\documentclass[10pt]{article}

\usepackage{fullpage}
\usepackage{setspace}
\usepackage{parskip}
\usepackage{titlesec}
\usepackage[section]{placeins}
\usepackage{xcolor}
\usepackage{breakcites}
\usepackage{lineno}
\usepackage{hyphenat}





\PassOptionsToPackage{hyphens}{url}
\usepackage[colorlinks = true,
            linkcolor = blue,
            urlcolor  = blue,
            citecolor = blue,
            anchorcolor = blue]{hyperref}
\usepackage{etoolbox}
\makeatletter
\patchcmd\@combinedblfloats{\box\@outputbox}{\unvbox\@outputbox}{}{%
  \errmessage{\noexpand\@combinedblfloats could not be patched}%
}%
\makeatother


\usepackage{natbib}




\renewenvironment{abstract}
  {{\bfseries\noindent{\abstractname}\par\nobreak}\footnotesize}
  {\bigskip}

\titlespacing{\section}{0pt}{*3}{*1}
\titlespacing{\subsection}{0pt}{*2}{*0.5}
\titlespacing{\subsubsection}{0pt}{*1.5}{0pt}


\usepackage{authblk}


\usepackage{graphicx}
\usepackage[space]{grffile}
\usepackage{latexsym}
\usepackage{textcomp}
\usepackage{longtable}
\usepackage{tabulary}
\usepackage{booktabs,array,multirow}
\usepackage{amsfonts,amsmath,amssymb}
\providecommand\citet{\cite}
\providecommand\citep{\cite}
\providecommand\citealt{\cite}
% You can conditionalize code for latexml or normal latex using this.
\newif\iflatexml\latexmlfalse
\providecommand{\tightlist}{\setlength{\itemsep}{0pt}\setlength{\parskip}{0pt}}%

\AtBeginDocument{\DeclareGraphicsExtensions{.pdf,.PDF,.eps,.EPS,.png,.PNG,.tif,.TIF,.jpg,.JPG,.jpeg,.JPEG}}

\usepackage[utf8]{inputenc}
\usepackage[ngerman,greek,english]{babel}



\usepackage{float}








\begin{document}

\title{Compact 4 \selectlanguage{ngerman}× 4 Butler matrix design-based switch beamforming antenna
array for 5G applications\selectlanguage{english}}



\author[1]{Ali Abdulateef  Abdulbari}%
\author[2]{Sharul Kamal Abdul Rahim}%
\author[3]{Tan KIM GEOK}%
\author[4]{Amna shibib kamel}%
\author[4]{Raya adil kamil}%
\author[5]{Hatem Oday Hanoosh}%
\author[4]{Mustafa Mohammed Jawad}%
\affil[1]{University of Technology- Iraq, Baghdad}%
\affil[2]{Universiti Teknologi Malaysia Wireless Communication Centre}%
\affil[3]{Multimedia University Faculty of Engineering and Technology}%
\affil[4]{Al-Turath University College}%
\affil[5]{Imam Ja'afar Al-Sadiq University}%


\vspace{-1em}



  
  \date{May 28, 2024}


\begingroup
\let\center\flushleft
\let\endcenter\endflushleft
\maketitle
\endgroup





\selectlanguage{english}
\begin{abstract}
This paper, presents a 4\selectlanguage{ngerman}×4 BM based on four direction switch BM antenna
array. The proposed design operated at 3.5 GHz. The use of multi-beam
antennas or switched-beam antenna arrays (SAAs) promised users of
high-gain and large coverage areas for 5G technologies. The BM was
implemented by combining 3-dB BLC, two crossovers, and 45
\textsuperscript{o} phase shifters fabricated on the RT5880LZ substrate,
with using a triangular slot and T-shape based on the BM design. The
proposed design focused on the miniaturization and enhancement of the
bandwidth. The return loss and isolation were better than -15 dB at all
the ports, according to the simulated and measured result showed that
with excellent insertion loss -6.1 ± 2 dB. A fractional bandwidth of
49.7\% and the overall dimension were reduced to 56\% as compared to the
conventional BLC and crossover. Hence, the proposed design of BM
performed an excellent size reduction of 80\% and improvement bandwidth
up to 836 MHz compared to the traditional BM. The switched beam
directions were measured at -34 \textsuperscript{o}, -40
\textsuperscript{o}, +32 \textsuperscript{o} and +35 \textsuperscript{o}
at 3.5 GHz for each input port of 1-4 excitation. The proposed design BM
is suitable of 5G application.%
\end{abstract}\selectlanguage{ngerman}%



\sloppy


Compact 4 \selectlanguage{ngerman}× 4 Butler matrix design-based switch beamforming antenna
array for 5G applications

Ali Abdulateef Abdulbari \textsuperscript{* 1,1,2}, Sharul Kamal Abdul
Rahim \textsuperscript{2,1}, Tan KIM GEOK\textsuperscript{3} , Amna
shibib kamel \textsuperscript{4,2}, Raya adil
kamil\textsuperscript{5,2}, Hatem Oday Hanoosh\textsuperscript{4,6}
,Mustafa Mohammed Jawad\textsuperscript{7,2}

\textsuperscript{1}Wireless Communication Centre (WCC), School of
Electrical Engineering, Universiti Teknologi Malaysia (UTM), Skudai
81310, Malaysia.

\textsuperscript{2}Department of Medical Devices Techniques Engineering,
Al-Turath University College, Baghdad, Iraq.

\textsuperscript{3}Faculty of Engineering and Technology, Multimedia
University, Melaka 75450, Malaysia.

\textsuperscript{4}Department of Computer Techniques Engineering,
College of Information Technology, Imam Ja'afar Al Sadiq
University,Samawah, Iraq.

\textbf{ABSTRACT}

This paper, presents a 4×4 BM based on four direction switch BM antenna
array. The proposed design operated at 3.5 GHz. The use of multi-beam
antennas or switched-beam antenna arrays (SAAs) promised users of
high-gain and large coverage areas for 5G technologies. The BM was
implemented by combining 3-dB BLC, two crossovers, and
45\textsuperscript{o} phase shifters fabricated on the RT5880LZ
substrate, with using a triangular slot and T-shape based on the BM
design. The proposed design focused on the miniaturization and
enhancement of the bandwidth. The return loss and isolation were better
than -15 dB at all the ports, according to the simulated and measured
result showed that with excellent insertion loss -6.1 ± 2 dB. A
fractional bandwidth of 49.7\% and the overall dimension were reduced to
56\% as compared to the conventional BLC and crossover. Hence, the
proposed design of BM performed an excellent size reduction of 80\% and
improvement bandwidth up to 836 MHz compared to the traditional BM. The
switched beam directions were measured at -34\textsuperscript{o},
-40\textsuperscript{o}, +32\textsuperscript{o} and
+35\textsuperscript{o} at 3.5 GHz for each input port of 1-4 excitation.
The proposed design BM is suitable of 5G application.

\textbf{Keyword:}Beamforing, Butler matrix, antenna array, 5G,
triangular slot, T-shape, branch line coupler (BLC), microstrip antenna,
antenna array.

