Optimized Design of a Patch Antenna

The assignment is about designing and optimizing a patch antenna using Computer Simulation Technology (CST) software. The initial design had a FR-4 substrate with copper layers, and the dimensions were adjusted to achieve a resonant frequency of 5.61 GHz. The S11 results showed that the antenna radiated best at this frequency with a magnitude of -14.63 dB. To optimize the design, the patch length was increased to shift the resonant frequency downwards. The optimized design had a patch length of 12.93 mm and a slot width of 3.5 mm. The S11 results showed that the antenna radiated best at 5.61 GHz with a magnitude of -15.22 dB. The report concludes that CST is useful for optimizing antenna designs, and comprehension of theoretical concepts is important for making changes to an antenna.

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Abstract The antenna in which we will be talking about in this report will be the stub feed dipole slot antenna. It is used a lot in
this industry. This is because of its easiness to make and its brilliant transmission distances. When you’re creating something like
this, the length, width and placement of the port can affect the antenna. So those dimensions need to be correct. The software that
is used to perfect this is CST. The CST software is used to prototype the work. The CST software assesses the information we
have created using that the S-parameter results are also analyzed. So every time the parameters are changed the information that
was made also changes. However they both need to be in agreement with each other that is when the design is made. The CST
software have an analyzer called the S11 analyzer, this tool helps the source transmit information to the antenna. If analysis is
good enough the design is made.
Keywords — Stub fed, antenna, CST, feed impedance.
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I. INTRODUCTION1
hen a wire goes through a magnetic field an electric
current is transferred to the wire inductively.an
electromagnetic wave is now created which now moves
back and forth. An antenna is a piece of wire. The wire is
moving through the magnetic field. This transfers a very
tiny current in the antenna. This is then amplified to a level
that can then be used, for example can be used as a
transistor. The transmitter converts an electrical signal into
radio wave then back to an electrical signal. A traditional
transmitting circuit can be seen in figure 1.
W
What does feed impedance mean?
The feed impedance is difference between load
impedance and the impedance of the transmission line. The
feed impedance of antenna depends on size and shape of
antenna, operating frequency, and its environment. The
impedance consists of resistive and reactive elements. So
that the signal transmission is improved the antenna
impedance must be similar to the antenna load so that the
signal is fully transmitted. This is because impedance is
related to power transmission. The terminal impedance of
antenna is represented by Z.
Figure 1
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Z = Za + Zbj
Where, Za- for real life and
Zb- for the imaginary.
The imaginary part of the antenna is related to the
power storage around the field. The real life part is the
impedance controls the power that is absorbed or radiated
in transmission process. Another way this can be
represented is Za = Rs + R1. This is a basic circuit
showing the voltage across load impedance.
The power generated from this circuit is
For full power dissipation
If you combine the first equation and the last Rr = R1. This
means that when the antenna impedance to the transmission
are opposite. System doesn’t generate anything because of
the reflected power. This measure is known as the feed
impedance of the antenna.
How does a dipole antenna work?
Interim ReportAmmar Ghazal E

