Fianl Year Project Report

SEMINAR REPORT
ON
DESIGN AND IMPLEMENTATION OF LOG-
PERIODIC ANTENNA
SUBMITTED BY
Shruti Nadkarni
Sneha Vyawahare
Gargi Mohokar
DEPT. OF ELECTRONICS & TELECOMMUNICATION
P.E.S’S MODERN COLLEGE OF ENGINEERING
PUNE – 411 005.
UNIVERSITY OF PUNE
2010 - 11
H.O.D. (E&TC) Project Guide
Prof .Mr.V.N.Patil Prof. Mrs.A.D.Adhyapak

PROJECT REPORT
ON
DESIGN AND IMPLEMENTATION OF LOG
PERIODIC ANTENNA
SUBMITTED BY
SHRUTI S. NADKARNI
GARGI R. MOHOKAR
SNEHA VYAVAHARE
DEPT. OF ELECTRONICS & TELECOMMUNICATION
P.E.S’S MODERN COLLEGE OF ENGINEERING
PUNE – 411005.
UNIVERSITY OF PUNE
2012 - 13

CERTIFICATE
This is to certify that
SHRUTI S. NADKARNI B8313092
GARGI R. MOHOKAR B8313077
SNEHA VYAVAHARE B8313080
Of B.E. E&TC have successfully completed the project titled ‘DESIGN AND
IMPLEMENTATION AND LOG PERIODIC ANTENNA’ during the academic during
the academic year 2012-13.This report is submitted as partial fulfillment of the
requirement of degree in E&Tc Engineering as prescribed by University of Pune.
Mrs. K. R. Joshi Prof. V.N. Patil Mrs.A. D. Adhyapak
Principal H.O.D. Project Guide
P.E.S’s MCOE, Pune-5 E&TC

ACKNOWLEDGEMENT
In our endeavour to achieve the successful completion of project and seminar for
Electronics and telecommunication degree course we are greatly thankful to a number of
people without whose help and guidance, this project would not have been possible.
We express with all sincerity and deep sense of gratitude our, indebtedness to
Prof. Mrs A.D.Adhyapak
We are equally thankful to Prof. V.N. Patil (HOD of E&TC dept), Prof.Kamthe
and the entire staff members in E&TC dept for providing us guidelines and facilities to
carry out our project work. We also would like to thank Mr Anantkrishnan Sir who
readily agreed to share his technical assistance for our project. We further thank
Mr.Golam who guided us.
Finally, we would like to thank god whose blessings have always been with us
and helped in believing in ourselves and boosted our confidence when we needed it the
most.

ABSTRACT
DESIGN AND IMPLEMENTATION OF LOG PERIODIC ANTENNAS
In our project, we will be designing a log periodic antenna. Log-periodic antennas
(LP antennas, also known as a log-periodic array or log periodic beam antenna/aerial) are
broadband, multi-element, directional, narrow-beam antennas that have impedance and
radiation characteristics that are regularly repetitive as a logarithmic function of the
excitation frequency. Log-periodic antennas are designed to be self-similar and are thus
also fractal antenna arrays. They have more directivity and gain. They operate at wide
bandwidth. Two such antennas will be placed pointing in the four cardinal directions.
These antennas are expected to have an operational bandwidth of about 1150MHz, from
350MHz to 1500MHz. The sensed signals will be fed to a single channel receiver. The
receiver will be designed such that it will receive signals from one antenna at a time using
a switching mechanism. The final direction finding algorithm will be implemented in the
computer.

TABLE OF CONTENTS
Sr. No. Page No.
1. Introduction 1
2. Literature Survey 4
3. Block Diagram and Description 12
4. Hardware Specifications 19
CAD drawings 20-26
5. Software Specifications 27
5.1 4NEC2 (Method of Moments) 27
5.2 Finite Element Method 28
5.3 Method of Mesh Generation 28
6. Experimental Results 30
7. Design and Simulation Results 40
8. Applications 45
9. Performance Evaluation 46
10. Conclusion 47
11. Component List and Cost Evaluation 48
12. References 49

