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Design of a Planar Monopole Antenna with U- and L-shaped slots

CHAPTER 1

INTRODUCTION AND SCOPE OF PROJECT

1.1 Introduction

Overview of Communication:

Communication is basically the transfer of information from one system to another through some

channel which may be wired or wireless. Nowadays for long distance communication,

electromagnetic spectrum is used. The electromagnetic spectrum is a natural resource and this

resource is fully utilized by antenna systems. In the communication industry, wireless

communication is growing very rapidly. From the last few years cellular systems have grown

exponentially and there are billions of users all over the world. The cellular systems have

become a major business tool in the world and an important part of our daily life in almost all the

leading countries. Cellular systems employ wireless communication. Wireless communication is

that in which there is no direct connection between two or more points and still there is transfer

of information between them. The name “Wireless” is basically used for referring a radio

transmitter and receiver.

1.2 Objective Of The Project

The main objective of the project is to design a planar monopole antenna using HFSS simulation

software .A compact antenna for PCS and WiMax application is proposed.

1.3 Motivation Of The Project

With the rapid development of the wireless communication system, multiband antennas are

becoming more and more favorable in modern wireless communications, and much significant

effort has been devoted to integrating various frequencies into a single portable device. The

multiband system has become a highly competitive topic and so much significant progress in the

design of multiband antennas has been reported recently, such as the modified sierpinski gasket

monopole antennas, the modified multiband planar inverted-F antennas and the interdigital

Department of Electronics and communication Engineering


capacitor-inserted multiband antenna.

CHAPTER 2



FUNDAMENTALS OF ANTENNA

2.1 Antenna

An antenna is a type of transducer which converts electrical energy into radio waves

(electromagnetic energy) and vice versa. An antenna is used with a radio transmitter or radio

receiver. During transmission, transmitter supplies a current which is oscillating at radio

frequency towards the terminals of antenna and the radiation of energy from the current in the

form of electromagnetic waves is done by antenna. During reception, the antenna seizes some

power of the electromagnetic wave and produces small amount of voltage at its terminals, which

is further applied to the receiver for amplification.

Fig 2.1 Antenna

The main use of radio transmitters and radio receivers is to carry signals or data

towards the systems which includes Wi-Fi, remote controlled instruments and point to point

transmission links. All systems would require an antenna that is non-bulky and occupies less

space. One such antenna is Micro-strip Patch Antenna.

The properties of antenna is as follows:



1. Field intensity for various directions (antenna pattern).

2. Total power radiated when antenna is excited by a current or voltage of known intensity.

3. Radiation efficiency which is the ratio of power radiated to the total power.

4. The input impedance of antenna for maximum power transfer.

5. The bandwidth of the antenna or range of frequencies over which the above properties are

nearly constant.

Different types of antennas:

1. Dipole antennas.

2. Loop antennas.

3. Aperture antennas.

4. Reflector antennas.

5. Array antennas.

1. Dipole antennas :

The dipole is one of the most common antennas. It consists of a straight conductor excited by a

voltage from a transmission line or a waveguide. Dipole antennas are easy to make.

Fig 2.1.1 Dipole Antenna

2. Loop antennas :

A loop of wire, with many turns, is used to radiate or receive electromagnetic energy.



Fig 2.1.2 Loop Antenna

3. Aperture antennas :

A horn in the below figure is the example of Aperture antenna.

Fig 2.1.3 Horn Antenna

4. Reflector antennas :

The parabolic reflector is a good example of reflector at microwave frequencies.



Fig 2.1.4 Parabolic Reflector

6.Array antennas :

A grouping of similar or different antennas form an array antenna. The control of phase shift

from element to element is used to scan electronically the direction of radiation.

Fig 2.1.5 Array Antenna

2.2 Antenna Parameters

Gain : Antenna gain is usually defined as ratio of the power produced by the antenna from a far

field source on the antenna beam axis to the power produced by a hypothetical lossless isotropic

antenna, which is equally sensitive to signals from all directions.



G=Eantenna . D

In electro-magnetic, an antenna's power gain or simply gain is a key performance which

combines the antennas directivity and electrical efficiency. In a transmitting antenna, the gain

describes how well the antenna converts input power into radio waves headed in a specified

direction. In a receiving antenna, the gain describes how well the antenna converts radio waves

arriving from a specified direction into electrical power. When no direction is specified, "gain"

is understood to refer to the peak value of the gain, the gain in the direction of the antenna's main

lobe. A plot of the gain as a function of direction is called the radiation pattern.

Radiation Pattern : A radiation pattern defines the variation of power radiated by antenna as a

function of the direction away from antenna. This power variation as a function of the arrival

angle is observed in the antenna’s far field as shown in the fig 1. 14. The energy radiated by an

antenna is represented by the Radiation pattern of the antenna. Radiation Patterns are diagrammatical

representations of the distribution of radiated energy into space, as a function of direction.

Fig 2.2.1 Radiation pattern

The figure given above shows radiation pattern of a dipole antenna. The energy being radiated is

represented by the patterns drawn in a particular direction. The arrows represent directions of

radiation.

To have a better understanding, consider the following figure 1.15, which represents the

radiation pattern of a dipole antenna.



Fig. 2.2.2 Lobes in Radiation pattern

Here, the radiation pattern has main lobe, side lobes and back lobe.

The major part of the radiated field, which covers a larger area, is the main lobe or major

lobe. This is the portion where maximum radiated energy exists. The direction of this

lobe indicates the directivity of the antenna.

The other parts of the pattern where the radiation is distributed side wards are known

as side lobes or minor lobes. These are the areas where the power is wasted.

