Printed_Dipole_Antenna

DESIGN AND DEVELOPMENT OF PRINTED DIPOLE ANTENNA FOR AIRBORNE APPLICATION

1. PREAMBLE

1.1 DEFINITION OF ANTENNA

A radio antenna is usually defined as - “An antenna is a transition device, or transducer,

between a guided wave and a free-space wave, or vice versa”. Antenna is a device which

interfaces a circuit and space.

On transmission, an antenna accepts electromagnetic energy from a transmission line

(coaxial cable or waveguide) and radiates it into space, and on reception, an antenna

collects the electromagnetic energy from an incident wave and sends it through the

transmission line.

In aircraft communication systems the antenna is one of the most critical components. A

good design of antenna can improve overall system performance and reduce system

requirements. In order to meet the system requirements of today’s aircraft communication

systems and the increasing demand on their performances, much advancement in the field

of antenna engineering have occurred in the last few decades. This increasing demand is

fuelled by digital and RF circuit fabrication improvements, new large scale circuit

integration and other miniaturisation technologies which makes antennas smaller, cheaper

and more reliable. Among the different types of antennas, printed antennas are the ideal

candidates for these applications due to their planar structure and compatibility with the

printed circuit fabrication techniques.

1.2 SCOPE OF THE PROJECT

The project deals with design of printed dipole antenna with Omni-directional radiation

characteristics along with the implementation of DC short. The antenna will be used for

on-board datalink communication for indigenous UAV systems, with appropriate

encapsulation and reinforcement.

1.3 AIM OF THE PROJECTDEPARTMENT OF ECE, CMRIT P a g e | 1


To design and develop a printed dipole antenna for Unmanned Aerial Vehicle (UAV)

data link communication in C Band with the following specialized features -

C Band operation with 800MHz bandwidth

Omni-directional radiation pattern

Vertical polarization

Integrated 'balun' and DC grounding

Compact , encapsulated and aerodynamic shape

1.4 MOTIVATION FOR THE PROJECT

There has always been a curiosity in our minds that, as to how a UAV is controlled from

the Ground Control Station (GCS). The commands that are transmitted by them, have to

be efficiently received by the UAV, and various UAV parameters during mission have to

be relayed back to the GCS. An Omni-directional antenna on-board is a key constituent

for successful operation of a UAV mission. It is a challenging task to design an antenna

which will ensure an uninterrupted communication datalink between the GCS and the

UAV. We attempted to do it, under the expertise guidance of ADE.

1.5 PROJECT IMPLEMENTATION METHODOLOGY

For designing and optimizing the designs, FEKO code has been used.

CADFEKO tool provides the platform for designing the antenna models, with the desired

specifications. RUNFEKO is used for simulating the designed models. POSTFEKO is

used for verifying the design by means of the various plots that can be plotted here.

The flow can be represented as –

DEPARTMENT OF ECE, CMRIT P a g e | 2

Y


Fig 1.1: Flow chart project implement methodology

1.6 ORGANIZATION OF THE REPORT


Familiarization with FEKO

Literature study on Printed Dipole Antenna

Design the Printed Dipole Antenna Using the Tool

Software Simulation

Fabrication of the optimized design

Testing and measurements in Anechoic chamber

Start

STOP

Optimization process (check for VSWR and Bandwidth)

Optimized?

N


CHAPTER 1: This chapter gives the introduction to the project, describing the

motivation behind the project, its scope, objectives to be accomplished and the

methodology that we followed to implement the assignment.

CHAPTER 2: This chapter deals with the fundamental concepts of the dipole antenna, its

radiation mechanism and the antennas derived from dipole.

CHAPTER 3: This chapter discusses about the printed dipole antenna and its feeding

method which forms the guidelines for this project.

CHAPTER 4: "Balun" concept has been discussed here. We also look into its types and

their advantages.

CHAPTER 5: Here the various design considerations are discussed, for designing the

printed dipole antenna.

CHAPTER 6: Introduction to the EM simulation code has been given here, discussing its

components and their functionality.

CHAPTER 7: This chapter gives an insight into the simulation results of the various

antenna models that have been designed, and their optimization process.

CHAPTER 8: The procedure of antenna fabrication and their testing description has

been given here.

CHAPTER 9: The experimental results of the antennas fabricated are plotted.

CHAPTER 10 & 11: The obtained results have been concluded and the scope of this

project for future utility have been arrived upon .

2. DIPOLE ANTENNA THEORY



2.1 HISTORY

Dipole antennas were invented by German physicist Heinrich Hertz around 1886 in his

pioneering experiments with radio waves. The dipole antenna he designed was in UHF

band. Since then extensive research and development of dipole antenna has been done

exploiting the new advantages such as light weight, low volume, low cost and compatible

with integrated circuits.

2.2 DIPOLE ANTENNA FUNDAMENTALS

A dipole antenna is a radio antenna that can be made of a simple wire, with a centre-fed

driven element. The dipole antenna is a balanced antenna and has two perfectly

symmetrical poles, made of wires that open out in opposite direction from the central feed

point. Since dipole antenna consists of two terminals or “poles” into which radio

frequency current flows, hence it is called a Dipole antenna. There are different types of

dipole antennae, but each have the same function of transmitting and receiving radio

signals. For resonance the conductor is an odd number of half wavelength’s long. In most

cases, a single half wavelength is used, although three, five,.. wavelength antennas are

equally valid. Half-wavelength dipoles are a unique type, with each wire measuring

exactly one-fourth of the electromagnetic wavelength, making it a total of one half

wavelength.

Fig2.1: Schematic of half-wave dipole antenna



The current and the associated voltage causes electromagnetic or radio signal to be

radiated. A Dipole is generally taken to be an antenna that consists of a resonant length of

conductor, cut to enable it to be connected to the feeder.

Fig2.2: The basic half wave dipole

The current distribution along a dipole is roughly sinusoidal. It falls to zero at the end,

and is at maximum in the middle. Conversely, the voltage is low at the middle and rises to

a maximum at the ends. It is generally fed at the centre, at the point where the current is at

a maximum and the voltage is a minimum. This provides a low impedance feed point

which is convenient to handle. High voltage feed points are far less convenient and more

difficult to use. When multiple half wavelength dipoles are used, they are similarly

normally fed in the centre. Here again the voltage is at a minimum and the current at a

maximum. Theoretically any of the current maximum nodes could be used.

Fig2.3: three half wavelength wave dipole antenna



2.3 DIPOLE RADIATION MECHANISM

The polar diagram of a half wave dipole antenna that the direction of maximum

sensitivity or radiation is at right angles to the axis of the RF antenna. The radiation falls

to zero along the axis of the RF antenna as might be expected.

Fig2.4: Polar diagram of a half wave dipole in free space

Fig2.5: Field distribution in E and H plane.

If the length of the dipole antenna is changed then the radiation pattern is altered. As the

length of the antenna is extended, it can be seen that the familiar figure of eight pattern

changes to give the main lobes and a few side lobes. The main lobes move progressively

towards the axis of the antenna as the length increases.



