Design and Analysis of Microstrip Leaky wave Antennas
Dual Degree Project Stage 1 Report
Submitted in partial fulfillment of the requirements
for the degree of
Master of Technology
by
Ayush Ambadas Dahale
(Roll No. 18D070041)
Under the guidance of
Prof. Jayanta Mukherjee
Department of Electrical Engineering
Indian Institute of Technology Bombay
2022-2023
Declaration
I declare that this written submission represents my ideas in my own words. I have cited
and referenced the original sources where others’ ideas or words have been included. I
also declare that I have adhered to all academic honesty and integrity principles and have
not misrepresented, fabricated, or falsified any idea/data/fact/source in my submission.
I understand that any violation of the above will result in disciplinary action by the
Institute. In addition, it can also evoke penal action from sources that are not correctly
cited or from whom proper permission has not been taken when needed.
Ayush Amabadas Dahale
Electrical Engineering
IIT Bombay
Acknowledgement
I would like to express my gratitude to Prof. Jayanta Mukherjee for his valuable guidance.
Also, I would like to thank Ms Vishakha Pandey and all my peers from the Integrated
systems laboratory for their constant support, guidance and encouragement through the
project.
Ayush Ambadas Dahale
Electrical Engineering
IIT Bombay
Abstract
Although Leaky Wave Antennas have been in existence since the 1940s, This field has
seen immense growth in the last decade as well as in recent years, with most of the recent
work being in the area of planar Leaky Wave Antennas, which are very low profile and
the ease of manufacturing is significant. Some of the recent developments in the Leaky
Wave Antennas field have been related to the metamaterials area, which has provided
new inspiration for novel designs. Various designs that overcome the stopband problem
at the broadside and allow for continuous beam scanning through the broadside have
been reviewed. Other developments that have been reviewed include LWAs that can scan
to endfire.
Since the 1970s, Microstrip Leaky Wave Antennas(MLWA) have undergone vigorous
development and are now widely used in a wide range of applications, including satellite communication, target tracking, cruise control, and collision avoidance. In the field
of MLWA, it is now widely accepted that the fundamental EH0-mode of the Microstrip
line(MSL) is a limited mode that is unable to produce the intrinsic leaky-wave radiation from the guided-wave MSL after several decades. All MLWAs must therefore be
implemented using these higher-order modes.
In this thesis, we investigated the various designs of microstrip leaky wave antennas,
analyzed their feasibility of implementation and studied various excitation modes. A
thorough literature survey was performed on various designs. Designs were analyzed for
various performance parameters by performing simulations in Anysys HFSS. In addition,
we suggest improvements that can be made to the analyzed designs to improve performance parameters.
KEYWORDS: Leaky-Wave Antennas, Microstrip line
Contents
List of Figures
3
1 Introduction
5
1.1
Organization of the Report . . . . . . . . . . . . . . . . . . . . . . . . . .
2 Microstrip Leaky Wave Antenna
5
6
2.1
Description of Microstrip Antenna . . . . . . . . . . . . . . . . . . . . . .
6
2.2
Radiation Patterns of Microstrip Antenna . . . . . . . . . . . . . . . . .
7
2.3
Advantages of Microstrip Antennas . . . . . . . . . . . . . . . . . . . . .
8
2.4
Disadvantages of Microstrip Antennas . . . . . . . . . . . . . . . . . . . .
8
2.5
Applications of Microstrip Antennas
9
. . . . . . . . . . . . . . . . . . . .
3 Related Work
3.1
Periodic Half-Width Microstrip Leaky-Wave Antenna With a Backward to
Forward Scanning
3.2
10
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10
3.1.1
Design Methodology . . . . . . . . . . . . . . . . . . . . . . . . .
11
3.1.2
Design Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12
3.1.3
Major Strengths . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14
The Half-Width Microstrip Leaky Wave Antenna With the Periodic Short
Circuis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14
3.2.1
Design Methodology . . . . . . . . . . . . . . . . . . . . . . . . .
14
3.2.2
Design Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15
3.2.3
Major Strengths . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18
4 Implementation
4.1
19
Microstrip Leaky-Wave Antenna With I-Shaped Slots . . . . . . . . . . .
19
4.1.1
Design Methodology . . . . . . . . . . . . . . . . . . . . . . . . .