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In figure 3 dipole antenna consists of two conductive
poles between insulated materials. Which has the same
objective as a half wave antenna? This means that half of
the pole is a quarter wavelengths long as seen in the figure
below. The half wave dipole is fed using a transmission
line. Which has a input impedance of 60-70 ohms. The
feedline is identical and have the same but opposite
transmission voltages. In a dipole each end has an open end
circuit. This means an infinite resistance and a coefficient
of 1. The signal in the front reflected back at the open
source and is out of phase the open ends give out high
voltages and the middle reaches a high current
Babinet’s Principle
Babinets’s principle is the principle of diffraction patterns
made by screens are exactly the same. Two screens are
complementary when the opaque parts are one which is
correspondent to the transparent ones. A metallic conductor
with a slot will have the same total energy of conducting a
metal sheet without slot. It is actually a good thing in
engineering to have a slot antenna in a dipole antenna. With
that being said the impedance of the a slot can also be seen
as
Converting antenna dipole into a slot dipole
The slot antenna is made of a radiator which is made by
cutting a narrow slot using a large metal surface. The length
of slot is half wavelength at the frequency of operation and
the width of antenna is a small segment of antenna. The slot
antenna is commonly compare with the half wave dipole
antenna which have two flat metal strips. Metal strip
dimensions need to fit with slot that was cut out of metal
surface. The slot antenna and its complementary dipole
antenna have same radiation pattern. But so many things are
different between slot antenna and its complementary
antenna. One of these is the electric and magnetic fields that
are interchanged between each other. The dipole antenna is
shown in figure 4.In case of dipole antenna electric lines are
horizontal while the magnetic lines are vertical which
creates loops. In case of slot antenna the magnetic lines are
horizontal and electric lines are vertical. The electric lines
are made across the small dimensions of the slot, because of
this the polarization of the radiation created by a horizontal
slot is vertical. If a vertical slot is being used then the
polarization is horizontal. When energy is apply to slot
antenna, current spreads out over the sheet and radiation
obtain on both side of both sides of the metal sheet.In the
case of the dipole, however, the currents are more compact
making it a much greater magnitude of current which is
required to make the power output using the dipole antenna.
What is a stub and how can a stub match impedances?
The stub can be the described as a look like the half of
dipole antenna and its placed vertically or by an angle close
to the ground. Ground is also known as earth stub antennas
are very useful as normally sold with a connector and
Figure 2
Figure 3
Figure 4

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comes with a casing of rubber or plastic. Then you plug it
into your device whether a receiver or transmitter that’s up
to you. The stub can be used for RF measurement devices
or calibration in RF lines. For calibration to be achieved
fully you need 50 0hms. 0 ohms and infinite impedance
using an open circuit. The impedance of the transmission
line switches with the length and the stubs connected in
such a way where the voltage is minimal. The impedance
match is important in understanding how much of the
antenna transmission is maintained. When you look at a
quarter waves. The reflected waves form a normal wave
which can create unwanted results. The reflected impedance
can be so big however this can cause a breakdown of
dielectric material.
The reflected wave can cause affect the performance of the
generator. This means to see whether there is no reflected
wave at the generator, it is useful to have a unity VSWR.
This proves the importance of the stub matching. A line
must match when it is in a load which is equal to the
characteristic impedance. The magnitude of the front wave
is consumed by the load leaving no reflected wave
detection. When it comes to the reflected waves it depends
on difference between the Zo which is the characteristic
impedance and the load impedance which is ZL.
The basic designs of stub feed dipole antenna.
The design have on the CST software. We were given a
specification we had to follow. The dimensions we had to
follow the maximum dimensions couldn’t exceed 32x32
mm this was including the substrate. The substrate was
made of the FR-4 and had a thickness of 1.6 mm and the
copper layer thickness is 0.035.
Simulation and optimization
Figure 5. The stub demminsions were 12.93 and the slot for port is 3.5mm.
This is the S parameter for figure 5
S11 results using the these dimensions are the length of the
slot will be 23.00, the width of slot and the stub together is
3.5mm and finally the length of the stub is 12.925. With
these dimensions being changed the resonant frequency was
now 5.61 and magnitude of the S11 was -14.63Db.
S11 results using the these dimensions are the length of the
slot will be 22.50mm, the width of slot and the stub
together is 3.5mm and finally the length of the stub is
10.50mm. With these dimensions being changed the
resonant frequency was now 5.60 and magnitude of the S11
was -15.34dB