The dipole antenna is a particularly important form of RF antenna which is very widely

used for radio transmitting and receiving applications. The dipole is often used on its own

as an RF antenna, but it also forms the essential element in many other types of RF

antenna. As such it is the possibly the most important form of RF antenna.

Dipole antenna is used in a variety of everyday electronics. Dipole antenna is used on

television sets to receive broadcasts and also dipole antennas are also widely used in the

military, where they are built into equipment such as navigation devices and radio’s.

2.4 DIPOLE FEED IMPEDANCE

The feed impedance of a dipole is determined by the ratio of the voltage and the current at

the feed point. A simple Ohms law calculation will enable the impedance to be

determined.

Although a dipole can be fed at any point, it is typically fed at the current maximum and

voltage minimum point. This gives low impedance which is normally more manageable.

Most dipoles tend to be multiples of half wavelength’s long. It is therefore possible to

feed the dipole at any one of these voltage minimum or current maximum points which

occur at a point , that is a quarter wavelength from the end, and then at half wavelength

intervals.

The vast majority of dipole antennas are half wavelength long. Therefore they are centre

fed – the point of the voltage minimum and current maximum.

The dipole feed impedance is made up from two constituents-

Loss resistance: The loss resistance results from the resistive or Ohmic losses

within the radiating element, i.e. the dipole. In many cases, the dipole loss

resistance is ignored as it may be low. To ensure that it is low, sufficiently thick

cable or piping should be used, and the metal should have a low resistance. Skin

effects may also need to be considered.

Radiation resistance: The radiation resistance is the element of the dipole antenna

impedance that results from the power being dissipated as an electromagnetic

wave. The aim of any antenna is to dissipate as much power in this way as

possible.



As with any RF antenna, the feed impedance of a dipole antenna is dependent upon a

variety of factors including the length, the feed position and the environment. A half wave

centre fed dipole antenna in free space has an impedance of 73.13 making it ideal to feed

with 75 ohm feeder.

2.4.1 FACTORS AFFECTING THE DIPOLE FEED IMPEDANCE

The feed impedance of a dipole can be changed by a variety of factors – the proximity of

other objects having a marked effect. The ground has a major effect. If the dipole antenna

forms the radiating element for a more complicated form of RF antenna, then elements of

the RF antenna will have an effect. Often the effect is to lower the impedance, and when

used in some antenna the feed impedance of the dipole element may fall to ten ohms or

less, and methods need to be used to ensure a good match is maintained with the feeder.

2.5 HALF WAVE DIPOLE

One of the most commonly used antennas is the half-wavelength (l = λ/2) dipole. Because

its radiation resistance is 73 ohms, which is very near the 50-ohm or 75-ohm

characteristic impedances of some transmission lines, its matching to the line is simplified

especially at resonance.

Fig2.6: (a) finite dipole geometry (b) geometrical arrangement for far field approximation

The geometry of a finite dipole along with far field approximation is shown above. Here

in this case far field approximations are done with phase and amplitude margin are

calculated as R≃r−z ' cosθ.This is margin for the phase.



The margin for amplitude is given below.

R≃r

As far as current plot of this dipole is considered the current distribution is almost same as

small dipole which is highest at the input at zero at ± l /2 . The above geometries are valid

for all other types of dipole except short dipole. Here for our case length l= λ/2. The

current plot for the same is shown below.

Fig2.7: Current distribution in half wavelength dipole

For a very thin dipole (ideally zero diameter), the current distribution can be written, to a

good approximation, as

I e ( x '=0 , y '=0 , z ')= az I 0sin ⌊k ( l2−z ') ⌋ 0 z l /2

az I 0 sin ⌊k ( l2+z ' ) ⌋−l /2 z0 eqn 2.1

This distribution assumes the antenna is centre-fed and the current vanishes at the end

points (z = ±l/2). Experimentally it has been verified that the current in a centre-fed wire

antenna has sinusoidal form with nulls at the end points. Here for half wavelength dipole

l= λ/2.

The finite dipole antenna of dipole length λ/2 in figure 4.5 is subdivided into a number of

infinitesimal dipoles of length Δz’. As the number of subdivisions is increased, each

infinitesimal dipole approaches a length dz’.



For an infinitesimal dipole of length ‘dz’ positioned along the z-axis at z’, the electric and

magnetic field components in the far field are given below:

d Eθ= jk I e(x ' , y ' , z ' )e− jkR sinθ dz '

4 πR eqn 2.2

d Er=d E∅=d H r=d H θ=0 eqn 2.3

d H∅= jk I e(x ' , y ' , z ' )e− jkRsin θ dz '

4 πR eqn 2.4

Where

R=√x2+ y2+(z−z ' )2 eqn 2.5

finally approximated as above formula. Using far field approximation it reduces to

d Eθ= jk I e ( x' , y ' , z ' ) e− jkr

4 πrsin θ e+ jkz ' cosθdz ' eqn 2.6

Summing the contributions from all the infinitesimal elements, the summation reduces, in

the limit to integration. Here limit is for l ± λ /2.

Eθ=∫−l /2

+l /2

d Eθ= j k e− jkr

4 πrsin θ[ ∫

−l /2

+l/2

I e (x ' , y ' , z ')e+ jkz ' cosθ dz ' ] eqn 2.7

The factor outside the brackets is designated as the element factor and that within the

brackets as the space factor. For this antenna, the element factor is equal to the field of a

unit length infinitesimal dipole located at a reference point (the origin). In general, the

element factor depends on the type of current and its direction of flow while the space

factor is a function of the current distribution along the source. Calculation factor

Total field = element factor X space factor eqn 2.8

The pattern multiplication for continuous sources is analogous to the pattern

multiplication of for discrete-element antennas (arrays). For the current distribution of can

be written as



Eθ= jI 0 k e− jkr

4 πrsinθ [∫−l

2

0

sin ⌊ k ( l2+z ') ⌋ e+ jk z' cosθ

d z '+¿ ∫0

+l /2

sin ⌊k ( l2−z ')⌋ e+ jkz ' cos θ dz ' ]

eqn 2.9

Putting l=λ/2 and since k=2π/λ and solving above integration the electric field and

magnetic field along the dipole is given by

Eθ= jI 0 e− jkr

2πr [ cos ( π2

cosθ)sin θ ] eqn 2.10

H∅=Eθ = j

I 0e− jkr

2 πr [ cos ( π2

cosθ)sin θ ] eqn 2.11

For the dipole average pointing vector is given by

W av=12

ℜ [ E × H ¿ ] eqn 2.12

¿12

ℜ [ aθ Eθ ×a∅ H∅¿ ] eqn 2.13

¿ 12

ℜ[ aθ Eθ × a∅

Eθ ] eqn 2.14

W av= ar W av ¿ ar|I 0|

2

8 π2r 2 [ cos( π2

cosθ)sin θ ]