\textbf{Introduction}The demand for wireless technology is substantially
increasing because of the rapid growth of wireless technological
innovations. Currently, several billion wireless-electronic devices are
linked to the internet network, and these figures are expected to rise
in the coming years. So, researchers have started to put tremendous
effort in the area of 5G technology{[}1{]}{[}2{]}{[}3{]}. The deployment
of 5G wireless, as well as the current and upcoming Beyond 5G (B5G)
communication system, point towards a revolutionary change in modern-day
telecommunications, leading to a complete paradigm shift in the way
end-users will communicate in the coming years {[}4{]}{[}5{]}.
Meanwhile, the number of co-channel interference users will increase and
improve the inferior quality of service {[}6{]}{[}7{]}. In the
development of 5G systems, it is envisaged that switched-beam antenna
arrays (SAAs) would play a vital role in obtaining the desired
performance at the transceivers. This is the main objective sought by
many researchers in the area of beam-forming network. Their focuses have
always been on the problem and quality enhancement of the communication
link {[}8{]}. Hence, the application of switch beam-forming networks
(SBFNs) has always been the area of interest among researchers{[}9{]}.
This technology significantly contributes to wider bandwidth and
directional antenna array that can transfer and focus radiated power in
the desired direction. It is widely applied in wireless communications
{[}4{]}. The SBFNs are categorised into several types, such as Nolen
matrix {[}10{]}, Blass matrix {[}11{]}, Rotman lens {[}12{]}, and Butler
matrix {[}13{]}. Butler matrix or BM is a popular technique due to its
low cost, simple configuration, and low power dissipation. This
technique is widely used in the filed beam-forming of antenna array
{[}14{]}. BM is a passive device with multiple input and output ports.
BM 4×4 consists of four 3-dB directional coupler, two phase shifters,
and a crossover {[}15{]}. The beam-forming and beam-steering procedures
are controlled by the BM design employing an antenna array. The
signal-to-noise and clutter ratio is improved by the BM design's usage
of frequency reuse {[}16{]}. In the last years, the BM 4×4 has been
studied and improved in different ways, such as in {[}17{]} and for low
loss {[}18{]}. The problem with conventional BM large size and
narrow-band characteristics {[}19{]}{[}20{]} is that these requirements
are unable to meet the fifth generation (5G) application. However, to
solve this issue, researchers have started to introduce a new design
using many techniques to improve the Butler matrix{[}21{]}. The reported
literature {[}22{]}{[}23{]}{[}24{]} has highlighted microstrip
artificial transmission lines (ATLs) triangular slot, BM without
crossover and phase shifter, and forward wave present in {[}25{]}. A
reduced BM network has also been implemented at stub loaded TL, as well
as presented and the multibeam antenna array has been validate. The size
achieved for the Butler matrix was approximately 55\% as compared to the
traditional BM design {[}26{]}. Another way of using miniaturisation
butler matrix design is through meandered line and dumbbell-shaped
cross-slot technique based on the branch line coupler. The fractional BW
was enhanced up to 37.5\% and size miniaturised of 17\% {[}27{]}. The
coupler, crossover, and phase shifter sizes were reduced by BLC using
artificial transmission lines, as in {[}28{]}. Recently, a triangular
slot type artificial transmission line (ATL) has also been proposed. The
artificial transmission line is, an easy-to-design, compact structure
and easy to adjust electrical parameters, which is also helpful to build
block for different microwave passive components {[}29{]}. The proposed
4 × 4 Butler matrix was design by using software Computer Simulation
Technology (CST). This design utilised modified BLC, respectively. The
BM Implementation was on the Rogers RT5880LZ with 0.25 mm thickness,
relative permittivity \selectlanguage{greek}ε\selectlanguage{english}r=2, and loss tangent
tan\(\delta\)=0.002. Several BM designs that have been reported
in previous work improved the bandwidth and size reduction. However,
none of them attained bandwidth improvement and size reduction, together
with an excellent performance for 5G beamforming network. Table 1
displays the specification design of the proposed designs. The novelty
of this paper includes design of the BLC, crossover and BM by using
triangular slot and T-shape structure, and antenna array based zig-zag
shape.\textbf{Table 1. Specification of proposes designs.}\selectlanguage{english}
\begin{longtable}[]{@{}llll@{}}
\toprule
\begin{minipage}[b]{0.22\columnwidth}\raggedright\strut
\textbf{Parameters}\strut
\end{minipage} & \begin{minipage}[b]{0.22\columnwidth}\raggedright\strut
\textbf{Coupler}\strut
\end{minipage} & \begin{minipage}[b]{0.22\columnwidth}\raggedright\strut
\textbf{Crossover}\strut
\end{minipage} & \begin{minipage}[b]{0.22\columnwidth}\raggedright\strut
\textbf{Butler matrix}\strut
\end{minipage}\tabularnewline
\midrule
\endhead
\begin{minipage}[t]{0.22\columnwidth}\raggedright\strut
\textbf{Frequency}\strut
\end{minipage} & \begin{minipage}[t]{0.22\columnwidth}\raggedright\strut
3.5 GHz\strut
\end{minipage} & \begin{minipage}[t]{0.22\columnwidth}\raggedright\strut
3.5 GHz\strut
\end{minipage} & \begin{minipage}[t]{0.22\columnwidth}\raggedright\strut
3.5 GHz\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.22\columnwidth}\raggedright\strut
\textbf{Technique}\strut
\end{minipage} & \begin{minipage}[t]{0.22\columnwidth}\raggedright\strut
Triangular slot and T-shape\strut
\end{minipage} & \begin{minipage}[t]{0.22\columnwidth}\raggedright\strut
Triangular slot and T-shape\strut
\end{minipage} & \begin{minipage}[t]{0.22\columnwidth}\raggedright\strut
Triangular slot and T-shape\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.22\columnwidth}\raggedright\strut
\textbf{BW}\strut
\end{minipage} & \begin{minipage}[t]{0.22\columnwidth}\raggedright\strut
1 GHz\strut
\end{minipage} & \begin{minipage}[t]{0.22\columnwidth}\raggedright\strut
1GHz\strut
\end{minipage} & \begin{minipage}[t]{0.22\columnwidth}\raggedright\strut
500 GHz\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.22\columnwidth}\raggedright\strut
\textbf{Phase difference}\strut
\end{minipage} & \begin{minipage}[t]{0.22\columnwidth}\raggedright\strut
90\textsuperscript{o}\selectlanguage{ngerman}±1\strut
\end{minipage} & \begin{minipage}[t]{0.22\columnwidth}\raggedright\strut
0\textsuperscript{o}\strut
\end{minipage} & \begin{minipage}[t]{0.22\columnwidth}\raggedright\strut
-45,135,-135,45\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.24\columnwidth}\raggedright\strut
\textbf{Insertion loss}\strut
\end{minipage} & \begin{minipage}[t]{0.24\columnwidth}\raggedright\strut
-3dB\selectlanguage{ngerman}±0.1\strut
\end{minipage} & \begin{minipage}[t]{0.24\columnwidth}\raggedright\strut
0dB\strut
\end{minipage} & \begin{minipage}[t]{0.24\columnwidth}\raggedright\strut
-6.1\selectlanguage{ngerman}±2dB\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.22\columnwidth}\raggedright\strut
\textbf{S11}\strut
\end{minipage} & \begin{minipage}[t]{0.22\columnwidth}\raggedright\strut
Below-10dB\strut
\end{minipage} & \begin{minipage}[t]{0.22\columnwidth}\raggedright\strut
Below -10dB\strut
\end{minipage} & \begin{minipage}[t]{0.22\columnwidth}\raggedright\strut
Below-10dB\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.22\columnwidth}\raggedright\strut
\textbf{S41}\strut
\end{minipage} & \begin{minipage}[t]{0.22\columnwidth}\raggedright\strut
Below-10dB\strut
\end{minipage} & \begin{minipage}[t]{0.22\columnwidth}\raggedright\strut
Below -10dB\strut
\end{minipage} & \begin{minipage}[t]{0.22\columnwidth}\raggedright\strut
Below-10dB\strut
\end{minipage}\tabularnewline
\bottomrule
\end{longtable}

Design of triangular slot The basic structure of the proposed microstrap
artificial model transmission lines (ATL) with triangular slot is
illustrated in Fig. 1(a). The equivalent circuit model of designed
triangular slot patch BLC as illustrate in Fig. 1(b). The circuit model
consists of combination inductors and capacitors both in series and
parallel. We included an inductor and capacitors for the splits for the
metal strip. The overall area of the triangular slot patch was
approximated to that of the low impedance line in this case. The related
parameters can be expressed as follows{[}30{]}:

T\textsubscript{ATL} = \(\left(\frac{L}{2}\right)^{2}\) (1)\(\frac{L}{2}\)
\textsubscript{=}\(\sqrt{{2W}_{\text{TL}}L_{\text{TL}}}\ \) (2)

Where TATL, L, WTL, and LTL, the width and length of the base line were
ATL and TTL, respectively. In order to miniaturise the common 3-dB BLC,
we proposed a triangular slot -type artificial model transmission lines
with modified slots. This ATL was an isosceles triangular slot formed by
folding a stepped impedance line (SIL) into a right angle, as shown in
Fig.2 (a) Sex triangular slot BLC.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image1/image1}

\end{center}
\end{figure}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image2/image2}

\end{center}
\end{figure}

(b)

\textbf{Fig. 1.} (a) Geometry of basic (ATL) building (b) Lumped element
equivalent circuit model of the design

The lumped equivalent circuit in Fig. 2 (d) to the impedance matrix
{[}Z{]} 90\textsuperscript{o} electrical lengths and certain
characteristic impedance were used in the calculation for the first step
of an ATL design.

{[}Z{]} = \(\par
\begin{bmatrix}\frac{Z_{2\ }\left(Z_{3}+Z_{2}\right)}{{2Z}_{2}+\ Z_{3}}\ Z_{1}\text{\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ }\frac{Z_{2}^{2}}{{2Z}_{2}+\ Z_{3}}\\
\frac{Z_{2}^{2}}{{2Z}_{2}+\ Z_{3}}\text{\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ }\frac{Z_{2\ }\left(Z_{3}+Z_{2}\right)}{{2Z}_{2}+\ Z_{3}}\ Z_{1}\\
\end{bmatrix}\) (3)

Where Z1 = jxL1, Z2 = -j/(wCb), Z3 = jwLc. L1,L2,L3 and w were the
lumped element values in Fig. 2 (b) and angular frequency,
respectivaly.The image impedance of the {[}Z{]}, Z0, for the
characteristic impedance of the ATL could then be calculated.

