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Development of a Magnetic Loop Antenna for the Detection of Jovian Radiowaves at 20.1 MHz

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Development of a Magnetic Loop Antenna for the Detection of Jovian Radiowaves at 20.1 MHz

Abstract and Figures

Radio waves coming from the planet Jupiter are electromagnetic phenomena generated by synchrotron emission mechanism, due to the interaction of Jovian magnetic field with charged particles produced by the satellite Io. These radio waves fall directly upon the ionosphere affecting earth's radio communications. At the Astronomical Observatory of the University of Technology of Pereira (OAUTP) the research group in Astro-engineering Alfa Orion, developed a magnetic loop antenna designed to resonate at 20.1 MHz, which coupled with the receptor and the software from NASA's Radio Jove project enabled the observation of radio sources A, B, C, IoA, IoB and IoC from Jupiter, allowing the construction of a database for the study of the Jovian activity in radio waves.
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DOI: htthttp://dx.doi.org/10.18180/tecciencia.2016.20.6
*Corresponding Author.
E-mail: hdgalvis@utp.edu.co
How to cite: Galvis Rodríguez, H.D., Quintero Salazar, E.A.,
Cardona Torres, L.F., Development of a Magnetic Loop Antenna for
the Detection of Jovian Radiowaves at 20.1 MHz, TECCIENCIA,
Vol. 11 No. 20, 41-46, 2016
DOI: http://dx.doi.org/10.18180/tecciencia.2016.20.6
Development of a Magnetic Loop Antenna for the Detection of Jovian
Radiowaves at 20.1 MHz
Desarrollo de una Antena tipo Loop Magnética para la Detección de Radio-ondas Jovianas a 20.1
MHz
Hamilton David Galvis Rodríguez1*, Edwin Andrés Quintero Salazar1, Luisa Fernanda Cardona
Torres1
1Universidad Tecnológica de Pereira, Colombia
Received: 24 Nov 2015 Accepted: 29 Jan 2016 Available Online: 29 Feb 2016
Abstract
Radio waves coming from the planet Jupiter are electromagnetic phenomena generated by synchrotron emission mechanism,
due to the interaction of Jovian magnetic field with charged particles produced by the satellite Io. These radio waves fall
directly upon the ionosphere affecting earth’s radio communications. At the Astronomical Observatory of the University of
Technology of Pereira (OAUTP) the research group in Astro-engineering Alfa Orion, developed a magnetic loop antenna
designed to resonate at 20.1 MHz, which coupled with the receptor and the software from NASA’s Radio Jove project enabled
the observation of radio sources A, B, C, IoA, IoB and IoC from Jupiter, allowing the construction of a database for the study
of the Jovian activity in radio waves.
Keywords: Synchrotron Emission, Jovian Radio Emissions, Magnetic Loop Antenna
Resumen
Ondas de radio provenientes del planeta Júpiter son fenómenos electromagnéticos generados por emisión de sincrotrón,
debidos a la interacción del campo magnético Joviano con partículas cargadas producidas por su luna Ío. Estas ondas de radio
interactúan con la ionósfera, afectando las radio-comunicaciones terrestres. En el Observatorio Astronómico de la Universidad
Tecnológica de Pereira (OAUTP) el grupo de investigación en Astroingeniería Alfa-Orión desarrolló una antena tipo Loop
Magnética diseñada para resonar a 20.1 MHz, la cual fue acoplada con el receptor y el software del proyecto de la NASA
Radio Jove. Esto permitió la observación de las fuentes de radio A, B, C, IoA, IoB y IoC desde Júpiter, permitiendo la
construcción de una base de datos para el estudio de la actividad Joviana en ondas de Radio.
Palabras clave: Emisión Sincrotrón, Emisiones de Radio Jovianas, Antena Tipo Loop Magnética.
1. Introduction
The decametric Jovian radio emissions (REDJ) are
electromagnetic phenomena generated by synchrotron or
cyclotron emission mechanism, due to the interaction of
Jovian magnetic field with charged particles produced by the
satellite Io or by particles close around its field. The
spectrum or radio emission of Jupiter ranges from 40MHz to
a few kHz, but the radio storms easily detectable from Earth
happen just above 15 MHz up to a limit of approximately 25
MHz. This frequency range is well characterized and
defined by two types of radio signals that evidence the
Jovian activity in decametric lengths: the type L bursts
(long) and the type S bursts (short) [1].
