micro strip patch antenna
DESCRIPTION
Design and implementation of microstrip patch antennaTRANSCRIPT
A Major Project report
On
“Design and Fabrication of Microstrip Patch Antenna”
Submitted in partial fulfilment of the requirements
for the award of the degree of
Bachelor of Technology
In
Electronics and communication Engineering
Project Guide: Submitted by:
Mr N.T .MARKAD Piyush
kumar(0181152806)
(Asst. professor) Harnek
Singh(0251152806)
Vanshaj
Kumar(0271152806)
Pawan Kumar(0281152806)
Bharati Vidyapeeth’s College of Engineering
Guru Gobind Singh Indraprastha University,
Kashmeere Gate, New Delhi-110006
(2006-2010)
Certificate
This is to certify that the major project report entitled “Design and
Fabrication of Microstrip Patch Antenna done by Mr. Piyush kumar,
Harnek singh, Vanshaj kumar, Pawan kumar,
roll No. 0181152806, 0251152806, 0271152806, 0281152806 respectively
is an authentic work carried out by them at BHARATI VIDYAPEETH’S
COLLEGE OF ENGINEERING under my guidance. The matter embodied in
this project work has not been submitted earlier for the award of any degree
or diploma to the best of my knowledge and belief.
Date: Signature of the Guide
Mr N.T. MARKAD
Asst. professor
Department of ECE
BVCOE, NEW DELHI
Date:
ACKNOWLEDGEMENT
We would like to express our gratitude to all those who gave us the possibility to complete this
thesis. We want to thank the Department of Electronics and Communication of the former
Bharati Vidyapeeth’s College of Engineering for giving us permission to commence this
thesis in the first instance, to do the necessary research work and to use departmental data.
We have furthermore to thank the honorable Guide, Mr N.T. MARKAD whose help,
stimulating suggestions and encouragement helped us in all the time of research for and
writing of this thesis. Especially, we would like to give our special thanks to him whose patient
help enabled us to complete this work.
We would like to show our greatest appreciation to Mr. A KUNDU sir and Lab assistant Ms.
DEEPA Ma’m for there tremendous help and support.
Piyush
kumar(0181152806)
Harnek
Singh(0251152806)
Vanshaj
kumar(0271152806)
Pawan Kumar(0281152806)
CONTENTS
...........................................................................................................................Abstract. .i
...........................................................................................................................List of Tables
.............................................................................................................................ii
...........................................................................................................................List of figures...
………………………………………………………………iii
...........................................................................................................................List of
Symbol/Abbreviation………………………………………………...iv
Chapter 1. Literature Survey .............................................................l
1.1 Introduction
1.2 Helix Antenna
1.3 Quadrifilar Helix
1.4 Printed Quadrifilar Resonant Helix Antenna
Chapter 2. Design of Software/design ofEquipment/DesignProcess/ Design of Circuit
2.1 Introduction
2.2 Quadrifilar Helix Design
2.3 Feed Network Design
2.4 Design of Q.H. Antenna Array
Chapter 3 Experimentation
3.1 Introduction
3.2 parameter measurement
3.3 polarization and radiation pattern
Chapter 4. Result/Analysis
4.1 Introduction
4.2 Parameter V. S. W. R. Vs. Frequency
4.3 Reflection Loss Vs. Frequency
4.4 Smith Chart
Chapter 5 conclusion/future scope
5.1 Conclusion
5.2 Remark
5.3 Future scope
References/Bibliography
ABSTRACT
The Quadrifilar Helix antenna and its antenna array are developed and it complex feed is
designed. The parameters of antenna and antenna array are measured using network analyzer.
The next factor is operating frequency band. (Most of the SPCN’s internal to use L-band (1.16 -
1.6265 GHZ)) for reception. The choice of the frequency band adds extra-complexity to the final
antenna design. The matter becomes even more complicated when the cellular system (e.g. GSM
800-- 900 Hz) has also to be served with the same handheld.
The Quadrifilar Helix (Q. H.) antenna can offer the cardioids (elevation) shaped radiation pattern.
Other antennas, like the patch and the crossed dipole, can offer the same shaped pattern, but the QH
seems to be preferred for its smaller structure, its advantage not to be too sensitive to the ground
plane and in the same way to the hand effect and the advantage of easily change its radiation pattern
by varying different parameters such as the diameter, pitch and the number of turns.
The Quadrifilar Helical (QH) Antenna is a highly resonant antenna invented by Dr. C. C. Kilgus in
the 70's. It consists of four helices placed at 90 ° difference (0°, 90°, 180°, 270°) alternatively said it
comprises two bifilar helical loops oriented in mutual orthogonal relationship on a common axis. The
terminals of each loop are fed in anti-phase and the currents in the two loops are in phase quadrature.
By selecting the appropriate configuration of the loops, a wide range of pattern shapes is available.
LIST OF TABLES
Table No.1. : - Impedance (Ω) - width (mm) table.
Table No.2 : - Phase shift (degree) - path length (cms) table.
