log-periodic.docx

CHAPTER 1 INTRODUCTION

Introduction

One of the major drawbacks with many RF antennas is that they have a relatively small

bandwidth. This is particularly true of the Yagi beam antenna. One design named the log periodic

antenna is able to provide directivity and gain while being able to operate over a wide bandwidth. In

particular the log periodic dipole array is the most widely used version of this antenna family.

A log-periodic antenna is an antenna that can operate on a wide frequency band and has the

ability to provide directivity and gain. It has radiation and impedance characteristics that are repeated as

a logarithmic function of excitation frequency. These antennas are fractal antenna (self-similar antenna)

arrays. A log-periodic antenna may also be referred to as a log-period array or a log-periodic beam

antenna.

The log periodic antenna is used in a number of applications where a wide bandwidth is

required along with directivity and a modest level of gain. It is sometimes used on the HF portion of the

spectrum where operation is required on a number of frequencies to enable communication to be

maintained. It is also used at VHF and UHF for a variety of applications, including some uses as a

television antenna.

Log periodic dipoles are a common, linearly polarized, broadband type of antenna. The LPDA

designed and constructed for this study was made using the principles and concept in our Transmission

Media and Antenna System lecture.

Background of the Study

In 1957, R.H. DuHamel and D.E. Isbell published the first work on what was to become known as

the log periodic array. These remarkable antennas exhibit relatively uniform input impedances, VSWR,

and radiation characteristics over a wide range of frequencies. The design is so simple that in retrospect

it is remarkable that it was not invented earlier. In essence, log periodic arrays are a group of dipole

antennas of varying sizes strung together and fed alternately through a common transmission line. Still,

despite its simplicity, the log periodic antenna remains a subject of considerable study even today.

The log periodic antenna works the way one intuitively would expect. Its “active region,” -- that

portion of the antenna which is actually radiating or receiving radiation efficiently -- shifts with

frequency. The longest element is active at the antenna’s lowest usable frequency where it acts as a

half wave dipole. As the frequency shifts upward, the active region shifts forward. The upper frequency

limit of the antenna is a function of the shortest elements.

Log periodic array capabilities

The log periodic antenna was originally designed at the University of Illinois in the USA in 1955.

This type of RF 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.

Types of log period antenna

There are several formats in which the log periodic antenna can be realised. 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

The type that is most widely used is the log periodic dipole array, LPDA, and that will be described here.

Log periodic dipole array basics

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 is coming

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 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.

Basic log periodic dipole array

Log 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.

Statement of the problem

In the past television is accompanied by either an indoor or outdoor antenna to have a better signal and

have variety number of channel from different station that it receives. The antenna can either own

made wire that acts as an antenna or a commercially available kind. These antennas are still in used

even nowadays like in the Philippines where digitalization is still under development especially in rural

areas. In own made antenna lack of knowledge in the background of antenna leads to poor antenna

quality meaning it can only receive a selected numbers of channels and sometimes with interference but

the worst case is it cannot receive anything.

Significance of the study

In the experiment, the students will create an actual antenna that would follow the concept regarding

antenna system. It will be tested via a television to check the quality and the number of channel that it

could receive.

Scope and Delimitation

The experiment will focuses on log periodic antenna design since any type of antenna can be used as

long as it can receive signal. The creation of antenna will be delimit in an ultra-high frequency range

(300 to 3000 MHz) based on the preferred range from the instructor.

Only 4 elements are used on this design.

The group limited their frequency of operation from 174 – 216 MHz (Channel 7-13)

CHAPTER 2 REVIEW OF RELATED LITERATURE

Foreign Literature

The Log-Periodic Loop Antenna with Ground Reflector (LPLA-GR) is investigated as a new type of

antenna, which provides wide bandwidth, broad beamwidth, and high gain. This antenna has smaller

transverse dimensions (by a factor of 2/π) than a log-periodic dipole antenna with comparable radiation

characteristics. Several geometries with different parameters are analyzed numerically using ESP code,

which is based on the method of moments. A LPLA-GR with 6 turns and a cone angle of 30° offers the

most promising radiation characteristics. This antenna yields 47.6 % gain bandwidth and 12 dB gain

according to the numerical analysis. The LPLA-GR also provides linear polarization and unidirectional

patterns. ( J. Kim, 1999 )

Log-periodic (LP) antennas are important with their ability to show nearly frequency

independent characteristics over wide bands of frequencies, although they have relatively simple

geometries. Numerous different configurations of LP antennas have been studied since late 1950s.

