micromachines

Article
Performance Analysis of an Aperture-Coupled THz Antenna for
Diagnosing Breast Cancer
Anupma Gupta 1 , Vipan Kumar 2 , Dinesh Garg 3 , Mohammed H. Alsharif 4, * and Abu Jahid 5, *

1 Department of Interdisciplinary Courses in Engineering, Chitkara University Institute of Engineering and

Technology, Chitkara University, Rajpura 140401, India; anupmagupta31@gmail.com
2 Department of Electronics and Communication Engineering, Sri Sai College of Engineering and Technology,
Pathankot 145001, India; er.vipingupta14@gmail.com
3 Department of Computer Science Engineering, Sri Sai College of Engineering and Technology,
Pathankot 145001, India
4 Department of Electrical Engineering, College of Electronics and Information Engineering, Sejong University,
209 Neungdong-ro, Gwangjin-gu, Seoul 05006, Republic of Korea
5 School of Electrical Engineering and Computer Science, University of Ottawa, 25 Templeton St.,
Ottawa, ON K1N 6N5, Canada
* Correspondence: malsharif@sejong.ac.kr (M.H.A.); ajahi011@uottawa.ca (A.J.)

Abstract: The most important technique for exposing early-stage breast cancer is terahertz imaging.
It aids in lowering the number of breast cancer-related fatalities and enhancing the quality of life.
An essential component of developing the THz imaging system for high-quality photos is choosing
the right sensor. In this article, a wideband antenna for microwave imaging of breast tissue with an
operating frequency of 30 GHz (107 GHz to 137 GHz) is constructed and analyzed. An aperture-
coupled antenna with an optimized ground aperture is proposed and analyzed, which made it
possible to obtain better and consistent impedance matching in the wideband spectrum. The variation
of backscattered signal energy in body tissue is assessed with healthy breast tissue and in the presence
of malignant cells. A significant difference in energy scattering is observed for both situations. The
suggested antenna’s linear and stable time domain characteristics make it an appropriate component
for THz imaging technology.

Citation: Gupta, A.; Kumar, V.; Garg, Keywords: aperture-coupled; breast cancer; THz imaging technology; polyamide
D.; Alsharif, M.H.; Jahid, A.
Performance Analysis of an
Aperture-Coupled THz Antenna for
Diagnosing Breast Cancer. 1. Introduction
Micromachines 2023, 14, 1281.
1.1. Background and Motivation
https://doi.org/10.3390/mi14071281
Terahertz imaging is growing rapidly as a noninvasive technology for the detection
Academic Editor: Antonella Battisti of unhealthy and cancerous cells in breast tissue. THz imaging is a non-ionizing and
Received: 19 April 2023
low-power technology, making it biologically hazardous and free for in vitro and in vivo
Revised: 11 June 2023
operations. One THz frequency requires an energy level of about 4.14 meV, whereas the
Accepted: 20 June 2023 minimum X-ray energy level is 0.12 Kev. Therefore, THz imaging is safe and reduces the
Published: 22 June 2023 ionization effects as compared to conventional methodologies. This non-ionizing behavior
is an important and critical feature that advances THz systems in healthcare applications [1].
High-frequency THz electromagnetic radiation has a fundamental time period of about
1-ps, which makes the biological investigation system faster and limits the thermal effects
Copyright: © 2023 by the authors. on healthy tissue. Due to shorter wavelengths, THz frequencies have a superior imaging
Licensee MDPI, Basel, Switzerland. resolution and have enhanced transmission properties in thick and fatty tissues. The
This article is an open access article electromagnetic spectrum for the terahertz frequency range is generally expected from
distributed under the terms and 0.1 THz (100 GHz) up to 10 THz [2].
conditions of the Creative Commons
In THz imaging systems, variations in water contents of healthy and unhealthy cells
Attribution (CC BY) license (https://
are analyzed to diagnose the existence of specific cancer cells and to measure the depth,
creativecommons.org/licenses/by/
location, and severity of damaged tissues. Unhealthy tumors and cancer cells have high
4.0/).