Z\textsubscript{0} = \(\sqrt{z_{11\ }^{2}-z_{22}^{2}}\) (4)

From S22 was given as Eq.(5) and the component of S21 should be zero for
any \selectlanguage{greek}λ/\selectlanguage{english}4 transmission line of \selectlanguage{greek}θ \selectlanguage{english}= 900, \selectlanguage{english}we could easily obtain the
relation of Eq.(6) for a 900 \selectlanguage{english}artificial model transmission lines (ATL).

S22 =\(\frac{2Z_{22\ }Z_{T}}{{(Z}_{11}+\ Z_{T)\ }{(Z}_{22}+\ Z_{T)-\ }Z_{22\ }Z_{21}}\)= \(\left|S_{21}\selectlanguage{greek}\right|e^{\text{jθ}}\selectlanguage{english}\) (5)

Z1Z3 + (2Z1 + Z3) Z2 + Z23 = 0 (6)

How to design an ATL with a Z0 characteristic impedance an electrical
length of 900. \selectlanguage{english}For the first step, we chose L and WTL x (x = 1, 2, and
3), considering the circuit size we needed, and obtained the LTL value
using Eq. (1).

Branch line coupler

The proposed design BLC in this paper was a compact design based on
microstrip artificial transmission lines (ATLs) with triangular slot
patch and T-shape, as shown in Fig. 2, i.e., the coupler fabricated
prototype. The horizontal and vertical TL's respective impedances were
Z0/\(\sqrt{2}\) and Z0, which were 35 and 50 . The width(W) and
length(L) arms of the BLC could be calculated by using the equations in
{[}31{]}. In our design, the chosen centre frequency of the proposed
design was 3.5GHz. The optimised dimensions of the triangular slot ATL
with 50 and 90\textsuperscript{o} electrical length were optimised as
Wp = 14.00mm, W1=1.56 mm, W2= 1.31 mm, Wf = 4.0 mm, Wt = 0.40 mm, Wts =
0.30 mm, Wg = 0.21 mm, Wm = 1.2 mm, L1 = 1.78 mm, L2 = 1.66 mm, Lm =
13.8 mm, Lp = 4.23 mm, Lf = 1.5 mm, Lt = 4.80 mm, Lts = 4.10 mm, Lg =
0.75 mm, respectively. The dimensions for vertical and horizontal of the
unit-call were optimised to achieve the BLC centre frequency of 3.5 GHz.
The main component considered the BLC for the BM design. The proposed
design coupler was simulated by )CST) microwave studio. Using the
proposed design of the impedances, 3 dB BLC Eq.(7) and (8) were computed
through the outputs phase difference \selectlanguage{greek}ϕ \selectlanguage{english}= 90\textsuperscript{o} with Z0 =
50 , the value of the horizontal and vertical arms, which were Z1 = Z0
= 50 , Z2 = Z3 = 35.36 . Z1 = Z0 from Eq.12, which can be simplified
as:

Z\textsubscript{1} = Z\textsubscript{0d} |sin [?] | (7)

Z\textsubscript{2} = Z\textsubscript{3} =\(\frac{Z_{o}d\ sin}{\sqrt{1+\ d^{2}\ \sin^{2\ }}}\)
(8)\(\theta_{1}\)\textsubscript{=}\(\selectlanguage{greek}\frac{\text{π\ }}\selectlanguage{english}{2}\) (9)

\(\theta_{2}\)=tan-1\(\left(\frac{\left(Z_{0}\tan\right)}{Z_{1}}\right)\)(10)

\(\theta_{3}\)=\(\pi\)--tan--1\(\left(\frac{\left(Z_{0}\tan\right)}{Z_{1}}\right)\)(11)

\(\text{\ \ }\theta_{2}\) = tan-1 (tan[?]) [?] (12)

Where, \selectlanguage{greek}ϕ \selectlanguage{english}is the phase difference at 3.5 GHz frequency and (d2) is the
power division ration for the coupler. From Eq (7), for a given phase
difference of BLC as 900, \selectlanguage{english}the electrical lengths were
\(\theta_{2}\) =\(\theta_{3}\) = 900. \selectlanguage{english}The simulated and
measured result for the return loss and phase difference to BLC are
summarised in Fig. 2. The simulated in Fig. 2(a) to BLC operated between
two bands for scattering parameter and isolation loss of 2.91GHz to
4.02GHz and 2.72GHz to 4.16 GHz. The results were below -10dB. The phase
difference to the simulated between the output ports was found to be
900, \selectlanguage{english}as shown in Fig. 2(c).However, the measured result to BLC is as
shown in Fig. 2(b) to the scattering parameter loss and isolation loss
which operated between 2.62GHz to 2.5GHz. The phase difference to the
measured between the output ports was found to be 87.50, \selectlanguage{english}as shown in
Fig. 2(c). This small loss error at 3.6GHz due the SMA and coaxial
cables. The insertion loss to the simulated and measured was also
indicated in Fig.2 (a-b) -2\selectlanguage{ngerman}±0.1dB and -3±0.2dB, respectively. There
small difference between simulated and measured results for the proposed
design BLC due fabricated and tools used. All of these measurements were
carried out using Keysight (AgilentTechnologies) FieldFox N9925A vector
network analyser (VNA). The \selectlanguage{greek}λ/\selectlanguage{english}4 for the artificial transmission lines
(ATLs) triangular slot patch provided good wide bandwidth and size
reduction. The performance parameters such as return loss, insertion
loss, isolation loss, and phase difference between output ports could be
analysed with VNA. The BLC with dimension is as shown in Fig. 3(a),
while the unused ports were terminated with 50 SMA terminator ports
when the measurement took place, are illustrated in Fig. 3(b). Table 2
summarized to comparison the proposed design BLC with the previously
published work.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image3/image3}

\end{center}
\end{figure}

\par\null

(a)\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image4/image4}

\end{center}
\end{figure}

(b)\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image5/image5}

\end{center}
\end{figure}

(c)

Fig. 2. (a) Simulated S-parameters result of the proposed BLC (b)
Measured S-parameters result of the proposed BLC (c) Comparison between
Simulated and measured Phase difference of BLC between two ports
S\textsubscript{12}and S\textsubscript{13}.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image6/image6}

\end{center}
\end{figure}

(a)\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image7/image7}

\end{center}
\end{figure}

(b)

Fig. 3. (a) Fabricated of the proposed design BLC using substrate
RT5880LZ, the BLC ports from 1-4, (b) The BLC under measurement with 50
SMA terminator.

\textbf{Table. 2. C} \textbf{omparison between the Proposed BLC Design
with previous work related}

\textbf{Ref.}

\textbf{Type substrate}

\textbf{Operating}

Freq. (GHz)

\textbf{Fractional}

Bandwidth (S11 = -10dB)

\selectlanguage{ngerman}\textbf{Size (mm × mm)}

\textbf{Loss Error (LE)}

(dB)

\textbf{PD Error (Deg)}

{[}5{]}

FR-4

3.5

30.22\%

27.2 × 16.5

± 0.9dB

-5°

{[}32{]}

Rogers RO4003

3.22

5\%

16.5 × 11.3

± 1dB

-3\textsuperscript{o}

{[}33{]}

FR-4

3.5

6.57\%

23.5 × 17.5

± 1.7dB

-4\textsuperscript{o}

{[}34{]}

Rogers RT5880LZ

3.5

30.81\%

22 × 24

± 0.9dB

-5\textsuperscript{o}

{[}35{]}

FR-4

3.5

14.6\%

16 × 12

± 0.9dB

-1\textsuperscript{o}

{[}36{]}

Rogers RO4003

3.5

17\%

10.5 × 15.5

± 0.5dB

-1.7\textsuperscript{o}

\textbf{{[}This}

work{]}

2023

\textbf{Rogers RT5880LZ}

\textbf{3.5}

\textbf{33.34\%}

\textbf{21.0 × 23.0}

\textbf{± 0.1dB}

\textbf{-1\textsuperscript{o}}

\textbf{Crossover 0dB}

The key feature of the crossover in BM is to avoid overlapping signals
at crossings and maintain a reasonable level of isolation between
signals at crossing lines. It means crossover allows two signals to
cross each other while retaining a high degree of isolation {[}31{]}.
The signal flowed to port 3 when port 1 was excited in contrast to the
signal flowed to port 2 when port 4 was excited. Theoretically,
crossover should be 0dB for the insertion loss. A 50\selectlanguage{english} microstrip
transmission line was used to design the crossover. It was fabricated by
using a single layer Rogers RT5880LZ with relative permittivity (\selectlanguage{greek}ε\selectlanguage{english}r)
1.96, a thickness of 0.25mm, and loss tangent \selectlanguage{ngerman}ð of 0.0009, respectively.
The insertion loss S13 and S24 and as well as the phase difference S13
and S24 were implemented by compact two 3-dB BLC. The simulated return
loss (S11) characteristics were achieved below -10dB within the range
between 2.76GHz to 4.16GHz frequency band. For the selected compact
design crossover for the development of the BM, the insertion loss to
simulated and measured results were -0.16 dB and -0.5 dB, at the centre
frequency of 3.5 GHz. The comparison between the S-parameters' response
compact 0dB crossover is as shown in Fig. 4(a). Meanwhile, the phase
differences between the simulated and measured results were similar to
S13 and S24 is 0\textsuperscript{o}, as shown in Fig. 4(b). The overall
dimension for the fabricated of this work was 40mm × 21mm, as shown in
Fig. 5(a).The proposed design under test of the S-parameters is
illustrated in Fig. 5(b). The loss extra between simulated and measured
induced by the SMA and coaxial cables.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image8/image8}