Table No.3:Antenna - Antenna Array - B.W. - centre freq. Table.
Table No.4: - Frequency – vertical polarization - Horizontal
Table No.5:- Polarisation - Axial Ratio table.
LIST OF FIGURES
1. Geometry of Helix
2. Quadrifilar Helical Antenna
3. Helix Structure
4 Power Divider Ckt
5. Setup for radiation pattern
6. Radiation Pattern of QHA
7. 3-D Illustration of Radiation Pattern
8. VSWR Vs Frequency for Antenna
9. Return Loss V s Frequency for Antenna
10. Smith Chart for Antenna
CHAPTER 1
LITERATURE SURVEY
The Quadrifilar helix was invented by C.C Kilgus in the early 1970’s . This antenna was
found to be very useful because of the excellent circular polarization. It offered and its inherent
radiation pattern characteristics. The antenna gave a stable performance and was found useful in
many applications where satellite signals were involved. Nowadays it has become a popular
choice for the GPS systems and a lot of weather monitoring systems. With the advent of
satellite telephony it is being looked at as a new generation antenna for satellite telephones.
1.1 INTRODUCTION
People worldwide are travelling more and more and at the same time they wish to
keep in contact. This is the reason for the fast development in the field of communication
systems. The biggest change in electronics was brought in due to the research and development
carried out in the field of digital techniques. The digital techniques made it to achieve Very
Large Scale Integration of semi-conductors. VLSI techniques have made it possible to increase
processing power to be packed in a much smaller volume of equipment space.
Mobile equipment nowadays includes portable handsets and even miniature units which can be
fitted on a wristwatch. For the antenna designer, there is a challenging demand to create
compact or even electrically small antennas that are compatible with modern technology. It is a
fact that electronic equipment is now also so reduced in size that the use of conventional
antenna should not be acceptable to the user and in any case make the equipment
miniaturization rather useless.
A clever design of antenna can give added value by employing additional system functions such
as diversity reception capability, reduction of multipath fading or selectivity of polarization
characteristics. Antenna design is no longer confined to the design of small, lightweight, low profile
of flush mounted, omni-directional antennas on a well-defied flat ground plane, But is rather the
creation of sophisticated electronic configuration that plays a important role in signal processing
while operating in a generally is defined time varying environment.
The nature of the mobile system to be worked with greatly influences the antenna design and it
can be divided into land, maritime,
aeronautical design and satellite mobile systems and the type of mobile platforms such a
vehicles,
ships, air crafts and portable equipment.
Frequency reuse capabilities, type of information, modulation and a personalisation of mobile
tem1inals are some of the factors, which are taken into account while designing antennas.
In zoned systems, radiation pattems have to match the some patterns to avoid interference.
Performance is also subject to variations in field strength 2ccording to the movement of mobile
terminals and environmental conditions in the propagation path.
Global Personal Communication Network (PCN) will provide telecommunication
functionality regardless of users location. The vision of PCN foccuses on the provision of a high quality
two-way communication service to both business users and consumers on the move outdoors and
indoors. The goal is to create a global PCN which will be complementary to the conventional Public
~\\'itched Telecommunication Network - wired - and to any other wireless system Satellite networks, by
their ubiquitous presence in Low Earth Orbits (LEO), "Medium Earth Orbits (MEO) or any other
combination of orbits, are well suited to fill the gaps in the land coverage left by the existing terrestrial
systems personal communication, services virtually everywhere on the globe.
The desire of the market is not only to have a global communication service but also to
use with that service handheld tem1inal similar in size, cost and performance with these currently
available for terrestrial cellular systel11s. A critical point in the user's terminal design, size and
performance is the antenna, In Global PCN this point becomes even more critical because of the pared
lei use of :he terrestrial al1d the satellite network (dual mode terminals).
Many more specific factors have to be taken into consideration at the start of the Design of an
antenna for a portable handset. In brief the designer should think About the antenna size, the
polarization characteristics, the matching requirements, the bandwidth, the effect of electrically
small ground plane, the noise figure, the transmitter efficiency, the need for diversity, the
electromagnetic compatibility, materials, the modeling, the manufacturing methods, the reliable
operation . the possible interaction effects with the handheld box, the cost the absorbing effect
of the human body, the body effect on the antenna characteristics and finally the system
compatibility. The last point is actually the most crucial since it defines the operational
frequency, the polarization characteristics, the radiation pattern shape and the required G/T of
the system.
The major Satellite PCN (SPCN) operators propose systems with different orbital
configurations and frequency bands,. These differences can affect the shape of the handset
antenna radiation pattern, the antenna environment, the radiation pattern can greatly affect the
average handset performance. Thus, the shape of the pattern has to be done with extra care,
taking, firstly into account the relative position of the transmitter and receiver and, secondly,
the fact that the not prepared to make many effort to find the correct orientation of their in
order to achieve optimum performance. What can be said as a conclusion is that in SPCN the
shape of the radiation pattern should be directed by the system’s orbital characteristics (a
minimum elevation angle, diversity, space the pattern shape of the satellite antenna and the
possible orientation of the handheld in use.
