is compared and shown in Fig. 7. It can
coefficient ­(S11) characteristic of this antenna is shown in Fig. 4. be observed that the proposed antenna offers an improve-
It operates at dual bands which covers a frequency range from ment in impedance matching by offering the desirable
0.407 to 0.533 THz and from 0.622 to 0.703 THz. The reflection value of VSWR over the entire operating frequency band
coefficients at the resonant frequencies 0.468 THz and 0.66 THz due to the suggested modifications in the structure of the
are −17 dB and −15.7 dB, respectively. However, the reflection patch.
coefficient characteristic shows impedance mismatching over a The impact of the proposed antenna geometry is also
specified range and does not support terahertz applications over investigated on the radiation parameters such as gain
the entire wide frequency spectrum.
As discussed in the previous section, the main objective
of this work is to suggest a compact THz antenna that will
offer maximum radiation efficiency and wideband resonance
characteristics to cover more terahertz applications. In order
to improve the impedance mismatching in the dual band
antenna and thus to achieve wideband characteristics, the
structure of the radiating patch is further modified which is
discussed in the next subsection.

Effect of the Rhombus‑Shaped Metallic Structure

Incorporated Within the Square Slot in the Presence
of Partial Ground Plane Structure (Wideband
Antenna)

The geometry of the proposed patch is developed by

adding a rhombus-shaped radiating element within the Fig. 9  Radiation efficiency characteristics of dual- and wide-band
square slot. This proposed antenna structure improves the antenna

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Plasmonics (2021) 16:2167–2177 2173

Fig. 10  Surface current distribution of proposed antenna at (a) 0.51 THz and (b) 0.67 THz

and radiation efficiency. Comparisons of the gain and Results and Discussion of the Proposed
radiation efficiency are demonstrated in Figs. 7 and 8, Wideband THz Antenna
respectively. It can be observed that the proposed wide-
band THz antenna offers a significant improvement in The Surface Current Distribution of the Proposed
radiation parameters attaining a maximum peak gain of Antenna
5.7 dB and a peak radiation efficiency of about 97.3%.
All the major characteristic parameters related to the The surface current distributions of the proposed antenna
designed dual-band antenna and proposed wide-band at the resonating frequencies (0.51 THz and 0.67 THz) are
antenna are summarized in Table 3. Maximum imped- examined and presented in Fig. 10a, b. As observed, the dis-
ance bandwidth, reflection coefficient, gain, directivity, tributed surface currents are highly concentrated along the
and radiation efficiency are obtained for the proposed edge of the feed line. Also, a high surface current concentra-
antenna. So, a conclusion can be drawn that the perfor- tion is noticed on the edges of the proposed patch structure.
mance of the proposed wide-band antenna is much bet- However, the surface current distribution on the rhombus-
ter compared to the results obtained for the dual-band shaped structure is stronger and prominent at the higher
design case (Fig. 9). resonant frequency which verifies its effect on the proposed

Fig. 11  Reflection coefficient (­ S11 parameter) of the proposed antenna Fig. 12  VSWR vs. frequency variations of the proposed antenna

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2174 Plasmonics (2021) 16:2167–2177

Fig. 13  E plane and H plane far-

field radiation patterns. (a) 0.51
THz. (b) 0.67 THz

antenna structure for the improvement of characteristics at important parameter is voltage standing wave ratio (VSWR)
the higher resonance. that is evaluated to check the impedance matching condi-
tion. VSWR defines the amount of the signal that is reflected
Resonance and Radiation Characteristics from the antenna due to impedance mismatching between
of the Proposed Antenna the source and antenna impedances. For a well-designed
antenna with good impedance matching, the VSWR values
The proposed antenna has been designed to support wide- should be less than 2 which signifies less reflection of power
band applications in the THz regime. To confirm its wide- and thus acceptable mismatch loss. The VSWR plot for the
band resonance behavior, the variations of reflection coef- proposed antenna is depicted in Fig. 12, which is less than
ficient ­(S11) vs. frequency are plotted in Fig. 11. It is well the maximum acceptable value of 2 within the operating
known that the reflection coefficient should be less than bandwidth of 0.445–0.714 THz. The minimum VSWR val-
−10dB for an antenna to achieve perfect impedance match- ues of 1.4 and 1.1 are obtained at the resonating frequencies
ing conditions. It can be observed from Fig. 11 that the pro- 0.51 and 0.67 THz, respectively. Figure 13 a and b show
posed antenna resonates at 0.51 THz and 0.67 THz with the polar plots of the far-field patterns in the E plane (black
a reflection coefficient of −15.37 dB and −26.4 dB. The curve) and H plane (red curve) at two resonant frequencies
antenna shows a wide operating bandwidth of 269 GHz 0.51 THz and 0.67 THz in the wide-band operating region. It
covering the entire frequency band from 0.445 to 0.714 is observed that at 0.51 THz, the antenna exhibits an almost
THz for S11 ≤ −10dB. The calculated fractional bandwidth bidirectional pattern in the E-plane and an omnidirectional
is 46.41% with a center frequency of 0.5795 THz. Another circle-shaped pattern in the H-plane. However, changes are

Fig. 14  Gain of the proposed antenna Fig. 15  Directivity of the proposed antenna

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Plasmonics (2021) 16:2167–2177 2175

the proposed antenna is highly acceptable and well opted for

several applications in the terahertz region.