\end{center}
\end{figure}

\par\null

(a)\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image9/image9}

\end{center}
\end{figure}

(b)

Fig. 4. (a) S-Parameters response of the crossover simulated and
measured of the compact 0 dB (b) Phase different between simulated and
measured of the compact 0 dB crossover.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image10/image10}

\end{center}
\end{figure}

) a)\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image11/image11}

\end{center}
\end{figure}

(b)

Fig. 5. (a) 0dB crossover fabricated by compact two 3-dB BLC with
dimension using RT5880LZ substrate (b) The proposed design 0dB crossover
under test.

\textbf{Design configuration butler matrix}

The proposed design of the 4 \selectlanguage{ngerman}× 4 BM was conducted using a computer
simulation technology (CST) microwave studio. The BM implementation was
created using combined 3dB BLC of Triangular slot and T-shape, two
crossover structures, and 45\textsuperscript{o} phase shifter at the
operate frequency of 3.5 GHz. The proposed design BM fabricated on a
single layer of RT588LZ substrate. The final fabrication of the proposed
BM design, which had the overall area of 87.5mm × 75mm, is as shown in
Fig. 6.

The BM provided four outputs with equal amplitude and phase difference
of -45\textsuperscript{o}, 135\textsuperscript{o},
45\textsuperscript{o}, and -135\textsuperscript{o}, respectively. As a
result, each input port, specifically as port 1, port 2, port 3, and
port 4 were designated as port 5, port 6, port 7, and port 8, was able
to produce four beams in various directions, as illustrated in Fig. 6.
This configuration was of a 4 × 4 BM. Table 3 shows the phase shift that
would be generated on each output based on the excited of the input
ports, and all other ports were terminated at 50\selectlanguage{english} loads. There were four
cases. When input port 1 is excited the phase difference between the
output ports -45\textsuperscript{o}. The output 135deg phase difference
when input port 2 is excited. The phase difference between the output
ports in the third case will be -135\textsuperscript{o} when input port
3 is excited. The last port phase difference of the output port is 45deg
when input port 4 is excited. The proposed BM was validated in
accordance with design criteria provided in Table 1.

\textbf{Table 3.} The phase difference between the outputs ports of the
Butler matrix feed.\selectlanguage{english}
\begin{longtable}[]{@{}lllll@{}}
\toprule
\begin{minipage}[b]{0.19\columnwidth}\raggedright\strut
\textbf{Ports}\strut
\end{minipage} & \begin{minipage}[b]{0.19\columnwidth}\raggedright\strut
\textbf{Output Port 5}\strut
\end{minipage} & \begin{minipage}[b]{0.19\columnwidth}\raggedright\strut
\textbf{Output} \textbf{Port 6}\strut
\end{minipage} & \begin{minipage}[b]{0.19\columnwidth}\raggedright\strut
\textbf{Output} \textbf{Port 7}\strut
\end{minipage} & \begin{minipage}[b]{0.19\columnwidth}\raggedright\strut
\textbf{Output} \textbf{Port 8}\strut
\end{minipage}\tabularnewline
\midrule
\endhead
\begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
\textbf{Input Port1}\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
1350\selectlanguage{english}\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
900\selectlanguage{english}\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
450\selectlanguage{english}\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
00\selectlanguage{english}\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
\textbf{Input Port 2}\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
450\selectlanguage{english}\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
1800\selectlanguage{english}\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
-450\selectlanguage{english}\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
900\selectlanguage{english}\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
\textbf{Input Port 3}\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
900\selectlanguage{english}\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
-450\selectlanguage{english}\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
1800\selectlanguage{english}\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
-450\selectlanguage{english}\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
\textbf{Input Port 4}\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
00\selectlanguage{english}\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
450\selectlanguage{english}\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
900\selectlanguage{english}\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
1350\selectlanguage{english}\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
\textbf{Phase Different Between Output ports}\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
\textbf{-450}\selectlanguage{english}\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
\textbf{+1350}\selectlanguage{english}\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
\textbf{-1350}\selectlanguage{english}\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
\textbf{+450}\selectlanguage{english}\strut
\end{minipage}\tabularnewline
\bottomrule
\end{longtable}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image12/image12}

\end{center}
\end{figure}

\textbf{Fig.6.}RT5880LZ substrate based fabricated prototype of the
proposed 4\selectlanguage{ngerman}×4 BM.

The simulated and measured S-parameters responses of the 4 × 4 Butler
matrix result for different ports are as shown in Fig. 7, respectively.
The P1 of the BM excited return loss was better than 17dB. This could be
seen in the simulation and measured results of the return loss and
insertion loss, which were S11 = -20.5 dB, S15 = -5.91 dB, S16 = -5.5
dB, S17 = -6.3 dB, S18 = -5.7 dB, and S11 = -18 dB, S15 = 6.41 dB, S16 =
-5.6 dB, S17 = -5.8 dB, S18 = -6.0 dB, illustrate in Fig. 7(a - b).
Hence, the average insertion loss for simulated and measured
(S15,S16,S17,S18) were -5.9, 6.0 ± 2 dB, respectively. The P2 of the BM
excited return loss was better than 14 dB. The simulation and measured
results of the return loss and insertion loss were S22 = -25 dB, S25 =
-6.35 dB, S26 = -6.4 dB, S27 = -5.43 dB, S28 = -5.85 dB, and S22 = -34
dB, S25 = -6.72 dB, S26 = -6.65 dB, S27 = -5.81 dB, S28 = -6.76 dB, as
illustrated in Fig 7(c - d), The average insertion loss for simulated
and measured (S25,S26,S27,S28) were -6.0, 6.5 ± 2, and dB, respectively.
The P3 of the BM excited return loss was better than 10 dB. The
simulated and measured results of the return loss and insertion loss
were S33= -24 dB, S35 = -5.3 dB, S36 = -6.2 dB, S37 = -6.25 dB, S38 =
6.4 dB, and S33= -15 dB, S35 = -5.8 dB, S36 = 6.7 dB, S37 = 6.56 dB, S38
= -7 dB, as shown in Fig. 7 (e-f), The average insertion loss for
simulated and measured (S35,S36,S37,S38) were -6.0 ±2 dB, respectively.
The P4 of the BM excited return loss was better than 15 dB. The
simulated and measured results of the return loss and insertion loss
were S44= -20 dB, S45 = -5.4 dB, S46 = -5.18 dB, S47 = -5.0 dB, S48 =
-6.19 dB, and S44= -24 dB, S45 = -5.95 dB, S46 = -6.37 dB, S47 = -7.1
dB, S48 = -6.65 dB, as shown in Fig. 7(g-h). The average insertion loss
for simulated and measured (S45,S46,S47,S48) were -6.1 ± 2dB,
respectively. All the results for P1, P2, P3, and P4 were at centre
frequency of 3.5 GHz. The overall results, when P1, P2, P3, and P4 were
excited, the simulated and measured proposed design 4 × 4 BM had good
agreement between them, although there some variation observed in the
results due to the extra loss phase shifts induced by the cable and
connector.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image13/image13}

\end{center}
\end{figure}

\par\null

(a)\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image14/image14}

\end{center}
\end{figure}

(b)\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image15/image15}

\end{center}
\end{figure}

(c)\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image16/image16}

\end{center}
\end{figure}

(d)\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image17/image17}

\end{center}
\end{figure}

(e)\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image18/image18}

\end{center}
\end{figure}

(f)\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image19/image19}

\end{center}
\end{figure}

(g)\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image20/image20}

\end{center}
\end{figure}

(h)

Fig. 7. Simulated and Measured response of the BM (a-b) for the input
P1, (c-d) for the input P2, (e-f) for the input P3, (g-h) for the input
P4.