Among them, LP dipole arrays have been the most popular. Analysis and design procedures of LP dipole

arrays can be found in antenna textbooks.( O. Ergül and L. Gürel )

Frequency independence of LP antennas is based on strictly theoretical principles, which are

difficult or impossible to satisfy in practical implementations. This forces the designers to rely on

intuition, assumptions, and approximations. Consequently, an LP antenna that is designed using

approximations of idealized theoretical recipes may not function as well as desired. A remedy can be

supplied by computational electromagnetics, powered by the recent advances in both the solution

algorithms and the computer hardware. In an electromagnetic simulation environment, performances of

a series of designs can easily be checked, and the necessary corrections can be implemented on the

antennas. In this paper, the benefit of employing electromagnetic simulations in addition to (not instead

of) theoretical principles will be demonstrated.( O. Ergül and L. Gürel )

Multiple LP antennas can be operated in an array configuration. In order to maintain a

frequency-independent operation, the array configuration should be specified in terms of angles, similar

to the LP antennas. Such a configuration can be achieved by placing the antennas on a circle.( O. Ergül

and L. Gürel )

It is essential to complement theoretical antenna design recipes with the numerical results

obtained from electromagnetic simulations. In this paper, the benefit of such a hybrid procedure is

demonstrated by using the design of an LP antenna as a case study. It is shown that significant

performance improvements can be obtained by applying corrections suggested by the simulation

results. ( O. Ergül and L. Gürel )

Arrays of LP antennas can also be designed and analyzed in an electromagnetic simulation

environment. Design of arrays made up of several LP antenna elements can be achieved by coupling

electromagnetic solvers to optimization methods, such as genetic algorithms.( O. Ergül and L. Gürel )

Log Periodic array Antenna is one of the most important and commercially used antennas for

T.V. reception. It is used in VHF and UHF bands. Although the analysis of this antenna is reported in

literature, the data of self impedance & mutual impedance is not fully available. But, this data is useful

for the optimal design of the antenna. In view of this the array above is considered and the analysis is

carried out in the present work. (B. Neelgar, 2011 )

This paper describes investigations into the current distributions on a log periodic dipole

antenna (LPDA) which was constructed on printed circuit board. The investigations involved measuring

the magnetic field magnitude and phase at each point on the antenna. The wave nature of the current

distribution could be readily observed and problems with the design such as standing waves on the

feeder lines are highlighted for attention in a revised design. Measured current distributions are

compared with predicted distributions obtained from Method of Moments (MoM) and Multiple

Multipole (MMP) analyses of the LPDA structure. Measured and predicted far field radiation patterns

are also compared. ( U. Lundgren and S. Jenvey )

Log-Periodic Dipole Antenna (LPDA) is a common and important broadband antenna, due to its

non-frequency dependent characteristic. However, in the conventional design, the physical size is

restricted to the longest oscillator dipole with the lowest resonant frequency, which is quite large and

constrains its application. To realize the antenna miniaturization, many methods, including loading

technology, fractal technology, meandering line technology etc. have been used to reduce the size of

antenna without reducing the antenna‘s performance. ( V. Lakshmi and G Raju )

In many applications, an antenna should operate over a wide range of frequencies. An antenna

with this characteristic is called broadband antenna. Log periodic antenna can be one of the broadband

antennas. Basic idea of log periodic antenna is using elements of varying lengths, which would resonate

at different frequencies. For any frequency within the design band, there are some elements, which are

nearly half-wave length dimensions. The currents on these elements are large compared to the currents

on the other elements. The elements with dimensions approximately half-wave lengths contribute most

of the radiation so the region where these elements take place is called active region. As the frequency

changes, the active region shifts from one group of elements to the next. The elements outside the

active region act as parasitic elements. They do not contribute the radiation much.( V. Lakshmi and G

Raju )

One of the major drawbacks with many RF antennas is that they have a relatively small

bandwidth. This is particularly true of the Yagi beam antenna. One design named the log periodic is able

to provide directivity and gain while being able to operate over a wide bandwidth. The log periodic

antenna is used in a number of applications where a wide bandwidth is required along with directivity

and a modest level of gain. It is sometimes used on the HF portion of the spectrum where operation is

required on a number of frequencies to enable communication to be maintained. It is also used at VHF

and UHF for a variety of applications, including some uses as a television antenna. (A. DAS, 2007)

