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 exhibit relatively uniform input 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 was not invented earlier. In essence, log periodic arrays are a group of dipole 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 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 frequency where it acts as a half wave dipole. As the frequency shifts shifts upward, the active region shifts shifts forward. The upper frequency limit of the antenna is a function f unction of the shortest elements.
Log periodic array capabilities The log periodic antenna was originally designed at the University of I llinois 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 ante nna 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 hybridmode 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 logperiodic 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
DWWXTV
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 ABSCBN) from 1969 –72)
DWET-TV
TV-5
ABC Development Corporation Currently broadcasting: TV5
1960/1992/2008
DZBB-TV
TV-7
GMA Network, Inc.
1961
DZKB-TV
TV-9
Radio Philippines Network and Solar Entertainment Currently broadcasting: ETC
1969 (frequency used by CBN (now ABSCBN) from 1958 –69)
DZOE-TV
TV-11
GMA Network, Inc. and ZOE Broadcasting Network Currently 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 Entertainment Currently broadcasting: Solar News Channel
1992
DWAC-TV
TV-23
ABS –CBN Corporation Currently 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 Corporation Currently broadcasting: Net 25
1999
DZRJ-TV
TV-29
Rajah Broadcasting Network and Solar Entertainment Currently broadcasting: 2nd Avenue
1993
DWKC-TV
TV-31
Radio Mindanao Network, Broadcast Enterprises and Affiliated Media, Inc. andSolar Entertainment Currently broadcasting: Jack City
1992/2011 (formerly branded as CTV31 and E! Philippines, and fizzled out in 2003)
DZOZ-TV
TV-33
ZOE Broadcasting Network Currently broadcasting: Light TV 33
2006
DWAOTV
TV-37
Progressive Broadcasting Corporation Currently broadcasting: UNTV
2004
DWBP-TV
TV-39
ACQ-Kingdom Broadcasting Network Currently broadcasting: Sonshine Media Network International
2005
DWNBTV
TV-41
Nation Broadcasting Corporation and ABC Development Corporation Currently broadcasting: AksyonTV
2001/2011 (formerly MTV Philippines)
DWVNTV
TV-45
Gateway UHF Broadcasting Currently broadcasting: 3ABN International & Hope Channel PHL
2001
DZCE-TV
TV-49
Christian Era Broadcasting Service Currently 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
Compute for the length of the first and last element
Decide for the number of elements of the antenna (N)
Compute for the tau constant of the antenna to determine the periodicity of the operation of the antenna
⁄ ( ) ⁄ ( )
Determine the lengths of the other elements
Determine the size of spacing of each element
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
3. Cut the aluminum tubes based from the desired length of elements.
1 m long
4. The size of the boom is determined by taking the sum of the spacing of t he 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 t he 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 co nnected 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 t he characteristic of the log periodic antenna, is its cr iss cross connections that allow it to have the c apability 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
WORKING Channel
Quality Yes
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, Jobert Guevara, Arnelson Legaspi, Kenneth
Bachelor of Science in Electronics Engineering
Submitted to: Engr. Leonardo Samaniego
27 SEPTEMBER 2013