There is other lobe, which is exactly opposite to the direction of main lobe. It is known

as back lobe, which is also a minor lobe. A considerable amount of energy is wasted

even here.

Polarization: Polarization refers to the path traced by the tip of the electric field vector as a

function of time. There are three forms of polarization: Linear, Circular, Elliptical as shown in

Fig 2.2.3

Linear polarization occurs either when there is only one component of the electric field or when

there are two components of the electric field and the phase difference between them is 0 or 180

degrees.

Circular polarization occurs when there are two components of the electric field and they are

equal in magnitude and one of the components leads the other by 90 degrees . Circular



polarization can be either left handed or right handed, depending on direction in which the

rotation of fields occurs with time.

Elliptical polarization occurs when the components of the electric field do not have the same

magnitude and have an arbitrary phase difference between them. The electric field vector traces

out an ellipse with time.

Fig. 2.2.3 Polarization of Linear, Circular, Elliptical

An antenna is said to be vertically polarized (linear) when its electric field is perpendicular to the

Earth’s surface. An example of a vertical antenna is a broadcast tower for AM radio or the

“whip” antenna on an auto-mobile. Horizontally polarized (linear) antennas have their electric

field parallel to the Earth’s surface. Television transmissions use horizontal polarization shown

in fig 2.2.4

Fig 2.2.4 Vertical and Horizontal Polarization

Circular polarized wave radiates energy in both the horizontal and vertical planes and all planes



in between. The difference, if any, between the maximum and the minimum peaks as the antenna

is rotated through all angles, is called the axial ratio or elliptically and is usually specified in

decibels (dB). If the axial ratio is near 0 dB, the antenna is said to be circular polarized, when

using a Helix Antenna. If the axial ratio is greater than 1-2 dB, the polarization is often referred

to as elliptical, when using a crossed Yagi.

Axial Ratio : This parameter is majorly used to describe the polarization nature of circularly

polarized antennas. The Axial Ratio (AR) is defined as the ratio between the minor and major

axis of the polarization ellipse. Recall that if the ellipse has an equal minor and major axis it

transforms into a circle, and we say that the antenna is circularly polarized. In that case the axial

ratio is equal to unity (or 0 dB). The axial ratio of a linearly polarized antenna is infinitely big

since one of the ellipse axis is equal to zero. For a circularly polarized antenna, the closer the

axial ratio is to 0 dB, the better.

Directivity : Directivity is a fundamental antenna parameter. It is a measure of how directional

an antenna’s radiation pattern is. An antenna that radiates equally in all directions would have

effectively zero directionality, and the directivity of this type would be 1(0 db).

Effective aperture: The effective antenna aperture is a theoretical value which is a measure of

how effective an antenna is at receiving power. The effective aperture /area can be calculated by

knowing the gain of the receiving antenna.

Antenna Efficiency: The antenna efficiency is a ratio of the power delivered to the antenna

relative to the power radiated from antenna. A high efficiency antenna has most of the power

present at the antennas input radiated away. Antenna efficiency is a number between 0 and 1.

2.3 Introduction to Patch Antenna

2.3.1. Introduction:

Basically micro-strip element consists of an area of metallization support above the

ground plane, named as micro-strip patch. The supporting element is called substrate material

which is placed between the patch and the ground plane. The micro-strip antenna can be

fabricated with low cost lithographic technique or by monolithic integrated circuit technique.



Using monolithic integrated circuit technique we can fabricate phase shifters, amplifiers and

other necessary devices, all on the same substrate by automated process. In majority of the cases

the performance characteristics of the antenna depends on the substrate material and its physical

parameters. This unit will give the basic picture regarding micro-strip antenna configurations,

methods of analysis and some feeding techniques.

In the micro-strip antenna the upper surface of the dielectric substrate supports the printed

conducting strip which is suitably contoured while the lower surface of the substrate is backed by

a conducting ground plane. Such antenna sometimes called a printed antenna because the

fabrication procedure is similar to that of a printed circuit board. Many types of micro-strip

antennas have been evolved which are variations of the basic structure. Micro-strip antennas can

be designed as very thin planar printed antennas and they are very useful elements for

communication applications.

Fig 2.3.1.1 Basic Structure of Micro-strip Patch Antenna

So many advantages and applications can be mentioned for micro-strip patch

antennas over conventional antennas. There are several undesirable features we encountered with

conventional antennas like they are bulky, conformability problems and difficult to perform

multiband operations so on. The advantages include planar surface, possible integration with



circuit elements, small surface, generate with printed circuit technology and can be designed for

dual and multiband frequencies. Disadvantages include narrow bandwidth, low RF power

handling capability, larger ohmic losses and low efficiency because of surface waves etc. For the

last two decades, researchers have been struggling to overcome these problems and they

succeeded many times with their novel designs and new findings.

The most popular methods for the analysis of micro-strip patch antennas are the

transmission line model, cavity model and full wave model (which include primarily integral

equations/moment method). The transmission line model is the simplest of all and it gives good

physical insight but it is less accurate. The cavity model is more accurate and gives good

physical insight but is complex in nature. The full wave models are extremely accurate, versatile

and can treat single elements, finite and infinite arrays, stacked elements, arbitrary shaped

elements and coupling.

The frequency of operation of patch antenna is determined by the length L.

The center frequency is given by:

fc = [c/2L√€r] = [ 1/2L√€0€rµ0 ]

The above equation says that the micro-strip antenna should have a length equal to

one half of a wavelength within the dielectric medium.

The width W of the micro-strip antenna controls the input impedance. Larger

widths also can increase the bandwidth. For a square patch antenna fed in the manner above, the

input impedance will be in the order of 300 ohms. By increasing the width, the impedance can be

reduced. However, to decrease the input impedance to 50 ohms often requires a very wide patch

antenna, which takes up a lot of valuable space. The width further controls the radiation pattern.