Fig. 8 shows the differences in results between simulated and measured
of the phase differences at BM centre frequency of 3.5 GHz. According to
the simulated, the phase differences for output at P1
-45\textsuperscript{o}was (S15, S16, S17, S18) -46\textsuperscript{o},
-43.3\textsuperscript{o}, -41.5\textsuperscript{o}. Correspondingly, the
measured phase differences were (S15, S16, S17, S18) -47.20, \selectlanguage{english}49.40,
\selectlanguage{english}51.10, \selectlanguage{english}respectively. So, the errors between output ports were 10, \selectlanguage{english}1.70,
\selectlanguage{english}3.50 \selectlanguage{english}and 2.20, \selectlanguage{english}4.40, \selectlanguage{english}6.10, \selectlanguage{english}which introduced the average errors of 2.00
\selectlanguage{english}and 4.20, \selectlanguage{english}as shown in Fig. 8 (a-b). However, the quartered phase is as
mentioned in Table 4. The phase differences when P2 excited by 1350 \selectlanguage{english}were
indicated by the simulated as in 1320 \selectlanguage{english}between (S26-S25), 1290 \selectlanguage{english}between
ports (S27 -- S26), and 139\textsuperscript{o} between ports (S28 --
S27), respectively. Thus, the errors between the output ports 30, \selectlanguage{english}60,
\selectlanguage{english}and 40 \selectlanguage{english}introduced the average errors of 4.30, \selectlanguage{english}respectively. The measured
phase differences indicated 1280 \selectlanguage{english}between ports (S26 - S25), 1420 \selectlanguage{english}between
ports (S27 -- S26), 1400 \selectlanguage{english}between ports (S28 -- S27) at center frequency,
as shown in Fig. 8 (c-d). Hence, the errors were 70,\selectlanguage{english}110, \selectlanguage{english}and 90,
\selectlanguage{english}introducing the average errors of 90. \selectlanguage{english}The phase difference between
simulated and measured results reflected very good agreement, as
summarised in Table 4. The output P3 of the BM excited revealed that the
adjacent port should be by -1350 \selectlanguage{english}per design, as summarised in Table 5.
In simulated and measured results, it was that found the phase
differences between the output results were -1330,-\selectlanguage{english}1380,-\selectlanguage{english}1410 \selectlanguage{english}and
-1420,-\selectlanguage{english}1270,-\selectlanguage{english}1310, \selectlanguage{english}at centre frequency of 3.5 GHz, respectively. These
values were different from the desired values by 20, \selectlanguage{english}30, \selectlanguage{english}60 \selectlanguage{english}and
70\selectlanguage{english}\textsuperscript{,} 80, \selectlanguage{english}40, \selectlanguage{english}introducing the average errors of
3.67\textsuperscript{0} \selectlanguage{english}and 6.330 \selectlanguage{english}at operation frequency of 3.5GHz,
respectively.

As show in Fig. 8 good performances between simulated and measured
results when output P4 excited. Table 4 as summarised the phase
difference between adjacent outputs ports should be
45\textsuperscript{o} as per design. For the simulation result, the
phase difference was 44\textsuperscript{0} \selectlanguage{english}between output P5, P6
(\emph{S} 45 - \emph{S} 46), 480 \selectlanguage{english}between P7, P6 (\emph{S} 47 -\emph{S}
46), 400 \selectlanguage{english}between P8, P7 (\emph{S} 48 -- \emph{S} 47), respectively. So,
the errors of the simulated result between outputs 10, \selectlanguage{english}30, \selectlanguage{english}and
5\textsuperscript{0} \selectlanguage{english}introduced the average errors of 30, \selectlanguage{english}respectively.
Meanwhile, the measured result of the phase difference was 500 \selectlanguage{english}between
output P5, P6 (S45 -- S46), 390 \selectlanguage{english}between P7, P6 (S47 -- S46), 520 \selectlanguage{english}between
P8, P7 (S48 -- S47), respectively, at operate frequency of 3.5GHz. So,
the errors of the measured results between outputs 50, \selectlanguage{english}60, \selectlanguage{english}and 70
\selectlanguage{english}introduced the average errors of 60, \selectlanguage{english}respectively. There small error in
phase difference between simulated and measured results due to the
variation for electrical permittivity parameter, as summarised in Table
5.

The comparison of S-parameters between the simulated and measured 4 \selectlanguage{ngerman}× 4
Butler matrix is as illustrated in Fig.9. This comparison between
simulated and measured has small difference with loss error due by SAM
and coaxial cable show in Fig 9. Tables 3 and Table introduce the
summarised simulated and measured results of the BM to the phase
difference between the ports and S-parameters of the proposed BM design
at centre frequency of 3.5GHz, respectively. From Tables 3 and 4, the
phase differences between all of the ports as good agreement with the
desired value. As for Table 5, it displays the comparison between the
proposed design 4 × 4 BW with the previous work.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image21/image21}

\end{center}
\end{figure}

\par\null

(a)\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image22/image22}

\end{center}
\end{figure}

(b)\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image23/image23}

\end{center}
\end{figure}

(c)\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image24/image24}

\end{center}
\end{figure}

(d)\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image25/image25}

\end{center}
\end{figure}

(e)\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image26/image26}

\end{center}
\end{figure}

(f)\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image27/image27}

\end{center}
\end{figure}

(g)\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image28/image28}

\end{center}
\end{figure}

(h)

\textbf{Fig. 8.} Simulated and Measured result of the phase differences
output ports, when P1 (-450\selectlanguage{english}) is excited, when P2 (1350\selectlanguage{english}) is excited, when
P3 (-1350\selectlanguage{english}) is excited, when P4 (450\selectlanguage{english}) is excited.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image29/image29}

\end{center}
\end{figure}

\textbf{Fig.9.} Comparison between simulated and measured S-parameters.

Design switched beamforming antenna array

The switched beamforming antenna array system was based on 4 \selectlanguage{ngerman}× 4 BM with
1 × 4 element antenna array. The use of BM is to shift the beam in a
different direction; the antenna array connected with BM was presented
to develop SAA, as shown in Fig.10. The proposed design of the BM and
antenna system operated at centre frequency of 3.5 GHz, respectively.
The proposed design 4 × 4 BM have four input and output ports, compact
four 3-dB BLC, two crossover structure, and two
45\textsuperscript{o}phase shifters. The use of BM was to shift the beam
in different directions. Depending on the input ports (P1, P2, P3, and
P4) which fed the output ports to the signal phase (P5, P6, P7, and P8)
of the proposed BM, they developed a
-45\textsuperscript{o},+135\textsuperscript{o}, -135\textsuperscript{o},
and +45o phase difference between the output ports. The results of the
simulated and measured radiation patterns, obtained by exiting various
input ports of the proposed BM, produced four orthogonal beams deposed
at -34\selectlanguage{english}0,320,-\selectlanguage{english}400 , \selectlanguage{english}and 350, \selectlanguage{english}as illustrated in Fig. 10. The four beams
steered were 1L, 2R, 2L, and 1R with excited input ports of P1, P2, P3,
and P4, respectively.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image30/image30}

\end{center}
\end{figure}

\textbf{Fig. 10.} Block diagram of the antenna array with the 4 \selectlanguage{ngerman}× 4 BW.

The microstrip patch antenna design was widely used due the small size,
simple structure, and easy fabrication. A microstrip patche antenna
operating at 3.5 GHz. After applying the zig-zag structure at resonating
frequency to 3.5GHz with simulated a return loss (S11) of -20dB and a
bandwidth of 410MHz (3.36GHz- 3.77). The zig-zag structure of the
antenna have measured return loss -31dB and bandwidth of 460MHz
(3.33GHz-3.79GHz) as show in Fig.11 obtained good return loss for the
simulated and measured of the single element patch antenna. The back
side ground plane was reduced due to the back lobe level. Hence, the BM
signal feeding structure to the patch should be carefully designed.
Taking this into consideration. We designed and implemented the block
level for the 4 × 4 Butler matrix and 1 × 4 patch antenna array, then
optimised their performance independently.