19
4.1.2
Design Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . .
21
2
5 Conclusion
24
6 Future Scope
25
3
List of Figures
2.1
Top View of Patch Antenna . . . . . . . . . . . . . . . . . . . . . . . . .
6
2.2
Side View of Microstrip Antenna . . . . . . . . . . . . . . . . . . . . . .
7
2.3
Radiation Pattern
8
3.1
3-D view of the proposed periodic half width MLWA with backward to
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
forward scanning capabilities . . . . . . . . . . . . . . . . . . . . . . . . .
3.2
11
Layout of periodic half width MLWA with backward to forward scanning
capabilities
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3
The measured radiation patterns for 4.4 GHz, 4.9 GHz, 5.3 GHz
3.4
The measured radiation patterns for 6.2 GHz, 6.7 GHz, 8 GHz
11
. . . .
12
. . . . .
13
3.5
reflection co-efficient (S11 ) . . . . . . . . . . . . . . . . . . . . . . . . . .
13
3.6
The 3D view of the half-width microstrip LWA with the periodic short
circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15
3.7
The layout of the proposed half-width microstrip LWA . . . . . . . . . .
15
3.8
Copolarization patterns the following frequencies 4.6GHz, 5GHz, 5.2GHz
16
3.9
Copolarization radiation patterns the following frequencies 6.5GHz, 7.5GHz, 8.5GHz 16
3.10 Copolarization radiation patterns the following frequencies 4.6GHz, 5GHz, 5.2GHz 17
3.11 Crosspolarization radiation patterns the following frequencies 6.5GHz, 7.5GHz, 8.5GHz 17
3.12 Reflection co-efficient (S11 ) . . . . . . . . . . . . . . . . . . . . . . . . . .
18
4.1
EH2 -mode microstrip LWA with an array of I-shaped slots . . . . . . . .
20
4.2
Feeding structure: Configuration of the EH0 -to-EH2 mode converter . .
20
4.3
The 3-D view of Microstrip Leaky-Wave Antenna With I-Shaped Slots .
20
4.4
Photograph of the design EH2 -mode LWA with I-shaped slots . . . . . .
21
4.5
Photograph of the design EH2 -mode LWA with I-shaped slots . . . . . .
21
4.6
Photograph of the design EH2 -mode LWA with I-shaped slots . . . . . .
22
4.7
Photograph of the design EH2 -mode LWA with I-shaped slots . . . . . .
22
4.8
Photograph of the design EH2 -mode LWA with I-shaped slots . . . . . .
23
4
Chapter 1
Introduction
.
1.1
Organization of the Report
The background and motivation behind the selected topic and the current objectives and
scope of the work have been listed above in the introductory chapter. The second chapter
discusses microstrip antennas and the method used to design the microstrip antennas..
The third chapter walks through the design process of antennas that were analysed in the
course of the project through a literature review. The fourth chapter walks through the
simulated results of the designed antennas. The final chapter discusses the conclusions
and improvements that can be made to the models in future work.
5
Chapter 2
Microstrip Leaky Wave Antenna
2.1
Description of Microstrip Antenna
Microstrip antennas also called patch antennas are becoming very popular owing to their
ease of production as they can be directly printed onto the circuit board. Consider the
figure below, The microstrip consists of the following components. The patch antenna,
microstrip transmission line, ground plane and a substrate. The substrate is made of
some dielectric circuit board, whereas rest of the three components are made up of high
conductivity metal just like a copper. The frequency of operation of the antenna shown
above is determined by length L. The centre frequency will be approximately given by
Figure 2.1: Top View of Patch Antenna
6
Figure 2.2: Side View of Microstrip Antenna
fc ≈
c
√
2L εr
=
1
√
2L ε0 εr µ0
According to the equation above, the microstrip antenna’s length inside the dielectric
(substrate) medium should be equal to one-half of a wavelength. The microstrip antenna’s
width W regulates the input impedance. The bandwidth can also be expanded by using
larger widths.