2

eqn 2.15

hence,

W av=

|I 0|2

8 π2r 2 [ cos( π2

cosθ)sin θ ]

2

≃ |I 0|2

8π2 r2 sin3 θ eqn 2.16

The radiation intensity can be calculated as

U=r2W av eqn 2.17

¿|I 0|

2

8 π2 [ cos ( π2

cosθ)sin θ ]

2

eqn 2.18



≃|I 0|2

8π2 sin3θ eqn 2.19

The total power radiated can be written as

Prad=∫0

2 π

∫0

π

r2 W av sinθ dθ d∅ eqn 2.20

Prad=|I 0|

2

4 π ∫0

π cos2( π2

cosθ)sin θ

dθ eqn 2.21

This on integration gives

Prad=|I 0|

2

8 π ∫0

2π

( 1−cos yy )dy eqn2.22

=|I 0|2

8 πC ¿ (2 π ) eqn 2.23

Where

C ¿ ( x)=∫0

x 1−cos yy

dy eqn 2.24

C ¿ ( x)=ln γ +ln x−C i ( x ) eqn 2.25

Where ln(γ)=.5722 also C i ( x )=−∫x

∞ cos yy

dy=∫∞

x cos yy

dy eqn 2.26

C ¿ (2 π )= .5722+ ln 2 π−C i (2 π ) eqn 2.27

Now since C i (2π )=−.02 eqn 2.28

Hence C ¿ (2π )= .5722+1.838−(−.02 ) = 2.435 eqn 2.29

Now Directivity = D 0=4 πU max

P rad eqn 2.30

¿4 πU|θ= π

2P rad

= 4

C¿ (2 π ) = 4

2.435 ≃ 1.643 eqn 2.31



In D0 (dB )=20 log1.643=2.15 dBi eqn 2.32

The corresponding maximum effective area is

Aem=λ2

4 πD0=

λ2

4 π(1.643 )≃ .13 λ2 eqn 2.33

and the radiation resistance, for a free-space medium (η=120π), is given by

Rr=2 Prad

|I 0|2 =

4 πC ¿ (2 π )=30 (2.435 )≃73 Ω eqn 2.34

The radiation resistance given above is also the radiation resistance of input terminals

since the current for a dipole of l=λ/2 occurs at input terminals. The reactance part for

l=λ/2 is 42.5 hence input impedance is Zin = 73+j42.5. If dipole length is .47 to .48 λ the

reactance part falls to zero approximately hence normally these two lengths are taken

2.6 ANTENNAS DERIVED FROM DIPOLE ANTENNA


Extension of Dipole AntennasLog Periodic AntennaYagi Uda AntennaPrinted Dipole AntennaDipoles in parabolic reflector


Fig2.8: Antennas derived from dipole antenna

2.6.1 YAGI-UDA ANTENNA

The Yagi-Uda antenna or Yagi Antenna is one of the most brilliant antenna designs. It is

simple to construct and has a high gain, typically greater than 10 dB. The Yagi-Uda

antennas typically operate in the HF to UHF bands (about 3 MHz to 3 GHz), although

their bandwidth is typically small, on the order of a few percent of the centre frequency.

We are familiar with this antenna, as they sit on top of roofs everywhere.

The Yagi antenna was invented in Japan, with results first published in 1926. The work

was originally done by Shintaro Uda, but published in Japanese.

2.6.2 LOG-PERIODIC ANTENNA

Log-Periodic antennas antennas are designed for the specific purpose of having a very

wide bandwidth. The achievable bandwidth is theoretically infinite; the actual bandwidth

achieved is dependent on how large the structure is (to determine the lower frequency

limit) and how precise the finer (smaller) features are on the antenna (which determines

the upper frequency limit).

Mathematically, due to the properties of logarithms, if all the elements grow by a constant

multiple then the ratios of the logarithm will be constant.

2.6.3 PARABOLIC ANTENNA

In parabolic antenna, the dipole antenna can be used at the focus of the parabolic antenna.

The radiation power received is reflected by the dish towards the dipole in the centre,

which can collect this power for its use, or vice versa.

2.6.4 PRINTED DIPOLE ANTENNA



These antennas are basically designed where there is need for small and compact antenna.

It is a dipole antenna, printed on a PCB. It has been discussed in detail in the next chapter.

3. PRINTED DIPOLE ANTENNA

3.1 INTRODUCTION

Printed dipole antenna is the antennas which are printed on Printed Circuit Board (PCB).

Basically, they are the printed version of the free-space cylindrical dipole. An antenna

with a narrow rectangular strip (typically strip width less than 0.05λ) is called a microstrip

dipole. Printed dipole antennas are the main focus of this thesis. The conventional design

geometry and the design implemented are as shown in the Fig: below.



Fig3.1: (a) Conventional design, (b) Design incorporated in this thesis

In Fig: (b), the coplanar strip of conductors are printed on the opposite surfaces of a

dielectric sheet to simplify the feed arrangement. The incorporated design is also very

simple to implement, as opposed to conventional design.

These antennas are chosen because they are simple and yet have potential for future

improvement. These antennas are used when an electronic device, which is implemented

on a PCB, is in need of a cheap, compact antenna.

Unlike the straight wire dipole antennas, the radiating elements (i.e. the dipole arms) of

the printed dipole antennas are on a dielectric substrate. Therefore, the selection of the

substrate material will affect the performance of the antennas. It nevertheless makes the

design of the antennas more flexible.

Most existing printed dipole antennas are based on the popular printed dipole design first

proposed in 1987. Unlike the traditional dipole antennas, this printed dipole antenna has

an integrated balun and can be fed by a 50-Ω single-ended microstrip line.

3.2 FEEDING THE DIPOLE

In the incorporated design, the dipoles are printed on the opposite surfaces of the

dielectric sheet. To feed such a configuration, a compatible feed structure is the printed

version of parallel strip line, as shown below.

Fig 3.2: dipole feeding

In the above design, this has been taken care of together with the balun structure.

3.3 ADVANTAGES OF PRINTED DIPOLE ANTENNA

1. Provides Omni-directional radiation coverage in the azimuth plane.



2. Easy to manufacture and low fabrication cost.

3. Small and compact size, less weight making it easy to integrate it on aircraft.

4. Compatible with microwave integrated technologies.

5. Performance parameters can be easily controlled, hence changes in the design is

easy to achieve.

6. When compared to patch antenna, these have smaller size, and hence arrays

occupy less area in the substrate.

7. The cross polar component is lower because the transverse current component on

the strip decreases as the width-to-length ratio decrease.

8. Dipoles are well suited for millimetre-wave frequencies in particular, where the

substrate can be electrically thick and therefore the bandwidth can be significant.

4. BALUN4.1 INTRODUCTION

The term balun is the acronym for balanced to unbalanced. It is a device which is used to

connect a balanced line (e.g. Dipole) to an unbalanced coaxial line. Balun usually solves

problems caused by an imbalance.