In this work, we carefully implemented the Butler matrix overall, the
antenna elements, and the interface structures between our extensive
co-optimization. Fig. 12 exhibits the proposed design of the beamforming
antenna array. The 4 × 4 Butler matrix and 1 × 4 antenna array under
tested, in anechoic chamber were printed on the single layer, as
illustrated in Fig. 13. The single element of the rectangular patch
antenna had the overall size of 16.4 × 16.4 mm2 and the feed line of
1.50 mm was placed with a distance of \selectlanguage{greek}λ\selectlanguage{english}0/2 (\selectlanguage{greek}λ\selectlanguage{english}0) as the wavelength. Due
to this, the overall performance of the Butler matrix and the antenna
elements' interfacing and interconnecting were likely to be affected.
The block diagram of the proposed Butler matrix with antenna array was
designed for the 5G application. The substrate chosen was a Rogers
RT5880LZ with the thickness of 0.25 mm, dielectric permittivity of 2,
and loss tangent of 0.0021, respectively. The inconsistencies may be due
to extra losses and phase shifts prompted by the SAM and coaxial cable.
From now onwards, discussions relating to the results will be based on
the compact structure of the SAA shown in Fig. 14. The radiation pattern
measurements of the fabricated SAA are then performed in the anechoic
chamber using Rohde \& Schwarz ZVL-vector network analyzer (VNA) and
horn antenna. The BFN and distance between the antenna elements selected
the direction of the main beam radiation, as shown in Fig.14\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image31/image31}

\end{center}
\end{figure}

\par\null

\textbf{Fig. 11.} Return loss of single element patch antenna\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image32/image32}

\end{center}
\end{figure}

\textbf{Fig.12.} Compact structure of the SAA, the spacing between the
antenna elements \emph{d} = 0.5\selectlanguage{greek}\emph{λ} \selectlanguage{english}Top layer.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image33/image33}

\end{center}
\end{figure}

\par\null

(a)\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image34/image34}

\end{center}
\end{figure}

(b)

\textbf{Fig.13.} Radiation pattern results of linear 1\selectlanguage{ngerman}×4 antenna array ,
when each input port of BM are excited (a) Simulated and (b) Measured
result, respectively\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image35/image35}

\end{center}
\end{figure}

\par\null

(a)\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image36/image36}

\end{center}
\end{figure}

(b)

\textbf{Fig. 14.} Radiation pattern measurement setup,(a) Butler matrix
inside anechoic chamber(b) Block diagram

\textbf{Table 4.} Simulated and measured Phase difference of the
proposed design BM at 3.5 GHz.\selectlanguage{english}
\begin{longtable}[]{@{}llllllll@{}}
\toprule
\begin{minipage}[b]{0.12\columnwidth}\raggedright\strut
\textbf{Ports}\strut
\end{minipage} & \begin{minipage}[b]{0.12\columnwidth}\raggedright\strut
\textbf{Phase difference between
(P5\textsuperscript{0},P6\textsuperscript{0})}\selectlanguage{english}\strut
\end{minipage} & \begin{minipage}[b]{0.12\columnwidth}\raggedright\strut
\textbf{Phase difference between
(P5\textsuperscript{0},P6\textsuperscript{0})}\selectlanguage{english}\strut
\end{minipage} & \begin{minipage}[b]{0.12\columnwidth}\raggedright\strut
\textbf{Phase difference between
(P6\textsuperscript{0},P7\textsuperscript{0})}\selectlanguage{english}\strut
\end{minipage} & \begin{minipage}[b]{0.12\columnwidth}\raggedright\strut
\textbf{Phase difference between
(P6\textsuperscript{0},P7\textsuperscript{0})}\selectlanguage{english}\strut
\end{minipage} & \begin{minipage}[b]{0.12\columnwidth}\raggedright\strut
\textbf{Phase difference between
(P7\textsuperscript{0},P8\textsuperscript{0})}\selectlanguage{english}\strut
\end{minipage} & \begin{minipage}[b]{0.12\columnwidth}\raggedright\strut
\textbf{Phase difference between
(P7\textsuperscript{0},P8\textsuperscript{0})}\selectlanguage{english}\strut
\end{minipage} & \begin{minipage}[b]{0.12\columnwidth}\raggedright\strut
\textbf{Required phase difference} \textbf{(Deg)}\strut
\end{minipage}\tabularnewline
\midrule
\endhead
\begin{minipage}[t]{0.10\columnwidth}\raggedright\strut
\strut
\end{minipage} & \begin{minipage}[t]{0.10\columnwidth}\raggedright\strut
\textbf{Simulatd}\strut
\end{minipage} & \begin{minipage}[t]{0.10\columnwidth}\raggedright\strut
\textbf{Measured}\strut
\end{minipage} & \begin{minipage}[t]{0.10\columnwidth}\raggedright\strut
\textbf{Simulatd}\strut
\end{minipage} & \begin{minipage}[t]{0.10\columnwidth}\raggedright\strut
\textbf{Measured}\strut
\end{minipage} & \begin{minipage}[t]{0.10\columnwidth}\raggedright\strut
\textbf{Simulated}\strut
\end{minipage} & \begin{minipage}[t]{0.10\columnwidth}\raggedright\strut
\textbf{Measured}\strut
\end{minipage} & \begin{minipage}[t]{0.10\columnwidth}\raggedright\strut
\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.10\columnwidth}\raggedright\strut
\textbf{Port 1}\strut
\end{minipage} & \begin{minipage}[t]{0.10\columnwidth}\raggedright\strut
-46\textsuperscript{0}\selectlanguage{english}\strut
\end{minipage} & \begin{minipage}[t]{0.10\columnwidth}\raggedright\strut
-47.2\textsuperscript{0}\selectlanguage{english}\strut
\end{minipage} & \begin{minipage}[t]{0.10\columnwidth}\raggedright\strut
-43.3\textsuperscript{0}\selectlanguage{english}\strut
\end{minipage} & \begin{minipage}[t]{0.10\columnwidth}\raggedright\strut
-49.4\textsuperscript{0}\selectlanguage{english}\strut
\end{minipage} & \begin{minipage}[t]{0.10\columnwidth}\raggedright\strut
41.5\textsuperscript{0}\selectlanguage{english}\strut
\end{minipage} & \begin{minipage}[t]{0.10\columnwidth}\raggedright\strut
51.1\textsuperscript{0}\selectlanguage{english}\strut
\end{minipage} & \begin{minipage}[t]{0.10\columnwidth}\raggedright\strut
\textbf{-45\textsuperscript{0}}\selectlanguage{english}\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.10\columnwidth}\raggedright\strut
\textbf{Port 2}\strut
\end{minipage} & \begin{minipage}[t]{0.10\columnwidth}\raggedright\strut
132\textsuperscript{0}\selectlanguage{english}\strut
\end{minipage} & \begin{minipage}[t]{0.10\columnwidth}\raggedright\strut
128\textsuperscript{0}\selectlanguage{english}\strut
\end{minipage} & \begin{minipage}[t]{0.10\columnwidth}\raggedright\strut
139\textsuperscript{0}\selectlanguage{english}\strut
\end{minipage} & \begin{minipage}[t]{0.10\columnwidth}\raggedright\strut
142\textsuperscript{0}\selectlanguage{english}\strut
\end{minipage} & \begin{minipage}[t]{0.10\columnwidth}\raggedright\strut
139\textsuperscript{0}\selectlanguage{english}\strut
\end{minipage} & \begin{minipage}[t]{0.10\columnwidth}\raggedright\strut
140\textsuperscript{0}\selectlanguage{english}\strut
\end{minipage} & \begin{minipage}[t]{0.10\columnwidth}\raggedright\strut
\textbf{135\textsuperscript{0}}\selectlanguage{english}\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.10\columnwidth}\raggedright\strut
\textbf{Port 3}\strut
\end{minipage} & \begin{minipage}[t]{0.10\columnwidth}\raggedright\strut
-133\strut
\end{minipage} & \begin{minipage}[t]{0.10\columnwidth}\raggedright\strut
-142\strut
\end{minipage} & \begin{minipage}[t]{0.10\columnwidth}\raggedright\strut
-138\strut
\end{minipage} & \begin{minipage}[t]{0.10\columnwidth}\raggedright\strut
-127\strut
\end{minipage} & \begin{minipage}[t]{0.10\columnwidth}\raggedright\strut
-141\strut
\end{minipage} & \begin{minipage}[t]{0.10\columnwidth}\raggedright\strut
\textbf{-131}\strut
\end{minipage} & \begin{minipage}[t]{0.10\columnwidth}\raggedright\strut
\textbf{-135\textsuperscript{0}}\selectlanguage{english}\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.10\columnwidth}\raggedright\strut
\textbf{Port 4}\strut
\end{minipage} & \begin{minipage}[t]{0.10\columnwidth}\raggedright\strut
44\strut
\end{minipage} & \begin{minipage}[t]{0.10\columnwidth}\raggedright\strut
50\strut
\end{minipage} & \begin{minipage}[t]{0.10\columnwidth}\raggedright\strut
48\strut
\end{minipage} & \begin{minipage}[t]{0.10\columnwidth}\raggedright\strut
39\strut
\end{minipage} & \begin{minipage}[t]{0.10\columnwidth}\raggedright\strut
40\strut
\end{minipage} & \begin{minipage}[t]{0.10\columnwidth}\raggedright\strut
52\strut
\end{minipage} & \begin{minipage}[t]{0.10\columnwidth}\raggedright\strut
\textbf{45\textsuperscript{0}}\selectlanguage{english}\strut
\end{minipage}\tabularnewline
\bottomrule
\end{longtable}