2.2
Radiation Patterns of Microstrip Antenna
The normalised radiation pattern of microstrip antennas is approximately given by
Eθ =
Eφ = −
sin
sin
kW sin θ sin ϕ
2
kW sin θ sin ϕ
2
kW sin θ sin ϕ
2
kW sin θ sin ϕ
2
cos
cos
kL
sin θ cos ϕ cos ϕ
2
kL
sin θ cos ϕ cos θ sin ϕ
2
In above equations the k is the free space wavenumber given by 2π/λ and the magnitude
q
of the feild is given by f (θ, ϕ) = Eθ2 + Eϕ2 .
The figure below represents the radiation pattern of the microstrip antenna. It is observed that a very high-quality factor is offered by a patch antenna. A large Q results in
a narrow bandwidth and low efficiency. However, this can be compensated by increasing
the thickness of the substrate. However, the increase in thickness beyond a certain limit
will cause an unwanted loss of power.
7
Figure 2.3: Radiation Pattern
2.3
Advantages of Microstrip Antennas
The antenna is lightweight and compact. It provides a simple fabrication procedure. It is
simple to install because of the low volume and tiny dimensions. It allows for simple device
integration. It is capable of operating at dual and triple frequencies. The construction
of the antenna’s arrays is simple. In comparison to rigid surfaces, it provides a high level
of toughness.
2.4
Disadvantages of Microstrip Antennas
The disadvantages of microstrip antennas are as follows, The efficiency of the antenna is
low. These antennas exhibit extremely delicate behaviour when exposed to environmental
conditions. These have a narrow bandwidth, poor gain, and low power handling capacity.
They are more susceptible to false feed radiation. In microstrip antennas, there are the
increased conductor and dielectric losses.
8
2.5
Applications of Microstrip Antennas
Microstrip antennas’ low profile allows for widespread application in wireless communications. This explains why these antennas display compatibility with mobile phones
and other handheld devices like pagers. These antennas are utilised as communication
antennas on missiles because of their thin structure. Microstrip antennas are used in
microwave and satellite communications due to their small size. One of the main benefits of microstrip antennas is GPS or the Global Positioning System. because it makes
monitoring trucks and marines simple. Phased array radars that can manage bandwidth
tolerance up to a certain percentage also use these antennas.
9
Chapter 3
Related Work
In this chapter, we look at various design processes and methodologies of antennas that
were analysed in the course of the project through a literature review. We have analyzed
the following designs for microstrip leaky wave antennas.
• Periodic Half-Width Microstrip Leaky-Wave Antenna With a Backward to Forward
Scanning Capability
• A Reconfigurable Microstrip Leaky-Wave Antenna With a Broadly Steerable Beam
• The Half-Width Microstrip Leaky Wave Antenna With the Periodic Short Circuits
• Compact Microstrip Patch Array Antenna With Parasitically Coupled Fee
• Microstrip Leaky-Wave Antenna With I-Shaped Slots
Each design has been analyzed on the basis of the innovation of the design and its
contribution to the field of microstrip leaky wave antennas, the design process, major
strengths and weaknesses of the design and the scope for improvements that exist.
3.1
Periodic Half-Width Microstrip Leaky-Wave Antenna With a Backward to Forward Scanning
This study introduces the periodic half-width microstrip leaky wave antenna (MLWA)
with a backward to forward scanning capability. The proposed antenna consists of a
string of MLWAs that are half the width. On the different sides of the transmission line,
the radiating periods occur. The periodic construction radiates the slow wave out along
the edge while the radiating period operates in the first higher-order mode’s cutoff zone.
10
3.1.1
Design Methodology
Ten radiating segments make up the periodic half-width MLWA as depicted in Figure
below. The proposed antenna is constructed on a substrate that has a relative permittivity of ϵr = 2.65 and a thickness of h = 0.8mm. The length L + l′ = 225mm long and
width W = 21mm wide. For the transmission s = 2.2mm and line impedence is 50 Ω.
The width of each radiating segment is close to λ0 /4, which is a half of the conventional
MLWA. A short connecting the antenna patch and the ground plane is created by integrating each of the exterior nonradiating edges with a set of shorting pins. The radius of
these pins is a = 3mm and the distance between shorting pins is r = 0.5mm.
Figure 3.1: 3-D view of the proposed periodic half width MLWA with backward to forward
scanning capabilities
Figure 3.2: Layout of periodic half width MLWA with backward to forward scanning
capabilities
11
3.1.2
Design Analysis
To analyze the design to greater details, we measured the radiation patterns of ye proposed periodic half width MLWA at different frequencies of operation. The measurements
were done for frequencies equal to 4.4GHz, 4.9GHz, 5.3GHz, 6.2GHz, 6.7GHz, 8GHz.