When we connect centre fed antennas, like dipoles, unless care is taken, it is not difficult

to end up with feeder radiation. Not only can the loss in power be quite significant, but

the radiation characteristics of the antenna system will also be seriously compromised. In

laymen's terms, it won't be what you are expecting from the pattern of your antenna. In a

simple dipole, the balun assures that the dipole, and not the feed line, is doing the

radiating.

In a coaxial cable, the currents on the inner conductor and the inside of the shield are

equal and opposite. This is because the fields from the two currents are confined to the

same space. With the presence of skin effect, a different current flows on the outside of

the shield than on the inside. In contrast to a balanced line, an unbalanced line has an

unequal magnitude of current or voltage in each conductor of the coaxial line.



In transmitting antennas, the current flowing on the outside of the coaxial cable is

eliminated by presenting high impedance (resistance), to RF currents flowing outside the

coax shield. This forces currents in each side of driven elements to be equal.

Fig4.1: Schematic showing unbalanced to balanced conversion using balun.

4.2 WORKING PRINCIPLE

In Fig below, a coaxial cable is connected to a dipole antenna. For a dipole antenna to

operate properly, the currents on both arms of the dipole should be equal in magnitude.

When a coaxial cable is connected directly to a dipole antenna however, the currents will

not necessarily be equal. To see this, note that the current along a transmission line should

be of equal magnitude on the inner and outer conductors, as is typically the case. Observe

what happens when the coax is connected to the dipole. The current on the centre

conductor (the red/pink centre core of the coax, labelled IA) has nowhere else to go, so

must flow along the dipole arm that is connected to it. However, the current that travels

along the inner side of the outer conductor (IB) has two options: it can travel down the

dipole antenna, or down the reverse (outer) side of the outer conductor of the coaxial

cable (labelled IC in Fig).

Ideally, the current IC should be zero. In that case, the current along the dipole arm

connected to the outer conductor of the coax will be equal to the current on the other

dipole arm - a desirable antenna characteristic. Because the dipole wants equal or

balanced currents along its arms, it is the balanced section. The coaxial cable does not

necessarily give this however - some of the current may travel down the outside of the

outer coax, leading to unbalanced operation - this is the unbalanced section.



The solution to this problem, however you come up with it, is a balun. A balun forces an

unbalanced transmission line to properly feed a balanced component. This would be done

by forcing IC to be zero.

Fig4.2: An unbalanced coaxial cable connected to a dipole antenna.

4.3 TYPES OF BALUN

4.3.1 CURRENT BALUN

An ideal current balun delivers currents that are equal in magnitude and opposite in

phase. A good current balun will approach the ideal condition. It will deliver

approximately equal currents with approximately opposite phase, irrespective of the load

impedance (including symmetry). Common mode current will be small. If the load

impedance is not symmetric, then the voltages at each output terminal will not be equal in

magnitude and opposite in phase. A parameter often used to quantify the effect of a balun

is its common mode impedance or choking impedance. An ideal current balun has infinite

common mode impedance; a good current balun has very high common mode impedance

(typically thousands of ohms for an effective general purpose balun in an antenna

system).

4.3.2 VOLTAGE BALUN

An ideal voltage balun delivers voltages that are equal in magnitude and opposite in

phase. A good voltage balun will approach the ideal condition. It will deliver

approximately equal voltages (with respect to input ground) with approximately opposite

phase, irrespective of the load impedance (including symmetry). Common mode voltage



will be small. If the load impedance is not symmetric, then the currents flowing in each

output terminal will not be equal in magnitude and opposite in phase. An ideal voltage

balun has zero common mode impedance; a good voltage balun has very low common

mode impedance (ohms).

4.4 IMPEDANCE TRANSFORMATION

An ideal balun performs an ideal impedance transformation, normally 1:1 unless specified

otherwise. Practical baluns depart from the ideal, and the departure is often specified as

Insertion VSWR.

It is possible to design a balun to not only facilitate the unbalanced to balanced transition,

but to perform a nominal impedance transformation (e.g. 4:1 is common).

Voltage baluns and current baluns are both capable of impedance transformation other

than nominally 1:1.

4.5 APPLICATIONS

If the application is one where current balance is important then a current balun is the

better choice. For example:

Reducing radiation from an antenna feed line by ensuring that the currents in each

feed line conductor are nearly equal but opposite in phase.

If the application is one where voltage balance is important then a voltage balun is the

better choice. For example:

Some audio applications where rejection of common node voltage injected into a

source is important.



5. DESIGN OF PRINTED DIPOLE ANTENNA

5.1 INTRODUCTION

The basic dipole antenna element is the two radiating arms of length ‘Ld’ and width ‘W’,

on a dielectric substrate of dielectric constant ‘ℰr’ and thickness ‘h’. The length of

microstrip balun is equal to the length of the dipole arm which is approximately quarter of

wavelength (λ/4).

5.2 DESIGN CONCEPTS

As shown in figure, the printed dipole antenna is fed using a co-axial feed line at feed

point 1 which behaves like unbalanced – to – balanced and a microstrip balun between

two printed dipole strips. The microstrip balun consists of two coplanar strips on the

bottom layer and a microstrip feed line on the top layer, the dipole radiating arms on the

bottom layer. Both the length of the dipole strip and microstrip balun is approximately

quarter of wavelength (λ/4). The base surfaces of the microstrip line and dipole antenna

strips are on the same plane. The metallic short in figure connects the microstrip line on

the top layer to the right dipole arm on the bottom layer. The dipole arm will now have

the same phase as the microstrip line. The coplanar strips serve as the ground plane for



the microstrip line. The phase difference between the coplanar strips and the microstrip

line is 180’. Since the left dipole arm is connected to the coplanar strips, the phase

difference between the two dipole arms will also be 180.

Fig 5.1: Designed Geometry

5.3 DESIGN SPECIFICATIONS

Three essential parameters for the design of the dipole antenna are:

Frequency of operation (fo): The resonant frequency of the antenna must be selected

appropriately. In this project the dipole antenna is designed in C band.

Dielectric constant of the substrate (ℰr): A substrate with a high dielectric constant

reduces the dimensions of the antenna.

Height of dielectric substrate (h): For the microstrip patch antenna to be used in certain

applications (such as cell phones) it is essential that it is not bulky and to ensure this the

height of the dielectric substrate cannot be more than a few mm.

The effect of all of the above 3 factors and the position of feed point on antenna

performance is studied by simulating the design several times.

SPECIFICATIONS:

Operating frequency ‘fo’ - 4.85GHz

Coaxial cable impedance - 50Ω


2Ld =

Lb = λ /

2


Dielectric Constant of the substrate ‘ℰr’- 2.5

Loss tangent ‘tan δ’ - 0.0001

Substrate thickness ‘h’ – 1.6 mm

5.4 DESIGN PROCEDURE

Step 1:

The length of the dipole arms and the balun is quarter of the wavelength. To calculate the

wavelength, the following formula is used

λ = cf o

eqn 5.1

λ: Wavelength in m

c: Speed of light =3x108m/s

Calculated value of λ = 0.061 m

Step 2:

The length of microstrip arms and microstrip balun line are equal and given by the below

formula

Ld = λ/4 = 15.46 mm

Lb = λ/2 = 30.92 mm

Step 3:

Typical width of strips which are going to printed on both sides for formation of dipole

are taken as width ≤ λ /10 for a printed dipole antenna for construction ease we have

taken it as width ≤ λ /20 which is approximately 3mm.



