2013 IEEE Business Engineering and Industrial Applications Colloquium (BEIAC)
Evaluation of Signal to Noise Ratio (SNR) of Log Periodic Dipole Antenna (LPDA) Z.S.Hamidi
N.N.M.Shariff
School of Physics and Material Science Faculty of Applied Sciences, MARA University of Technology, 40450, Malaysia
[email protected]
Dept. of Science & Technology Studies Faculty of Science,University of Malaya 50603 Kuala Lumpur Malaysia
[email protected] Up to date, Log Periodic Dipole Antenna (LPDA) is one of the best types that used for receiving & transmitting a radio wave through a conductor. In principle, the array of this antenna consists of elements which are connected by crossing the double line (boom) with each other. It caused pattern characteristics to be repeated periodically with the logarithm of the driving frequency. One of the main reasons that we choose this type compare with others is because of gain factor. For example Yagi antenna, just covers the UHF band (narrow bandwidth) which is not suitable for monitoring Sun. The other, such as FM antenna receives a gain of 3dB which is a small value of gain. We need to choose an antenna with high gain in the wide range. To date various methods have been developed to study the solar activities in radio region. E-CALLISTO network is one of the systems that possible to monitor the Sun within 24 hours[9,10].In this work, we construct the antenna with the value of gains more than 5dB. We decided to alternate the elements with the same size with 180° (π radians) of phase shift from one another. This can be done by connecting individual elements to alternating wires of a balanced transmission line.
Abstract— Logarithmic periodic dipole antenna (LPDA) was constructed for monitoring Sun in the range of (45 -870) MHz to precisely match the solar monitoring requirements. In our work, we choose rod aluminium’s type as a conductor with nineteenth (19) elements of different sizes. Beside established construction techniques, several test setups have done to make sure that we possibly obtain a good data. The performance testing has been done at National Space Agency (PAN), Sg. Lang, Banting Selangor by connecting to the CALLISTO spectrometer. In this case, we choose input impedance, R0 = 50 ohm for this LPDA antenna. We also select element factor (τ) and spacing factor (σ) give in the subtended angle of 3.43 degrees. As a result, a bandwidth ratio (B = 870 MHz /45MHz) of 19.33 gives a bandwidth as 2.14. The power flux density of the burst is 4.53841 x 10-21 W/m2Hz. From the evaluation, we found that the signal to noise ratio is 3.9 dB. Although there are still needs to be improved, this construction of LPDA is considered successful and suitable for to observe the Sun activities at low frequencies. Keywords -Log Periodic Dipole Antenna (LPDA), signal to Noise Ration (SNR); Sun; e-CALLISTO; low frequency
I.
INTRODUCTION (HEADING 1)
Logarithmic periodic dipole antenna (LPDA) is a wellknown scientific instrumentation for power spectrum radio data monitoring used wideband antennas at its front end [1] . It considers as one of the most antennas that widely used for normalized site attenuation (NSA) and radiated emission (RE) testing [2]. It plays a key role in the successful detection of solar radiation as they provide the sensitive component of the radio detector [3] . This type of antenna is considered as basic receiving element used in the present system which has an almost continuous coverage of a wide range of frequencies and one of the broadband antennas that suitable for many applications such as FM broadcasting, scanning, government applications, VHF/UHF television air band communications and business band use [4]. It is well known that LPDA arrays have been excellent solutions for operating bandwidth expansion [5,6,7,8]. There are many criteria of antenna design and normally aspects such as gain and bandwidth that antenna can offer is a factor of the antenna is chosen. Once dealing with antenna, definition of various parameters is necessary to be understood for design a good antenna performance. These include parameter such as gain, polarization, radiation pattern, directivity and bandwidth.
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The size of each element is based on the standard design for monitoring solar in the range of 45MHz- 870 MHz for solar monitoring at low frequency region. Mechanically, this LPDA uses a specially shaped high quality aluminum boom that lets for movement of the phasing line. The boom to mast bracket is made of a lightweight and rugged aluminium alloy. In order to understand the principle of log periodic antenna and test performance of log periodic dipole antenna we evaluate the signal to noise ratio (SNR) of this antenna. We then assemble the antenna with a proper tripod that suitable with the size of the antenna. Figure 1 shows the LPDA that has been successfully assembled at National Space Centre, Banting Selangor.
