fianl year project report

SEMINAR REPORTON

DESIGN AND IMPLEMENTATION OF LOG-PERIODIC ANTENNA

SUBMITTED BYShruti Nadkarni

Sneha VyawahareGargi Mohokar

DEPT. OF ELECTRONICS & TELECOMMUNICATIONP.E.S’S MODERN COLLEGE OF ENGINEERING

PUNE – 411 005.

UNIVERSITY OF PUNE2010 - 11

H.O.D. (E&TC) Project Guide

Prof .Mr.V.N.Patil Prof. Mrs.A.D.Adhyapak

PROJECT REPORTON

DESIGN AND IMPLEMENTATION OF LOG PERIODIC ANTENNA

SUBMITTED BYSHRUTI S. NADKARNIGARGI R. MOHOKARSNEHA VYAVAHARE

DEPT. OF ELECTRONICS & TELECOMMUNICATIONP.E.S’S MODERN COLLEGE OF ENGINEERING

PUNE – 411005.

UNIVERSITY OF PUNE2012 - 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. AdhyapakPrincipal 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 10deg45degand 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 1500MHzGain: - 6.9σ:- 0.06τ=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

1MHz

10MHz

1GHz

1.5GHz

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

ADG904/904R

-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 antennasSr.No. ANTENNA GAIN HPBW VSWR BANDWIDTH

1 λ/2 2.14dB 80° 1.417 52MHz2 3λ/4 2.94dB 80° 11.34 03 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 antennaFREQUENY GAIN HPBW VSWR BANDWIDTH FBR

300MHzλ=1

9.05dB 50° 1.81dB 8MHz 14.1dB



Table No. 3. Table for Yagi- Uda antennasSr.No FREQUENCY GAIN HPBW VSWR BANDWIDTH FBR

1 300MHzλ=1

12.09dB 40° 1.397 12MHz 17.36dB

2 400MHzλ=0.75

1.38dB 40° 2.099 0 12.3dB

3 500MHzλ=0.6

7.43dB 60° 1.114 9MHz 16.49dB

4 600MHzλ=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 1.4GHzFREQUENCY 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.

Figure 7.5S-parameters

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 EVALUATIONTASK 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

Problems occurred during completion of project no heading

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 CostAluminium 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, 20053. J. D. Kraus, “Antennas”, Mc Graw Hill. 4. http://www.radio-electronics.com5. 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.

fianl year project report

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