The bandwidth of a microwave reflector telescope is limited by the size and figure accuracy of

the mirror elements and by the feed which couples focused radiation to the receiver. A single or hybrid-

mode feedhorn can efficiently illuminate a telescope aperture with low ohmic loss. Its gain varies

quadratically with frequency, however, limiting its effective bandwidth to less than an octave. A log-

periodic antenna (LP) can illuminate a telescope aperture over multi-octave bandwidths, but it has

greater spillover and ohmic loss than a well-designed feedhorn. Moreover, in contrast to a horn, an LP is

a large open structure, requiring a long twin-lead or coaxial cable to carry signals away from the near

field region, before amplification. Loss in such cables can be greater than 1 dB, contributing more than

60 K to the receiver noise temperature. Also, motion with frequency of the phase center along the

antenna axis may require a mechanical actuator to move the feed into focus for good illumination

efficiency of the telescope. (G. Engargiola, 2002)

The Sun is considered as one of the strongest radio sources and observation in radio region can

provide information on structures throughout the solar atmosphere. In radio wavelengths, we could

possible to investigate high quality images within an arc second resolution at different layers of the solar

atmosphere. Solar monitoring in this wavelength makes various demands on the used antennas.

Therefore, Logarithmic Periodic dipole Antenna (LPDA) was constructed for monitoring Sun in the range

of (45−870) MHz to precisely match the environmental requirements by constructing and understanding

the principle of the log dipole periodic antenna and then connect it to the CALLISTO spectrometer as

receiver, some solar activities observations such as solar flares and Coronal Mass Ejections (CMEs) can

be done. In conclusion, the log-periodic dipole antenna (LPDA) is remains the simplest antenna with

reliable bandwidth and gain estimates. ( Z.S.Hamidi et. Al., 2012 )

Local Literature

The List of Television Stations in the Philippines that are working in the Very High and

Ultra High Frequencies

VHF Stations

Call sign Ch. # Owner Launch

DWWX-TV

TV-2 ABS–CBN Corporation 1953 (original frequency was Channel 3 (ABS) from 1953–69)

DWGT-TV TV-4 People's Television Network 1974 (frequency used by CBN (now ABS-CBN) from 1969–72)

DWET-TV TV-5 ABC Development CorporationCurrently broadcasting: TV5

1960/1992/2008

DZBB-TV TV-7 GMA Network, Inc. 1961

DZKB-TV TV-9 Radio Philippines Network and Solar EntertainmentCurrently broadcasting: ETC

1969 (frequency used by CBN (now ABS-CBN) from 1958–69)

DZOE-TV TV-11 GMA Network, Inc. and ZOE Broadcasting NetworkCurrently broadcasting: GMA News TV

1998 (frequency used by MBC from 1960–72)

DZTV-TV TV-13 Intercontinental Broadcasting Corporation

1960

UHF Stations

DWCP-TV TV-21 Southern Broadcasting Network and Solar EntertainmentCurrently broadcasting: Solar News Channel

1992

DWAC-TV TV-23 ABS–CBN CorporationCurrently broadcasting: Studio 23

1996 (frequency used by EEC (formerly Philippine provider of MTV Asia/Channel V) from May 1992 – July 1996)

DZEC-TV TV-25 Eagle Broadcasting CorporationCurrently broadcasting: Net 25

1999

DZRJ-TV TV-29 Rajah Broadcasting Network and Solar EntertainmentCurrently broadcasting: 2nd Avenue

1993

DWKC-TV TV-31 Radio Mindanao Network, Broadcast Enterprises and Affiliated Media, Inc. andSolar EntertainmentCurrently broadcasting: Jack City

1992/2011 (formerly branded as CTV-31 and E! Philippines, and fizzled out in 2003)

DZOZ-TV TV-33 ZOE Broadcasting NetworkCurrently broadcasting: Light TV 33

2006

DWAO-TV

TV-37 Progressive Broadcasting CorporationCurrently broadcasting: UNTV

2004

DWBP-TV TV-39 ACQ-Kingdom Broadcasting NetworkCurrently broadcasting: Sonshine Media Network International