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flare and the formation of new sunspot. Meanwhile type V is very rare but normally can be seen after type III formation. In Malaysia, the study of solar burst is just in beginning phase. Malaysia has started joining this research since February 2012 and routinely monitor 12 hours per day at National Space Centre, Selangor [13]. We started by proposing this research in early 2011, through the National Space Agency of Malaysia (ANGKASA), University of Malaya (UM), MARA University of Technology (UiTM) and National University of Malaysia (UKM). It is remarkable that the effect of temperature is one of the main factors that will affect the data of solar burst. Seems we are in the equatorial country, the range of temperature varied from 26-35° Celcius throughout a year. Generally, the signal from the log periodic dipole antenna antenna is directed to the (Compound Astronomical Low-cost Low-frequency Instrument for Spectroscopy in Transportable Observatory) CALLISTO spectrometer, which is housed in a steel case, via a low loss coaxial cable, LMR-240[14]. Physically, the system is characterized by the wide range of frequency which can occupy the solar bursts. Similar to another site, the instrument holders have set up an FTP-server at their host-site with a local archive. All data are stored with a scale factor and an offset applied so that the measured ADC digits range fits into the byte data range (0 - 255). These works also as a part of a project where we are also participating internationally with the latest technologies of solar astrophysics instrument. Figure 2 shows the detail of the CALLISTO system that connected to the LPDA in the control room.
Figure. 1. The Log Periodic Dipole Antenna at National Space Centre, Banting Selangor for solar burst monitoring
The solar burst research has directed the attention other space weather community and more significant during the solar maximum cycle which is expected in the beginning of 2013. Monitoring the solar activity such as solar flare and Coronal Mass Ejections (CMEs) from photosphere till interplanetary medium is generally for space weather condition. Solar flares and Coronal Mass Ejections (CMEs) can excite plasma oscillations which can release radiation at metric and decimetric wavelengths[11]. Characteristic studies of solar radio bursts are a great importance for determining the solar flare and Coronal Mass Ejections (CMEs) phenomenon in radio wavelengths, we could possible to investigate high quality images within an arc second resolution at different layers of the solar atmosphere[12]. The structure of the Sun is determined by the conditions of mass conservation, momentum conservation, energy conservation, and the mode of energy transport. Meanwhile, the magnetic field of the Sun confined to the convective envelope and is generated there by a dynamo mechanism, thereby consuming energy liberated by thermonuclear reactions in the gravitationally stabilized fusion reactor of the Sun. But as usual in science, answering a basic question leads to many more detailed ones. Therefore, we need to know more about the inner structure of the Sun. Observations of solar burst by low spectral and spatial resolution instruments can provide us only the light curve and a crude spectrum of the whole flare which may consist of many distinct sources with different characteristics. Indirectly, solar burst potentially produced many negative impacts to the Earth. By very-high-energy particles that release from intense solar bursts can be as injurious to humans as the lower energy radiation from nuclear blasts. This project is under the International Space Weather Initiative (ISWI) which focuses on solar radio research. Here, we study on solar burst in decimetric region. In principle, there are five (5) main solar bursts which based on solar activities. Type I solar burst is associated with solar storm, type II is due to Coronal Mass Ejections (CMEs) events. Type III and IV are caused by solar
Figure. 2. The CALLISTO spectrometer that connected to the notebook for acquisition data
There are a few software that helps to transfer the data such as TP-watchdog could replace a function of FTP server and make the process of the data can be automatically transferred into a table based on the timing of the solar activities. For the basic data reduction purpose, we can use a JAVA software to subtract the data from background noise. All data can be analyzed in detail with IDL (Interactive Data Language) program.
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19
II.