1. INTRODUCTION
An antenna is an electrical device which converts electric power into radio waves,
and vice versa. It is usually used with a radio transmitter or radio receiver.
In transmission, a radio transmitter supplies an oscillating radio frequency electric current
to the antenna's terminals, and the antenna radiates the energy from the current
as electromagnetic waves. In reception, an antenna intercepts some of the power of an
electromagnetic wave in order to produce a tiny voltage at its terminals that is applied to
a receiver to be amplified.
Radiation pattern, gain, impedance matching, bandwidth, size are some of the
parameters that are considered while selecting an antenna. For broadband applications,
the Log-Periodic Dipole Antenna (LPDA) type has been commonly used. Its advantage is
that within the design band its performance is essentially frequency-independent,
including radiation resistance (hence VSWR) and radiation pattern (hence gain and front-
to-back ratio). Also it is highly directional, narrow beam and has the impedance and
radiation characteristics that are regularly repetitive as a logarithmic function of
excitation frequency.
In this project we will design a multi-element log periodic antenna with the
bandwidth of 1150MHz. This antenna will operate in the range of 350MHz to
1500MHz.The antennas will be acting as receiver. There are many areas wherein
reception of noise free signals is of highest priority. But practically reception of noise
free signals is next to impossible. It is very important to find the direction of interference
of noise in the signals. The antennas will be used to find the direction of interference. The
antennas will be placed pointing in the four directions and the received data is further
given to the receiver. The receiver demodulates the received signal which is further fed to
computer. The designing of the antenna will be done in the 4nec2 software.
1.2 WHY ANTENNAS RADIATE?
An oscillating source is connected to a wire. During positive half cycle,
electrons start moving from A to B with uniform velocity. Magnetic field is generated
due to this. During negative half cycle, electrons change their direction and start moving
from B to A. This change in direction gives rise to acceleration of electrons, launching

RF signal. Due to change in velocity of electrons, magnetic field also changes. The
changing magnetic field gives rise to a varying electric field. These fields propagate with
velocity c (3*10^8 m/s).
Figure 1.1
1.3 RADIATION IN DIPOLE ANTENNA
A dipole is that in which opposite charges are separated by some finite distance.
An oscillating source is applied to dipole antenna using two transmission wires. Initially
there is no charge on the wires and the antenna. During positive half cycle the electrons
start flowing with uniform velocity in the lower transmission wire. Electrons reach the
end of the dipole and get accumulated at the end of the dipole end, creating negative
potential at the lower transmission line and positive potential at the upper transmission
line. Hence voltage is maximum at the end of the dipole. When polarity is changed
electrons flow in the opposite direction, giving rise in acceleration of electrons, producing
electromagnetic wave. Again the potential difference occurs in the dipole having opposite
polarity as of the previous one. The electrons at the end of the dipole try to excite the free
space region surrounding it. During the mobility of electrons in opposite direction
continuously a standing wave appears to be formed in the transmission line, storing
energy in it. In this way the dipole antenna radiates.

Figure 1.2
2. LITERATURE SURVEY

An antenna forms the interface between the free space and the transmitter or
receiver. The choice of an antenna normally depends on factors such as gain and the
bandwidth an Antenna can offer. Signals from satellites travel thousands of kilometers to
the earth and as the Friss equation shows, they will only be detected as weak signals.
Under these conditions, high gain antennas are required.
The log periodic dipole array basically consists of a number of dipole elements.
These diminish in size from the back towards the front. The element spacing also
decreases towards the front of the array where the smallest elements are located. In
operation, as the frequency changes, there is a smooth transition along the array of the
elements that form the active region. To ensure that the phasing of the different elements
is correct, the feed phase is reversed from one element to the next. One of the major
drawbacks with many RF antennas is that they have a relatively small bandwidth. The log
periodic antenna is able to provide directivity and gain while being able to operate over a
wide bandwidth.
2.1Log periodic array capabilities
The log periodic antenna design is directional and is normally capable of
operating over a frequency range of about 2:1. It has many similarities to the more
familiar Yagi because it exhibits forward gain and has a significant front to back ratio. In
addition to this the radiation pattern of this RF antenna design stays broadly the same
over the whole of the operating band as do parameters like the radiation resistance and
the standing wave ratio. However it offers less gain for its size than does the more
conventional Yagi.
2.2 Types of log period antenna
There are several formats in which the log periodic antenna can be realized. The
exact type that is most applicable for any given application will depend upon the
requirements.
The main types of log periodic array include:
• Zigzag log periodic array