Apart from measuring raiation patterns, The reflection co-efficient (S11 ) was measured for
the given frequency range. The experimental results show the main lobe scans electronically and continuously from 149 °to 28 °in H-Plane towards the endfire when operating
frequency iccreases from 4.2 GHz to 8.9 GHz.
Figure 3.3: The measured radiation patterns for 4.4 GHz, 4.9 GHz, 5.3 GHz
12
Figure 3.4: The measured radiation patterns for 6.2 GHz, 6.7 GHz, 8 GHz
Figure 3.5: reflection co-efficient (S11 )
13
3.1.3
Major Strengths
Compared with the conventional half-width MLWA, this new design has the advantage
of the main lobe scanning from backward to forward. The bandwidth of the antenna is
wider than the conventional antenna, too. The construction is simpler than the right/lefthanded leaky wave antenna.
3.2
The Half-Width Microstrip Leaky Wave Antenna
With the Periodic Short Circuis
This study introduces a microstrip leaky wave antenna, where periodic short circuits
are present. The backwards-to-forward scanning capability is achieved by the periodic
construction of this antenna. The proposed antenna consists of a rectangular patch with
short circuits that are placed with help of shorting pins between the antenna patch and
the grounding plane.
3.2.1
Design Methodology
As shown in the figure below, the microstrip antenna consists of a rectangular copper
patch, mounted over a substrate of dielectric constant ϵr = 2.65 and loss tangent equal to
0.0015. The thickness of the substrate is h = 0.8mm. The patch was 11.6mm wide and
210mmlong. The transmission line’s width in the feeding circuit is 50Ω i.e s = 2.2mm
and the width of the feeding line is 15 mm. The length of this antenna is just half of
what was presented earlier in this chapter.
There are several short circuits in the periodic architecture. The large rectangular patch
appears to have short circuits on two different edges alternately. The ground plane and
antenna patch are intermittently linked by shorting pins along the patch’s long edge.
There shouldn’t be two shorting pins on two long radiating edges in the same place due
to the power leakage. In each short circuit, there are only 7 shorting pins, with the
exception of the short circuit at the patch’s feeding terminal, which has 8 shorting pins.
The space between shorting pins a = 3mm and the radius of shorting pins is r = 0.5mm.
14
Figure 3.6: The 3D view of the half-width microstrip LWA with the periodic short circuits
Figure 3.7: The layout of the proposed half-width microstrip LWA
3.2.2
Design Analysis
To analyze the design in greater detail, we measured the radiation patterns of ye proposed periodic short circuits are measured in far-field conditions. The co-polarization
and cross-polarization radiation patterns have been observed for the following frequencies
4.6GHz, 5GHz, 5.2GHz, 6.5GHz, 7.5GHz, 8.5GHz. With the increase in the frequency
of operation, the main lobe elevation steers from the backward direction to the forward
direction in the y-z plane. Apart from measuring radiation patterns, The reflection coefficient (S11 ) was measured for the given frequency range. Due to the similar radiation
characteristics, the S-parameter agrees closely with the one from the periodic half-width
microstrip LWA present in the design presented earlier.
15
Figure 3.8: Copolarization patterns the following frequencies 4.6GHz, 5GHz, 5.2GHz
Figure 3.9:
Copolarization
6.5GHz, 7.5GHz, 8.5GHz
radiation
16
patterns
the
following
frequencies
Figure 3.10:
Copolarization
4.6GHz, 5GHz, 5.2GHz
Figure 3.11:
Crosspolarization
6.5GHz, 7.5GHz, 8.5GHz
radiation
radiation
17
patterns
patterns
the
following
frequencies
the
following
frequencies
Figure 3.12: Reflection co-efficient (S11 )
3.2.3
Major Strengths
This new antenna design is simpler and cheaper than the conventional periodic antenna
and the right/left-handed leaky wave antenna. This antenna design will be useful in
manufacturing the automotive radar system or other consumer products.