0.07143311
0.100006365
0.020001271
BASIC PROPERTIES OF LPDA AND SIGNAL TO NOISE RATIO MEASUREMENT EASE OF USE
A. Basic Properties of LPDA In this section, we will highlight some theoretical aspect and parameter that need to be considered for evaluation. We began with a relationship between element factor (τ) with the size of the element represented as equation below: (1) (2) Figure. 3. The Dataflow from observatories to the archive (Credited to C.Monstein, ETH Zurich, Switzerland)
In order to make a portable Log Periodic Dipole Antenna, the size of boom length becomes an issue. We divided into three of sizes, 2 meters respectively. We then need to make a hole for the screw to join it again. We used the logarithmic periodic antenna directly connected via a low loss coaxial cable to the measuring instrument. The antenna is mounted horizontally on a steerable azimuth/elevation tower, and controlled by the computer to automatically point the sun during the daytime. In order to make sure the log periodic antenna is high quality, aspect of material cannot be neglected. Therefore, we used the aluminium type a conductor material for elements and the PVC as an insulator of LPDA. These materials will be against lighting strokes if happened. Table 1 shows the specification of LPDA.
where f= frequency of each element and element factor can be represented with this equation: (3) Meanwhile, the spacing d of each element can be represented by: ,
(4) On the other hand, we can measure a noise ratio or excess noise ratio is a term to describe the output of the noise source used as an input stimulus. For the figure to be valid, the lower noise level must be equal to the noise generated by a (theoretical) resistor at the standard reference temperature of Tref = 290K.
TABLE I SPECIFICATION OF LPDA No of elements
L(m)
R(m)
D(m)
1
3.96533329
5.551466963
1.110293326
2
3.17226668
4.441173636
0.888234674
3
2.53781338
3.552938962
0.710587750
4
2.03025073
2.842351212
0.568470208
5
1.62420061
2.273881003
0.454776173
6
1.29936050
1.819104830
0.363820944
7
1.03948842
1.455283885
0.291056759
8
0.83159075
1.164227125
0..232845411
…
log
9
0.66527261
1.164227125
0.186276331
10
0.53221809
0.745105382
0.149021067
11
0.42577448
0.596084315
0.119216855
12
0.34061959
0.476867459
0.095373486
13
0.27249567
0.381493973
0.076298790
14
0.21799654
0.305195182
0.061039032
15
0.17439723
0.244156150
0.048831227
16
0.13951779
0.195324922
0.039064982
17
0.11161423
0.156259940
0.031251986
18
0.08929139
0.125007954
0.025001589
1
(5)
Without going into great detail regarding derivation, the noise can be related to input stimulus and Y-factor as follows or in the case where T1 (representing the “cold” condition of the noise source) equals the standard reference temperature, T0= (290K): 10 log
1
10 log
1
(6)
Therefore, We can simplify this equation with: 10 log
1
(7)
In terms of equipment accuracies, there are two (2) major factors to consider (i) the noise source output and (ii) our ability to ascertain the Y-factor. These two (2) sets a minimum uncertainty for any noise figure measurement. Calculation Y-factor of the Sun (Y-Sun) is also called hotcold measurement method [15] . The solar flux, Y-Sun can be estimated by using the Java FITS Viewer. The Java FITS
This work is sponsored by the Faculty of Science, MARA University of Technology, National Space Centre and University of Malaya .
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Viewer uses in terms of the analog–digital converter (ADC) 10-bit resolution. The power value in terms of 10-bit AC output has been reduced to 8 bits by dividing it by four (4). 3.46
(12) Our next task is to find the value of solar flux density, S = 146 sfu taken from the NOAA list at spaceweather.com on 9th March 2012. From that we can measure the system noise temperature, Tsys . In this equation, k, and T is a Boltzmann constant and antenna temperature of the Sun respectively. The power flux density due to the system noise temperature, PFDsys is also calculated.
(8)
In order to calculate the SNR, first we have to measure Power Flux Density, PFD we need to calculate the effective area of the antenna, Aeff at the first stage. In this case, the symbol G(dB) is a gain in dB units. Seems the solar burst data is at frequency, f =240 MHz, we select this value and c is the speed of light in m/s. We have calculated that the gain is equal to 5dB and the wavelength, is 1.25 meter. Therefore,
1.85
(13)
Therefore, 0.6217
(9)
17.43
177.33 3.9 (14) This LPDA was modelled with a low loss coaxial cable, RG8, 5.5m long. Therefore the cable attenuation at 50, 450 and 900 MHz is 0.7, 2.1 and 3.0 dB respectively. When the transmission line is soldered to the antenna, side of the antenna effectively has less inductance and a higher velocity factor. Finally, the signal noise ratio is getting from the difference between the power flux density of receiving solar flux PFDburst and the power flux density of system noise PFD the calculation, 3.9 dB indicates that the power level of the solar burst is higher than the receiver system noise.
