research article first radio astronomy examination of the low...

Research ArticleFirst Radio Astronomy Examination of the Low-FrequencyBroadband Active Antenna Subarray

A A Stanislavsky1 I N Bubnov1 A A Konovalenko1 A A Gridin1

V V Shevchenko1 L A Stanislavsky2 D V Mukha1 and A A Koval1

1 Institute of Radio Astronomy 4 Chervonopraporna Street Kharkiv 61002 Ukraine2 Kharkiv Radio Engineering College 1820 Sumskaya Street Kharkiv 61057 Ukraine

Correspondence should be addressed to A A Stanislavsky astexukrnet

Received 26 January 2014 Accepted 19 March 2014 Published 8 April 2014

Academic Editor Dieter Horns

Copyright copy 2014 A A Stanislavsky et al This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

We present the 25-element active antenna array and its remote control in the framework of the GURT project the Ukrainian RadioTelescope of a new age To implement beamforming the array is phased with the help of discrete cable delay lines in analogmannerThe remote control of the array is carried out through the paired encoder and decoder that can transmit parallel data about antennacodes serially The microcontroller provides the online interaction between personal computer and beamformers with the help ofthe encoder-decoder system through wires or wireless The antenna pattern has been measured by radio astronomy methods

1 Introduction

The discovery of cosmic radio signals by Karl Jansky wasstarted with low frequencies (more precisely 205MHz)[1] Although the low-frequency technology was easier toimplement radio astronomy migrated to higher frequen-cies together with the development of technology This isexplained by crucial disadvantages of longer wavelengths inspatial resolution of antennas proportional to a wavelengthand because of ionospheric effects limiting radio observationquality as well as the ionospheric cut-off below 10MHzNevertheless low-frequency cosmic radio emission containsexclusive information about the universe In particular thereis a wide range of astrophysical problems accessible forstudies only at low radio frequencies (sim10ndash100MHz) [2]the epoch of reionization (to search emission from the firststars and galaxies) transient phenomena and others Forthis purpose the low-frequency astronomy continues to bedeveloped fruitfully in our days One aspect of this progressis to build a low-frequency antenna array with excellentsensitivity and high spatial resolution This trend becomesa reality in new radio telescopes such as the LOFAR (TheNetherlands) [3] E-LOFAR (LOFAR stations in Europe)

LWA (USA) [4] and MWA (Australia) [5] Similar project isrealized in France (LSS-LOFAR Super Station) [6] as well asin Ukraine (Giant Ukrainian Radio Telescope (GURT)) [7]The implementation of new effective systems for steering theantenna arrays is the key point in such scientific programs

2 The GURT Project

The GURT radio telescope will operate as a large arrayconsisting of many identical subarrays The construction isin progress Now we have built 9 subarrays (one of them isrepresented in Figure 1) and in perspective the number ofsubarrayswill increase to reach about 100 covering the area of2 square kilometers Each of the subarrays is a square regularantenna array using active dipole techniques It includes 5 times5 wideband active (with preamplifier) dipoles All turnstileantenna elements are mounted at a height of 16m above theground

Active antennas give some very useful advantages incomparison with passive ones In particular below about30ndash40MHz where the external (Galactic) noise exceeds theinternal one considerably shortening the radiator length of

Hindawi Publishing CorporationAdvances in AstronomyVolume 2014 Article ID 517058 5 pageshttpdxdoiorg1011552014517058

2 Advances in Astronomy

Figure 1 Active antenna array of 5 times 5 elements as a basic part ofthe GURT radio telescope

a tuned antenna does not affect the signal-to-noise ratio at theantenna output but shortening the radiator will dramaticallychange its input impedance and therefore the preamplifiertransforms the dipole impedance back to the cable oneThusthe length of a short-wave antenna can be reduced notice-ably The dipole and preamplifier permit us to obtain themaximum possible ratio between the antenna temperaturedue to Galactic noise 119879sky and the noise temperature of thepreamplifier 119879pre that is 10 log 119879sky119879pre asymp 10 dB over thewhole 10 to 70MHz range [8] To implement beamformingthe subarray is phased with the help of discrete cable delaylines (analog beamformer) Next the signals received by suchsubarrays will be digitized and transferred to the centralcomputer for subsequent phasing and data processing Thedual polarization dipoles of the GURT radio telescope areoptimized for operation at 10ndash70MHz to have a steady (noresonance) frequency response In this paper we are going toconsider only constructive features of one separate subarray(for short array) and its remote control