The normalized radiation pattern is approximately given by



Fig 2.3.1.2 Normalized Radiation Pattern

2.3.2. Measurement of Antenna Characteristics:



The antennas, in general, are characterized by parameters like gain, input impedance, directivity,

radiation pattern, effective area and polarization properties. The experimental procedure to find

the parameters of the antenna is discussed in the following sections. The S parameters can be

determined with Vector Network Analyzer and radiation patterns can be computed through the

antenna measurement setup in connection with Network analyzer. The cables and connectors

have its losses associated at higher frequency bands. The measuring instrument should be

calibrated before using it. There are many calibration procedures are available in network

analyzer. Single port, full two port and TRL calibration methods are generally used. Return loss,

VSWR and input impedance can be measured using single port calibration method.

Radiation Pattern:

A patch antenna radiates power in certain directions and we say that the antenna has

directivity (usually expressed in dBi). If the antenna had a 100% radiation efficiency, all

directivity would be converted to gain. Typical half wave patches have efficiencies well above

90%. The directivity of a patch can be estimated quite easily: The radiating edges of a patch can

be seen as two radiating slots placed above a ground plane and, assuming all radiation occurs in

one half of the hemisphere (on the patch side of the ground), we get a 3 dB directivity increase.

This would be an antenna with a perfect front-to-back ratio where all radiation occurs towards

the front and no radiation towards the back. This front-to-back ratio is highly dependent on

ground-plane size and shape in real life. Another 3 dB can be added because there are 2 slots.

The length of these slots typically equals the impedance width (length in the y-axis) of the patch

and the width of these slots equals the substrate height. These slots typically have a directivity of

2 to 3 dB compared to an isotropic radiator and behave like a dipole. All of this results in a total

maximum directivity of 8 to 9 dBi. The rectangular patch excited in its fundamental mode has a

maximum directivity in the direction perpendicular to the patch (z-axis or broadside). The

directivity decreases when moving away from broadside towards lower elevations. The 3 dB

beamwidth is the width at which the gain of the beam decreases by 3 dB relative to the gain in

broadside to either side of the main beam.



Fig 2.3.2 Typical radiation pattern of a simple square patch

So far, the directivity has been defined relative to an isotropic radiator and we use dBi.

An isotropic radiator emits an equal amount of power in all directions and it has no directivity.

Antenna directivity can also be specified relative to that of a dipole. A dipole has 2.15 dBi of

directivity over an isotropic radiator. When we specify the directivity of an antenna relative to a

dipole, we use dBd. No antenna losses have been included so far and the integrated average of

the directivity pattern over an entire sphere has to be 0 dBi. This implies that creating directivity

in a certain direction reduces directivity in other directions.

Antenna Gain:

Antennas do not have gain because they are passive structures. Antenna gain is defined as

antenna directivity times a factor representing the radiation efficiency. Radiation efficiency is

always lower than 100% so the antenna gain is always lower than antenna directivity. This

efficiency quantifies the losses in the antenna and is defined as the ratio of radiated power (Pr) to

input power (Pi). The input power is transformed into radiated power, surface wave power and a

small portion is dissipated due to conductor and dielectric losses. Surface waves are guided



waves captured within the substrate and partially radiated and reflected back at the substrate

edges. Surface waves are more easily excited when materials with higher dielectric constants

and/or thicker materials are used. Surface waves are not excited when air dielectric is used.

Several techniques to prevent surface wave excitation exist, but this is beyond the scope of this

article. Antenna gain can also be specified using the total efficiency rather than just the radiation

efficiency. This total efficiency is a combination of the radiation efficiency and efficiency linked

to the impedance matching of the antenna.

Return loss and VSWR:

The reflection coefficient at the antenna input is the ratio of the reflected voltage to the incident

voltage and is same as the S11 when the antenna is connected at the port1 of the network

analyzer. It is the measure of the impedance mismatch between the antenna and the source line.

The degree of mismatch is usually described in terms of Return loss or VSWR . The return loss

(RL) is the ratio of the reflected power to the incident power, expressed in dB as

RL=−20 log (|s11|)=−¿ s11∨dB

The frequency corresponding to return loss minimum is taken as resonant frequency of the

antenna. The range of frequencies for which the return loss value is less than -10 dB points is

usually treated as bandwidth of the antenna. The bandwidth of the antenna can be expressed as

percent of bandwidth

%bandwidth= bandwidthCenter frequency

∗100

The voltage standing wave ratio (VSWR) is the ratio of the voltage maximum to the minimum of

the standing wave existing on the antenna input terminals. VSWR equals to 2 gives a return loss

of approximately equals to 10 dB and it is set as the reasonable limits for a matched antenna.

CALCULATION OF Q – FACTOR:

it represents the antenna loss factor and it is given by

1Qt

= 1QR

+ 1QC

+ 1QC

+ 1Qsw

Where Qt represents total Q factor of the patch antenna, Qr is Q factor due to the radiation

losses, Qc is due to conduction losses and Qd is due to dielectric losses. Forthin substrates losses



due to the surface wave Qsw are very small and can be neglected, thus

1Qt

=[ 1QR

+ 1QC

+ 1QD ]−1

2.3.3 Benefits or advantages of Micro-strip Antenna

Following are the benefits or advantages of Micro-strip Antenna:

1. They operate at microwave frequencies where traditional antennas are not feasible to be

designed.

2. This antenna type has smaller size and hence will provide small size end devices.

3. The micro-strip based antennas are easily etched on any PCB and will also provide easy

access for troubleshooting during design and development. This is due to the fact that micro-

strip pattern is visible and accessible from top. Hence they are easy to fabricate and comfortable

on curved parts of the device. Hence it is easy to integrate them with MICs or MMICs.