1.2 HELIX ANTENNA
The antenna is the transitional structure between free-space and a g device. The guiding
device or transmission line may take the form of a co-axial or a hollow pipe (wave-guide) and
it is used to transport electromagnetic from the transmitting source to the antenna, or form the
antenna to the receiver.
An antenna converts bound circuit fields into propagating electromagnetic waves, and by
reciprocity recovers power from travelling electromagnetic waves, . An antenna serves to link
the receiver & thus achieves communication between any two points. Antenna is a matching
network that couples a transmission line to free space with as much efficiency as possible. Thus
a radio antenna may be defined as "the structure associated with the region of transition
between a guided wave and a free space wave or vice-versa"
One of the most important parameters associated with the antenna is
“POLARIZATION”
Polarization is the physical orientation of the radiated waves in space. Waves are said to be
polarized if they have the same alignment in space. Polarization direction is labeled generally
after the electric intensity, this makes the direction of polarization the same as the
direction of antenna, Thus when we say an antenna is vertically or horizontally polarized, it
is actually their radiation that is so polarized. Antennas can be also circularly or elliptically
polarized.
When I undertake the discussion of antennas involved in the communication and
tracking connected with the interplanetary Probes popularly used.
These antennas radiate electromagnetic waves of circular polarization by properly
proportioning the area and pitch of the turns with relation to the wavelength. The helix is a
superposition of electric and magnetic dipoles to radiate a wave with circular polarization.
Circular polarization requires two relations between the crossed fields in a wave. They must
have an equal intensity and phase quadrature in time. The direction of rotation of the
polarization depends on phase sequence of the crossed components of either field. Then
antenna inherently obtains the phase quadrature. The equality of intensity of the crossed
components is obtained by making the area of each turn equal to the product of the pitch of the
turn times the wavelength.
The circular polarization sense is determined by the screw direction of the Helix. A
right - hand screw helix radiates Right Hand Circular Polarization.
The helix antenna has three basic modes of radiation:
Normal Mode : In normal mode radiation peaks occur at +- 90 from the helix
axis.
Axial Mode: In Axial mode the peak radiation is along The axis of the helix, this
radiation
mode is Required for the fixed terminal antenna.
Conical Mode: Conical Pattern is useful for mobile terminal Data links. Conical patterns
not require that the antenna be manually or automatically aligned.
One of the application of the helix antenna is their use for Mobile and Fixed Terminal.
In case of the mobile antenna, the azimuth (Az) and elevation (EI) angles are changed while
the terminal is in operation. According to the application required the antenna can be designed
keeping in context the mode of radiation.
The geometry of the helix can be understood by looking at the figure below
The symbols that define the Helix parameters are:
N = NUMBER OF TURNS
D = DIAMETER OF HELIX
α = PITCH ANGLE
S = SPACING BETWEEN TURNS (ie., CENTER TO CENTER)
I = LENGTH OF ONE TURN
L = TOTAL LENTH OF HELIX
When one turn of the helix is unrolled on a flat plane, the triangle shown in figure above
interrelates these dimensions.
I = (π.D) / Cos α
S = I. (Sin α) = π . D (Sin α ) / (Cos α)
We can rewrite the relation for center –to- centre spacing as
S / λ = ( π.D / λ) tan α
For operation in the axial mode
(3 / 4) < π. D/ λ < (4 / 3)
For a helical antennas , the values of ( π.D / λ) = 1 is commonly used by the designers
Therefore
S / λ = tan α
Total length of the helix is given by
L = N.S
Using the above mentioned parameters a helix antenna design was undertaken.
The design on paper for a centre frequency of 2.6GHz , having co-axial mode radiation.
1.3 QUADRIFILAR HELIX
The Quadrifilar helix is an electronically small antenna providing circular polarization over a
broad angular region. A Quadrifilar antenna generally consist of four helices, equally spaced
circumferentially on a dielectric cylinder or one dielectric disk support, and fed with equal
amplitude signals driven in phase quadrature (0 ", 90 ° , 180°, 270 ° ) . The Quadrifilar also can
be described as two rthogonal bifilars fed in phase quadrature, where a bifilar is a two
orthogonal element helical antenna.
The Quadrifilar helix antenna (QHA) offers a Cardioid ( or elevational ) shaped radiation
pattern. This type of pattern is very favorable for a Satellite Personal Communication Network
(SPCN) hand-held terminal (HHT) which requires the radiation pattern of the antenna to have
elevational directionality to compensate for propagation losses ( free space, fading)
Experienced at different elevation angles, omni directionality in the azimuth plane and
circular polarization. Other antennas like the patch and the crossed dipole, can offer similar
shaped patterns, but the Quadrifillar helix seems be preferred for the following reasons:
Smaller structure
Not too sensitive to the ground plane and in the same \vay to the hand effect in case of
SPCN HHT
Its radiation pattern is easily shaped by varying geometrical patterns such as diameter, the
pitch and the number of turns,
Wide circular polarized beam.