6. FEKO

6.1 INTRODUCTION TO THE FEKO SUITEThe name FEKO is an abbreviation derived from the German phrase FEldberechnung bei

Körpernmit beliebiger Oberfläche (Field computations involving bodies of arbitrary

shape). As the name suggests, FEKO can be used for various types of electromagnetic

field analyses involving objects of arbitrary shapes.

6.2 FEKO OVERVIEWFEKO is a software Suite intended for the analysis of a wide range of electromagnetic

problems. Applications include EMC analysis, antenna design, microstrip antennas and

circuits, dielectric media, scattering analysis and many more. The kernel provides a

comprehensive set of powerful computational methods and has been extended for the

analysis of thin dielectric sheets, multiple homogeneous dielectric bodies and planar

stratified media. Figure below illustrates some of the numerical analysis techniques

available in FEKO and the types of problems for which they are intended.



Fig 6.1: Illustration of the numerical analysis techniques in FEKO

6.3 FEKO SOLUTION ENGINEThe Method of Moments (MoM) technique forms the basis of the FEKO solver. Other

techniques such as the Multilevel Fast Multipole Method (MLFMM), the Finite Element

Method (FEM) Uniform Theory of Defraction (UTD), Geometrical optics (ray launching)

and Physical Optics (PO) have been implemented to allow the solving of electrically large

problems and inhomogeneous dielectric bodies of arbitrary shape. Special approximations

and acceleration techniques are available for problems of specific types.

Method of Moments

The core of the program FEKO is based on the Method of Moments (MoM). The MoM is

a full wave solution of Maxwell’s integral equations in the frequency domain. An

advantage of the MoM is that it is a “source method” meaning that only the structure in

question is discretised, not free space as with “field methods”. Boundary conditions do

not have to be set and memory requirements scale proportional to the geometry in

question and the required solution frequency.

MLFMM



The MLFMM is an alternative formulation of the technology behind the MoM and is

applicable to much larger structures than the MoM, making full-wave current-based

solutions of electrically large structures a possibility. This fact implies that it can be

applied to most large models that were previously treated with the MoM without having

to change the mesh.

Adaptive Cross Approximation (ACA)

The ACA is a fast method similar to the MLFMM but is also applicable to low frequency

problems or when using a special Green’s function. It approximates the impedance matrix

by constructing a sparse H-matrix (only a few selected elements are computed).

Uniform Theory of Diffraction

FEKO hybridizes the current-based accurate MoM with the UTD in the truest sense of the

word with the coupling between the MoM and UTD being maintained in the solution, i.e.

modifying the interaction matrix and ensuring accuracy. Frequency does not influence the

memory resources required for UTD treatment of a structure as only points of reflection

from surfaces and diffraction from edges or corners are considered without meshing the

structure. Insights into the propagation of rays are provided in POSTFEKO during post

processing.

Geometrical Optics (ray launching)

The Geometrical optics (ray launching) is a ray-based method intended for the

consideration of electrically large dielectric and perfect electrically conducting structures

in applications like the analysis of lens antennas. The GO method is hybridized with the

MoM in a similar fashion to the UTD. The GO method in FEKO employs ray-launching

and transmission, reflection and refraction theory to model the interaction between the

dielectric region and the MoM.

Physical Optics

PO is formulated for use in instances where electrically very large structures are modeled.

PO is an asymptotic high frequency numerical method of the same nature as the UTD.

Users will typically attempt a solution with the MoM at first and when they realize that

the structure is electrically too large to solve with their available resources (platform

memory, time) they will turn to one of the asymptotic high frequency techniques.



Large Element Physical Optics

Large element PO is formulated for use in instance where electrically very large smooth

structures are modeled. This method is only to be used when there are no discontinuities

in the incident field (e.g. if the incident field closely represents a point source). Large

element PO is similar to PO in that it is an asymptotic high frequency numerical method

of the same nature as the UTD.

Finite Element Method

The FEM is applicable to the modeling of electrically large or inhomogeneous dielectric

bodies, which are not efficiently solvable with FEKO’s extensions to the MoM. The FEM

is a volume meshing technique that employs tetrahedra to accurately mesh arbitrarily

shaped volumes where the dielectric properties may vary between neighboring tetrahedra.

FEM modeling is advantages in these instances because FEM solution matrices are

sparse, where MoM matrices are densely populated, making FEM matrices significantly

more scalable with an increase in frequency.

General non-radiating networks

General networks (defined using network parameter matrices) as well as ideal non-

radiating transmission lines may be used in FEKO simulations. These non-radiating

networks may be interconnected (cascaded) and excited or loaded directly at the ports.

The voltages and currents at the ports of these ideal representations of networks may

interact with currents and voltages on parts of the model that are solved using other

solution methods, though no radiation-based coupling is taken into account.

Periodic boundaries

Large, equally-spaced periodic structures may be simulated in FEKO using an infinite

periodic boundary approach. This approach may be used to provide an accurate

accelerated solution for many applications like frequency selective surface analysis and

large array analysis.

6.4 FEKO SUITE COMPONENTSThe graphical user interface consists of the components:

CADFEKO is used to create and mesh the geometry and to specify the solution

settings and calculation requirements in a graphical environment.



EDITFEKO is used to construct advanced models (both the geometry and solution

requirements) using a high level scripting language which includes repetitive FOR

loops and conditional IF–ELSE statements.

POSTFEKO reads results from binary output files (*.bof) and can display the

results on 2D graphs or in combination with the geometry in 3D views.

POSTFEKO is also used to visualize optimization results during and after

optimization, as well as the meshed geometry of the FEKO model, with

excitations, field requests points etc. before the actual FEKO run.

QUEUEFEKO facilitates the creation of packages which can be transported to

remote cluster machines where the package is placed in an execution queue (such

as PBS).

FEKO_UPDATE is a command line tool that can be used to check if updates are

available from a master (internet) or local repository SECFEKO_GUI is a

visualization of the FEKO license manager. See SECFEKO for more details on

the license management tool.

Other components that form part of the FEKO Suite do not provide a graphical interface.

These are:

PREFEKO processes the model and prepares the input file (*.fek) for the FEKO

solution kernel.

FEKO is the actual solver code. The ASCII (*.out) and binary (*.bof) output files

generated by FEKO contain all the solution information.

OPTFEKO is a tool that is used for the optimization of a FEKO model according

to specific requirements. OPTFEKO calls the FEKO solver as required during

optimization.