4. As the patch antennas are fed along centerline to symmetry, it minimizes excitation of other

undesired modes.

5. The micro-strip patches of various shapes e. g. rectangular, square, triangular etc. are easily

etched.

6. They have lower fabrication cost and hence they can be mass manufactured.

7. They are capable of supporting multiple frequency bands (dual, triple).

8. They support dual polarization types viz. linear and circular both.

9. They are light in weight.

10. They are robust when mounted on rigid surfaces of the devices.

2.3.4 Drawbacks or disadvantages of Micro-strip Antenna

Following are the disadvantages of Micro-strip Antenna:

1. The spurious radiation exists in various micro-strip based antennas such as micro-strip patch

antenna, micro-strip slot antenna and printed dipole antenna.

2. It offers low efficiency due to dielectric losses and conductor losses.

3. It offers lower gain.

4. It has higher level of cross polarization radiation.

5. It has lower power handling capability.



6. It has inherently lower impedance bandwidth.

7. The micro-strip antenna structure radiates from feeds and other junction points.

2.4 Introduction to Coplanar Waveguide

2.4.1. Introduction:

Coplanar waveguide is a type of electrical planar transmission line which can be fabricated

using printed circuit board technology, and is used to convey microwave-frequency signals. On a

smaller scale, coplanar waveguide transmission lines are also built into monolithic microwave

integrated circuits. Conventional coplanar waveguide (CPW) consists of a single conducting

track printed onto a dielectricsubstrate, together with a pair of return conductors, one to either

side of the track. All three conductors are on the same side of the substrate, and hence

are coplanar. The return conductors are separated from the central track by a small gap, which

has an unvarying width along the length of the line. Away from the central conductor, the return

conductors usually extend to an indefinite but large distance, so that each is notionally a semi-

infinite plane.

Fig 2.4.1.1 Basic Structure of CPW

As shown in the figure, Coplanar Waveguide consists of a conductor strip at the middle and two

ground planes are located on either sides of centre conductor. All these lie in the same plane.



In coplanar waveguide, EM energy is concentrated within the dielectric . The leakage of the

Electromagnetic energy in the air can be controlled by having substrate height (h) twice that of

the width (S). The coplanar waveguide supports quasi TEM mode at low frequencies while it

supports TE mode at high frequencies.

The effective dielectric constant of CPW is same as that of slotline. The characteristic impedance

of a coplanar waveguide is not affected by thickness and depends on width(W) and space(S). The

lowest characteristic impedance of 20 Ohm can be achieved by maximum strip width(W) and

minimum slot space(S). It typically ranges from 200 to 250 Ohm.

2.4.2 Comparision of Microstrip And CPW:

High-frequency circuit designers must often consider the performance limits, physical

dimensions, and even the power levels of a particular design when deciding upon an optimum

printed-circuit-board (PCB) material for that design. But the choice of transmission-line

technology, such as microstrip or grounded coplanar waveguide (GCPW) circuitry, can also

influence the final performance expected from a design. Many designers may be familiar with

the stark differences between high-frequency microstrip and stripline circuitry. But GCPW

circuitry, while also having its differences from traditional microstrip, also offers many benefits

for high-frequency circuit designers to consider. In making the choice, it can help to understand

just what different types of PCB material can have on the microstrip and GCPW circuits. The

differences between the two structures can be seen in the following simple illustration.

Fig 2.4.2.1 structures of microstrip and coplanar waveguide



Microstrip supports moderate-bandwidth circuits through microwave frequencies, although with

high radiation loss at higher, millimeter-wave frequencies and difficulty at achieving mode

suppression at millimeter-wave frequencies. Microstrip circuits suffer minimal sensitivity to

PCB fabrication techniques and material characteristics, such as copper plating thickness and

copper thickness variations. In contrast, GPCW suffer only moderate radiation loss at millimeter-

wave frequencies, and are capable of moderate or better mode suppression at millimeter-wave

frequencies, making this circuit technology a strong candidate for designs at 30 GHz and higher.

In addition, GCPW circuits are only moderately sensitive to PCB fabricate techniques and

variations, making them well suited for production-volume applications at higher frequencies.

2.4.3 Advantages of CPW:

1. Low dispersion.

2. Simple realization due to etching on one side.

3. Broadband performance.

2.4.4 Disadvantages of CPW:

1. Fabrication of coplanar waveguide is costlier.As gold ribbons are needed to suppress higher

order modes at every quarter wavelengths.

2. Relative thickness of substrates are needed.

2.5 Introduction to Slot Antenna

2.5.1 Introduction:

A slot antenna consists of a metal surface, usually a flat plate, with one or more holes or slots cut

out. When the plate is driven as an antenna by a driving frequency, the slot

radiates electromagnetic waves in a way similar to a dipole antenna. The shape and size of the

slot, as well as the driving frequency, determine the radiation pattern. Often the radio waves are

provided by a waveguide, and the antenna consists of slots in the waveguide. Slot antennas are

often used at UHF and microwave frequencies instead of line antennas when greater control of



the radiation pattern is required. Slot antennas are widely used in radar antennas,

particularly marine radar antennas on ships, for the sector antennas used for cell phone base

stations, and are often found in standard desktop microwave sources used for research purposes.

A slot antenna's main advantages are its size, design simplicity, and convenient adaptation to

mass production using either waveguide or PC board technology.

Fig 2.5.1.1 structure of slot antenna

Frequency Range:

The frequency range used for the application of Slot antenna is 300 MHz to 30 GHz. It works

in UHF and SHF frequency ranges.