Micromachines 2023, 14, 1281. https://doi.org/10.3390/mi14071281 https://www.mdpi.com/journal/micromachines

Micromachines 2023, 14, 1281 2 of 15

water levels, and THz photons are highly sensitive to water absorption. It helps in the
characterization of THz radiation in biological and medical imaging [3]. Pulsed THz
radiation can sense very small cancer cells and has the potential to differentiate between
healthy and cancer cells. THz imaging is useful for quick imaging during surgery, with clear
differentiation between peritumoral and cancerous cells, and provides accurate boundary
margins (thickness between cancer and normal cells) to the surgeon to aid in the removal
of unhealthy cells [4]. The THz radiation source is the most significant part of the THz
biomedical imaging system [5,6].

1.2. Related Works

Antennas with small planar geometry, high directivity, broad bandwidth, and on-chip
fabrication capabilities have the potential to be a promising component of the imaging
system as a THz radiation source. Photoconductive antennas (PCA) are the most commonly
used antennas for biomedical imaging in the THz range. A high-resistance thin film of
semiconductor materials such as gallium arsenide (GaAs) or zinc oxide (Zno) with two
metallic contacts is used to design the PCA [7,8]. Microstrip patch antennas with transparent
radiators (consisting of indium tin oxide) and low-resistance materials (such as graphene)
are also gaining research interest as a practical alternative to match the coming requirements
of the medical healthcare industry [9,10]. Metamaterial technology is incorporated with
THZ patch antennas to enhance the radiation characteristics such as efficiency, directivity,
and gain [11–14].
Arraying of planar and patch antennas is used to improve the gain [15,16]. However,
high resolution is the most important characteristic of imaging applications, which can
be gained through a broad bandwidth. In order to achieve a wider frequency spectrum,
various types of antenna structures are proposed for a wider frequency spectrum for
THz medical imaging, for example, the Yagi-Uda antenna is designed [17] with a 27%
bandwidth. Fractal geometry [18], a multiband spectrum [19], aperture coupling [20],
MIMO with reconfigurable structures [21], and PBG and SIW technology-based graphene
antenna [22] are the different planar antenna technologies for a wider bandwidth. However,
the best existing THz antenna structures possess lower bandwidth and poor far-field
characteristics. They show hitches to be practically implemented in medical imaging. For
the easiness of understanding and readability, a brief of some THz antenna structures is
depicted in Table 1. Apart from this free space antenna, studies have shown that layered
structures, graphene-based technology, and metamaterial technology have excellent effects
on radiating characteristics [23–25]. In this work, a layered structure is used for breast
cancer detection application in the THz region.

Table 1. Summary of the design methodology of investigated antennas for THz imaging.

Performance
Refs. Type Technique Limitation
Enhancement Factor
Dipole with GaAs Wide spectrum (120 GHZ)
[7] Not analyzed for application
substrate and higher directivity
Photo Conductive
Antenna Bow-Tie structure with
(PCA) plasmonic gratings by
[8] Reduce leakage current Not analyzed for application
etching widows in
substrate
improved gain and beam performance not evaluated for
[9] array with inset feed
width time domain response
Microstrip Patch Graphene and characterized for on-chip application based performance not
[10]
antenna reconfigurable patch application evaluated
Not evaluated for practical
Array of slotted patch
[16] higher gain application and omnidirectional
radiator
radiation pattern
Micromachines 2023, 14, 1281 3 of 15

Table 1. Cont.