18
Chapter 4
Implementation
4.1
Microstrip Leaky-Wave Antenna With I-Shaped
Slots
We have designed a microstrip leaky-wave antenna (LWA) for a single main beam. The
suggested antenna with an array of I-shaped slots radiates just one primary radiation
beam at the cross-sectional centre plane, unlike its typical second higher-order leakymode counterpart with two symmetric radiation beams. The cross-polarization of the
antenna may be significantly improved by adding a transversally loaded slot array along
the microstrip line, but a longitudinally loaded slot array disrupts the current flow and
essentially lowers the two original radiation beams. The strip conductor is then etched
with a series of I-shaped slots, comprising transverse and longitudinal slot segments, and
its special properties are examined to produce a single primary radiation beam in the
centre plane.
4.1.1
Design Methodology
A three-way power dividing structure with pre-matched amplitudes and phases are built,
and it is then used to excite the pure EH2-mode along the radiating strip conductor in
order to validate the suggested LWA. The aforementioned feeding structure is erected
and connected to a compatible load in order to efficiently absorb the residual power at
the end of the LWA. LWA has slots in an I form. The table below gives the specific
dimensional dimensions.
19
Parameter
w0
wt
lt
w1 w2
Value (mm) 2.38 3.8
4.9
1.5
3
Parameter
ls
li
p
20.2 10
16
W
ws
Value (mm) 36.4
1
The design Schematics are as follows
Figure 4.1: EH2 -mode microstrip LWA with an array of I-shaped slots
Figure 4.2: Feeding structure: Configuration of the EH0 -to-EH2 mode converter
Figure 4.3: The 3-D view of Microstrip Leaky-Wave Antenna With I-Shaped Slots
20
Figure 4.4: Photograph of the design EH2 -mode LWA with I-shaped slots
4.1.2
Design Analysis
The measured reflection coeffiefcient below 10 dB ranged from 4.59 to 5.10 GHz, which
means that the obtained leakage band is consistent. The single primary radiation beam
of the suggested LWA demonstrates an appealing beam-scanning capability from 20 to
55 at E-plane, which is often required, as the frequency fluctuates from 5.1 to 4.6 GHz in
the leakage band. At 4.9 GHz, the greatest gain attained is around 14.6 dBi. Over the
leakage band, the simulated and observed gain flatness are, respectively, 2.4 and 2.1 dB.
The proposed LWA’s radiation patterns in the H-plane and E-plane are produced when
the test antenna is positioned along the z-axis on the xz plane, as illustrated in Figure
below.
Figure 4.5: Photograph of the design EH2 -mode LWA with I-shaped slots
21
Figure 4.6: Photograph of the design EH2 -mode LWA with I-shaped slots
Figure 4.7: Photograph of the design EH2 -mode LWA with I-shaped slots
22
Figure 4.8: Photograph of the design EH2 -mode LWA with I-shaped slots
23
Chapter 5
Conclusion
In this work, we provide a mathematical model and HFSS simulations for evaluating
the reflection coefficient of the designed EH2 mode LWA, Radiation pattern in E-plane
for various θ. The I-shape slots are taken into account in the model. The I-shaped
slots have finally been created up after the impacts of transversal and longitudinal slots
along the strip conductor have been examined. It has been clearly demonstrated that
the longitudinal slots significantly lower the radiation intensity of two θ-polarized beams,
whereas the transversal slots primarily contribute to the amplification of ψ-polarized
single main-beam radiation. Over the entire leakage band, the designed LWAs have
exhibited an attractive beam-scanning capability along the E-plane as well
24
Chapter 6
Future Scope
There is a scope of improvement in:
1. Size of antenna
• In the structure proposed the size of the antenna is around 360 mm limiting
the utility of antennas in communication devices and radar systems. The size
can be reduced by reducing the no. of array elements or making each array
element smaller.
2. Shape of slots
• The shape of slots currently used is I. in I-shaped slots the longitudinal slots
restrict the flow of current directly affecting the power output of the antenna,
we should innovate new slotting patterns that don’t hurt the current flow in
the antenna patch.
3. Feeding Structure
• The main aim to use a power divider is to activate higher order modes of LWA,
whereas it also results in power losses, when acting as a power divider, we can
improve the efficiency of power divider to ensure maximum throughput
4. Fabrication Technology
• The fabrication technology used limits the size of the antenna that can be
manufactured to around 280 mm, making it impossible to produce antennas
of larger size.
25