\textbf{Table 5} . Comparison between proposed design BM at 3.5 GHz with
previous work\selectlanguage{english}
\begin{longtable}[]{@{}llllll@{}}
\toprule
\begin{minipage}[b]{0.14\columnwidth}\raggedright\strut
\textbf{Ref}\strut
\end{minipage} & \begin{minipage}[b]{0.14\columnwidth}\raggedright\strut
\textbf{Frequency}\strut
\end{minipage} & \begin{minipage}[b]{0.14\columnwidth}\raggedright\strut
\textbf{Material}\strut
\end{minipage} & \begin{minipage}[b]{0.14\columnwidth}\raggedright\strut
\textbf{Technique}\strut
\end{minipage} & \begin{minipage}[b]{0.14\columnwidth}\raggedright\strut
\textbf{Bandwidth}\strut
\end{minipage} & \begin{minipage}[b]{0.14\columnwidth}\raggedright\strut
\textbf{Size (mm)}\strut
\end{minipage}\tabularnewline
\midrule
\endhead
\begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
{[}24{]}\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
3.5\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
FR-4\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
Open-circuit coupled line and capacitor unit cell\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
550\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
70 \selectlanguage{ngerman}× 73.7\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
{[}27{]}\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
2.4\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
Rogers 4003C\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
Circularly polarized (CP)\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
900\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
170 \selectlanguage{ngerman}× 170\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
{[}37{]}\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
2.44\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
FR-4\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
Without crossover\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
200\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
96 \selectlanguage{ngerman}× 96\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
{[}38{]}\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
2.5\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
FR-4\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
Open-stub and removal crossover\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
200\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
115.18 \selectlanguage{ngerman}× 64.4\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
{[}39{]}\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
2.5\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
FR-4\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
Two section branch line coupler\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
400\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
120 \selectlanguage{ngerman}× 150\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
{[}40{]}\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
1.8\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
ARLON\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
Composite right/left handed CRLH-TL\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
200\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
109 \selectlanguage{ngerman}× 119\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
{[}41{]}\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
6\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
Roger 4003C\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
Mushroom-like\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
2300\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
100 \selectlanguage{ngerman}×110\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
{[}42{]}\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
0.86\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
RT/duroid 5880\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
double spiral lines (SDSLs)\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
150\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
109.0 \selectlanguage{ngerman}× 89.3\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
{[}43{]}\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
2.4\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
Plastic\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
complimentary square split ring resonators (CS-SRRs)\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
300\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
154 \selectlanguage{ngerman}× 117\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.16\columnwidth}\raggedright\strut
\textbf{This work} \textbf{2023}\strut
\end{minipage} & \begin{minipage}[t]{0.16\columnwidth}\raggedright\strut
\textbf{3.5}\strut
\end{minipage} & \begin{minipage}[t]{0.16\columnwidth}\raggedright\strut
\textbf{RT/5880LZ}\strut
\end{minipage} & \begin{minipage}[t]{0.16\columnwidth}\raggedright\strut
\textbf{Triangular slot and T-shape}\strut
\end{minipage} & \begin{minipage}[t]{0.16\columnwidth}\raggedright\strut
\textbf{836}\strut
\end{minipage} & \begin{minipage}[t]{0.16\columnwidth}\raggedright\strut
\selectlanguage{ngerman}\textbf{85.5 × 75}\strut
\end{minipage}\tabularnewline
\bottomrule
\end{longtable}\selectlanguage{ngerman}

Conclusion

This work presented a 4 × 4 Butler matrix to feed the direction-switched
beamforming antenna array for 3.5 GHz 5G wireless application. The
desired result was achieved via Computer Simulation Technology (CST).
So, the finalised proposed design for BM and antenna array system array
was fabricated on single layer Rogers RT5880LZ. The measured result of
the BM and antenna array system showed a good agreement compared to the
simulated result, which successfully steered radiation beams of
-34\textsuperscript{o}, -40\textsuperscript{o}, +32\textsuperscript{o},
and +35\textsuperscript{o}. The overall size of the antenna and Butler
matrix was 121mm × 143mm. The result demonstrated that the proposed
four-beam antenna array revealed a good agreement for communication
system, as well as beam-forming for 5G wireless application.

\textbf{Reference}

{[}1{]} S. Roshani, S. I. Yahya, S. Roshani, and M. Rostami, ``Design
and Fabrication of a Compact Branch-Line Coupler Using Resonators with
Wide Harmonics Suppression Band,'' \emph{Electron.} , vol. 11, no. 5,
pp. 1--19, 2022.

{[}2{]} A. A. Abdulbari, S. K. Abdul Rahim, P. J. Soh, M. H. Dahri, A.
A. Eteng, and M. Y. Zeain, ``A review of hybrid couplers:
State-of-the-art, applications, design issues and
challenges,''\emph{Int. J. Numer. Model. Electron. Networks, Devices
Fields} , vol. 34, no. 5, pp. 1--19, 2021.

{[}3{]} N. Syahira, M. Suhaimi, N. Muzlifah, and W. Ismail,
``Miniaturized 4 × 4 switched-beam switched-beam Butler Matrix with
bandwidth enhancement for 5G communication system,'' \emph{Alexandria
Eng. J.} , vol. 61, no. 12, pp. 13089--13103, 2022.

{[}4{]} T. S. Rappaport \emph{et al.} , ``Wireless communications and
applications above 100 GHz: Opportunities and challenges for 6g and
beyond,'' \emph{IEEE Access} , vol. 7, pp. 78729--78757, 2019.

{[}5{]} A. A. Abdulbari \emph{et al.} , ``New design of wideband
microstrip branch line coupler using T-shape and open stub for 5G
application,'' \emph{Int. J. Electr. Comput. Eng.} , vol. 11, no. 2, pp.
1346--1355, 2021.

{[}6{]} S. A. Babale, S. K. Abdul Rahim, O. A. Barro, M. Himdi, and M.
Khalily, ``Single Layered 4 × 4 butler matrix without phase-shifters and
crossovers,'' \emph{IEEE Access} , vol. 6, pp. 77289--77298, 2018.

{[}7{]} A. A. Abdulbari \emph{et al.} , ``Single-Layer Planar Monopole
Antenna-Based Artificial Magnetic Conductor ( AMC ),'' \emph{Int. J.
Antennas Propag.} , vol. 2022, 2022.

{[}8{]} D. Muirhead, M. A. Imran, and K. Arshad, ``A Survey of the
Challenges, Opportunities and Use of Multiple Antennas in Current and
Future 5G Small Cell Base Stations,'' \emph{IEEE Access} , vol. 4, no.
c, pp. 2952--2964, 2016.

{[}9{]} K. Wincza and S. Gruszczynski, ``Broadband Integrated 8 x 8
Butler Matrix Utilizing Quadrature Couplers and Schiffman Phase Shifters
for Multibeam Antennas With Broadside Beam,'' \emph{IEEE Trans. Microw.
Theory Tech.} , vol. 64, no. 8, SI, pp. 2596--2604, Aug. 2016.

{[}10{]} H. Ren, H. Zhang, Y. Jin, Y. Gu, and B. Arigong, ``A Novel 2-D
3 X 3 Nolen Matrix for 2-D Beamforming Applications,'' \emph{IEEE Trans.
Microw. Theory Tech.} , vol. 67, no. 11, pp. 4622--4631, 2019.

{[}11{]} F. Casini, R. V. Gatti, L. Marcaccioli, and R. Sorrentino, ``A
novel design method for Blass matrix beam-forming networks,'' \emph{2007
Eur. Radar Conf. EURAD} , no. October, pp. 232--235, 2007.

{[}12{]} K. Tekkouk, M. Ettorre, L. Le Coq, and R. Sauleau, ``Multibeam
SIW Slotted Waveguide Antenna System Fed by a Compact Dual-Layer Rotman
Lens,'' \emph{IEEE Trans. Antennas Propag.} , vol. 64, no. 2, pp.
504--514, 2016.

{[}13{]} H. Ren, B. Arigong, M. Zhou, J. Ding, and H. Zhang, ``A Novel
Design of 4 × 4 Butler Matrix With Relatively Flexible Phase
Differences,'' \emph{IEEE Antennas Wirel. Propag. Lett.} , vol. 15, no.
c, pp. 1277--1280, 2016.

{[}14{]} Y. S. Lin and J. H. Lee, ``Miniature butler matrix design using
glass-based thin-film integrated passive device technology for 2.5-GHz
applications,'' \emph{IEEE Trans. Microw. Theory Tech.} , vol. 61, no.
7, pp. 2594--2602, 2013.

{[}15{]} P. Bhowmik and T. Moyra, ``Modelling and Validation of a
Compact Planar Butler Matrix by Removing Crossover,'' \emph{Wirel. Pers.
Commun.} , vol. 95, no. 4, pp. 5121--5132, Aug. 2017.