Performance
Refs. Type Technique Limitation
Enhancement Factor
analyzed for breast cancer
Metamaterial with
[11] miniaturization detection, only for front-to-front
defected ground
configuration
Miniaturization and
Metamaterial time domain analysis not
[12] CSIR loaded structure increasing the resonance
performed and narrow bandwidth
frequency
Improved reflection
[13] Slotted patch with PBG Sensitivity very low for cancer cell
properties
Size reduction and application based performance not
[17] Yagi-Uda PBG gratings
bandwidth enhancement evaluated
Reducing Q-factor to
[20] Circular radiator 4-graphene arc loaded Low gain
enhance bandwidth
[22] SIW Graphene and PBG Wider bandwidth Sensitivity very low for cancer cell

1.3. Contributions
The present study introduces and investigates an aperture-coupled THz antenna
with a polyamide substrate for the purpose of breast cancer detection in medical imaging.
Drawing from the relevant literature, THz imaging is based on the principle that changing
the electrical properties of bodily tissue leads to alterations in the backscattered parameters.
Cancerous tissue, possessing a higher dielectric constant than normal breast tissue due
to its high water content, is the focus of an investigation, with the deviation of the S11
signal being analyzed. The antenna developed in this study contributes to the field in the
following ways:
(1) It features a planar and straightforward structure that can be easily traced onto non-
planar breast tissue.
(2) Its wider impedance bandwidth allows for radiation penetration into tissue at different
depths.
(3) It offers higher gain.
(4) It displays good sensitivity to unhealthy tissue.

1.4. Paper Organization

The paper is divided into the following sections: the introduction and literature review
are found in Section 1. The proposed aperture-coupled antenna’s design technique is
presented in Section 2. The proposed experiment setup, together with its outcomes and
analysis, are presented in Section 3.

2. Antenna Topology and Performance Analysis on Free Space

An aperture-coupled THz antenna is operated over a wide-frequency spectrum of
30 GHz (from 0.107 THz to 0.137 THz). In the aperture-coupled structure, a metallic
ground plane is sandwiched between the two dielectric substrates. The radiating element is
designed on the upper side of the first substrate layer, and the microstrip feed line (to excite
the radiator) is designed on the lower surface of the second substrate layer. To generate the
coupling effect between microstrip line and radiating element, a rectangular slot (working
as the aperture) is engraved in the ground. The antenna is designed using a low-permittivity
dielectric substrate polyamide of permittivity (εr ) of 3.5. The configuration of the designed
THz antenna is represented in Figure 1. The topological parameter values of the proposed
design are given in Table 2. The surface area of the antenna is 3.5 mm × 3.5 mm. The power
is coupled from the microstrip line to radiating patch through the rectangular aperture
on the ground layer. The position and width of the aperture are optimized to achieve the
Micromachines 2023, 14, 1281 4 of 15

maximum impedance matching and −10 dB bandwidth. The |S11| parameter for the
proposed antenna with a rectangular aperture is represented in Figure 2. The antenna
shows a −10 dB impedance bandwidth from 0.107 THz to 0.137 THz. A wide bandwidth
of 30 GHz is suitable to achieve good resolution for breast cancer imaging. The VSWR plot
in Figure 3 represents the impedance matching of the antenna over the operating frequency
band. A VSWR value less than two is desired for the impedance matching.

Figure 1. Topology of the different parts of the proposed aperture-coupled structure: (a) uppersub-
strate printed with a radiator, (b) bottom substrate with a feedline, (c) ground plane with the aperture
below the bottom substrate, and (d) perspective view.

Table 2. Geometrical values of the designed antenna.

Parameter Name Size (mm) Parameter Name Size (mm)

W 3.5 L 3.5
Wp 2 Lp 2
Wg 0.5 Lg 1.5
Wc 0.9 Lc 0.3
Wf 0.2 Lf 2.8

Figure 2. The |S11| parameter of the proposed antenna.

Micromachines 2023, 14, 1281 5 of 15

Figure 3. The VSWR of the proposed antenna.