Another interesting property of the QHA is that it produces a hemispherical pattern without
the need for a ground plane. In general the radiation characteristics are insensitive to the
presence of a metal structure behind the antenna, provided that it is mounted at least a quarter-
wavelength above the conducting surface. The back lobe radiation patterns are suppressed as the
ground plane gets close 0 a quarter wavelength. The presence of the ground plane in different
distances from the QHA can change the input impedance, the back lobes and the movement of
the phase center but the main lobe is essentially unaffected.
One of the major disadvantages of the QHA is the complex feed network that it
requires. One approach is to feed each Bifilar Helix with the assistance of a balun. In such a case
most configuration need a 90 0 phase difference hybrid and two baluns are needed to feed both
Bifilar Helices. The other way is to separately feed each one of the four helical elements, with
90 0 phase difference. This issue is discussed further in a later section on Feed "Networks.
1.4 PRINTED QUADRIFILAR RESONANT HELIX ANTENNA
Wire antennas such as the QHA have found many applications in both air borne
and land-based systems. These circularly polarized antennas have widely been used principally
for their hemispherical coverage and good axial ratio. The electrical properties of wire antennas
are modified when the wires are copper strips printed on dielectric support. This construction
gives us the Printed Quadrifilar Resonant Helix Antenna (PQRHA).
The behavior of the PQRHA can be understood by considering it like two
orthogonal uncoupled bifilar helices fed in phase quadrature. Thus every bifilar helix is
considered as two parallel printed suspended lines on an place and can transform the system into
equivalent transmission line with conductors of circular cross-secretion and a coaxial dielectric.
The PQRHA can achieve both Normal mode and Axial mode radiation. Thus it can be
used for a variety of applications depending on the requirement.
NORMAL MODE:
For communications between beacon and maritime mobiles, the emission an d reception of
different signals over the sea requires the antenna provide circularly polarized radial radiation, with
good axial ratio
The optimum parameters as realized in reference are:
C = Circumference = 0.315 λ
L = Strip Length = 2λ
N = number of turns = 1.8
Λ = free space wavelength
Axial Mode:
For the axial mode of operation the optimum parameters realized 111 reference are
C = Circumference =
α = pitch angle
L = strip Length =
N = number of turns
In this project using the reference and parameters mentioned above ,vo antenna models
were built. The antennas models were built for a center frequency of -2.6 GHz. The models were
designed for the Normal mode of radiation.
The antennas were built using a wooden rod of required length as a support base. In the
antenna Copper wires were wound around the wooden rod to serve as the helical structure. In
the antenna the Pitch Angle a and the Strip length L were taken into account while winding the
helices. A detailed analysis of the design of the antenna and feed network is given further in a
separate section on Antenna Design and array Design.
FEED NETWORK
One of the major disadvantages of the Quadrifilar Helix Antenna is the complex feed
network that it requires. The design requires, that the four Helices placed at 90° phase difference
( 0°, 90°, 180°, 270°). One of the methods to satisfy this condition is to separately feed each one
of the four helical elements, with 90° phase quadrature. Such a feed network can be designed
using microstrip circuits.
The basic requirement of the circuit is to split the signal into four equal signals of lesser
power, each signal being 90 ° apart in phase to the other and then feed them individually to each
helix. A Wilkinson Power Divider circuit as mentioned in [1] can be used for this purpose. This
circuit has the useful property of being losses when the Output ports are matched; that is only
reflected power is dissipated. It also presents isolation between output ports. This divider is
often made in microstrip or strip line form.
The key to the design of the circuit, when designing in a microstrip form is to achieve
the requisite widths of the microstrip line, which would result in the path with the required
impedance. The design of the circuit can be depicted in the figure.
MICROSTRIP LINE
Microstrip line is one of the most popular types of transmission lines, primarily
because it can be fabricated by the photolithography processes and is easily integrated with other
passive and active microwave devices. Microstrips are printed circuits for very high frequency
electronics and microwaves. When made of conducting strips deposited upon a dielectric
substrate, they are called microwave integrated circuits (MICs).
Physically, any microstrip structure consists of a thin plate of low loss insulating
material, the substrate, covered with metal completely on one side, the ground plane, and partly
on the other, where the circuit or the antenna patterns are printed.
The substrate fulfills two functions:
1. It is a mechanical support that ensures that implanted components are properly positioned and
mechanically stable, just as in printed circuits for low-frequency electronics.
2. It behaves as an integral part of connecting transmission lines and deposited circuit components;
its permittivity and thickness determine the electrical characteristics of the circuit or antenna.
The presence of the dielectric, and particularly the fact that the lectric does not fill the air region
above the strip, complicates the behavior and ysis of microstrip line. The microstrip has some
(usually most) of its field - in the dielectric region, concentrated between the strip conductor and
the d plane, and some fraction in the air region above the substrate. Thus we came across a
constant Єe, which is defined as the effective dielectric constant of the microstrip line.
Since some of the field lines are in the dielectric region and some are in air, the effective dielectric constant
satisfies the relation.