2.5.2 Working of Slot Antennas:

When an infinite conducting sheet is made a rectangular cut and the fields are excited in the

aperture (which is called as a slot), it is termed as Slot antenna.

The principle of optics is applied to electromagnetic waves for the wave to get radiated. It is

true that when a HF field exists across a narrow slot in a conducting plane, the energy is

radiated.



The Advantages of Slot Antennas:

1.One benefit of the slot antenna is its sheer simplicity. Widen the slot, and it is equivalent to a

thicker dipole. This is equivalent to increasing the bandwidth.

2.Slotted antennas can transmit high power levels. This is why they are popular in applications

like navigation systems and weather radar.

3.When you’re selecting an outdoor antenna, the low wind load of the slot antenna is a point in

its favor.

4.Slot antenna radiation patterns are roughly omni-directional.

5.More current is required to produce a given power output with a dipole antenna than is

achieved with a slot antenna.

6.Slot antennas are more efficient than a comparably sized dish antenna. This makes slot

antennas an ideal choice for radar dishes in the nose cone of an aircraft, since you can make the

slot antenna smaller where a few more inches dramatically improves the aerodynamics.

The Disadvantages of Slot Antennas:

1.Slot antennas have low radiation efficiency.

2.Slot antennas have high cross-polarization levels.

3.Waveguide slot antennas are heavy compared to their dipole equivalents.

Applications:

1.Usually for radar navigational purposes

2.Used as an array fed by a wave guide



CHAPTER 3

LITERATURE SURVEY

3.1 Design of a Planar Monopole Multiband Antenna with U- and L-

shapedslots:

3.1.1 K.C.HWANG:

A broadband planar Sierpinski fractal antenna for multiband application is proposed, designed,

and tested. The perturbed Sierpinski fractal patch and slotted ground plane are employed to

achieve broadband characteristics. The implemented antenna including the ground plane has a

total dimension of 100 times 53.7 times 0.8 mm3. The measured 10-dB return loss bandwidths

are 808-1008 MHz (22%) and 1581-2760 MHz (54.3%), which cover the GSM/DCS/PCS/IMT-

2000/ISM/satellite DMB bands. The measured return loss, radiation patterns, and gain of the

proposed antenna are presented and compared with simulated results.

3.1.2 Marco A. Antoniadis and George v:

A compact multiband antenna is proposed that consists of a printed circular disc monopole

antenna with an L-shaped slot cut out of the ground, forming a defected ground plane. Analysis

of the current distribution on the antenna reveals that at low frequencies the addition of the slot

creates two orthogonal current paths, which are responsible for two additional resonances in the

response of the antenna. By virtue of the orthogonality of these modes the antenna exhibits

orthogonal pattern diversity, while enabling the adjacent resonances to be merged, forming a

wideband low-frequency response and maintaining the inherent wideband high-frequency

response of the monopole. The antenna exhibits a measured -10 dB S 11bandwidth of 600 MHz

from 2.68 to 3.28 GHz, and a bandwidth of 4.84 GHz from 4.74 to 9.58 GHz, while the total size

of the antenna is only 24 times 28.3 mm. The efficiency is measured using a modified Wheeler

cap method and is verified using the gain comparison method to be approximately 90% at both

2.7 and 5.5 GHz.



3.1.3 Jing-Xian Liu and Wen-Yan Yin: A new compact interdigital capacitor loaded

open slot antenna and its lumped model are presented in this letter. Equivalent model analysis

shows that the introduction of the interdigital structure increases the capacitive element of the

slot and thus reduces the operating frequency of the slot antenna. And the antenna operating

frequency as well as its size can be easily reduced by simply increasing the capacitance of the

interdigital capacitor and the characteristic impedance of the slot. Experimental results of the

exemplary antenna agree well with those of the full-wave simulation, proving that the proposed

open slot antenna structure is viable in antenna design.

3.1.4 Wang-Sang Lee, Won-Gyu Lim, and Jong-Won Yu:A multiple band-notched

planar monopole antenna for multi-band wireless systems is presented. The proposed antenna

consists of a wideband planar monopole antenna and the multiple U-shape slots, producing band-

notched characteristics. In order to generate two band-notched characteristics, we propose that

three U-shape slots are required. This technique is suitable for creating ultra-wideband (UWB)

antenna with narrow frequency notches or for creating multi-band antennas.



CHAPTER 4

SIMULATION OF PROPOSED ANTENNA

4.1 Introduction to HFSS

The name HFSS stands for High Frequency Structural Simulator. HFSS is a high-

performance full-wave electromagnetic (EM) field simulator for arbitrary 3D volumetric passive

device modeling that takes advantage of the familiar Microsoft Windows graphical user

interface. It integrates simulation, visualization, solid modeling, and automation in an easy-to-

learn environment where solutions to 3D EM problems are quickly and accurately obtained.

Ansoft HFSS employs the Finite Element Method (FEM), adaptive meshing, and brilliant

graphics to give unparalleled performance and insight to all of 3D EM problems. HFSS is an

interactive simulation system whose basic mesh element is a tetrahedron. This allows to solve

any arbitrary 3D geometry, especially those with complex curves and shapes, in a fraction of the

time it would take using other techniques. Ansoft pioneered the use of the Finite Element

Method(FEM) for EM simulation by developing/implementing technologies such as tangential

vector finite elements, adaptive meshing, and Adaptive Lanczos-Pade Sweep.