The size and position of the aperture are the most important design parameters of
aperture-coupled structures. Coupled power varies the resonance current and resistivity of
the patch and stimulates the multiple resonance mode, which helps to attain the broader
bandwidth. The position of the aperture is centered below the patch, as it provides the
dominant magnetic polarization and maximum coupling effect. Hence, it is required to
adjust the size of the aperture. The size of the coupling aperture should be smaller than
the radiator to agree with the maximum impedance matching, lower back scattered power,
and enhanced efficiency [21]. As the area of the aperture slot is increased, the coupling
effect is enhanced, but it leads to an increase of the antenna impedance. In turn, it causes
the deterioration of impedance matching [22]. Thus, to gain the optimum impedance
matching and broader bandwidth, the width (‘wc’) of the aperture slot is varied and
analyzed through a parametric sweep. The plot for varying the width reflection coefficient
is shown in Figure 4. The slot width is varied from 0.7 mm to 1.0 mm. Optimum coupling
is achieved at the width ‘wc’ of 0.9 mm. The bandwidth for the lower cut-off frequency
increases with the increasing slot width but reduces the impedance matching.

Figure 4. The |S11| parameter for the varying slot widths (wc).
Micromachines 2023, 14, 1281 6 of 15

The radiation efficiency of the antenna over the entire frequency spectrum is plotted
in Figure 5. The antenna shows more than a 75% radiation efficiency. A 3D power pattern
is represented in Figure 6. It can be observed that gains of 6.38 dBi at 115 GHz, 4.96 dBi
at 125 GHz, and 6.34 dBi at 135 GHz are obtained. The maximum power is oriented
towards the front lobes, representing the low power loss in the back and side lobes. The
wide bandwidth and efficient radiation characteristics of the proposed antenna make it an
appropriate candidate for THz imaging.

Figure 5. The radiation efficiency of the antenna.

Figure 6. The gain of the antenna (a) at 115 GHz (b), 125 GHz (c), and 135 GHz.

3. Performance Analysis of Antenna for Breast Cancer Detection

3.1. Design of Breast Phantom and Simulation Setup for Imaging of Breast Cancer
The definitive objective of the proposed structure is to extricate the unhealthy tissues
inside a breast by detecting the dissimilarity in the |S11| signal (backscattered signal)
of the antenna between healthy and unhealthy tissues. In order to accomplish this, an
equivalent breast tissue phantom in a spherical shape with a 20 mm radius (average value)
is considered. It consists of a 2 mm skin layer (εr = 38 and conductivity = 1.49 S/m), 16 mm
of a fat layer, a tumor radius of 2 mm, εr = 67, and conductivity of 47 S/m [26,27]. The
designed phantom model, along with the simulation setup, are shown in Figure 7a. To
accumulate the antenna backscattered signal, two setups are considered. Figure 7b,c depict
two antenna structures arranged in a face-to-face position with a 1 mm separation between
each antenna and the tissue.
Micromachines 2023, 14, 1281 7 of 15

Figure 7. (a) Breast tissue with a tumor. (b) Simulation setup for cancer detection: a side-by-side
view and (c) a face-to-face view.

3.2. Backscattered Signal Analysis for Tumor Detection

According to the literature, unhealthy tissue has a higher water content and higher
relative permittivity as compared to healthy tissue. Thus, at the interface of two diverse
mediums, electromagnetic radiation will undergo multiple reflection and scattering effects.
Figure 8 represents the backscattered signal of the antenna for the free space, without
tumor, and with tumor (side-by-side and face-to-face) configurations. In the free space,
the antenna has enclosed the frequencies from 0.107 THz to 0.137 THz; that is significant
for the dispersion of radiated power at different depths. As the antenna is positioned
corresponding to the tissue (healthy breast), a large difference in the |S11| parameters
(backscattered signals) can be noticed over the whole frequency spectrum. Similarly,
when placing the antenna on the cancerous breast tissue, a dissimilarity in the scattering
parameters can be detected. For both the evaluation setups, it can be observed that the
maximum deviation of the scattering signal is obtained at 118 GHz. For the face-to-face
configuration, there is a deviation of 7 dB, and for the side-by-side configuration, a deviation
of 5 dB is found. The entire operational band’s |S11| displays substantial change, which
qualifies the antenna to detect the presence of tumor cells. Further, a summary of the
variations that happen in the value of the reflection coefficient at different frequencies of
the transmitted THz pulse is shown in Table 3.