• Trapezoidal log periodic
• Slot log periodic
• V log periodic
• Log periodic dipole array, LPDA
2.3 Log periodic dipole array
The most common is the log periodic dipole array basically consists of a number
of dipole elements. These diminish in size from the back towards the front. The main
beam of this RF antenna comes from the smaller front. The element at the back of the
array where the elements are the largest is a half wavelength at the lowest frequency of
operation. The element spacing also decreases towards the front of the array where the
smallest elements are located. In operation, as the frequency changes there are a smooth
transition along the array of the elements that form the active region. To ensure that the
phasing of the different elements is correct, the feed phase is reversed from one element
to the next.
Figure 2.1 Basic log periodic dipole array
2.4Log periodic performance

The log periodic antenna is a particularly useful design when modest levels of
gain are required, combined with wideband operation. A typical example of this type of
RF antenna design will provide between 4 and 6 dB gain over a bandwidth of 2:1 while
retaining an SWR level of better than 1.3:1. With this level of performance it is ideal for
many applications, although a log periodic antenna will be much larger than a Yagi that
will produce equivalent gain. However the Yagi is unable to operate over such a wide
bandwidth.
2.5Basic Definitions:
 Antenna pattern:
The radiation pattern or antenna pattern is the graphical representation of the
radiation properties of the antenna as a function of space. That is, the antenna’s pattern
describes how the antenna radiates energy out into space (or how it receives energy). It is
important to state that an antenna radiates energy in all directions, at least to some extent,
so the antenna pattern is actually three-dimensional. It is common, however, to describe
this 3D pattern with two planar patterns, called the principal plane patterns. These
principal plane patterns can be obtained by making two slices through the 3D pattern
through the maximum value of the pattern or by direct measurement. It is these principal
plane patterns that are commonly referred to as the antenna patterns. Characterizing an
antenna’s radiation properties with two principal plane patterns works quite well for
antennas that have well-behaved patterns – that is, not much information is lost when
only two planes are shown. Figure shows a possible coordinate system used for making
such antenna measurements.

Figure 2.2Antenna Measurement Coordinate System
 Lobes:
Any given antenna pattern has portions of the pattern that are called lobes. A
“lobe” can be a main lobe, a side lobe or a back lobe and these descriptions refer to that
portion of the pattern in which the lobe appears. In general, a lobe is any part of the
pattern that is surrounded by regions of relatively weaker radiation. So a lobe is any part
of the pattern that “sticks out” and the names of the various types of lobes are somewhat
self-explanatory. Figure 3 provides a view of a radiation pattern with the lobes labeled in
each type of plot.

 Isotropic radiator:
An isotropic radiator is a hypothetical lossless antenna that radiates its energy
equally in all directions. This imaginary antenna would have a spherical radiation pattern
and the principal plane cuts would both be circles (indeed, any plane cut would be a
circle).
 Gain:
The gain of an antenna (in any given direction) is defined as the ratio of the power
gain in a given direction to the power gain of a reference antenna in the same direction. It
is standard practice to use an isotropic radiator as the reference antenna in this definition.
Note that an isotropic radiator would be lossless and that it would radiate its energy
equally in all directions. That means that the gain of an isotropic radiator is G = 1 (or 0
dB). It is customary to use the unit dBi (decibels relative to an isotropic radiator) for gain
with respect to an isotropic radiator. Gain expressed in dBi is computed using the
following formula:
GdBi = 10*Log (GNumeric/GIsotropic) = 10*Log (GNumeric)
Occasionally, a theoretical dipole is used as the reference, so the unit dBd (decibels
relative to a dipole) will be used to describe the gain with respect to a dipole. This unit
tends to be used when referring to the gain of omni-directional antennas of higher gain. In
the case of these higher gain Omni-directional antennas, their gain in did would be an
expression of their gain above 2.2 dBi. So if an antenna has a gain of 3 dBd it also has a
gain of 5.2 dBi.
Note that when a single number is stated for the gain of an antenna, it is assumed that this
is the maximum gain (the gain in the direction of the maximum radiation).
It is important to state that an antenna with gain doesn’t create radiated power. The
antenna