42
The first type is characterized by the slow variation of its
intensity in the time domain, and generally last for a few tens
of seconds, with an instantaneous bandwidth of a few MHz.
On the other side, type S bursts are characterized by having
much shorter duration and by having a bandwidth of some
tens of kHz, presenting hundreds of bursts by second [2].
Generally, Jovian activity in radio waves is studied by radio
astronomers through radio telescopes with dipole antennas.
For example, in [3], REDJ are studied at 18.0, 22.2 and 27.6
MHz, and their relation with the behavior of the great red
spot on Jupiter’s surface. Likewise, in [4] it is analyzed how
these same radio emissions influence the activity and
physical appearance of the equatorial area of the planet. In
both cases the data employed is provided by a radio wave
receptor and a dipole antenna, and their measurements are
correlated with photometric coefficient data supplied by
optical observations, finding that the correlation coefficients
are high, which make evident a close relation between the
optical and radio wave behavior in Jupiter. It is clear that
dipole antennas have had an important role in the study of
the REDJ, as they have a bidirectional radiation pattern,
which makes them appropriate for the follow up of the planet
Jupiter if they are oriented in the right way. They also have
a broad bandwidth, which makes them the indicated type of
antenna for the wide spectrum of the Jovian emission.
Therefore, between 2007 and 2013 the production of
scientific articles about the Jovian phenomena where dipole
antennas are used has been high. This way in [5] and [6]
dipole antennas are used to study the probability of Jovian
emission production and its relation with the corresponding
angular variables to each of the sources of radiofrequency of
Jupiter; in [7] and [8] the scientific developments are
focused in the proper configuration of the radio telescope,
from its optimal location through GPS devices and
meteorological measurements to the implementation of
software and additional hardware to improve the audio
records and the correct prediction of events. In [9] and [10],
the authors focus on the wave receptor and the antenna, the
electronic design of frequency filters and the optimization of
the electromagnetic parameters, in a way that the system as
a whole is more efficient when recording and acquiring the
data.
Nevertheless, it is clear in these works that dipole antennas
present two significant disadvantages. The first one, and
most relevant, consist in the fact that as these antennas are
significantly big demand, correspondingly, a space with a
big free area to install them, which is not always easy to find.
For example, for the particular case of the data acquisition
at 20 MHz, an area of 21 m2 is required. Furthermore, these
antennas are highly affected by electrical noise, so they must
be located in remote areas, away from electronic devices or
electric energy transport networks. Unfortunately, the
OAUTP does not have the necessary space to set up a dipole
antenna, and even if it could be located there, the local
electronic noise would be too high due to the activity of the
building where it is located and the electric network close
by.
This situation makes it necessary to explore the possibility
to study the Jovian activity in radio waves through smaller
size antennas and antennas with less susceptibility to electric
noise than recorded in dipole antennas. In [11], the
construction of a radio telescope is made with a particular
antenna that accomplishes all the wanted characteristics, it
is called magnetic loop antenna or isoloop (isolated loop).
The antenna is employed, in this case, to study Jovian storms
that produce electromagnetic activity in radio waves, an
objective related to this project’s. The isoloop antenna is
commonly used in earth’s HF radio communications by
amateurs or in military communications, due to its high
factor of quality and its versatility, which makes it very
effective for the modulation, transport and installation
issues. In spite of that, it can also be found in diverse projects
as the identification by radiofrequency (RFID) [12], wireless
biomedical instrumentation [13], and different applications
of radio frequencies and communications [14].
This document presents the design and construction of a
magnetic loop antenna with which the radio receptor and
software of the project Radio Jove from NASA, allows to
record the Jovian activity at 20.1 MHz, without appealing to
the installation of the traditional dipole antennas, and
diminishing the susceptibility of the system to electric noise.