Figure 8. Backscattered signal of the proposed antenna.

Micromachines 2023, 14, 1281 8 of 15

Table 3. Comparison of |S11| variations in the absence and presence of tumor w.r.t. (Figure 8).

Difference in Difference in
|S11| on Breast |S11| on Breast
Frequency at |S11| on Breast Magnitude of Magnitude of
with Tumor (dB) with Tumor (dB)
which |S11| is Tissue without |S11| with and |S11| with and
in Face-to-Face in Side-by-Side
Analyzed (GHz) Tumor (dB) without Tumor without Tumor
Configurations Configurations
(Face-to-Face) (Side-by-Side)
119 −26.5 −20 −22 6.5 dB 4.5 dB
130 −18 −21.5 −21.5 3.5 dB 3.5 dB

As studied in the literature [28–30], breast tissue includes different dielectric layers
with varying thickness. Variations in the dielectric materials have a significant impact on the
antenna performance and sensitivity to tumors. Thus, an analysis of the backscattered signal
for varying breast sizes of the radius R with a tumor and without a tumor is performed.
Figure 7a depicts a phantom model with a fat layer. In the case of a 70 mm spherical
phantom, the skin layer has a thickness of 3 mm, the fat layer has a thickness of 62 mm,
and a 5 mm tumor is present. For the 50 mm phantom, the skin layer thickness is 2.8 mm,
the fat layer radius is 42.2 mm, and the tumor measures 5 mm. In the case of a 30 mm
phantom, the skin thickness is 2.5 mm, the tumor radius is 4 mm, and the fat layer has a
radius of 23.5 mm. The reflection coefficient for varying the phantom sizes is shown in
Figure 9. It is evident that, as the phantom size increases, the backscattered signal shifts
upwards to 125 GHz and downwards towards higher frequencies. With a tissue size of
70 mm, the antenna covers the entire bandwidth spectrum from 112 GHz to 135 GHz,
exhibiting significant deviations in the reflection coefficient in the presence of unhealthy
tumor cells within the breast. For a radius of 70 mm, a maximum deviation of 7 dB is
observed at 127 GHz, while, for a radius of 30 mm, a maximum deviation of 4 dB occurs
at 117 GHz. These findings underscore the impact of breast size and tumor presence on
the backscattered signal. The results demonstrate the ability of the antenna to detect and
differentiate tumor-related deviations in the reflection coefficient within specific frequency
ranges. Such insights contribute to the understanding and development of efficient antenna
systems for terahertz imaging in breast cancer detection.

Figure 9. Backscattered signal for varying phantom sizes with the radius (R).

Figure 10 shows the transmission coefficient |S21| of the antenna for the two matching
antennas in a side-by-side and face-to-face configuration for different phantom sides. |S21|
Micromachines 2023, 14, 1281 9 of 15

is examined to take the far-field effect of the two antennas on each other over the whole
bandwidth. It should be low, as it indicates a direct power transfer from one antenna to
another. The |S21| value is below −30 dB for all the phantom sizes in both the side-by-side
and face-to-face configurations. Except at 137 GHz in the face-by-face configuration, a stable
|S21| is accomplished in both operational scenarios. The transmission coefficient exhibits
a similar type of volatility as shown in [21]. The electric field distribution is measured and
depicted in Figure 11 to support the fluctuation of the power distribution in heterogeneous
body tissues. It is obvious that the power absorbed by the tissue layers is not uniform,
and some of the absorbed power is taken up by the tumor, which causes deflections in the
radiation patterns coming from various ray directions.

Figure 10. Transmission coefficient (|S21|) of the antenna.

Figure 11. Electric field distribution for a face-to-face (a–c) and side-by-side (d–f) configuration.
Micromachines 2023, 14, 1281 10 of 15

Although the antenna’s frequency domain performance is consistent, imaging requires

research into the time domain performance. Figures 12 and 13 display the input signal
and the received signal for the two evaluation setups with and without a tumor. For all
configurations, the received waveform is aligned with the transmitted signal with minimal
variations. As a result, the convenience of an antenna for THz imaging is represented by
both a time and frequency domain analysis. In Table 4, a comparison of the proposed THz
antenna for imaging applications with the existing structures is listed.