2005

DWNB-TV

TV-41 Nation Broadcasting Corporation and ABC Development CorporationCurrently broadcasting: AksyonTV

2001/2011 (formerly MTV Philippines)

DWVN-TV

TV-45 Gateway UHF BroadcastingCurrently broadcasting: 3ABN International & Hope Channel PHL

2001

DZCE-TV TV-49 Christian Era Broadcasting ServiceCurrently broadcasting: INC TV

2005/2012

Source: KBP Manual

CHAPTER 3 METHODOLOGY

1. Compute the necessary lengths of the elements for the desired frequency of operation

On this design we used 4 elements and frequency of 174 – 216 MHz (Channel 7-13)

Determine the upper and lower frequency of your decided band of operation

f L=174Mhz

f L=216Mhz

Compute for the length of the first and last element

l1=λ12; λ1=

cf L

= 3x 108m /s174 x106Hz

=1.7241m

l1=1.7241m2

=0.862m=86.2cm

lN=λN2; λN=

cf N

= 3x 108m /s216 x106Hz

=1.388m

lN=1.388m2

=0.694m=69.4 cm

Decide for the number of elements of the antenna (N)

n=4 elements

Compute for the tau constant of the antenna to determine the periodicity of the

operation of the antenna

τ=( flfh)1N−1

τ=( 174216 )14−1=0.9305

Determine the lengths of the other elements

τ=l2l1

=l3l2=l4l3

l2=τ x l1=0.9305 x86.2cm=80.2091cm

l3=τ x l2=0.9305 x80.2091cm=74.6346 cm

l4=τ x l3=0.9305 x 74.6346cm=69.4475cm

Determine the size of spacing of each element

d1=0.1λ1=0.1 x1.7241m=0.17241m=17.24cm

τ=d2d1

=d3d2

=d4d3

d2=τ x d1=0.9305 x17.24 cm=16.0418cm

d3=τ x d2=0.9305 x 16.0418cm=14.9269cm

2. Prepare the materials needed

Quantity Material Size

2 Aluminum Round Tube 43.1 cm long

2 Aluminum Round Tube 40.1046 cm long

2 Aluminum Round Tube 37.3173 cm long

2 Aluminum Round Tube 34.7238 cm long

2 Aluminum Square Tube 2ft long

5 Clamp

1 Balun Transformer

27 Screws

1 Coaxial Cable 1 m long

3. Cut the aluminum tubes based from the desired length of elements.

4. The size of the boom is determined by taking the sum of the spacing of the elements. We

manually made holes to the aluminum tube, making sure that the screw fit the hole, according

to the calculated spacing of the elements.

5. The aluminum round tube will serve as our antenna elements. Next thing we do is to drill holes

on the aluminum tube to be able to put screws to lock the antenna in the clamp so that it will

hold its place in any weather disturbances outdoor.

6. After drilling all the holes, insert the aluminum round tube on the clamp and securing it with the

screws.

7. When all the elements have been connected and screwed to the clamp. The next thing to do is

to connect the clamp to the antenna boom or aluminum square tube. And then, securing it with

crews so that it can withstand weather disturbances.

8. After the antenna elements have been setup to the antenna boom, the connections will be

made to the elements so it would properly receive signal frequencies. One of the characteristic

of the log periodic antenna, is its criss cross connections that allow it to have the capability to

capture high frequencies signals.

9. The antenna construction is almost finished. One thing it lacks is the feed point to connect it to

the television. For that, we had a balun transformer to match the impedance of our antenna to a

coaxial cable that would be directly connected in the television.

10. After the balun transformer is connected to the smallest element, coaxial cable will be connected to it. Then, testing can now be done.

CHAPTER 4

TESTING AND RESULTS

ChannelWORKING

QualityYes No

PAMANTASAN NG LUNGSOD NG MAYNILA(University of the City of Manila)

Intramuros, Manila

COLLEGE OF ENGINEERING AND TECHNOLOGY

4-Element Log Periodic Antenna

In Partial Fulfilment of the Course Transmission Lines and Antenna Theory

Submitted by:De Leon, Charlene Ann

Gargoles, JobertGuevara, ArnelsonLegaspi, Kenneth

Bachelor of Science in Electronics Engineering

Submitted to: Engr. Leonardo Samaniego

27 SEPTEMBER 2013