The viewer is set to automatic background subtraction so it determines the average background noise level for the entire spectrum and subtracts it when the spectrum is displayed. The background also can be subtracted manually by selecting a region that having the noise level. By using the zoom function and the mouse cursor, the quiet or cold sky and the hot sky value are observed and recorded as in Figure 4. Quiet sky is indicated by blue (dark) stripe and hot sky represented by red (bright) area.
III.
Figure 4: The cold (left) and hot (right) section
From the calculation, the power flux density (PFD) of the burst can be calculated by using the value of the antenna effective area, Aeff .
4.53841 (10) With the temperature of the Sun and the CALLISTO system are:
328.9
RESULTS AND DISCUSSIONS
A part of measurement, we also make an experiment the LPDA by taking some observations from 7.30 am till 17.30 pm. We then analyze a y-factor of a data by select a range of frequency from 220 MHz till 250 MHz. The reason we choose this range is because of the there is a burst detected within that frequency. We choose input impedance, R0= 50 ohm for this LPDA antenna. We then select element factor (τ) and spacing factor (σ) give in the subtended angle of 3.43 degrees. As a results bandwidth ratio (B = 870 MHz /45MHz) of 19.33 gives a bandwidth as 2.14. Although the solar activities have experienced rapid growth recently, high-level management of CALLISTO system has remained successfully manage the storage of data. Further actions need to be taken to prove solar monitoring studies are very important and should be extended. As sensing and monitoring technology continues to improve, there is an opportunity to deploy sensors in this system in order to improve their management. It is also not easy to maintain the future data seems the number of sites are also growing from time to time. In this work, we highlighted the potential role of Malaysia as one of the candidate sites that possible gives a good data and focusing on a few aspects such as optimization, and performance evaluation data and visualization. IV.
CONCLUSIONS
Although there are still needs to be improved, this construction of LPDA is considered success. This antenna will receive a signal from Sun by connecting the antenna to the CALLISTO spectrometer. Noise ratio calculated shows that antenna receives signals more than noise. There was time
(11)
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consuming in techniques of joining booms and the elements. It can be improved by using pop riveting as its fastening also tight. In order to reduce noise, the LPDA is recommended to install as far as possible from radio frequency interference sources. Even there are no electronic calibration means available, at present, indirect calibration was done by using quiet Sun flux. Fieldwork has been ongoing at the National Space Centre site since February 2012, towards monitoring solar maximum. There is much work to be done, but it is sufficiently challenging and potentially rewarding in terms of interesting physics and novel of sun activities. Our next plan is to discover the potential for dynamic optimization of an array's of antenna with a focus on mitigation of fault conditions and optimization of power output under non-fault conditions. Finally, monitoring system design considerations such as the type and accuracy of measurements, sampling rate, and communication protocols are considered. It is our hope that the benefits of monitoring presented here will be sufficient to offset the small additional cost of a sensing system, and that such systems will become common in the near future. We conclude that this antenna is suitable for to observe the Sun activities at low frequencies.
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[9]
ACKNOWLEDGMENT The authors would like to thank to University of Malaya, MARA University of Technology, National Agency Space of Malaysia (ANGKASA) and the National Space Centre for the collaborations of e-CALLISTO. The development, production and distribution of CALLISTO spectrometers it supported by ETH engineer. Solar burst monitoring is a project of cooperation between the Institute of Astronomy, ETH Zurich, Switzerland, University of Malaya and UiTM. Also thanks to NOAA Space Weather Prediction Center for the sunspot data.
[10] [11] [12] [13] [14]
This research has made use of the National Space Centre Facility. This work was partially supported by PPP UM PV071/2011B grants. The project is an initiative work of the International of Space Weather Initiative (ISWI) program.
[15]
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