The main parameters of the active antenna array are thefollowing

(i) array step equal to 375m(ii) electric scan sector plusmn766∘ from the zenith in both

coordinates(iii) array size 1875 times 1875m

(iv) effective area 275m2(v) beamwidth 25∘ times 25∘ in the mid-frequency range at

40MHz(vi) antenna amplifier dynamic range gt 90 dB relative to

1 120583V

For each polarization the turnstile antenna element has itsown independent beam steering system and the system isidentical for both polarizations

3 Beam Steering System

Figure 2 shows the functional block diagram of the active an-tenna array describing its beam steeringThe system providesremote automatically changes in the orientation of the main

Table 1 Beamformer codes and beam angles from the zenith

Codes Beam position NU NV01000 minus766∘ minus801001 minus583∘ minus701010 minus469∘ minus601101 minus374∘ minus500100 minus291∘ minus400111 minus214∘ minus300010 minus14∘ minus200001 minus7∘ minus100000 0∘ 011000 766∘ 811001 583∘ 711110 469∘ 611111 374∘ 511100 291∘ 410101 214∘ 310110 14∘ 210011 7∘ 1

beam lobe position in two planes by a given program Thebeam steering device of the array consists of 6 identical 5-bit beamformers Firstly signals of 5 active dipoles in a roware phased and summed in 119906 coordinate and then the sixthbeamformer is used for phasing the array in V coordinateThe discrete time delay lines of beamformers are coaxial cablesegmentsThe devices switching the lines are high-frequencyrelays The isolation of the radio frequency circuits and thedigital control equipment is carried out by optocouplers Eachbeamformer provides 17 beam positions (see Table 1)

The basic parameters of the beamformer were measuredand show its good quality as follows

(i) frequency range 10ndash70MHz(ii) voltage standing wave ratio (VSWR) le 14(iii) maximum loss on the upper frequency le 3 dB(iv) isolation between any two inputs ge 30 dB(v) maximum phase error relative to the calculated valuele 5

To manage the beam steering it is necessary to supply 5-bitcontrol signals from a remote control system to beamformersof the antenna array through wires or wireless

4 Remote Control

The remote control system (Figure 3) of the array is basedon the paired encoder and decoder to transmit 20 bits ofantenna codes (5 bits of NU and 5 bits of NV in twopolarizations) As an encoder-decoder pair we used chipsHT12E and HT12D made by ldquoHoltek Semiconductorsrdquo Theencoder chip takes parallel data and converts them into serialdataThe decoder does the oppositeThe two devices are veryuseful in implementing a communication protocol Encodersends a packet and decoder receives it Each packet has its

Advances in Astronomy 3

Analogbeamformer

Analogbeamformer

Analogbeamformer

Analogbeamformer

Analogbeamformer

Analogbeamformer

Output

Figure 2 Block diagram of the active antenna array in one polarization Red triangles denote amplifiers

address (8 bits) and data (4 bits) But the packet is acceptedby the decoder if only the encoder address is equal to thedecoder one Otherwise the decoder saves a previous stateobtained from a true packet The encoder chip can transmitonly 4 bits of data To transmit 20 bits of antenna code datawe divide them into five independent packets with differentaddresses serially The remote control is implemented frompersonal computer through microcontroller where the USBport is configured as aVirtual COMPort For reliability whenthe computer sends 20-bit data to microcontroller we use aspecial protocol It has two delimiters in the beginning and inthe end of each parcel to protect the sent data from possiblerandom errors during the data exchange The two delimitersare different and fixed The special protocol assumes 7characters Immediately behind the start delimiter we passfive characters (data about antenna codes) in hexadecimalnotation Final seventh character is another delimiter Themicrocontroller serves as an interface device between theencoder and the computer The latter calculates the antennacodes NU and NV to track a cosmic object according to itssky coordinates