The Ansoft HFSS Desktop provides an intuitive, easy-to-use interface for developing passive RF

device models. Creating designs, involves the following:

1. Parametric Model Generation – creating the geometry, Parametric Model Generation

boundaries and excitations

2. Analysis Setup – defining solution setup and frequency sweep Analysis Setup

3. Results – creating 2D reports and field plots Results

4. Solve Loop - the solution process is fully automated Solve Loop.



4.1.1 Application Of Hfss

Today, HFSS continues to lead the industry with innovations such as Modes-to-Nodes and

Full-Wave Spice. Ansoft HFSS has evolved over a period of years with input from many

users and industries. In industry, Ansoft HFSS is the tool of choice for high-productivity

research, development, and virtual prototyping. HFSS finds applications in wide range of

areas. Ansoft HFSS can be used to calculate parameters such as S-Parameters, Resonant

Frequency, and Fields.

Some of applications of HFSS are:

1. Package Modeling–BGA, QFP, Flip-Chip

2. PCB Board Modeling–Power/Ground planes, Mesh Grid Grounds, Backplanes

Silicon/GaAs-Spiral Inductors, Transformers

3. EMC/EMI –Shield Enclosures, Coupling, Near-or Far-Field Radiation

4. Antennas/Mobile Communications–Patches, Dipoles, Horns, Conformal Cell Phone

Antennas, Quadrafilar Helix, Specific Absorption Rate(SAR), Infinite Arrays, Radar Cross

Section(RCS),Frequency Selective Surfaces(FSS)

5. Connectors–Coax, SFP/XFP, Backplane, Transitions

6. Waveguide–Filters, Resonators, Transitions, Couplers

7. Filters–Cavity Filters, Microstrip, Dielectric.

8. Microwave transitions

9. Waveguide components

10. Three-dimensional discontinuities

11. Passive circuit elements

4.1.2 Hfss Features

HFSS has many significant features which attracts the user. Some of the features of HFSS are:

1. Computes s-parameters and full-wave fields for arbitrarily-shaped 3D passive structures.

2. Powerful drawing capabilities to simplify design entry.

3. Field solving engine with accuracy-driven adaptive solutions.



4. Powerful post-processor for unprecedented insight into electrical performance.

5. Advanced materials.

6. Model Library-including spiral inductors.

7. Model half, quarter, or octet symmetry.

8. Calculate far-field patterns.

9. Wideband fast frequency sweep .

10. Create parameterized cross section models- 2D models .

4.2 Design Procedure For Edge Feed U Slot Circular Microstrip Patch

Antenna

STEP: 1 Launching Ansoft HFSS

To access Ansoft HFSS, click the Microsoft Start button, select Programs and select the Ansoft

> HFSS program group. Click HFSS.

Fig.4.1 The HFSS Environment



STEP: 2 Setting Tool Options

To set the tool options:

1. Select the menu item Tools > Options > HFSS Option

2. HFSS Options Window

i) Click the General General tab

Use Wizards for data input when creating new boundaries: Checked

Duplicate boundaries with geometry: Checked

ii) Click the OK button

3. Select the menu item Tools > Options > Modeler.

4. 3D Modeler Options Window

i) Click the Operation tab

Automatically cover closed polylines: Checked

ii) Click the Drawing tab

Edit property of new primitives: Checked

iii) Click the OK button

STEP : 3 Opening a New Project

To open a new project:

1. In an Ansoft HFSS window, select the menu item File > New.

2. From the Project menu, select Insert HFSS Design

Fig.4.2 Project Manager Window



STEP : 4 Set Solution Type

To set the solution type:

1. Select the menu item HFSS > Solution

2. Solution Type Window:

Choose Driven Terminal Click the OK button

Fig.4.3 Solution Type Selection Window

STEP: 5 Creating the 3D Model

Set Model Units

Fig.4.4 Model Unit Window



To set the units

1. Select the menu item Modeler > Unit

2. Set Model Units

Select Units: mm

Click the OK button

STEP: 6 Set Default Material

To set the default material:

1. Using the 3D Modeler Materials toolbar, choose Select .

Fig.4.5 3D Modeler Materials toolbar

2. Select Definition Window:

FR4_eproxy Click the OK.

Fig.4.6 Definition Window



STEP : 7 Create Substrate

1) To create the substrate1:

i) Select the menu item Draw > Box

ii) Using the coordinate entry fields, enter the box position shown in window.

iii) Using the coordinate entry fields, enter the opposite corner of the box.

2) To set the name:

1. Select the Attribute tab from the Properties window.

2. For the Value of Name type: Sub1

3. Change the Color to Light Gray

4. Change the Transparency to 0.6

5. Click the ok button.

Fig 4.7 Substrate Attributes window

To fit the view:

1. Select the menu item View > Fit All > Active or press the CTRL+D key



Fig.4.8 Substrate Creation

STEP: 8 Create Ground

1) To create the Ground:

i) Select the menu item Draw >Rectangle

ii) Using the coordinate entry fields, enter the rectangle position shown in window.

iii) Using the coordinate entry fields, enter the opposite corner of the rectangle shown in

Attributes window.

2) To set the name:


2. For the Value of Name type: GND

3. Change the Color to orange


5. Click the OK button



Fig 4.9 Ground attribute window

Fig.4.10 Ground Creation

To fit the view:

1. Select the menu item View > Fit All > Active Or press the CTRL+D key

STEP: 9 Create Patch

To create Patch

1. Select the menu item Draw > Rectangle

2. Using the coordinate entry fields, enter the rectangle position shown in

attributes window.



3. Using the coordinate entry fields, enter the opposite corner of the base

rectangle shown in attributes window.

2) To set the name:


2. For the Value of Name type: GND

3. Change the Color to orange



Fig 4.11 Patch attributes window



Fig 4.12 Patch Creation

STEP: 10 Create Strip line

To Create Strip line



attributes window.


Rectangle as shown in attribute window.