2. Materials and Methods
The isoloop antennas are composed by two conducting loops
named primary and secondary loop. The last one operates as
an inductor of only one winding and its terminals are
connected to a variable capacitor of high voltage that allows
the tuning of the antenna’s resonance in a particular
frequency. The loop mentioned previously induces the
detected electromagnetic signal on the primary loop, which
is located inside the antenna on the opposite side to the
capacitor, and with its terminals connected by coaxial cable
to a transmitter or a radio waves receptor [15].
The diameter of the isoloop antennas, meaning the size of
the secondary loop, defines the desired frequency of
operation and the type of antenna. Antennas with C~λ,
where C is the secondary loop circumference, are called
electrically large, while antennas with C<0.1λ are called
electrically small. In this project an electrically small
antenna was built (C=2.51 m), in such a way that for a loop
of constant current I, the radius (a) must satisfy:
43
(1)
The relation given by (1) is obtained from the approximation
of first order of the Bessel first grade function, which
establishes a range of possible values for the size of an
electrically small isoloop antenna. On the other side, the
electric (E) and magnetic (H) fields in distant zone are given
by:
(2)
Where J1 represents the first order Bessel function, while β
y η are the phase constant and the intrinsic impedance of the
medium, respectively. From these two expressions the
power pattern is obtained for an isoloop antenna, which is
given by (3), being identical to the pattern generated by a
dipole antenna, as it was mentioned beforehand.
(3)
Finally, the radiated power (P) and the radiation resistance
(R) can be obtained through the next expressions:
(4)
Where A is the secondary loop area and η = 120 Ω in vacuum
[16]. From these values, the frequency of operation at 20.1
MHz, and the set of equations (1) through (4), the parameters
of the designed antenna were obtained, which can be seen in
Table 1.
On the other hand, Figure 1 shows the circuital equivalent of
the designed antenna. The values of the electrical parameters
are identified in Table 1.
Table 1 Physical and electrical parameters of the designed
isoloop antenna.
Parameter
Value
Unity
Loss Resistance
200
mΩ
RF Power
1.0
W
Bandwidth
64.94
KHz
Efficiency
35.67
%
Loop area
0.50
m2
Radiation resistance
162.81
mΩ
Total loss Resistance
293.64
mΩ
Circumference of the loop
2.51
m
Wavelength percentage
16.88
%
Loop inductance
2.23
µH
Distributed capacitance
6.77
pF
Quality factor (Q)
309.51
--
Adjustment capacitor
28.02
pF
Capacitor’s Voltage
295.72
V
Frequency: 20.1 MHz, Loop Diameter: 0.8 m,
Conductor diameter: 12 mm
Figure 1 Equivalent circuital sketch of the designed
antenna.
The antenna was built from a 3 m copper tube of 1 cm width
for the secondary loop, 60 cm of naked copper wire number
12 caliber for the primary loop, a variable capacitor of 10-
200 pF set on 28 pF, and coaxial cable RG-59 for the
communication with the receptor. For the design, the
maximum work frequency is 30 MHz, in a way that it’s
possible to tune the antenna at 20.1 MHz and, with a λ/4
coupling, the total secondary loop length is 2.53 m [11],
achieving this way the physical parameter of input shown in
Table 1. Consequently, the primary and secondary loop’s
diameter are 16 cm and 80 cm, respectively. In Figure 2 the
built antenna is presented. For the efficiency and bandwidth
calculation the simulation of the designed antenna was
carried out using the software Small Magnetic Loop
Calculator V.1.22A, developed by Steve Yates [17]. As it is
showed in Figure 3, for an operation frequency of 20.1 MHz
a capability of -4.5dB was obtained, with a bandwidth of 60
kHz.
44
Likewise, through the software 4Nec2 of Arie Voors [18],
the radiation patterns in 2 and 3 dimensions were obtained
both for the horizontal and vertical planes.
The result of this simulation is showed in the Figure 4, in
which a radiation pattern very similar to the pattern of the
dipole antenna can be seen, bidirectional in the horizontal
plane and covering all angles in the vertical plane, which
leads to the conclusion that for data recording the antenna
must be located parallel to the movement of Jupiter and it
does not need to be moved to follow the planet in its transit
across the sky vault in the observation period.
Finally, Figure 5 shows the behavior detailed previously
through a tridimensional radiation pattern in which the
maximum gain of the antenna is identified in the parallel
direction to itself.