Simply directs the way the radiated power is distributed relative to radiating the power
equally in all directions and the gain is just a characterization of the way the power is
radiated.
 3-dB beam width:
The 3-dB beam width (or half-power beam width) of an antenna is typically
defined for each of the principal planes. The 3-dB beam width in each plane is defined as
the angle between the points in the main lobe that are down from the maximum gain by 3
dB. This is illustrated in Figure 3. The 3-dB beam width in the plot in this figure is shown
as the angle between the two blue lines in the polar plot. In this example, the 3-dB beam
width in this plane is about 37 degrees. Antennas with wide beam widths typically have
low gain and antennas with narrow beam widths tend to have higher gain. Remember that
gain is a measure of how much of the power is radiated in a given direction. So an
antenna that directs most of its energy into a narrow beam (at least in one plane) will
have a higher gain.
 Front-to-back ratio:
The front-to-back ratio (F/B) is used as a figure of merit that attempts to describe
the level of radiation from the back of a directional antenna. Basically, the front-to-back
ratio is the ratio of the peak gain in the forward direction to the gain 180-degrees behind
the peak. Of course on a dB scale, the front-to-back ratio is just the difference between
the peak gain in the forward direction and the gain 180-degrees behind the peak.
 VSWR:
The voltage standing wave ratio (VSWR) is defined as the ratio of the maximum
voltage to the minimum voltage in a standing wave pattern. A standing wave is
developed when power is reflected from a load. So the VSWR is a measure of how much
power is delivered to a device as opposed to the amount of power that is reflected from
the device. If the source and load impedance are the same, the VSWR is 1:1; there is no

reflected power. So the VSWR is also a measure of how closely the source and load
impedance are matched. For most antennas in WLAN, it is a measure of how close the
antenna is to a perfect 50 Ohms.
 VSWR bandwidth:
The VSWR bandwidth is defined as the frequency range over which an antenna
has a specified VSWR. Often, the 2:1 VSWR bandwidth is specified, but 1.5:1 is also
common.
2.6 Directional Antennas:
A directional antenna or beam antenna is an antenna which radiates greater power
in one or more directions allowing for increased performance on transmit and receive and
reduced interference from unwanted sources. Directional antennas like Yagi-Uda
antennas provide increased performance over dipole antennas when a greater
concentration of radiation in a certain direction is desired. All practical antennas are at
least somewhat directional, although usually only the direction in the plane parallel to the
earth is considered, and practical antennas can easily be Omni-directional in one plane.
The most common types are the Yagi-Uda antenna, the log-periodic antenna, and the
corner reflector, which are frequently combined and commercially sold as residential TV
antennas. Cellular repeaters often make use of external directional antennas to give a far
greater signal than can be obtained on a standard cell phone. Satellite Television receivers
usually use parabolic antennas. For long and medium wavelength frequencies, tower
arrays are used in most cases as directional antennas.

2.7 COMPARISON OF YAGI-UDA AND LOG-PERIODIC
ANTENNAS:
The focus here is on low cost antennas and since the standard ones like the half
wave dipole and the folded dipole cannot offer the much needed gain and bandwidth, the
attention is thus shifted to the Yagi-Uda and the log-periodic dipole array antennas. The
gain of the Yagi antenna can be increased by approximately 1 dB for every additional
director. However, properties such as the radiation pattern, side lobe level and input
impedance have to be taken into account. The question that comes to the fore is then;
how many directors will suite an antenna with certain properties? To encompass all these
factors, optimization software packages for the Yagi antennas have been developed over
the years. Some of these software packages use the genetic algorithm to find the optimum
length for the elements and their spacing. The algorithms employ the method of moments
(MOM) based electromagnetic codes to compute current distributions on the antenna
structure while taking into account the mutual coupling between elements. Yagi antennas
have narrow bandwidths of the order of 2% when designed for high gain. On the other
hand, log-periodic dipole array (LPDA) antennas offer a wider bandwidth and can have
gains as high as 10 dB. The dipoles are connected to the source using a twin transmission
line in such a way that the phase is reversed at each connection relative to the adjacent
elements. When connected this way, the bandwidths of the dipoles add-up to give a
broader bandwidth. The transmission line is often replaced with a pair of metal boom
structures separated by the dielectric material. R. L Carrel, who conducted intense studies
on log-periodic antennas, has prepared curves and also devised the formulas for
calculating parameters such as the required number of dipoles and their spacing, that are
invaluable for the design of the LPDA.
2.8 Log Periodic Dipole Array (LPDA) Antenna:
The broadband properties of this antenna make it a better choice for operation
over a wider frequency range. It consists of small closely spaced half-wave dipoles. The
length ratio between adjacent dipoles is a constant (t) and the ratio of element spacing to
twice the next larger element length is a constant (s). The dipoles are connected to the