To set the name:


2. For the Value of Name type: Strip line




Fig 4.13 Strip line attribute window

Select Patch + Strip line then right click Edit > Boolean > unite.

Fig 4.14 Strip line creation

To fit the view:

1. Select the menu item View > Fit All > Active View Or press the CTRL+D key

STEP : 11 Create Slots

To create Slot1 and Slot2





attributes window.


Rectangle as shown in attribute window.

To set the name:


2. For the Value of Name type: Slot1 and Slot2.


Fig 4.15 Slot1 attribute window

Fig 4.16Slot2 attribute window



Select Patch + Slot1 and Slot2 then right click Edit > Boolean >Subtrate.

Fig 4.17Slots creation

To fit the view:

1. Select the menu item View > Fit All > Active View Or press the CTRL+D key

STEP: 12 Create Slot3

1) To create the Slot3:


ii) Using the coordinate entry fields, enter the rectangle position as shown in attribute

window.

iii) Using the coordinate entry fields, enter the opposite corner of the rectangle as shown in

attribute window.

2) To set the name:


2. For the Value of Name type: Slot3

3. Change the Color to red





Fig 4.18 Slot3 attribute window

Fig 4.19 Slot3 Creation

To fit the view:


STEP : 13 Create feed

1) To create the feed:


ii) Using the coordinate entry fields, enter the rectangle position as shown in attribute

window.



iii) Using the coordinate entry fields, enter the opposite corner of the rectangle as shown in

attribute window.

2) To set the name:


2. For the Value of Name type: feed

3. Change the Color to blue



Fig 4.20 Feed attribute window

Fig 4.21Feed creation

To fit the view:




Step : 14 Creation Of Radiation Box

Note: Radiation box is used to measure the far field radiation pattern and is generally created at

¼ wavelength distance all around the patch.

1) To create the radiation box:

Select Draw> Region> Padding type > Percentage offset > 7.389 mm.

2) To set the name:


2. For the Value of Name type: radiation box

3. Change the Color to yellow

4. Change the Trasparency to 5.4


To fit the view:


ASSIGNING BOUNDARIES:

Step: 15 Assign a Perfect E boundary to the Ground

To select the feed:

1. Select the menu item Edit > Select > By Name

2. Select Object Dialog,

i) Select the objects named: Ground


To assign the Perfect E boundary



1. Select the menu item HFSS > Boundaries > Assign > Perfect E

2. Perfect E Boundary window

i) Name: PerfE_Ground

ii) Infinite Ground Plane: Unchecked


Fig.4.22 Perfect E Boundary window

Step: 16 Assign a Perfect E boundary to the Patch

To select the Patch:



i) Select the objects named: Patch


To assign the Perfect E boundary



i) Name: PerfE_Patch





Fig.4.23 Perfect E Boundary window

STEP :17 Assign Radiation To Radiation Box:

To select the Radiation:



i) Select the objects named: Radiation


To assign the Radiation boundary



i) Name: PerfE_patch



STEP : 18 Create a Radiation Setup



To define the radiation setup

1. Select the menu item HFSS > Radiation > Insert Far Field Setup > Infinite >Sphere

2. Far Field Radiation Sphere Setup dialog :

Select the Infinite Sphere Tab i) Phi: (Start: 0, Stop: 90, Step Size: 90) ii) Theta: (Start: -180, Stop: 180, Step Size: 2) Click the OK button

Fig.4.24 Far Field Radiation Sphere Setup dialog

Step: 19 Assign Excitation

To select the object Source:



i) Select the objects named: Feedii) Click the OK button

Note: You can also select the object from the Model Tree

To assign lumped port excitation

1. Select the menu item HFSS > Excitations > Assign > Lumped Port

2. Place Feed in the Conducting Object list and Ground in the Reference Conductor list



3. Click the OK button.

Fig.4.25 Lumped Port Reference Conductor For Terminal Window

STEP: 20 Creating Analysis Setup

To create an analysis setup

1. Select the menu item HFSS > Analysis Setup > Add Solution HFSS > Analysis Setup > Add

Solution Setup

2. Solution Setup Window:

1. Click the General tab:

Solution Frequency:10.15 GHz

Maximum Number of Passes: 10

Maximum Delta S: 0.02

2. Click the Options tab:

Enable Iterative Solver: Checked




Fig.4.26 HFSS Setup Window

STEP : 23 Adding a Frequency Sweep

To add a frequency sweep:

1. Select the menu item HFSS > Analysis Setup > Add Frequency Sweep

i) Select Solution Setup: Setup1


2. Edit Sweep Window:

1. Sweep Type: Interpolating

2. Frequency Setup Type: Linear Step

Start: 9.0GHz

Stop: 11.0GHz

Step size: 0.1GHz



Save Fields:Checked

4. Click the OK button.

Fig.4.27 Frequency Sweep Window

STEP : 24 Save The Project .

STEP : 25 Model Validation

To validate the model:

1. Select the menu item HFSS > Validation

2. Click the Close button.

Analyze :

To start the solution process: Select the menu item HFSS > Analyze All.



Fig.4.28 Validation Window



CHAPTER 5

DESIGN AND ANALYSIS OF PLANAR MONOPOLE

ANTENNA WITH U AND L-SHAPED SLOTS

5.1 Introduction To Proposed Antenna:With the rapid development of the wireless communication system, multiband antennas are

becoming more and more favorable in modern wireless communications, and much significant

effort has been devoted to integrating various frequencies into a single portable device. The

multiband system has become a highly competitive topic and so much significant progress in the

design of multiband antennas has been reported recently, such as the modified sierpinski gasket

monopole antennas, the modified multiband planar inverted-F antennas and the interdigital

capacitor-inserted multiband antenna etc.