Comparative Analysis of the Proposed

Wideband THz Antenna With Other
Reported THz Antennas

The performance comparative discussion is presented in

this section. The resonant frequency, operating bandwidth,
and size of the designed antenna are compared with some
other THz microstrip antennas as reported in the state of
the art [25–31]. The comparison study is summarized
in Table 4. In [25], the RT/Duroid 6006 substrate-based
reported THz antenna operates at 0.692 THz an impedance
Fig. 16  Radiation efficiency of the proposed antenna bandwidth of only 22.47% and occupies a large size of 1000
× 1000 µm2. In [26], the pyrex substrate–based narrowband
observed at the radiation patterns at a higher resonant fre- antenna operates at 0.67 THz with a large dimension of 500
quency, 0.67 THz. The radiation pattern slightly deteriorates × 500 µm2. In [27], the reported antenna designed using
with the increase in operating frequency. At 0.67 THz, the polyimide substrate occupies a large area of 800 × 600 µm2
E plane patterns look like a sectorial pattern with a shift in and resonates at 0.6308 THz with a limited impedance
the direction of the main beam while the H-plane pattern is bandwidth of only 5.73%. In [28], another antenna designed
almost similar to omnidirectional oval-shaped. using polyimide substrate requires an area of 600 × 600
The gain, directivity, and radiation efficiency parameters µm2 and operates from 0.5 to 0.7 THz with an impedance
of the proposed antenna are also investigated. The varia- bandwidth of 33.33%. In [29], the THz microstrip patch
tions in gain throughout the operating band are clarified in antenna designed using RT/Duroid 6006 substrate shows
Fig. 14. The proposed antenna shows positive gains over the an impedance bandwidth of 19.35% covering the frequency
entire operating band (0.445−0.714 THz). It can be observed band from 0.7 to 0.85 THz but the size of the structure
that the gain of the antenna increases with an increase in is large enough (1000 × 1000 µm2) at the operating fre-
the operating frequency leading to a maximum peak gain quency of 0.7408 THz. In [30], another RT/Duroid 6006
of 5.7 dB at 0.714 THz within the operating band, which substrate–based antenna is reported which exhibits the same
is quite acceptable for a micro-sized designed antenna. The operating bandwidth (19.35%, 0.7 to 0.85 THz) in a reduced
directivity characteristics over the operating band obtain a antenna dimension (700 × 600 µm2). In [31], comparatively,
peak value of 6 dB at 0.714 THz as shown in Fig. 15. The a well-miniaturized antenna is designed using polyimide
radiation efficiency plot is depicted in Fig. 16. As observed substrate material scaling a dimension of 433.2 × 208.98
in Fig. 16, it can be stated that the designed gold-based µm2, but it is capable to work in the limited frequency band
antenna is highly efficient for terahertz applications. The (0.725–0.775 THz) with a narrow impedance bandwidth
radiation efficiency is balancing from 93.8 to 97.3% over of only 6.67%.
the entire band (0.445–0.714 THz). So, the performance of

Table 4  Comparison with other THz microstrip antennas

Ref Antenna size (μm2) −10 dB bandwidth (THz) Fractional band- Radiation efficiency (%) Substrate material
width (%)

[25] 1000 × 1000 0.645–0.8 22.47 Not reported RT/Duroid 6006

[26] 500 × 500 Narrowband (bandwidth not Not reported Not reported Pyrex
reported)
[27] 800 × 600 0.615–0.6514 5.73 85.93 Polyimide
[28] 600 × 600 0.5–0.7 33.33 90.84 Polyimide
[29] 1000 × 1000 0.7–0.85 19.35 55.88 RT/Duroid 6006
[30] 700 × 600 0.7–0.85 19.35 75 RT/Duroid 6006
[31] 433.2 × 208.98 0.725–0.775 6.67 86.85 Polyimide
Proposed 300 × 300 0.445–0.714 46.41 97.3 Polyimide

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2176 Plasmonics (2021) 16:2167–2177

In this paper, a microstrip antenna model using the poly- Declarations

imide substrate is presented. The patch and ground plane
of the suggested structure is constructed using gold as the Consent to Participate Informed consent was obtained from all authors.
conducting material. The structure of the antenna is very
Consent for Publication The authors confirm that there is informed
compact and it occupies an area of only 300 × 300 µm2. consent to the publication of the data contained in the article.
The designed antenna achieves a wide impedance bandwidth
of 46.41% from 0.445 to 0.714 THz and a peak radiation Conflict of Interest The authors declare no competing interests.
efficiency of 97.3%. It can be concluded that the dimension
of the proposed rhombus-shaped THz antenna is the small-
est and it offers better impedance bandwidth and radiation References
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antenna has been modified by introducing a square slot on munications. IEEE Trans Terahertz Sci Technol 1(1):256–263
the surface of the patch which results in dual band reso- 6. Siegel PH (2002) Terahertz technology. IEEE Trans Microw
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