source using a twin transmission line in such a way that the phase is reversed at each
connection relative to the adjacent elements. Figure2.2 shows a simplified way of
connecting the dipoles to a transmission line. Each dipole is effective over a narrow band
of frequencies determined by its length. When they are all connected to the twin
transmission line, their narrow bandwidths add up to give a wider bandwidth. The length
ratio (t) is chosen such that the antenna’s performance will be uniform over the whole
bandwidth. The shortest dipole corresponds to the highest frequency band and the longest
dipole to the lowest frequency band of an antenna.
Figure 2.4

3. BLOCK DIAGRAM AND DESCRIPTION
Figure 3.1 Block Diagram
3.1 DESCRIPTION:
In our project, we will be designing a log periodic antenna. Four such antennas
will be placed pointing in four cardinal directions. These antennas are expected to
have an operational bandwidth of about 1150MHz, from 350MHz to 1500MHz. The
antennas which are acting as receivers will collect data and feed it to the computer.
As mentioned already there are four antennas but data will be taken from a single
antenna at a time. This can be achieved by the switching mechanism for which RF
switches are used. The switch will switch to other antenna after a specific period of
time. An RF (Radio Frequency) switch is a device to route high frequency signal
through transmission paths. Incorporating a switch into a system enables us to route
signals from the four antennas to a single channel receiver. The receiver demodulates
the signal and feds them to the computer.

Log-Periodic Antenna:
The log-periodic antenna is so called because its performance is periodic as a
function of logarithm of frequency. For a given bandwidth, the structure is independent
of variations in frequencies. The ratio of lengths, diameters, relative spacing, and
distances from vertex is constant for two successive elements.
1/τ= ln+1/ln = Rn+1/Rn = dn+1/dn = sn+1/sn
Here,
τ = geometric ratio= f1/f2 f1> f2
LPDA has two types of connections,
1. Straight Connection: The feed is given to the smallest element. In this type of
connection, adjacent elements are is phase with each other and the phase
progression is towards long elements. The beam is end-fired. Interference is high
in this type of connection.
2. Criss-cross Connection: The feed is connected to the smallest element. The
adjacent elements are 180o
out of phase and the phase progression is towards the
smaller elements. The beam is end fired and directed towards the smaller
elements.
The coaxial cable connection is the practical application of criss-cross connection. The
directivity of the antenna is lower for a larger bandwidth and higher gain. The log-
periodic antenna, ideally, gives an infinite structure for infinite bandwidth. The maximum
frequency corresponds to the shortest element and the minimum frequency to the longest
element. Active region is a region of high current distribution and consists of 4-5
elements. The active region moves towards the smaller elements as the frequency
increases. It consists of elements whose lengths are slightly smaller than /2 . Typical log-

periodic antenna designs have 10deg
45degand 0.95o.7. For higher values of, the value is
smaller with less number of elements. Also, the numbers of active elements are less.
Design of log periodic antenna
The log-periodic antenna is the array antenna. It is more robust, has more
directivity than Yagi-Uda antennas. The no of elements of the antenna required depend
upon the frequency range for which it is designed. Depending on the frequency the no of
active elements change.
The 20 element log-periodic antenna is designed using following formulae (taken
from Modern antenna design by Thomas Milligan)
Figure 3.2
Above figure shows the log-periodic dipole antenna with a criss-cross feeder line.
The longest dipole length is denoted by L1 . The element ends lie along the lines
eventually meeting at the virtual apex. The distance of the dipole from the virtual apex is

given by Rn . The distance between elements is dn. Using the initial dimensions we find
all other dimensions using the scaling factor τ.
L2 = τL1 R2 = τR1 d2 = τd1 L3 = τL2
Question:
Frequency range: - 300MHz to 1500MHz
Gain: - 6.9
σ:- 0.06
τ=0.88
Solution:
λLowest = 1/fH and λhighest = 1/fL
where, fH= highest frequency i.e. 1500MHz
fL= lowest frequency i.e. 300MHz
L1= K1*L
K1=1.01-0.519 τ= 0.543
K2=7.08 τ3
-21.3 τ2
+21.98 τ-7.30+σ(21.82-66 τ+62.12 τ2
-18.29 τ3
)
= 19.76≈20
N=1+ (log(K2/K1)+log(fL/fH)/log( τ))
Where L1= longest length of the dipole
K1 and K2 are truncation constants
N= number of dipoles in the antenna