Figure 12. (a) Transmitted and (b) received pulses for the face-to-face setup.
Micromachines 2023, 14, 1281 11 of 15

Figure 13. (a) Transmitted and (b) received pulses for the side-by-side setup.
Micromachines 2023, 14, 1281 12 of 15

Table 4. Comparison of the proposed THz imaging antenna with existing structures.

Frequency Cancer Evaluation Deviation

Refs. Size Bandwidth Gain
(THz) Parameter Value
[9] 0.312 1105 × 500 × 100 (µm3 ) - 6.04 dB Not performed -
[11] 1.00 800 nm × 800 nm 30 GHz 20 dBi E-field -
[12] 1.5 480 nm × 480 nm 0.3 THz 24 dBi E-field -
Reflection
3 dB for 200 µm
[13] 0.198 600 × 600 (µm2 ) 15 GHz 3.4 dBi coefficient and
tumor
E-field
[16] 0.132 500 × 960 (µm2 ) 58 GHz 5.6 dB Not analyzed -
Reflection
[20] 0.7 300 × 300 (µm2 ) 34 GHz 2.07 dB coefficient and 7 dB
Q-factor
0.0395 THz
Resonance
[22] 4.6 - 1.5 THz 5 dB frequency
Frequency and SAR
deviation
Reflection
This 7 dB for 2 mm
0.120 3.5 mm × 3.5 mm 32 GHz 6.38 dBi coefficient and
work radius tumor
E-field

The provided Table 4 presents a comparison of various studies on terahertz imag-

ing for cancer evaluation, highlighting the frequency, size, bandwidth, gain, evaluation
parameters, and deviation values. It offers insights into different approaches and their
performances in detecting and evaluating cancerous conditions. Reference [9] reported a
frequency of 0.312 THz, but no bandwidth was specified. The evaluation parameter and
deviation value were not provided, making it challenging to assess the effectiveness of the
approach. Similarly, References [11,12] provided specific sizes and gains, but the evaluation
parameters and deviation values were not mentioned. This lack of information limits our
understanding of their effectiveness in cancer evaluation. Reference [13] focused on a fre-
quency of 0.198 THz, with a size of 600 × 600 µm2 . The evaluation parameters included the
reflection coefficient and E-field, and a deviation value of 3 dB was reported for a 200 µm
tumor. Reference [16] provided a frequency of 0.132 THz and a size of 500 × 960 µm2 .
While the gain was given as 5.6 dB, the evaluation parameters and deviation values were
not analyzed or reported. Thus, it is challenging to determine the performance of this
approach in cancer evaluation. Reference [20] explored a frequency of 0.7 THz and a size of
300 × 300 µm2 . The evaluation parameters included the reflection coefficient and Q-factor,
with a reported deviation value of 7 dB. Reference [22] examined a higher frequency of
4.6 THz with an unspecified size. The resonance frequency and SAR (specific absorption
rate) were evaluated, reporting a deviation of 0.0395 THz. This demonstrated the capability
of the method in detecting frequency variations associated with cancerous tissues. This
work focused on a frequency of 0.120 THz and a size of 3.5 mm × 3.5 mm. The evaluation
parameters included the reflection coefficient and E-field, with a reported deviation value
of 7 dB for a 2 mm radius tumor. This indicated the sensitivity of the proposed approach in
detecting tumors within the specified size range. This study and Reference [13] considered
the reflection coefficient and E-field. However, Reference [13] additionally analyzed the
backscattered signal’s deviation value for a specific tumor size of 200 µm, reporting a 3 dB
deviation. In comparison, the current study presents a deviation value of 7 dB for a 2 mm
radius tumor. In terms of bandwidth and gain, Reference [13] specified a bandwidth of
15 GHz and a gain of 3.4 dBi. In contrast, the current study reports a bandwidth of 32 GHz
and a gain of 6.38 dBi. These parameters affect the system’s ability to capture a wide range
of frequencies and enhance the received signal.
Micromachines 2023, 14, 1281 13 of 15