NU = minusround [8 cos 120575 sin 119905sin |120579|

]

NV = minusround [8 (0762 cos 120575 cos 119905 minus 0647 sin 120575)sin |120579|

]

(1)

where 119905 is the hour angle 120575 the declination and 120579 denotesthe maximum possible angle of the antenna beam inclinationfrom the zenith (see the upper row of Table 1) The normal-ization coefficient sin |120579| characterizes a view field of thisantenna array By using the second paired encoder-decoderthe antenna array informs the microcontroller and the uservia his personal computer about the codes obtained by thearray The feedback defends the antenna applying againstany false switching in the process of tracking cosmic objects(Figure 3)

5 Testing in Real Observations

Traditionally power patterns of antennas in radio astronomyare examined by using calibrator sources such as the SunCas-siopeia A or other bright radio sources [9] However thesesources only traverse a limited range of sky and require thatthe radio telescope in question would be steered Fortunatelyour array possesses such capabilities Figure 4 is a chart ofthe radio source Cassiopeia A taken when the rotation ofthe Earth moved the beam of our active antenna array across


Personalcomputer

Microcontroller

Encoder

Encoder

Decoder

Decoder

Antenna beamformers

Figure 3 Block diagram of the remote control system for the activearray

this region of the sky The radio source size is a point forthis antenna pattern and its signal capture width is equal tothe width of the main lobe taking into account the sourcevelocity on the sky To improve the signal-to-noise relation ingetting the antenna array pattern properties the correlationmethod is very useful [10] In this case a reference antenna(eg another antenna array) is permanently directed in thechosen cosmic radio source following it and the pattern ofthe tested antenna scans relative to this source Both antennasare connected to a two-channel correlation receiver formingthe interferometer Consequently we can observe not only themain lobe of this tested array but also its nearest sidelobes Infact the correlation method considerably reduces the impactof radio disturbances and the distributed radiation of galacticbackground noise The records were obtained by using aspecial two-channel wideband digital receiverspectrometer[11] It works in the band 0ndash33MHz with the samplingfrequency of 66MHz The maximal resolution in frequencyand in time is about 4 kHz and 1ms respectively Usinghigh-resolution analog to digital conversion in 16 bits thespurious-free dynamic range (SFDR) of this device is about112 dBc (decibels relative to the carrier) The detection ofradio astronomy signals above 33MHz was realized byundersampling (or in other words bandpass sampling) thesignals

During July-August of 2013 the remote control devicehas been tested in real radioastronomical observations ofradio emission from the Sun Jupiter radio sources and

minus100

minus102

minus104

minus106

minus108

minus112

minus110

minus114

minus116

Relat

ive i

nten

sity

(dB)

0 20 40 60 80 100120572 (deg)

Figure 4 Strip chart of Cassiopeia A passing through the antennaarray pattern due to the Earthrsquos rotation at 57105MHz The angle120572 = V

120575

119905 is proportional to the travel time 119905 of Cassiopeia A and thesource velocity on the celestial sphere for the declination 120575 is definedas V120575

= 15(

10158401015840

sec) cos 120575 in angular seconds per (time) second

others Preliminary results have shown that with help ofthe above-mentioned remote control system the procedureof radio astronomy observations has become easier andmore effective The detailed astrophysical analysis of theobservations will be reported elsewhere

6 Conclusion

We have reported some results about the active antenna arrayand its remote control system that was carried out in theframework of the radio telescope building of a new genera-tionWehave shown that the progress in computer and digitaltechnology opens wide doors in the development of thebest antenna arrays for low-frequency radio astronomy Thecurrent conjunction of the parameters of GURT subarraysand back-end facilities meets modern requirements of radioastronomy at the frequency range 10ndash70MHz This allows usto use different observational modes (tracking scans on-offand others) including synchronized observations togetherwith other radio telescopes

Conflict of Interests

The authors declare that there is no conflict of interests re-garding the publication of this paper

Acknowledgment

This research was partially supported by Research grantldquoSynchronized simultaneous study of radio emission of solarsystem objects by low-frequency ground- and space-basedastronomyrdquo from the National Academy of Sciences ofUkraine