The lengths and spacing of the elements are as follows
Lengths:-
Length Dimension(mm) Length Dimension
L1 543 L11 151.22
L2 477.84 L12 133.07
L3 420.49 L13 117.1
L4 370.039 L14 103.05
L5 325.63 L15 90.68
L6 286.55 L16 79.8
L7 252.17 L17 70.229
L8 221.91 L18 61.802
L9 195.28 L19 54.38
L10 171.84 L20 47.85
Spacing:-
Spacing Dimension(mm) Spacing Dimension(mm)
R1 543 R11 150.16
R2 477 R12 132.84
R3 419 R13 116.9
R4 369.3 R14 102.8
R5 325.06 R15 90.53
R6 286.05 R16 79.6
R7 251.72 R17 70.1
R8 221.52 R18 61.6
R9 194.93 R19 54.23
R10 171.54 R20 47.775

The diameters of all the dipole elements are taken to be 3mm as it is the standard
diameter available.
The angle between the dipole endpoints and the centreline (α), the half apex
angle, in terms of the constants τ and σ is given by
α = tan-1
(1- τ/4*σ)
RF SWITCHES
An RF switch (Radio frequency) is a device to route high frequency signal
through transmission paths.
Typical switch configurations are
1. Single pole double throw (SPDT):- one input two outputs
2. Single pole multiple throw (SPMT):- one input multiple outputs
3. Double pole double throw (DPDT):- 2 inputs 2 outputs
4. Bypass switches: - insert or remove test components from a single path.
Considering our project, we have 4 input signals and one output so we need
SPMT switch i.e. 4:1 switch.
Parameters needed to select RF switches
1. Frequency range
Application based frequency range should be present.
2. Insertion loss
Losses should be less than 1 to 2 dB
3. Return loss
It is caused by impedance mismatch between circuits. Switches should have
excellent return loss performance.
4. Repeatability
Low insertion loss repeatability reduces sources of random errors.
5. Isolation
It is the degree of attenuation from an unwanted signal detected at the port of
interest. Isolation should be high.
6. Switching speed
It is the time taken to change the state of a switch port. Switching speed should be
high.
7. Power handling

It is the ability of the switch to handle power and it depends on the design and
materials used. Power handling should be high.
8. Video leakage
It refers to the spurious signals present at the RF ports of the switch when it is
switched without an RF signal present. It should be low or nil.
Table for selection of different types of switches
Switch Isolation s11 s21 s12 s22 Cost IP3
1
MHz
10
MHz
1
GHz
1.5
GHz
AS192-000 -46dB -45dB -27dB -26dB 55dBm
AS221-306 -50dB -45dB -30dB -27dB 55dBm
SKY13296-
340LF
-80 -70 -40 -35 13-
18
40dBm
SKY13322-
37SLF
-20 -40 -28 -25 22 54dBm
ADG904/904
R
-69 -69 -37 -35 27 60 60 22 77.46/- 31dBm
ZSWA-4-
30DR
90 90 48 45 7918/-
PD5731T6M -60 -59 -37 -31
Depending on the specifications required ADG904/904R is selected.

4. HARDWARE SPECIFICATIONS
Properties Values
No of log-periodic antennas 4
Frequency range 350MHz to 1500MHz

Bandwidth 1150MHz
Gain 7 to 8dBi
No of elements 20
Height 543mm
Width 500mm
RF switch 4:1
Impedance 50 Ohms
5. SOFTWARE SPECIFICATIONS
5.1 4NEC2 (METHOD OF MOMENTS)
The Numerical Electromagnetics code (NEC-2) is a computer code for analyzing the
electro-magnetic response of an arbitrary structure consisting of wires and surfaces in
free space or over a ground plane. The analysis isaccomplished by the numerical solution