Ultimately, with the exception of References [11,12], aperture-coupled technology

exhibits a higher gain compared to simple planar geometry. However, a sensitivity analysis
for unhealthy tissues was not performed in these references. Additionally, the designed
structures had wider bandwidths, except for References [16,22]. Nevertheless, the proposed
structure demonstrates a significantly higher sensitivity in diagnosing unhealthy cells.
Furthermore, the designed structure is simple, cost-effective, and offers better gain, along
with excellent sensitivity, when detecting small-sized tumors.

4. Conclusions
The configuration employed for the aperture-coupled patch antenna follows a stan-
dard design, which is specifically chosen to achieve two main objectives: a broad −10
dB impedance bandwidth and consistent operating characteristics across a wide range
of frequencies known as ultra-wideband (UWB) frequencies. This is accomplished by
utilizing a rectangular patch as the main element of the antenna, along with an optimized
coupling slot that facilitates the desired performance. To assess the antenna’s effectiveness
in the terahertz (THz) range, an equivalent tissue phantom is used as the testing medium.
The tissue phantom serves as a representative model for the evaluation of the antenna’s
performance. When the antenna is positioned on heterogeneous tissue, it exhibits a notable
ability to differentiate the backscattered signal. This means that the antenna is capable of
distinguishing between different signals reflected by various types of tissues. It is worth
noting that the electrical characteristics of the tissue tend to change with the variations in
the magnitude of the backscattered signal. This property can be effectively utilized to obtain
imaging information. By analyzing the variations in the |S11| parameter, which quantifies
the reflection coefficient of the antenna, significant differences can be observed. Specifically,
in a face-to-face scenario at 125 GHz, there is a maximum deviation of 5 dB, while, in a side-
by-side scenario at the same frequency, the maximum deviation is 7 dB. These deviations
indicate the potential for acquiring valuable information through the backscattered signal.
Moreover, the distribution of the electric field generated by the antenna is assessed to
evaluate the presence of a nonuniform power distribution. This analysis helps to determine
if there are any areas where the power concentration is significantly imbalanced, which
could affect the antenna’s overall performance. Additionally, the linearity of the timing
signals is evaluated using the received and transmitted pulses. By examining the timing
characteristics of these pulses, it is possible to determine whether the antenna operates
linearly and accurately in terms of timing. This assessment is crucial to ensure reliable and
precise signal transmission and reception. In summary, the configuration of the aperture-
coupled patch antenna is carefully designed to achieve a broad impedance bandwidth
and stable performance at UWB frequencies. By utilizing an equivalent tissue phantom,
the antenna’s performance in the THz range was evaluated, particularly in terms of its
ability to differentiate backscattered signals. The variations in the electrical characteristics
of the tissue, caused by changes in the backscattered signal magnitude, can be exploited
for imaging purposes. The analysis of the |S11| parameter reveals significant deviations,
allowing for valuable information extraction. The distribution of the electric field and the
linearity of timing signals were also examined to assess the power distribution and signal
timing accuracy, respectively.

Author Contributions: Conceptualization, A.G. and V.K.; methodology, A.G. and D.G.; software,
A.G.; validation, M.H.A. and A.J.; investigation, D.G. and M.H.A.; resources, A.G.; data curation,
A.G.; writing—original draft preparation, A.G. and V.K.; writing—review and editing, M.H.A., A.J.
and D.G.; and visualization, A.G. and V.K. All authors have read and agreed to the published version
of the manuscript.
Funding: This research received no external funding.
Data Availability Statement: Not applicable.
Conflicts of Interest: The authors declare no conflict of interest.
Micromachines 2023, 14, 1281 14 of 15

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