TIMEFEKO provides a Fourier-transform based time-domain analysis mechanism

for FEKO. TIMEFEKO calls the FEKO solver as required during the solution

process.

ADAPTFEKO is used in the generation of continuous adaptively sampled results.

ADAPTFEKO is called as required by the FEKO kernel when continuously

sampled results are required.

CADFEKO_BATCH is a command line tool that can be used to modify variable

values in a CADFEKO model file from a command-line interface without

launching the CADFEKO GUI.



SECFEKO is the FEKO license manager and shows all the licenses in the

specified license file (secfeko.dat) for node locked licenses or connects to the

floating license servers and retrieves license information.

6.5 GUI Features

Large array of primitives for model creation (e.g helix, cone, rectangle, circle,

cylinder, paraboloid, hyperboloid, bezier curves).

Importation of externally computed lists of points for creation of lines, polygons,

etc.

Tree based access to simulation elements (settings, materials, grids, results, etc.)

Selection, zooming, 3-D mouse-only based handling, etc.

Full Solver control via GUI.

6.6 Excitations

Voltage or current source at a port

Port definitions at wires, edges, waveguide aperture or stripline

Plane Wave

Magnetic point source

Electric point source

Point source with specified radiation pattern

Impressed line currents

Near-field aperture

Spherical modes

6.7 CAD Import and Export Features

Parasolid import and export are standard components of FEKO

AutoCAD DXF, IGES, STEP, ProEngineer, Unigraphics, CATIA V4, CATIA

V5

6.8 Mesh Import Features

FEKO mesh import is a standard component of FEKO

FEMAP neutral, NASTRAN, meshed AUTOCAD DXF, STL mesh,

PATRAN mesh, Ansys CDB file mesh, Concept mesh, ABAQUS mesh,

ASCII data format as additional mesh options

.

6.9 Meshing FeaturesDEPARTMENT OF ECE, CMRIT P a g e | 30


Variable mesh densities in a single model to accurately and efficiently model

small features

Mesh density specifiable on faces and edges

Mesh fixing tools

6.10 Post Processing Features

2-D and 3-D views

2-D XY plots, polar plots, Smith Chart

Radiation Pattern(3-D in model , 2-D XY/Polar)

Radiation and far-field data, Radar Cross-Section (RCS) etc.

SAR (IEEE standard compliant whole body average, 10g cube localized, 1g cube

localized)

Full multiport S-parameter extraction

Several visualization options for surfaces, incl. isosurfaces , 2-D field cuts

Multiple results displayable in same viewport for comparison

64-bit enabled for large model viewing

Export views to image formats

6.11 Applications

Antennas: analysis of horns, microstrip patches, wire antennas, reflector

antennas, conformal antennas, broadband antennas, arrays

Antenna placement: analysis of antenna radiation patterns, radiation hazard

zones, etc. with an antenna placed on a large structure e.g aircraft, ship

EMC: analysis of diverse EMC problems including shielding effectiveness of an

enclosure, cable coupling analysis in complex environments, e.g wiring in a car,

radiation hazard analysis

Bio-electromagnetics: analysis of homogenous or non-homogenous bodies ,

SAR-extraction

RF-components: analysis of waveguide structures , e.g filter, slotted antennas,

directional couplers

3D EM circuits: analysis of microstrip filters, couplers, inductors, etc.

Radomes: analysis of multiple dielectrics layers in a large structure

Scattering problems: RCS analysis of large and small structures



7. SIMULATION RESULTS

7.1 GETTING STARTED WITH FEKO

Fig 7.1: CADFEKO window for making new models



Fig 7.2: Substrate selection and its properties window

Fig 7.3: Setting the frequency range for simulation



Fig 7.4: Creating the mesh

Fig 7.6: Window for selection of solver settings after meshing



Fig 7.7: Initialisation of RUNFEKO for beginning the simulation

7.2ANTENNA DESCRIPTION - PRINTED DIPOLE DESIGN 1

Simplest Geometry; Card size:- 40mm X 20mm.

The design was initidated with dipole length l = λ/2, but with some tuning procedure it

has been currently reduced to .43λ.. The geometry has not been optimised for

compactness. The required operational band is from 4.4 to 5.2 GHz, hence VSWR is

maintained at a lower value than 2 (VSWR<2) in the operational band for compensating

the variations that may arise from fabrication process.



Fig 7.9: Dual layer Schematic view

Fig 7.10: VSWR Plot

The VSWR plot indicates that VSWR = 1.07 at 5.1 GHz; Operational Bandwidth

(VSWR<2): 1.8 GHz (3.7GHz to 5.5 GHz).

Fig 7.14: (a) 2D Azimuth plane, (b) 2D Elevation plane



Fig 7.15: (a) 3D Pattern at 4.5GHz , (b) 3D Pattern at 5 GHz

The radiation pattern in 2D azimuth shows the omnidirectional pattern and in elevation

shows the figure of eight, which is as per the characterstics of dipole antenna. The

omnidirectional pattern in 3D clearly shows dipole nature.

CONCLUSION:

The basic dipole has been implemented in the above design. Further optimization to make

the antenna more compact have to be done.

7.3 ANTENNA DESCRIPTION - PRINTED DIPOLE DESIGN 2

Card dimensions 42.5mm X 13mm

In this model length minimisation has been done by bending balun. The separation

between the balun and the dipole has also been done. The input feed has been placed in

centre to provide constructional symmetry and for ease of fabrication. This symmetrical

feeding also helps maintain the aerodynamics of the antenna.

Fig 7.16: Dual layer Schematic viewDEPARTMENT OF ECE, CMRIT P a g e | 37


Fig 7.17: VSWR Plot


(VSWR<2): 0.9 GHz (4.2GHz to 5.1GHz).


3D Pattern:




CONCLUSION:

Centre feeding an antenna not only provides a symmetrical geometry, but also results in

improved performance in the desired range of frequencies. Although the bandwidth has

reduced by 900MHz but antenna is still covering the desired band and also providing

symmetry in the design.


Card size- 49.5mm X 13mm

The innovation process which was maintained right from the start by moving away from

conventional design and using a new design is continued here also. The solution for

grounding of static charge in aircraft which are produced due to friction between aircraft

body and air during flight is implemented through new and innovative design

approach.This approach maintains performance of antenna along with effiecient

grounding.




DC short:

Here it is implemented through a short using a small rectangular strip which is connects

the live and neutral lines in the two layers.

The approach involved studying the current density plot of previous antenna model to

determine the maximum current density zone. The current density plot, used for location

selection of the short is as below:

Fig 7.21: current density

Then the short of minimum width are placed at those places are their performance is

checked. The optimum location for the short was determined to avoid compromise in

performance or for minimum degradation in performance. The DC short was found to be

affecting the matching performance of the antenna in good manner. It is found to be

acting as impedance matching approach if employed in appropriate manner.

A comprehensive study was done at dc short after the fabrication of above model which

includes variation in different parameters like width, length and distance from dipole

centre.