of integral equations for inducedcurrents. The excitation may be an incident plane wave
or a voltage source on a wire while the output may include current and charge density,
electricor magnetic field in the vicinity of the structure, and radiated fields.NEC-2
includes several features not contained in NEC-1, including anaccurate method for
modeling grounds, based on the Sommerfeld integrals, and an option to modify a
structure without repeating the complete solution.
The Numerical Electromagnetics Code (NEC-2) is a user-oriented computer code for
analysis of the electromagnetic response of antennas and other metalstructures. It is built
around the numerical solution of integral equationsfor the currents induced on the
structure by sources or incident fields.This approach avoids many of the simplifying
assumptions required by othersolution methods and provides a highly accurate and
versatile tool forelectromagnetic analysis.
The code combines an integral equation for smooth surfaces with one specialized for
wires to provide for convenient and accurate modeling of awide range of structures. A
model may include nonradiating networks andtransmission lines connecting parts of the
structure, perfect or imperfectconductors, and lumped element loading. A structure may
also be modeled over a ground plane that may be either a perfect or imperfect
conductor.The integral equation approach is best suited to structures with dimensionsup
to several wavelengths. Although there is no theoretical size limit, thenumerical solution
requires a matrix equation of increasing order as the structure size is increased relative to
wavelength. Hence, modeling verylarge structures may require more computer time and
file storage than ispractical on a particular machine. In such cases standard high-
frequencyapproximations such as geometrical optics, physical optics, or geometrical
theory of diffraction may be more suitable than the integral equationapproach used in
NEC-2.
5.2 FINITE ELEMENT METHOD
The log periodic antenna is designed using CST microwave studio which uses
finite element method algorithm for simulation.

Finite element method is a numerical technique for finding approximate solutions
to boundary value problems. This is achieved using two steps;
1. Firstly, the domain of the problem is divided into many sub domains and each
sub domain is represented by equation.
2. Secondly, the equations of all the sub domains are collected together to give the
final result.
3. In CST, any conducting surface is divided into small areas called cells,
collectively known as mesh.
4. Then the electric field density of each cell is calculated.
5. Further, the electric field densities of all cells or mesh are grouped together to
give final result.
6. This technique is used during simulations and gives corresponding radiation
patterns.
5.3 METHODS OF MESH GENERATION
There are three different ways to define a mesh
1. Manual
2. Automatic
3. Adaptive meshing
 Manual meshing
A manual mesh can be defined at any time by the user even before the
geometrical design is generated. This is the old fashioned way of meshing which is
not generally used now.
 Automatic meshing
The mesh generator determines the important features of the design and
automatically creates a mesh, which represents the structure and fields equally well.
This is the most effective way of working with CST microwave studio.
 Adaptive meshing

Adaptive meshing replaces the expertise by repeatedly running the simulation
and evaluating the solutions. Usually regions with high field concentration or field
gradients are recognized, where the mesh is to be locally refined. If the deviation in
the results falls below a given accuracy level, the adaption is terminated. This
approach always improves the start solution at the expense of the simulation time.
We have used adaptive meshing because it is convenient and gives accurate
result.
6. EXPERIMENTAL RESULTS
Table No. 1. Table for dipole antennas
Sr.No. ANTENNA GAIN HPBW VSWR BANDWIDTH
1 λ/2 2.14dB 80° 1.417 52MHz
2 3λ/4 2.94dB 80° 11.34 0
3 λ 3.86dB 45° 14.908 0
λ/2 dipole

Figure 1.1 figure 1.2
Figure 1.3 figure1.4
3λ/4 dipole

Figure2.1 figure 2.2
Figure 2.3 Figure 2.4
λ dipole

Table No. 2. 3-element Yagi-Uda antenna

FREQUENY GAIN HPBW VSWR BANDWIDTH FBR
300MHz
λ=1
9.05dB 50° 1.81dB 8MHz 14.1dB
Table No. 3. Table for Yagi- Uda antennas

Sr.No FREQUENCY GAIN HPBW VSWR BANDWIDTH FBR
1 300MHz
λ=1
12.09dB 40° 1.397 12MHz 17.36dB
2 400MHz
λ=0.75
1.38dB 40° 2.099 0 12.3dB
3 500MHz
λ=0.6
7.43dB 60° 1.114 9MHz 16.49dB
4 600MHz
λ=0.5
11.91dB 40° 1.58 20MHz 12.55dB
Yagi-Uda at 300MHz
Yagi-Uda at 400MHz