References

[1] T L Wilson ldquoTechniques of radio astronomyrdquo in Planets Starsand Stellar Systems T D Oswalt andH E Bond Eds vol 2 pp283ndash323 Springer Dordrecht The Netherlands 2013

[2] S M White N E Kassim and W C Erickson ldquoSolarradioastronomy with the LOFAR (LOw Frequency ARray)radio telescoperdquo in Innovative Telescopes and Instrumentationfor Solar Astrophysics vol 4853 of Proceedings of SPIE pp 111ndash120 Waikoloa Hawaii USA August 2002

[3] N E Kassim T J W Lazio P S Ray et al ldquoThe low-frequencyarray (LOFAR) opening a new window on the universerdquoPlanetary and Space Science vol 52 no 15 pp 1343ndash1349 2004

[4] S W Ellingson T E Clarke A Cohen et al ldquoThe longwavelength arrayrdquo Proceedings of the IEEE vol 97 no 8 pp1421ndash1430 2009

[5] S J Tingay R Goeke J D Bowman et al ldquoThe MurchisonWidefield array the square Kilometre array precursor at lowradio frequenciesrdquo Publications of the Astronomical Society ofAustralia vol 30 article e007 21 pages 2013

[6] P Zarka J N Girard M Tagger and L Denis ldquoLSSNenuFARthe LOFAR super station project in Nancayrdquo in SF2A-2012Proceedings of the Annual Meeting of the French Society ofAstronomy and Astrophysics S Boissier P de Laverny NNardetto R Samadi D Valls-Gabaud and H Wozniak Edspp 687ndash694 2012

[7] A A Konovalenko I S Falkovich N N Kalinichenko et alldquoThirty-element active antenna array as a prototype of a hugelow-frequency radio telescoperdquo Experimental Astronomy vol16 no 3 pp 149ndash164 2003

[8] I S Falkovich A A Konovalenko A A Gridin et al ldquoWide-band high linearity active dipole for low frequency radioastronomyrdquo Experimental Astronomy vol 32 no 2 pp 127ndash1452011

[9] J D Kraus Radio Astronomy McGraw-Hill New York NYUSA 1967

[10] A V Kalinin V P Malrsquotsev and K S Shcheglov ldquoInvestigationof the characteristics of a large reflector antenna via a corre-lation radioastronomical methodrdquo Journal of CommunicationsTechnology and Electronics vol 52 no 5 pp 510ndash526 2007

[11] R V Kozhyn V V Vynogradov and D M Vavriv ldquoLow-noisehigh dynamic range digital receiverspectrometer for radioastronomy applicationsrdquo in Proceedings of the 6th InternationalKharkov Symposium on Physics and Engineering of MicrowavesMillimeter and Submillimeter Waves and Workshop on Tera-hertz Technologies (MSMW rsquo07) vol 2 pp 736ndash738 KharkovUkraine June 2007

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

High Energy PhysicsAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014


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Hindawi Publishing Corporationhttpwwwhindawicom

AerodynamicsJournal of

Volume 2014


PhotonicsJournal of


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ThermodynamicsJournal of


Figure 1 Active antenna array of 5 times 5 elements as a basic part ofthe GURT radio telescope

a tuned antenna does not affect the signal-to-noise ratio at theantenna output but shortening the radiator will dramaticallychange its input impedance and therefore the preamplifiertransforms the dipole impedance back to the cable oneThusthe length of a short-wave antenna can be reduced notice-ably The dipole and preamplifier permit us to obtain themaximum possible ratio between the antenna temperaturedue to Galactic noise 119879sky and the noise temperature of thepreamplifier 119879pre that is 10 log 119879sky119879pre asymp 10 dB over thewhole 10 to 70MHz range [8] To implement beamformingthe subarray is phased with the help of discrete cable delaylines (analog beamformer) Next the signals received by suchsubarrays will be digitized and transferred to the centralcomputer for subsequent phasing and data processing Thedual polarization dipoles of the GURT radio telescope areoptimized for operation at 10ndash70MHz to have a steady (noresonance) frequency response In this paper we are going toconsider only constructive features of one separate subarray(for short array) and its remote control