Figure 2 Final appearance of the designed antenna.
Figure 3 Efficiency (red line) and Bandwidth (blue line)
curves of the antenna as functions of the operation frequency
(20.1 MHz).
Figure 4 Radiation patterns in 2D for the horizontal (red)
and vertical (blue) planes.
45
Figure 5 Tridimensional radiation pattern. Detect that the
maximum gain is reached in the parallel direction to the
antenna.
3. Results
Once the antenna was built (Figure 2) the radiation pattern
was measured by the Cassy Lab module which emits a
sinusoidal signal towards a rotational platform on which the
test antenna is located. Figure 6 shows the collected results.
The green circumference is associated to the received signal
by the system without the antenna (in empty space).
Afterwards the isoloop antenna was permanently installed
and facing the source the radiation pattern was measured,
obtaining the red curve as result. Then, keeping the antenna
fixed and locating it parallel to the source, the blue
circumference pattern was obtained. Finally, activating the
rotation of the antenna through the module platform the
pattern indicated by the black continuous line was obtained.
In this figure, the gain of the antenna remains between -30
and -35 dB throughout all the circumference, which
confirms the omnidirectional behavior of the developed
antenna.
Through the spectrum analyzer MSA700 the received
signals of the antenna were identified, in such a way that by
adjusting the tuning capacitor to the specified value by
design, the antennas resonance was located in 14 MHz, with
a high gain at 20.1 MHz, frequency at which the signals
coming from Jupiter were registered.
Figure 6. Radiation patterns of the developed antenna
measured experimentally. Green: empty. Red: frontal. Blue:
Side. Black: using the rotation platform.
The developed antenna is operating from the start of July of
2015 in the terrace of the Astronomical Observatory of the
University of Technology of Pereira, main office of the
Research Group in Astro-engineering Alfa Orion. The
installation was made in East-West line, with a parallel
orientation to the movement of the planet Jupiter across the
sky vault.
The antenna is currently operative with the receptor Radio
Jove from NASA tuned on 20.1 MHz, the software Radio
SkyPipe for the visualization and the storage of the
registered signals, and the program Radio Jupiter Pro for the
prediction of possible events and the creation of the
observation schedule.
Figure 7 presents the record accomplished by the system of
Jovian activity class A in radio waves, which occurred the
22nd of July of 2015 between 00:44H and 00:46H UTC.
This type of activity is characterized by prominent pikes of
short duration that contrast with the background noise.
46
Figure 7 Registration of Jovian activity class A from the
22nd of July of 2015 between 00:44H and 00:46H UTC.
4. Conclusions
The construction of an antenna of reduced size, compared
with the traditional dipole antennas used for the record of
Jovian activity, was achieved, keeping a similar radiation
pattern and efficient operation at 20.1 MHz. The developed
antenna was installed in the terrace of the Astronomical
Observatory of the University of Technology of Pereira, with
an East-West orientation, parallel to the transit of the planet
Jupiter, using only a vertical area of only 2 m2, in contrast
with the 21m2 required to install a dipole antenna. The built
antenna has a bandwidth of 60 kHz, as a disadvantage
compared with the dipole antennas, given that the reduced
bandwidth does not allow the record of all the emissions of
radiofrequency produced by the Jovian activity, although it
does register the most important, as it is the case of the class
A event presented in Figure 6.
Even though the design demonstrated a tuning capacitance
value of 23 pF, when the signals received by the antenna
were observed through the spectrum analyzer it was detected
that the resonance was located in 14 MHz, with a high gain
at 20.1 MHz, with which in future works the diameters of
primary and secondary loops can be adjusted to match the
frequencies of resonance and the registering signal, in a way
that maximizes the efficiency of the system.
References
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[4] D. Basu and C. J. Banos. “Relation between Jupiter's decametric radio
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Altitudes,IJEST, vol. 4, no. 06, pp. 3029-3038, 2012.