Yagi-Uda at 500MHz

Yagi-Uda at 600MHz
Table No. 4. Table for 13-element Yagi-Uda at 1.4GHz

FREQUENCY GAIN HPBW VSWR BANDWIDTH FBR
1.4GHz 9.13dB 50° 1.056 118MHz 9.2dB
13-element Yagi-Uda at 1.4GHz
Table No. 5. Table for 16-element Log-Periodic at 10MHz

FREQUENCY GAIN HPBW VSWR BANDWIDTH FBR
10MHz 6.79dB 290° 2.99 - 25.59dB
7. DESIGN AND SIMULATION RESULTS

Figure 7.1 Design of Log-periodic antenna in CST

Figure 7.2 Radiation pattern at 1150 MHz

S-parameter:-
In practice, the most commonly quoted parameter in regards to antennas is S11.
S11 represents how much power is reflected from the antenna and hence is known as the
reflection coefficient (Γ) or return loss. If S11=0 dB, then all power is reflected from the
antenna and nothing is radiated. If S11= -10dB, this implies that if 3dB of power is
delivered to the antenna -7dB is the reflected power. This power is either radiated or
absorbed as losses within the antenna. Since antennas are designed to be low loss, ideally
the majority of the power delivered to the antenna is radiated. From the results obtained it
is very clear.

8. APPLICATIONS
8.1 APPLICATIONS
1. For direction finding, particularly to identify sources of disruptive signals.
2. To monitor local radio frequency interference for critical applications, e.g. police
communication networks, fire department communication networks.
3. Such a device would be extremely useful in helping to identify man-made
interference to sensitive radio-astronomy instruments like the Giant Metre-wave
Radio Telescope (GMRT).
4. For building early warning systems for coastal surveillance.

9. PERFORMANCE EVALUATION
Problems occurred during completion of project no heading
TASK STATUS
Design of Log-periodic antenna in CST Completed
Manufacture of Log-periodic antenna Completed
Testing of Log-periodic antenna Completed
Modifications in Log-periodic antenna Completed
Final testing of Log-periodic antenna Completed

10. CONCLUSION
In many real life applications we need highly directional antennas with high gain.
We also need to identify the source of disruptive signals and reduce them to minimum
value or eliminate them. The radio frequency interference is also needed to be known to
prevent the original signal from getting disrupted. All these requirements are
accomplished using log periodic antenna which we have designed for a bandwidth of
350MHz to 1500MHz using CST.

11. COMPONENT LIST AND COST ESTIMATION
Component Dimension Cost
Aluminium square rod 1.5m 40/-
Aluminium coil 3m 20/-
Total cost= 60/-

12. REFERENCES
1. A. O. Benz .E C. Monstein. H. Meyer. P. K. Manoharan.R. Ramesh. A.
Altyntsev.ALara. J. Paez. K.-S. Cho, “A World-Wide Net of Solar Radio
Spectrometers: e-CALLISTO”, 10 April 2008.
2. C Balanis, “Antenna Theory Analysis and design” Wiley, 2005
3. J. D. Kraus, “Antennas”, Mc Graw Hill.
4. http://www.radio-electronics.com
5. NOWATZKY, D.: Logarithmisch periodische Antennen. Technische
Mitteilungen desRFZ, Jahrg. 7/Heft 2, June 1963, pp. 77-80, and Jahrg. 7/Heft 3,
Sept. 1963, pp. 127-133.
(http://home.t-online.de/home/Dieter.Nowatzky/doc.htm)
6. SEVERNS, R., BEEZLEY, B., HARE, E.: Log Periodic Arrays. In The ARRL
AntennaBook [CD-ROM]. The American Radio Relay League, Inc. Newington,
CT 06111-1494.
7. BANIC, B., HAJACH, P.: Design and Simulation of Properties of Log-Periodic
DipoleAntenna. InRadioelektronika 2000, Bratislava, 12-16. Sept. 2000, pp.
P_108-P_109.
8. C. A. Chen and D. K. Cheng, “Optimum Element Lengths for Yagi-Uda Arrays. ”
IEEE Trans. Antennas propag.,Vol. AP-23, pp. 8-15, January 1975.
9. Thomas Milligan, “Modern Antenna Design” Wiley & Sons, 2005.

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