1 < e < r
And is dependent on the substrate thickness d, and conductor width W
The design formulas as mentioned in [1] for the effective dielectric constant and characteristic impedance of
microstrip line are presented below
Effective Dielectric Constant:
The effective dielectric constant of a microstrip line is given approximately by-
e = ( ) / 2 + ( r - 1) / 2 1 + 12 d/w1/2
The effective dielectric constant can be interpreted as the dielectric constant of a
homogeneous medium that replaces the air and dielectric regions of the microstrip
For given characteristic impedance Zo and dielectric constant r the w/d ratio can be found as :
w/d = 2 / П [ B - l –ln (2B - 1) + ( r - 1) / 2 r In (B-1) + 0.39 - 0.61/ r ]
for w/d > 2
w/d = 8eA / (e2A – 2) for w/d < 2
Where,
A = Zo / 60 ( r + 1) / 2 1/2 + ( r - 1) / ( r + 1) 0.23 + 0.11 / r
Considering the above equations a required Power Divider can be designed.
SPECIFICATIONS
1. Frequency - S Band ( 2.1 GHz to 2.4 GHz)
2. Polarization - Circular
3. Impedance - 50 ohm
4. VSWR Bandwidth - 1.4% - 3.4%
3. Substrate - Glass Epoxy
CHAPTER 2
ANTENNA DESIGN
INTRODUCTION :
2.1 QUADRIFILAR HELIX DESIGN
The Quadrifilar Helix Antenna (QHA) is an extension of the Helix antenna, While in a Helix antenna
there is a single helix wound for a particular number if turns, in the Quadrifilar helix there are four
such helices which are wound alongside each other. This kind of a helical structure gives the
advantages of a good elevation radiation pattern and a very prominent Circular Polarization. The basic
structure of the QHA can be understood by looking at the fig.
The QHA volute with one turns (a) front (b) top and (c) trimetric view
Another advantage of the Quadrifilar Helix is that the radiation pattern can be easily changed
by varying different parameters such as the diameter, the pitch and the number of turns,
However there is no fixed trend which can be followed regarding the change in the radiation
pattern with the modification of different parameters, In most of the references concerning the
QHA, there is information on how the radiation pattern is shaped or changed by different
variations of the geometrical characteristics, most of this information is empirical and some-
times contradictory.
In this project the Quadrifilar Antenna and its array were designed for Normal
mode of radiation with a center frequency of 2.6 GHz. As mentioned in a previous section on
the QHA, reference realizes the optimum parameters required to achieve the given results.
These parameters were used to design the helical structure of the antenna. The design is as
given below.
The optimum parameter values as given in reference are:
1. Circumference of Helix, C = 0.315 λ o
2. Pitch Angle, α = 72°
3. Length of Helix, l =
2.2 FEED NETWORK DESIGN
In this project antenna and its array were designed each using a different Power
Divider Network. The design was etched on a glass epoxy substrate using the Printed Circuit
Board technique used for fabrication of Microstrip components.
Antenna
In this model the idea of using a power divider circuit as a Feed for the
Quadrifilar helix antenna was first explored, therefore most of the design parameters used are
based on approximate values which were suggested to be close to the original calculated value.
1. Dielectric Constant of Substrate -
The basic design was started with taking into consideration the Dielectric Constant of the
substrate used. The value was taken as 1.4]
i.e. o = 1.41
2. Calculation of Wavelength in Free Space-
o = C / f
Where,
C - Velocity of light = 3 x 1010 cm/sec.
f - Center frequency = 2.6 x 106 Hz
o = (3 x 1010 cm/sec) x (2.6 x 106 Hz) -1
o = 11.358 cm
2. Calculation of Wavelength in Substrate –
g = o / r
g = 11.538 cm / 1.41
g = 81mm
Calculation of Extra Length for Phase Shift of 90° in each Helix -
Extra Length = g / 4
g / 4 = 81 / 4
= 20.25 - 21 mm
Let the basic length of the Microstrip path = x
For 90° phase shift length of path = x + g / 4
For 180° phase shift length of path = x + 2 g / 4
For 270° phase shift length of path = x + 3 g / 4
From the Microstrip circuit etched out we get the following path length.
PHASE SHIFT PATH LENGTH(cm)
0° 4
90° 6.1
180° 8.2
270° 10.3 10.3
5. Width of the Micro Strip line of Different Impedance Values -
The following values were assumed for the basic design:
IMPEDANCE (Ω) WIDTH (mm)
50 5
75 3.5
100 2.4
6. Construction of the Microstrip Network
Using the above-mentioned values a Power Divider Feed Network was developed and is as
shown in figure 2. The substrate used was Glass Epoxy. A SMA Connector was used to
provide connection of the Microstrip circuit to the
Co-axial cable adapter-bullet. It is to be noted that the lengths of all Microstrip lines without
the end extension for Phase shifts are g / 4
Antenna 2
Seeing the feasibility of the second model was done using exact .formulate, and this model was
developed as an improvement on the first model. In this antenna the helical structure was
developed by winding Copper wire strips instead of the Aluminum flat-strips used in the first
model. The formulae used here have already been discussed in the previous section on Feed
Networks.