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at 20.1 MHz SAO, Nov, 2009. [Online]. Available:
http://rfrench.org/astro/papers/P143-HET608-RobertFrench.pdf
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frequency radio telescope for Jovian radio emission”, Electromagnetics
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[11] J. L. Lombardero. “Radiotelescopio loop” CPAN-Ingenio, pp. 1-16,
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https://www.i-cpan.es/concurso4/docs/radiotelescopio-loop.pdf
[12] W. Kwon et al., “A magnetic resonant loop antenna to enhance the
operating distance of 13.56 MHz RFID systems”, ISOCC IEEE, pp. 013-
014, 2013.
[13] F. El Hatmi et al. “Magnetic loop antenna for wireless capsule
endoscopy inside the human body operating at 315 MHz: Near field
behavior,MMS IEEE, pp. 81-87, 2011.
[14] H. Martinez and M. R Ghezzi. “La antenna cuadro o Magnetic loop,”
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argentina.com.ar/lu6etj/tecnicos/loop/antena_de_cuadro.htm
[15] J. D. Kraus, Antennas. New Delhi, USA: McGraw Hills, Press 1997.
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[16] N. K. Nikolova, Hamilton, Loop Antennas. Canada, 2014, [Online].
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... Once the J's integrals are found analytically, it is possible to build expansion formulas for the magnetic field straightforwardly with (13). For instance, the φ-component given by Eq. (13) requires to compute the coefficients defined in Eq. (14) via the residue theorem (see Appendix Section 4.1 for a detailed explanation). ...
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Given the rise of satellite television, radio telescopes in the Ku‐band (12–18 GHz) constitute a potential alternative to introduce low‐scale astronomical observatories and amateur astronomers to radio astronomy. In this paper, we show a methodology for the calibration of Ku‐band radio telescopes and the evaluation of the techniques used for the observation of celestial bodies in this frequency range. To reduce the pointing error, we present a method of observation through matrix windows around the Sun. By observing the solar transits, our methodology allows to determine the system temperature, the beamwidth, the gain, the effective area, and the efficiency of the radio telescope. In addition, we developed the Compact Radio Telescope (CRT) software, designed to perform the calibration, and carry out observations. We tested our methodology with the Ku‐band radio telescope of the Observatorio Astronómico of the Universidad Tecnológica de Pereira (OAUTP), Colombia. After observing the Sun and the Moon, we obtained a brightness temperature of 8,600 ± 800 K and 240 ± 50 K, and radiation fluxes of 2,970,000 ± 690,000 Jy and 55,000 ± 10,000 Jy, respectively. These observations demonstrated the usefulness of our methodology and CRT software in the calibration of compact Ku‐band radio telescopes for the observation of celestial bodies in radio waves.
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It is well known that planet Jupiter produces strong radio bursts at decametric wavelengths from regions of temporary radio emission in its magnetosphere. Like the man made radio signals, these signals do interfere in the low frequency radio telescope data while observing a different extraterrestrial source. Identification and characterization of this interfering signal is important in radio astronomy. In most of the radio astronomy sites, spectrum monitoring stations are available for such purposes. These instruments record any strong signal within the band and also aim to locate its position. Depending on the properties of different categories of sources, special modules can be attached to these instruments for obtaining a more detailed picture. These modules can be added at the front end of the instrument using a selector switch and can be connected whenever necessary. Construction of one such module for capturing and recording the Jupiter radio bursts has been described with all the engineering details. It consists of an antenna system followed a receiver ( connected to a spectrum recorder). An improvement in the antenna system has been made as compared to the contemporarily available single antenna Jupiter radio telescopes, thereby enabling to record the radio emissions over a larger period using a fixed beam. The receiver system has been designed to process the low frequency Jovian signals from 18 to 25 MHz. The back end is that of a spectrum monitoring system which serves as an automated data analyzer and recorder. It offers flexibility and various setup choices to the user. The mathematical analysis of the instrument and computed system characteristics have been produced in detail for ease of reproductions, direct use in radio astronomy and future design developments.
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Eleven years of data on decametric radio emission from Jupiter at 18.0, 22.2, and 27.6 MHz are analyzed to determine whether there is any relation between this emission and visible features on the Jovian surface other than the Great Red Spot. A statistically significant correlation is found between the emission and observed peculiar activity in the equatorial zone of the planet. The correlation coefficients and respective significance levels are given for each frequency.
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