The main parameters of the active antenna array are thefollowing

(i) array step equal to 375m(ii) electric scan sector plusmn766∘ from the zenith in both

coordinates(iii) array size 1875 times 1875m

(iv) effective area 275m2(v) beamwidth 25∘ times 25∘ in the mid-frequency range at

40MHz(vi) antenna amplifier dynamic range gt 90 dB relative to

1 120583V

For each polarization the turnstile antenna element has itsown independent beam steering system and the system isidentical for both polarizations

3 Beam Steering System

Figure 2 shows the functional block diagram of the active an-tenna array describing its beam steeringThe system providesremote automatically changes in the orientation of the main

Table 1 Beamformer codes and beam angles from the zenith

Codes Beam position NU NV01000 minus766∘ minus801001 minus583∘ minus701010 minus469∘ minus601101 minus374∘ minus500100 minus291∘ minus400111 minus214∘ minus300010 minus14∘ minus200001 minus7∘ minus100000 0∘ 011000 766∘ 811001 583∘ 711110 469∘ 611111 374∘ 511100 291∘ 410101 214∘ 310110 14∘ 210011 7∘ 1

beam lobe position in two planes by a given program Thebeam steering device of the array consists of 6 identical 5-bit beamformers Firstly signals of 5 active dipoles in a roware phased and summed in 119906 coordinate and then the sixthbeamformer is used for phasing the array in V coordinateThe discrete time delay lines of beamformers are coaxial cablesegmentsThe devices switching the lines are high-frequencyrelays The isolation of the radio frequency circuits and thedigital control equipment is carried out by optocouplers Eachbeamformer provides 17 beam positions (see Table 1)

The basic parameters of the beamformer were measuredand show its good quality as follows

(i) frequency range 10ndash70MHz(ii) voltage standing wave ratio (VSWR) le 14(iii) maximum loss on the upper frequency le 3 dB(iv) isolation between any two inputs ge 30 dB(v) maximum phase error relative to the calculated valuele 5

To manage the beam steering it is necessary to supply 5-bitcontrol signals from a remote control system to beamformersof the antenna array through wires or wireless

4 Remote Control

The remote control system (Figure 3) of the array is basedon the paired encoder and decoder to transmit 20 bits ofantenna codes (5 bits of NU and 5 bits of NV in twopolarizations) As an encoder-decoder pair we used chipsHT12E and HT12D made by ldquoHoltek Semiconductorsrdquo Theencoder chip takes parallel data and converts them into serialdataThe decoder does the oppositeThe two devices are veryuseful in implementing a communication protocol Encodersends a packet and decoder receives it Each packet has its


Analogbeamformer

Analogbeamformer

Analogbeamformer

Analogbeamformer

Analogbeamformer

Analogbeamformer

Output




]


]

(1)





Personalcomputer

Microcontroller

Encoder

Encoder

Decoder

Decoder

Antenna beamformers




minus100

minus102

minus104

minus106

minus108

minus112

minus110

minus114

minus116

Relat

ive i

nten

sity

(dB)

0 20 40 60 80 100120572 (deg)


120575


= 15(

10158401015840



6 Conclusion




Acknowledgment



References

















FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics




Analogbeamformer

Analogbeamformer

Analogbeamformer

Analogbeamformer

Analogbeamformer

Analogbeamformer

Output




]


]

(1)





Personalcomputer

Microcontroller

Encoder

Encoder

Decoder

Decoder

Antenna beamformers




minus100

minus102

minus104

minus106

minus108

minus112

minus110

minus114

minus116

Relat

ive i

nten

sity

(dB)

0 20 40 60 80 100120572 (deg)


120575


= 15(

10158401015840



6 Conclusion




Acknowledgment



References

















FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics




Personalcomputer

Microcontroller

Encoder

Encoder

Decoder

Decoder

Antenna beamformers




minus100

minus102

minus104

minus106

minus108

minus112

minus110

minus114

minus116

Relat

ive i

nten

sity

(dB)

0 20 40 60 80 100120572 (deg)


120575


= 15(

10158401015840



6 Conclusion




Acknowledgment



References

















FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics




References

















FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics








FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics



research article first radio astronomy examination of the low...

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