1. Dielectric Constant of Substrate -
The substrate used was Glass Epoxy. The dielectric constant of glass epoxy was
found to be 5.3 (reference)
i.e. r = 5.3
The measured thickness of the material is 1.4 mm
i.e. d = 1.4 mm
2. Calculation of the Width of the Microstrip Line -
a) For Characteristic Impedance = Zo = 50 ohm
we have formula
w/d = 2 / П [ B - l –ln (2B - 1) + ( r - 1) / 2 r In (B-1) + 0.39 - 0.61/ r ]
for w/d > 2
B = 377 П / 2 Zo ( r)1/2
Where,
w = width of Microstrip Line
d = thickness of substrate = 1.4 mm
B = 377 П / (2 x 50 x (5.3)1/2)
= 5.1446
w/d = 2 / П [ 5.1446 - l –ln (2 5.1446 - 1) + ( 5.3 -1 ) / 2 x 5.3 ln
(5.1446-1) + 0.39 - 0.61/ 5.3]
w/d =1.6564 < 2
since w/d < 2
we use formula : w/d = 8eA / (e2A - 2) for w/d
A = Zo / 60 ( r + 1) / 2 1/2 + ( r - 1) / ( r + 1) 0.23 + 0.11 / r
= 50 / 60 (6.3) / 21/2 + (4.3) / (6.3) (0.23 + 0.11 / 5.3)
= 1.65010
w/d = 8e1.65010 / (e3.300 - 2)
= 1.658
Now since,
d = 1.4 mm
w = 2.8186 mm
b) For Characteristic Impedance = Zo = 21/2 x 50 ohm = 70.710 ohm
We use the same formula as used in the above case for w/d < 2
Therefore using:
w/d = 8eA / (e2A – 2) for w/d < 2
A = Zo / 60 ( r + 1) / 2 1/2 + ( r - 1) / ( r + 1) 0.23 + 0.11 / r
We get,
A = 2.26273
w/d = 0.85095
since,
d = 1.4 mm
w = 1.18 mm
3. Calculation of Effective Dielectric Constant e of Microstrip Line-
a) For Characteristic Impedance Zo = 50 ohm
e = ( r + 1) / 2 + ( r - 1 ) /2 1 + 12 d/w-1/2
e = (6.3/2) + (4.3/2) (1/2.8700)
e = 3.89912
b) For Characteristic Impedance Zo = 70.710 ohm
e = ( r + 1) / 2 + ( r - 1 ) /2 1 + 12 d/w-1/2
e = (6.3/2) + (4.3/2) (1/3.8860)
e = 3.70325
4. Calculation of Wavelength in Substrate -
a) For Characteristics Impedance Zo = 50 ohm
g = g / e
g = 11.538 / 3.899
g = 2.959 cm
b) For Characteristics Impedance Zo = 70.71 0 ohm
λg = λg/ εc
λg = 11.538/3.703
λg = 3.11563
4. Calculation of Extra Strip Length for Phase Shift -
a) For Characteristic Impedance Zo = 50 ohm
Extra Length = λg/4
λg/4 = 2.959/4
λg/4 - = 0.73975 cm
Let the basic length of the Microstrip path = x
F.or 90° phase shift length of path = x + λg /4
For 180° phase shift length of path = x + 2 λg /4
For 270° phase shift length of path = x + 3 λg /4
From the Microstrip circuit etched out we get the following path length.
PHASE SHIFT PATH LENGTH (cm)
0° 4 90° 6.1 180° 8.2 2700 10.3
b) For Characteristics Impedance Zo = 70.710 ohm
Extra Length = λg /4
λg/4 = 11.538/3.7032
It is to be noted that the lengths of all Microstrip lines without the end extension for Phase shifts
are λg /4.
Antenna 2
Seeing the feasibility of the second model was done using exact formulae, and this model was
developed as an improvement on the first model. In this antenna the helical structure was developed
by winding Copper wire strips instead of the Aluminum flat-strips used in the first model. The
formulae used here already been discussed in the previous section on Feed Networks.