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S11 results using the these dimensions are the length of the
slot will be 22.50mm, the width of slot and the stub
together is 2.5mm and finally the length of the stub is
10.45mm. With these dimensions being changed the
resonant frequency was now 5.61 and magnitude of the S11
was -15.22dB
S11 results using the these dimensions are the length of the
slot will be 23.60mm, the width of slot and the stub
together is 3.5mm and finally the length of the stub is
11.50mm. With these dimensions being changed the
resonant frequency was now 5.60 and magnitude of the S11
was -15.69dB
II.RESULTS AND DISCUSSION
Network analyzer used to test final design. Unfortunately
I didn’t complete testing to compare results which would
give me better understanding of this.
III. CONCLUSION
This report will be helpful in designing antenna using
theoretical concept and CST software. Learning that by
changing the parameters means you achieve the success and
new findings within your work. CST is useful as optimizing
can be very stressful but with the use of CST makes it
easier. From resonance frequency can happen when you
change the parameters but this will cause miss match in the
impedance. The S11 results between the source and
impedance show a mismatch. This causes data to be lost
whilst transferring data. The implementation of an antenna
will prove whether it is wise or not. Comprehending
theoretical concepts is important in making an antenna
because when making an antenna to make changes to an
antenna you will need to know some knowledge regarding
the antenna
APPENDIX
Computer simulation is the use of a computer to show the
dynamic responses of one system by the behaviour of
another system modelled after it. A simulation uses a
mathematical description of a real system in the form of a
computer program.
PATCH ANTENNA
An antenna is a type of transducer so it is basically a device
that converts changes in a physical quantity such as
pressure or brightness into an electrical signal, or turns
electrical energy into electro-magnetic energy in form of
electromagnetic field.
A patch antenna can also be called as micro-strip patch
antenna is made of a radiating patch on one side of a
dielectric substrate which as a ground plane on the other
side.

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Patch antenna dimensions and its resonant frequency
c = speed of light ( )
L = length of the patch antenna
The resonant frequency of the patch antenna is determined
by the length.
S-PARAMETERS
S-parameters describes the electrical behaviour of linear
electrical networks so the input-output relationship between
ports in an electrical system.
S11 represents how much power is reflected from the
antenna and it is known as the reflection coefficient. If
S11=0 dB then all the power is reflected from the antenna
and nothing is radiated. So If S11=-10 dB, this then means
implies that if 3 dB of power is transferred to the antenna, -
7 dB is the reflected power.
VECTOR NETWORK ANALYZER
Usually there are two types of networks analyzers scalar
network analyzer and vector network analyzer.
A vector network analyser is an instrument use to measure
both amplitude and phase of the incident and the reflected
waves.
DESIGNING A PATCH ANTENNA
Show your optimized design the dimensions of the antenna
should be clearly presented and the corresponding S11
results that verify that your antenna works within the
desired frequency range.
Explain the S11 results
The antenna radiates best at 5.8196 GHz, where S11= -
15.309 dB. From the picture we infer that the higher the
GHz value is the lower the radiation will be this means
more power is reflected with the increased value of GHz.
How did you optimize your design?
To get the best out of my design, I had to shift down the
resonant frequency. In order to do that I increased my

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inductance increasing as well my patch length. If you want
to shift the resonant frequency towards your left side you
should increase the patch length instead if you want to shift
the resonant frequency towards your right side you should
decrease the patch length. The patch width effects only on
the bandwidth.
REFERENCES
[1] https://qrznow.com/wp-content/uploads/2015/09/dipole_antenna.jpg
[2] https://encyclopedia2.thefreedictionary.com/Babinet%27s+principle
[3] http://electriciantraining.tpub.com/14183/css/Basic-Slot-Antenna-
And-Its-Complementary-Dipole-163.htm
[4] https://www.quora.com/What-is-an-antenna-stub
[5] https://journals.ieeeauthorcenter.ieee.org/create-your-ieee-journal-
article/authoring-tools-and-templates/ieee-article-templates/
[6] http://www.antenna-theory.com/antennas/patches/
antenna.php#introduction
[7] http://www.antenna-theory.com/basics/impedance.php
[8] https://www.electronics-notes.com/articles/antennas-propagation/
antenna-theory/feed-impedance-matching.php
[9] https://ham.stackexchange.com/questions/7081/what-is-the-
impedance-of-an-end-fed-half-wave-antenna
[10] https://rsgb.org/main/get-started-in-amateur-radio/antennas/end-fed-
wire-antennas
[11] http://www.ijettcs.org/Volume2Issue5/IJETTCS-2013-10-21-
053.pdf
[12] http://www.antenna-theory.com/antennas/patches/patch4.php
[13] http://www.antenna-theory.com/definitions/sparameters.php
[14] http://materias.fi.uba.ar/6644/info/anredes/basico/Network
%20Analyzer%20Basics.pdf