In this study it is found that even though maximum bandwidth was found at different

locations compare to fabricated model but they provide marginal performance at some

critical frequencies, which is undesirable.

Fig 7.22: figure showing the various parameters that are varied to study their effect on the

performance.

One of the parameter with reference to fabricated piece is varied keeping other

parameters constant. The parameters whose variation is checked are

1. Length of DC short L (mm) from feed of shorting

2. Distance or position of DC short from dipole centre P (mm)

3. Width of DC short W (mm)

Their variations have been plotted below.


P(mm)

L(mm)

W(mm)


Fig 7.23: The above plot shows the variation of bandwidth with variation in the position

of DC short.

Fig 7.24: The above plot shows the variation of bandwidth with variation in the length of

DC short.



Fig 7.25: The above plot shows the variation of bandwidth with variation in the width of

DC short.

The parameters of performance which are plotted below are based on the most optimum

configuration of DC short, based on the study of the above parameters.

Fig 7.26: VSWR Plot


(VSWR<2): 1.8 GHz (4.3GHz to 6.1 GHz)





CONCLUSION:

We can see that by using DC short we obtain a wider bandwidth. The radiation patterns

are also as per the dipole characteristics. DC short is placed in vertical manner which

may interfere with the performance of the dipole antenna upon fabrication. This happens

if the short is too close to the dipole. Therefore care must be taken while designing the

short regarding its length and closeness to the dipole.




(SHORT DIPOLE)

Card size- 50mm X 13mm

To overcome the problems associated with the previous design, bending of short was

done by 45° to provide it a smooth finish and to keep it off the axis of the dipole. This

way, the length of the short may not have to be compromised upon. Since the short is now

away from the dipole arms, hence least effect on the radiation pattern of the dipole is

seen. Though the bandwidth has been reduced by 300MHz with reference to the previous

design, still it is covering the required band of frequencies.


Fig 7.30: VSWR Plot


(VSWR<2): 1.5 GHz (4.3GHz to 5.8 GHz).





CONCLUSION:

The inclination of the short is not resulting in major difference in the performance, while

maintaining the good bandwidth coverage. The patterns are providing Omni-directional

coverage in azimuth plane and figure of eight in elevation plane.

7.6 ANTENNA DESCRIPTION - PRINTED DIPOLE DESIGN 5DEPARTMENT OF ECE, CMRIT P a g e | 46


(LONG DIPOLE)

Card size- 115mm X 13mm

This antenna has been designed keeping the application of this antenna in mind. This

antenna is to find application in an UAV platform. Basically, antennas are placed on a

projected platform. This projection can lead to blocking of the pattern in the lower side,

when we use the previous design, because of the presence of a base surface which is

larger than the dimension of the antenna. Therefore, to nullify the effect of this base, we

have increased the height of antenna by λ. This does not affect the performance of the

antenna by any means.


Fig 7.37: VSWR Plot


(VSWR<2): 0.9 GHz (4.3GHz to 5.2 GHz)





CONCLUSION:

The elevation in height has slightly reduced the bandwidth but antenna is still providing

good coverage in the desired band. The elevation results in comparatively higher gain

margin at required elevation plane if mounted on a base.



8. ANTENNA FABRICATION AND TESTING

The designed and simulated antenna is to be fabricated. The detail process of fabrication

is illustrated below:

8.1 FABRICATION PROCEDURE

The fabrication procedure adopted in realizing the hardware is given below. The process

diagram is given in figure.

1. A rectangular strip of red Mylar sheet of dimensions designed is cut and pasted on

a transparent Mylar sheet, which is also rectangular, but with bigger dimensions.

This forms the negative.

2. By using suitable photographic procedures a positive photo of strip is taken

which consist of a transparent portion instead of the red rectangular strip and the

rest of the portions being black.

3. Now the substrate coated with copper is cut to the dimensions in excess of the

dimensions of the patch desired.

4. The substrate is cleaned by using chromic acid and cleaning cloth and water

5. The cleaned substrate is dried in an oven.

6. The dried substrate is now coated with a film of a polymer photo resist on both

sides and left for cooling.

7. The positive is then placed on a substrate coated with resist in a suitable position

and fixed in that position.

8. Except the desired patch, which is still in the form of transparent portion of the

photo film, opaque sheets cover all other portions of the photo resist polymer. But

opposite side is left as it is.



9. U.V. light is exposed to the set up so that only the transparent portion that is the

patch dimensions, are hardened and the rest of the photo resist polymer is not

sticky and hardened, but loose. But the whole of the opposite side, which is the

ground plane portion, is hardened.

10. The loose photo resist is manually removed.

11. Etching of copper is done for the exposed copper not covered by photo resist.

12. The rest of the photo resist is then removed using ammonia solution mixed with

water.

13. Thus the microstrip patch is ready.

14. The corporate feed network is fabricated the same way.

15. Soldering is done using flux, lead and soldering iron.

16. The resulting final microstrip antenna is cleaned using a cleaning solution

isopropyl alcohol. The microstrip antenna is ready for testing.



Fig8.1: Fabrication procedure



8.2 FABRICATED MODEL

Fig 8.2: Fabricated Model 4


1ST MODEL FABRICATED2ND STAGE OF DEVELPOMENTFINAL HARDWARE

FINAL HARDWARE2ND STAGE OF DEVELPOMENT 1ST MODEL FABRICATED


Fig 8.3: Fabricated Model 5

8.3 VSWR / RETURN LOSS MEASUREMENT TEST

Fig 8.4: VSWR/ Return loss measurement test setup (Network Analyser)

PROCEDURE FOR VSWR/ RETURN LOSS MEASUREMENT:

Make the connections as shown in the figure. Switch on the power supply for the test

equipments.

Monitor the VSWR/ Return loss directly in the Network Analyzer display. At the centre

frequency it should be <=2.0

Move the cursor both sides from the centre frequency and mark the frequencies where

VSWR=2.5. The span of frequency where VSWR<=2.5 will give the measurement for

bandwidth of the antenna.



8.4 PROCEDURE FOR RADIATION PATTERN MEASUREMENT

1. The radiation pattern measurement of an antenna will be performed inside the

Anechoic Chamber. The antenna under test will be placed on the wooden turntable/

positioner with appropriate ground plane.

2. The test antenna operates in receiving mode.

3. Power on to all the equipments. Transmit continuous wave signal at the test

frequency. Observe IF signal indication at the receiver. Adjust attenuation and gain

parameters to obtain optimum signal.

4. Rotate the positioned by its controller and monitor the response of the amplitude of

the signal in the pattern recorder. Plot on the rectangular/ polar chart by rotating 360

degree.

5. Replace the test antenna with a standard antenna at the same frequency and plot the

maximum amplitude level on the chart. Compare the level with the test antenna

radiation pattern and calculate the gain.