1. Dielectric Constant of Substrate -
The substrate used was Glass Epoxy. The dielectric constant of glass epoxy
was found to be 5.3 (reference)
i.e. £r=5.3
The measured thickness of the material is 1.7 mm
i.e. d = 1.7 mm
2. Calculation of the Width of the Microstrip Line -
a) For Characteristic Impedance = Zo = 50 ohm
we have formula
w/d = 2 / IT [B-1-ln(2B - 1) + (£r- 1)/2£r In (B-1) + 0.39 ~ 0.61/£r ]
for w/d >2
where,
W = width of Microstrip Line
D = thickness of substrate = 1.7 mm
B - 377 π ( I (2 x 50 X (5.3)1/2) =5.1446
w/d = 2/ π ( [5.1446 - 1-In (2x5.1446 -) + (5.3 -1)/ (2 x 5.3) In (5.1446-1)+0.39 0.61/5.3]
w/d = 1.6564 < 2
since w/d < 2
we use formula:
w/d = 8eA I e2A -2 ) for w/d < 2
A = Zo/ 60 (£r + 1) /2 1/2 + (£r - 1 ) / (£r' +1) 0.23 + 0.11/ £r
' = 50/60 (6.3/2)1/2 + 4.3/ 6.3 (0.23 + 0.11/5.3)
=1.65010
w/d = 8e
= 1.658
Now since, d = 1.7mm
W =2.8186mm
b) Characteristic Impedance = Zo =2 = 70.710 ohm
We use the same formulae as used in the above case for w/d < 2
therefore using:
w/d= 8eA I (e 2/\ - 2) for w/d < 2
A = Zo 160 ( CI' + 1) 12 l + (ci - 1 ) I (E, + 1 ) 0.23 + 0.1] lEI)
We get,
A = 2.26273
w/d = 0.850959
since,
d = 1.7 mm w=1.44 mm
3. Calculation of Effective Dielectric Constant Ce of Microstrip Line-
b) For Characteristic Impedance Zo = 50 ohm
Cc = (cr + 1) 12 + ( Cr - 1 ) /2 1 + 12 d/wrl/2
£e = (6.3/2) + (4.3/2) (1/2.8700)
£e = 3.89912
b) For Characteristic Impedance Zo = 70.710 ohm
Cc = (cr + 1)/ 2 + ( £r -1 )/2 1+ 12 d/w -112
£c = (6.3 12) + (4.3 12) ( 1/3.8860)
Cc = 3.70325
4. Calculation of Wavelength in Substrate -
a) For Characteristics Impedance Zo = 50 ohm
λg = λg / £c
λg = 11.538/3.899
λg = 2.959 cm
CHAPTER 3
EXPERIMENTATION
3.1 INTRODUCTION:
All antennas are described by various general parameters of their radiation patterns
and impedance. These parameters include impedance, VSWR, Bandwidth, Polarization, 3dB
Bandwidth and Directivity.
IMPEDANCE AND DIRECTIVITY
These two terms almost always appear together. Impedance is a prime- determining
factor in the amount of power transferred from the component to the associated circuitry and vice-
versa.! When referring to antennas we must know how well energy is transferred from free space and
a transmission line.
A more convenient term is VSWR. A high VSWR indicates a large measure of
reflected power and a poor transfer of power, a low VSWR' 'characterizes a good power transfer.
One consideration when specifying VSWR is the application for which the antenna
will be used. For E.g. the VSWR of an antenna used in receiving setup can be set as high as 3:1. But
use of 3:1 VSWR in a transmitting antenna would cause losses that would put a great burden on the
final power stages.
3 dB BEAMWIDTH
This specification is very similar to the 3dB Bandwidth used in describing the operation
of filters. It is a number, expressed in degrees, which indicates where the strength of the radiation pattern
of an antenna decreases to half power ( or 3dB) . With filters, this term measures the number of degrees
between the points.
POLARIZATION
An electromagnetic wave is made up of just two components. One electric (E) and one
magnetic (M). Polarization refers to the orientation of the E component or E - vector. Three types of
polarization are commonly considered Linear, Circular and Elliptical. The E vector is associated with
only a single either vertical or horizontal plane i.e. the electrical field (E) is in a plane oriented vertically
or horizontally.
Circular polarization involves more than one plane and is characterized as being involved with the tri -
plane. The E-vector rotates either in clockwise or counter clockwise direction. If it moves clockwise it is
said to be
.
Right Hand Circularly Polarized (RHCP). And counterclockwise means Left Hand
Circularly' Polarized (LHCP)
For circular polarization, the E vector must remain at constant amplitude. If it changes
magnitude as it rotates, its tip traces an ellipse and the wave is said to be Elliptically Polarized.
DIRECTIVITY
This specification is a measure of the ability of an antenna to
concentrate energy in a preferred direction. Antennas with narrow bandwidths have a greater
directivity than conventional Omni-directional antennas. The gain of the antennas is closely linked
with its directivity - if antenna has no heat losses and is perfectly matched to the· source or load, then
the gain is equal to the
directivity. However, the gain decreases proportionally to the losses. For e.g., if -he antenna is 50%
efficient then the gain 50% ( or 3dB) is less than the directivity.
GAIN
Antenna gain is basically a comparison of one phenomenon to another. The gain of an antenna in a
given direction is the ratio of the power radiated by the antenna in that direction to the power which
would be radiated by a losses isotropic radiator with the same power accepted through its input
terminals.
The term 'Gain' is often taken to mean the maximum gain of the antenna hence the gain
at the peak of the main lobe.
BANDWIDTH
It is the frequency range over which the specifications listed apply. outside this region, the antenna
does not behave as predicted. In terms of the ','SWR the bandwidth can be set for a particular value
for e.g. 1.4 : I. At frequencies outside this range the specifications cannot be truly achieved.