5.2 Geometrical Configuration:

The prototype structure of the antenna we proposed, consists of an E-shaped patch fed through a

coplanar waveguide (CPW) transmission line, which was in turn connected to a coaxial cable

through a standard 50Ω SMA connector. The antenna was designed on a low-cost, durable FR4

substrate with relative dielectric constant εr=4.4, loss tangent tanδ=0.02 and height h=1.6 mm.

The overall size of the antenna is 33.5×50 mm2 while the patch is 18×28 mm2 .To achieve the

multiple band-notched characteristics, we make some changes on the initial antenna. The

modified structures shown in the Fig. 5.2.1 and fig 5.2.2contain two L-shaped slots in the ground

and one U-shaped slot in the patch. Fig.5.2.2 shows the ultimate design. The U-shaped slot

mainly affects the impedance matching at 1.9 GHz. The ground of the feed line is designed into a

patch with L-shaped slots for band-notched feature on high frequency. Table I summarizes the

geometrical parameters of the antenna.



TABLE I: GEOMETRICAL PARAMETERS OF THE PROPOSED ANTENNA

(UNIT: MILLIMETERS)

T1 T2 T3 T4 T5 T6

9.2 1 3 0.75 13 6

W1 W2 W3 W4 Ux Uy

28 20 11 49 4.5 6

Uw Ut Lx Ly Lw Lt

21 9.2 5.6 2 5 15

The main characteristics are measured with Agilent E8357A vector network analyzer. The

measured and simulated reflection coefficients of the proposed antenna are presented in Fig. 3,

with the commercial software High Frequency Structure Simulator (HFSS) implemented for the

simulation.

Fig 5.2.1 structure of antenna without slots



Fig 5.2.2 structure of antenna with L slots

Fig 5.2.3 structure of antenna with L slots and U slots



CHAPTER 6

SIMULATED RESULTS AND DISCUSSIONS6.1 Return Loss:

Fig 6.1.1 Return loss at Resonant frequencies: f1 = 1.8GHz, f2 = 9.6GHz

Discussions

We can see that the proposed antenna achieves return loss at 1.8GHZ and 9.6GHZ. These

frequencies are used in some applications like TV broadcasts, microwave ovens, mobile phones,

wireless LAN, Bluetooth, GPS.



6.2 GAIN:

Fig 6.2.1 3D Polar Plot at 1.8GHz



Fig 6.2.2 3D Polar Plot at 9.6GHz

Discussions

The measured peak gains at 1.8GHZ and 9.6GHZ are shown in fig 6.2.1 and fig 6.2.2

respectively.



6.3 Radiation Patterns:

Fig 6.3.1 Radiation pattern at 1.8GHZ

Discussions

The radiation pattern of the measured antenna is as shown in the above fig 6.3.1.



CHAPTER 7

MEASURED RESULTS AND DISCUSSIONS

7.1 Return Loss:

Fig 7.1.1 Return loss at Resonant frequencies: f1 = 1.8GHz, f2 = 6.8GHz,f3=9.18Ghz

Discussions

We can see that the proposed antenna achieves return loss at 1.8GHZ, 6.8GHz and 9.18GHZ.

These frequencies are used in some applications like TV broadcasts, microwave ovens, mobile

phones, wireless LAN, Bluetooth, GPS.



7.2 Radiation Patterns:

Fig 7.2.1 Radiation pattern at 1.8GHZ

Discussions

The radiation pattern of the measured antenna is as shown in the above fig 7.2.1.



7.3 VSWR:

Fig 7.3.1 VSWR of the antenna

Discussions

TheVSWR of the measured antenna is as shown in the above fig7.3.1.



7.4 Final results

Gain Details

S. No Freq(GHz) Gain(dBi)

1 1.8 3.2

2 6.8 ----

Beam Width Details

Beam Width VERTICAL POLARIZATION(VP)-

Deg

HORIZONTAL POLARIZATION(HP)-

Deg

1.8 GHz OMNI FIGURE OF 8

6.8 GHz No proper shape No proper shape

CHAPTER 8

CONCLUSION



A planar monopole antenna is used for PCS and WiMax applications.The antenna has

omnidirectional pattern and sufficient impedance bandwidth. The antenna is more preferable

because of its simple structure and cost. This antenna achieves return loss at 1.8GHZ, 6.8GHz

and 9.18GHZ. These frequencies are used in some applications like TV broadcasts, microwave

ovens, mobile phones, wireless LAN, Bluetooth, GPS.

8.1References:

[1] Kuem C. Hwangˈ “A Modified Sierpinski Fractal Antenna for Multiband Application,” IEEE

Antenna and Wireless Propagation Letters, vol. 6, 2007.

[2] Marco A. Antoniades and George V, “A Compact Multiband Monopole Antenna with a

Defected Ground Plane,” IEEE Antennas And Wireless Propagation Letters, vol. 7, 2008.

[3] Jing-Xian Liu and Wen-Yan Yin ˈ “A Compact Inter digital Capacitor-Inserted Multiband

Antenna for Wireless Communication Applications,” IEEE Antennas and Wireless Propagation

Letters, vol. 9, 2010. [4] Marco A. Antoniades and George V. Eleftheriades, “A Compact

Multiband Monopole Antenna with a Defected Ground Plane,” IEEE Antennas And Wireless

Propagation Letters, Vol.7, 2008.

[5] Wang-Sang Lee, Won-Gyu Lim, and Jong-Won Yu, “Multiple Band-Notched Planar

Monopole Antenna for Multiband Wireless Systems,” IEEE Microwave and Wireless

Components Letters, Vol. 15, NO. 9, September 2005.


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