Fig 8.5: Acquisition controller setup for pattern measurement

Fig 8.6: Anechoic chamber with the antenna

This is the actual setup for the testing of the antenna. We can see that the dipole antenna

is mounted on a turn-table acting as a receiver. A standard gain Horn antenna acts as the

transmitter for the measurement of the radiation patterns. The radiation intensities at

different frequencies in azimuth and elevation planes are plotted here.



9. EXPERIMENTAL RESULTS

9.1 SHORT DIPOLE

Fig 9.1: VSWR plot

Bandwidth-1.9GHz (VSWR: 2 for 4 to 5.9GHz). We can see that fabricated hardware has

got good bandwidth in comparison to simulated model.

Fig 9.2: Return Loss (dB)

Return loss clearly shows the bandwidth portion has return loss less than -10 dB



RADIATION PATTERN (2D)

Fig 9.3: Azimuth Plane Patterns with reference to standard antenna at (a) 4.5GHz, (b)

5GHz

Above pattern shows the comparison of azimuth plane patterns with standard gain horn

antenna at frequencies 4.5 GHz and 5 GHz

Fig 9.4: Azimuth and Elevation plane Patterns

In the azimuth plane, we see the omnidirectional coverage, and in the roll and piitch plane

we see the nulls along the axis of the dipole as is expected.



9.2 LONG DIPOLE

Fig 9.5: VSWR plot

Bandwidth-1.1GHz (VSWR < 2 for 4.25 GHz to 5.35GHz). The bandwidth obtained on

fabrication is more than simulated.

Fig 9.6: Return Loss (dB)

Return loss clearly shows the bandwidth portion has return loss less than -10 dB



RADIATION PATTERNS (2D)

Fig 9.7: Azimuth Plane Patterns with reference to standard antenna at (a) 4.5GHz, (b)

5GHz

The azimuth pattern shows higher gain at 5GHz than 4.5GHz due to frequency

dependency of gain.

Fig 9.8: Azimuth and Elevation plane Patterns

In the azimuth plane, we see the omnidirectional coverage, and in the roll and piitch plane

we see the nulls along the axis of the dipole as is expected.



10. CONCLUSION

The design and development of printed dipole antenna in C-Band has been carried out.

The design process involved a new and innovative technique of DC grounding. The DC

grounding technique imparts to the antenna a great deal of compactness and also

enhances its performance.

The following observations with respect to DC grounding technique have been made:-

1) DC grounding helps to reduce the size of the dipole by 15%.

2) This technique also increases the bandwidth by approximately 36%.

Enhanced bandwidth is achieved without parasitic elements, only by optimizing the

feeding balun, thus providing greater bandwidth while maintaining structural simplicity.

The fabricated antenna has been experimentally tested and found to at par with the

simulated results. It has been encapsulated in a compact and aerodynamically shaped

radome.

The developed antenna has the potential to be used as a compact and light-weight Omni-

directional antenna for aircraft systems.



11. FUTURE SCOPE

The concept of DC short can be used to:

1) Reduce size of large antenna:

Typically, UHF dipoles have large size, limiting their use on an aircraft. By using the

technique of DC grounding, as we have already seen, we can reduce the length of the

dipole and make it more compact. This technique when used in conjunction with other

size reduction technique could result in a compact UHF antenna, which can readily be

used for airborne applications.

2) Increase antenna bandwidth:

Some antennas have inherently small bandwidth (narrow band antennas). But their utility

is subject to the condition that they need to have a certain minimum bandwidth to ensure

safe performance. In such cases, the proposed concept could come handy, increasing the

bandwidth significantly, and rendering the antenna useful.



REFERENCES

1. Constantine A. Balanis, Arizona State University, “Antenna Theory: Analysis and

Design” , 3rd Edition, John Wiley & Sons, Inc.

2. Ramesh Garg, Prakash Bhartia, Inder Bahl, Apisak Ittipiboon, “Microstrip Antenna

Design Handbook” , Artech House.

3. Randy Bancroft, “Microstrip and Printed Antenna Design”, Noble Publishing

corporation Atlanta, GA

4. R.C. Johnson editor,”Antenna Engineering Handbook”,McGraw-Hill Inc, 3rd

Edition

5. D. M. Pozar, Microwave Engineering, Wiley, 1998.

6. R. Hartman and Jack Berlekamp, “Fundamentals of Antenna Test and

Evaluation”, Microwave Systems New and Communications Tracking, June 1988

7. Lei, J., et al., “An omnidirectional printed dipole array antenna with shaped

radiation pattern in the elevation plane,” Journal of Electromagnetic Waves and

Applications, Vol. 20, No. 14, 1955– 1966, 2006.

8. H. R. Chuang and L. C. Kuo, “3-D FDTD design analysis of a 2.4 GHz

polarization – diversity printed dipole antenna with integrated balun and

polarization– switching circuit for wlan and wireless communication

application,” IEEE Transactions on Microwave Theory and Techniques, Vol. 51,

No. 2, 2003.

9. G. S. Hilton, C. J. Railton, G. J. Ball, A. L. Hume, and M. Dean, “Finite–difference

time–domain analysis of a printed dipole antenna,” 19th Int. IEEE Antennas and

Pro- pagation Conference, 1995, pp. 72–75.

10. D. Edward and D. Rees, “A broadband printed dipole with integrated balun,”

Microwave J, 1987, pp. 339–344.

11. X. Li, L. Yang, S.-X. Gong, Y.-J. Yang, and J.-F. Liu “A COMPACT FOLDED

PRINTED DIPOLE ANTENNA FOR UHF RFID READER”, Progress In

Electromagnetics Research Letters, Vol. 6, 47–54, 2009

12. SI.PRIYO DEY. C K AANANDAN, P MOHANAN AND K G NAIR, FMM

“Novel Wide Band Printed Dipole Antenna”, IEEE TECHNICAL REVIEW. Vol

10, No. 3, 1993



13. M C Bailey, “Broad-band half wave dipole”. IEEE Trans. Amara Propagat, vol 37,

pp 410-412, Apr 1984.

14. Z. G. Fan, S. Qiao, J. T. Huangfu, and L. X. Ran “A MINIATURIZED PRINTED

DIPOLE ANTENNA WITH V-SHAPED GROUND FOR 2.45 GHZ RFID

READERS”, Progress In Electromagnetics Research, PIER 71, 149–158, 2007

15. Constantinos VOTIS, Vasilis CHRISTOFILAKIS, Panos KOSTARAKIS “

Geometry Aspects and Experimental Results of a Printed Dipole Antenna”, Int.

J. Communications, Network and System Sciences, 2010, 3, 204-207

16. Reto Zingg “Printed Dipole Antenna”, University of Colorado at Boulder

17. Roy lV. Lewallen “Baulns:”What They Do And How They Do lt”

18. Broadband Dipoles (http:/ / www. antenna-theory. com/ antennas/ broaddipole. php)

Antenna-Theory.com

19. Baluns for 88–108 MHz B. Beezely (K6STI) http:/ / www. ham-radio. com/ k6sti/

balun. html

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