3.1 PARAMETER MEASUREMENT
The HP8714E vector network analyzer was used to measure the various
parameters of the antennas (Antenna 1 and Antenna 2 ) namely VSWR, Impedance
Character4istics, Return loss.
The HP8714E is a high performance vector network analyzer for laboratory or
production measurements of reflection or transmission parameters. It integrates a high
resolution synthesized RF source, an S - parameter test set, and a dual channel three input
receiver to display and measure the magnitude, phase and group delay responses of active and
passive RF networks.
Two independent display channels and a large screen color display show the
measured results of one or both of the channels, in rectangular or polar /
Smith chart formats. The frequency range ofHP8719Dis from 300KHz to 3 GHz.
The experimental setup for measurements is as shown in fig.
Before taking the actual measurements, calibration of the network analyzer was carried out using
standard procedure of calibration using standard loads like short, open and matched.
The readings were taken with a Start frequency of 2 GHz and a Stop frequency of 3
GHz.
The results as observed all the HP87l4E are attached in form of printouts The results are attached in the
following sequence.
VSWR Vs. Frequency for Antenna (Fig)
Return loss Vs. Frequency for Antenna (Fig).
Smith Chart representation for Antenna (Fig.)
From the graphs of VSWR Vs. Frequency the VSWR bandwidth of
the antennas is as follows.
Antenna Bandwidth (HZ ) Center Frequency (GHz)
1 1.785 2.355
2 . 2.3076 2.214
A VSWR of 1.4: 1 is chosen when calculating the bandwidth, Which is good for an
antenna acting as a receiving antenna.
3. 2 Polarization and Radiation Pattern:
For good performance the antenna need to be circularly polarized.
To measure the quality of circular polarization we use a parameter called as Axial Ratio. Axial ratio is
defined as the ratio of the major to minor axes of the polarization ellipse. For circular polarization the
axial ratio (AR) = 1. The Quadrifilar Helix antenna can offer a very good circular polarization over a
wide elevation angle beam, a value lower than 5dB inside the coverage is considered adequate.
The axial ratio of the two antennas was found out by using a linearly polarized HORN antenna. The
HORN antenna was used once with Horizontal polarization and once with Vertical polarization. The
difference in the value of the return loss was the axial ratio.
The results have been tabulated for both the antennas.
ANTENNA
Table No.4
Frequency Vertical Horizontal Axial Ratio (dB)
(GHz) Polarization (dB) Polarization (dB)
2.7 -59 -49 10
3.0 -66 -51.6 13.4
As mentioned before the Quadrifilar Helix antenna offers the CARDIOD shaped radiation
pattern. The optimum radiation patterns are as shown below in the figures. The radiation
pattern of the antenna was observed with the help of another antenna and it was tested in the
elevational plane. It was found to be quite in accordance with the ideal patterns as shown by
the figures below.
Fig: Radiation pattern of QHA backfire configuration
CHAPTER 5
CONCLUSION AND FUTURE SCOPE
5.1 CONCLUSION
The following observations were made from the measurements taken for different Antenna
parameters.
1. The 50 Ω best impedance matching for Antenna 1 was observed at 1.995 GHz.
2. The minimumSWR for Antenna 1 was observed at 1.995 GHz (VSWR = 1.328).
3. For a VSWR of 1.4:1 the % bandwidth of bandwidth for Antenna 1 is 1.785%.
4. The Circular polarization for Antenna 1 was the best at 1.995 GHz. The value of axial
ratio at this frequency was 3.4.
5. The Circular polarization for antenna 1 was best at 1.995 ghz., the value of axial ratio
at this frequency was 1.7.
5.2 REMARKS
Form the observed results, the VSWR for two antennas is good with sufficient bandwidth. Most
of the parameters are as predicted for a Quadrifilar Helix of similar dimensions. The shift in the actual
designed frequency and the actual measured frequency could be attributed to the low quality of
substrate used. Due to unavailability of better materials. Still the results are quite satisfactory
considering the use of Glass Epoxy substrate. Which is not a favored substrate for use in microstrip
designs. Better results can be anticipated with the use of a more high quality substrate like RT
DURIOD etc. which would be less lossy also compared to the present substrate used.
5.3 FUTURE SCOPE
The Quadrifilar Helix antenna has been widely' selected as a preferred handset antenna for
mobile satellite communication, It has the key attributes of near-hemispherical pattern with good
circular polarization within a compact form-factor. Concern has been expressed, however, with regard
to the impact of relatively high transmit powers on absorption in the human head. Two methods have
been proposed to minimize these interactions. Still compared to the presently used antennas for mobile
communications, this antenna has been found quite superior. The Quadrifilar helix antenna is already a
popular choice for the use in "Global Positioning Systems (GPS) and is incorporated for the same by
many companies like GRAMIN for their designs.
The antennas built in this project can be used to built a high quality satellite receiving system and can
be used for any service in the range of 2 GHz to 2.4 GHz.
When array using 94 antenna are developed in L - band, then this system will work as mobile band
telescope. When this antenna used in S - band as base station and some modification is made in
EPBAX, then this system will work as P.C.S. for limited area.