{[}16{]} N. A. Muhammad, S. K. A. Rahim, N. M. Jizat, T. A. Rahman, K.
G. Tan, and A. W. Reza, ``Beam Forming Networks Using Reduced Size
Butler Matrix,'' \emph{Wirel. Pers. Commun.} , vol. 63, no. 4, pp.
765--784, Apr. 2010.

{[}17{]} L. Ma, Y. Wu, and W. Wang, ``Design of Wideband Butler Matrix
with Equal/Unequal Phase Differences for Flexible
Beam-Controllability,'' \emph{IEEE Trans. Circuits Syst. II Express
Briefs} , vol. 7747, no. c, pp. 2--6, 2021.

{[}18{]} Y. Wang, K. Ma, and Z. Jian, ``A low-loss butler matrix using
patch element and honeycomb concept on SISL platform,'' \emph{IEEE
Trans. Microw. Theory Tech.} , vol. 66, no. 8, pp. 3622--3631, 2018.

{[}19{]} S. Shi \emph{et al.} , ``Wideband Planar Phased Array Antenna
Based on Artificial Magnetic Conductor Surface,'' \emph{IEEE Trans.
Circuits Syst. II Express Briefs} , vol. 67, no. 10, pp. 1909--1913,
2020.

{[}20{]} L. Markley and G. V. Eleftheriades, ``An ultra-compact
microstrip crossover inspired by contra-directional even and odd mode
propagation,'' \emph{IEEE Microw. Wirel. Components Lett.} , vol. 24,
no. 7, pp. 436--438, 2014.

{[}21{]} A. Imani and M. S. Bayati, ``A novel design of compact
broadband 4 × 4 Butler matrix-based beamforming antenna array for C-Band
applications,'' \emph{AEU - Int. J. Electron. Commun.} , vol. 138, no.
July, p. 153901, 2021.

{[}22{]} S.-Y. O. and H.-Y. Hwang, ``A MINIATURIZED BRANCH-LINE COUPLER
USING TRIANGULAR PATCH TYPE ARTIFICIAL TRANSMISSION LINE
Song-Yi,''\emph{Microw. Opt. Technol. Lett.} , vol. 55, no. 11, pp.
1718--1721, 2013.

{[}23{]} S. A. Babale, S. K. A. Rahim, O. A. Barro, M. Himdi, and M.
Khalily, ``Single Layered 4 x 4 Butler Matrix Without Phase-Shifters and
Crossovers,'' \emph{IEEE ACCESS} , vol. 6, pp. 77289--77298, 2018.

{[}24{]} A. Karimbu Vallappil, M. K. A. Rahim, B. A. Khawaja, and M. N.
Iqbal, ``Compact Metamaterial Based 4 × 4 Butler Matrix with Improved
Bandwidth for 5G Applications,'' \emph{IEEE Access} , vol. 8, pp.
13573--13583, 2020.

{[}25{]} T. H. Lin, S. K. Hsu, and T. L. Wu, ``Bandwidth enhancement of
butler matrix using broadband forward-wave directional coupler and phase
difference compensation,'' \emph{IEEE Trans. Microw. Theory Tech.} ,
vol. 61, no. 12, pp. 4099--4109, 2013, doi: 10.1109/TMTT.2013.2288597.

{[}26{]} S. Kim, S. Yoon, Y. Lee, and H. Shin, ``A miniaturized butler
matrix based switched beamforming antenna system in a two-layer hybrid
stackup substrate for 5g applications,'' \emph{Electron.} , vol. 8, no.
11, 2019, doi: 10.3390/electronics8111232.

{[}27{]} and M. F. K. K. T. Chandrasekaran, N. Nasimuddin, A. Alphones,
``Compact circularly polarized beam-switching wireless power transfer
system for ambient energy harvesting applications,'' Int. J. RF Microw.
Comput.-Aided Eng. , vol. 29, no. 1, p. e21642, 2019,'' \emph{Int. J. RF
Microw. Comput} , vol. 29, no. 1, p. 21642, 2019.

{[}28{]} C. W. Wang, T. G. Ma, and C. F. Yang, ``A new planar artificial
transmission line and its applications to aMiniaturized Butler
Matrix,''\emph{IEEE Trans. Microw. Theory Tech.} , vol. 55, no. 12, pp.
2792--2801, 2007.

{[}29{]} S.-Y. Oh and H.-Y. Hwang, ``A slotted triangular-patch type
artificial transmission line coupler,'' \emph{J Korean Inst Electromagn
Eng Sci} , vol. 22, no. 5, pp. 510--515, 2011.

{[}30{]} S. Oh, H. Hwang, E. Engineering, and S. Korea, ``A MINIATURIZED
BRANCH-LINE COUPLER USING TRIANGULAR PATCH,'' vol. 55, no. 8, pp.
1718--1722, 2013.

{[}31{]} D. M. Pozar, ``Microwave Engineering, 3rd ed: John ,Wiley and
Sons 2005.''

{[}32{]} X. K. Zhang, C. Zhou, G. C. Wu, and Y. Q. Zhuang, ``Design of
miniaturized branch-line coupler based on novel center-symmetrical
spiral-interdigital resonators,'' \emph{2013 Cross Strait Quad-Regional
Radio Sci. Wirel. Technol. Conf. CSQRWC 2013} , pp. 27--30, 2013.

{[}33{]} Y. Cao, J. Wen, H. Hong, and J. Liu, ``Design of planar
dual-band branch-line coupler with \selectlanguage{greek}π-\selectlanguage{english}shaped coupled lines,'' \emph{Prog.
Electromagn. Res. Lett.} , vol. 55, no. August, pp. 113--120, 2015.

{[}34{]} A. A. Abdulbari \emph{et al.} , ``Design compact microstrap
patch antenna with t-shaped 5g application,'' \emph{Bull. Electr. Eng.
Informatics} , vol. 10, no. 4, pp. 2072--2078, 2021.

{[}35{]} I. Zahraoui, A. Errkik, J. Zbitou, A. Tajmouati, and A. S.
Mediavilla, ``A novel design of a fractal antenna for IMT and WiMAX
applications,'' \emph{Int. J. Microw. Opt. Technol.} , vol. 11, no. 6,
pp. 428--434, 2016.

{[}36{]} H. Zhang, W. Kang, and W. Wu, ``A novel compact dual-band
branch-line coupler with cross-shaped stubs,'' \emph{2016 IEEE Int.
Conf. Ubiquitous Wirel. Broadband, ICUWB 2016} , pp. 1--4, 2016.

{[}37{]} G. A. Adamidis, I. O. Vardiambasis, M. P. Ioannidou, and T. N.
Kapetanakis, ``Design and implementation of single-layer 4\selectlanguage{ngerman}×4 and 8×8
butler matrices for multibeam antenna arrays,'' \emph{Int. J. Antennas
Propag.} , vol. 2019, pp. 1--12, 2019.

{[}38{]} P. Bhowmik and T. Moyra, ``Modelling and Validation of a
Compact Planar Butler Matrix by Removing Crossover,'' \emph{Wirel. Pers.
Commun.} , vol. 95, no. 4, pp. 5121--5132, 2017.

{[}39{]} S. Kuwana, H. Hayashi, and R. Ueda, ``Simple design of
four-element planar butler matrix using two-section branch-line
hybrids,'' \emph{IEEJ Trans. Electr. Electron. Eng.} , vol. 12, pp.
S187--S188, 2017.

{[}40{]} H.-X. Xu, G.-M. Wang, and X. Wang, ``Compact Butler matrix
using composite right/left handed transmission line,'' \emph{Electron.
Lett.} , vol. 47, no. 19, pp. 1081--1082, Sep. 2011.

{[}41{]} R. K. M. Lou, M. Naser-Moghadasi, and R. A. Sadeghzadeh,
``Broadband Planar Aperture-Coupled Antenna Array for WLAN and ITS
Beam-Steering Applications,'' \emph{RADIO Sci.} , vol. 53, no. 2, pp.
200--209, Feb. 2018, doi: 10.1002/2016RS006155.

{[}42{]} M. X. Du and H. X. Peng, ``Ultra-compact electromagnetic
metamaterial transmission line and its application in miniaturized
butler matrix,'' \emph{Prog. Electromagn. Res. C} , vol. 55, no.
January, pp. 187--197, 2014.

{[}43{]} O. A. Safia, M. Nedil, M. C. E. Yagoub, and W. Yusuf,
``Optically transparent compact 4 × 4 Butler matrix for Wi-Fi
applications,'' \emph{Prog. Electromagn. Res. Lett.} , vol. 58, no.
October 2015, pp. 119--124, 2016.

\selectlanguage{english}
\FloatBarrier
\end{document}

