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  • 1.
    Fernandez, R.C.
    et al.
    ETSI Aeronáuticos, UPM, Madrid.
    Stenberg, Gustav
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Electric propulsion applications for lunar cargo missions2006Conference paper (Refereed)
    Abstract [en]

    Different nations are currently developing a number of plans to put man back on the moon by 2020. The natural extension of returning humankind to the Moon is to create a permanent presence there. This implies that large amount of cargo must be transported on a regular basis to the Moon, so there is a need to develop new techniques to create an economical way of achieving this goal. The success of the SMART - 1 mission demonstrates Electric Propulsion as a valid propulsion method that can be employed to reduce the amount of propellant needed for the mission. This paper will study the use of Electric Propulsion in order to transport cargo to the moon, and the requirements that such systems will have to fulfill. The main advantage of using Electric Propulsion over traditional liquid/solid propellants is the reduction in the weight budget, due mainly to the reduction in the amount of propellant needed and the use of solar energy as the main power source. Electric Propulsion gives an 1sp higher than liquid or solid propellant rocket engines, with a lower thrust, with a consequent increase in the duration of the mission

  • 2.
    Johansson, Gustav
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Beamforming and timing design issues for a large aperture array radar applied to atmospheric research2009Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis describes the work done by the author during the development of a Large Aperture Array Radar (LAAR) receiver for the EISCAT 3D project. The main focus was on digital beamforming of a bandpass-sampled wide band signal in base-band and the development of a picosecond-level distributed timing system applicable over hundreds of meters.The next generation of atmospheric research radars all have the common goal of increasing their capabilities with improved versatility and dynamic observation capability. Past radars have mostly been capable only of observing a single volume of the atmosphere at one time, thereby limiting scientists to looking only at small-scale phenomena in the ionosphere. By allowing simultaneous observation of multiple volumes with a high level of accuracy, EISCAT 3D will give scientists a new tool for improving our knowledge about Earth's atmosphere.To provide instantaneous coverage of multiple volumes of the ionosphere, it is necessary to have a multiple beam receiver. The goal of the antenna design in this project was to create digitally steered arrays that will provide easy scalability, such as increasing the number of beams, after the arrays have been built, and make the stringent targets of the radar's capabilities achievable.This thesis is divided into introductory chapters and ve attached papers. The introductory chapters describe the background and some of the reasons behind atmospheric research, Incoherent Scatter Radar (ISR) technology and use, and the EISCAT 3D project, speci cally, the technological challenges encountered on the LAAR receiver. The technologies evaluated and implemented in the test array for the EISCAT 3D project are detailed, and the results and conclusions are discussed.The technological investigation showed that digital beamforming and high accuracy timing are critical issues for the EISCAT 3D LAAR. Digital beamforming is necessary primarily due to the large array size and stringent demands on pointing accuracy, which render the use of analog beamforming impractical at best. The inter-element timing error in the array is shown to have a maximum standard deviation of 120 ps. This requirement is set on an array where the distance between two elements can be in the kilometer range. Two different solutions capable of achieving a timing error of less than 25 ps are detailed, as well as digital beamforming lters that have a maximum error of less than 5 ps. In conclusion, it is shown to be possible to build the EISCAT 3D LAAR with technology that exists today.

  • 3. Johansson, Gustav
    et al.
    Borg, Johan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Johansson, Jonny
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Nordenvaad, Magnus Lundberg
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Wannberg, Gudmund
    Swedish Institute of Space Physics.
    Simulation of post-ADC digital beamforming for large aperture array radars2010In: Radio Science, ISSN 0048-6604, E-ISSN 1944-799X, Vol. 45, no RS3001Article in journal (Refereed)
    Abstract [en]

    This paper presents simulations and methods developed to investigate the feasibility of using a Fractional-Sample-Delay (FSD) system in the planned EISCAT_3D incoherent scatter radar. Key requirements include a frequency-independent beam direction over a 30 MHz band centered around 220 MHz, with correct reconstruction of pulse lengths down to 200 ns. The clock jitter from sample to sample must be extremely low for the integer sample delays. The FSD must also be able to delay the 30 MHz wide signal band by 1/1024th of a sample without introducing phase shifts, and it must operate entirely in baseband. An extensive simulation system based on mathematical models has been developed, with inclusion of performance-degrading aspects such as noise, timing error, and bandwidth. Finite Impulse Response (FIR) filters in the baseband of a band-pass-sampled signal have been used to apply true time delay beamforming. It has been confirmed that such use is both possible and well behaved. The target beam-pointing accuracy of 0.06° is achievable using optimized FIR filters with lengths of 36 taps and an 18 bit coefficient resolution. Even though the minimum fractional delay step necessary for beamforming is ∼13.1 ps, the maximum sampling timing error allowed in the array is found to be σ ≤ 120 ps if the errors are close to statistically independent.

  • 4. Johansson, Gustav
    et al.
    Hägglund, Fredrik
    Carlson, Johan E.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Johansson, Jonny
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Picosecond level error detection using PCA in the hardware timing systems for the EISCAT_3D LAAR2010In: Radio Science Bulletin, ISSN 1024-4530, no 333, p. 45-50Article in journal (Refereed)
    Abstract [en]

    While developing the timing system for the receiver arrays for the EISCAT_3D system, several approaches to detect and adjust for timing errors within the array have been explored. The demand on the timing error between all elements in the array is to have a standard deviation of less than 120 ps, thus requiring high quality error detection systems to guarantee radar operation. This paper investigates the qualities of a secondary error detection system based on statistical analysis of captured data. The measurements are assembled with a Signal-to-Noise Ratio (SNR) of -30 dB implying that the elements in a 2112 element array need to be grouped into sub-arrays of 48 elements each. The captured data is then evaluated by Principal Component Analysis (PCA) and averaged over 20,000 measurements, or about half a second. Timing errors between sub-arrays of down to ~120 ps and a percentage of faulty sub-arrays of up to 20% are detectable. As a secondary error detection system PCA is cheap to implement since the only need of the analysis is a small amount of computer time. It also provides a valuable detection system for hardware errors in the primary timing system that can otherwise be hard to find.

  • 5. Johansson, Gustav
    et al.
    Johansson, Jonny
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Delsing, Jerker
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Lindgren, Per
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Öman, Joakim
    Sverige.
    Projekt: ESiS EP2009Other (Other (popular science, discussion, etc.))
    Abstract [sv]

    Sammanfattningsvis är forskningsmålet att optimera kretskortsproduktion för små och medelstora serier. Huvudsakligen handlar det om att undersöka och modellera det termiska systemet mellan kretskort och lödugn. Modellen kommer sedan att användas för att ge bättre konfigurationsparametrar för produktionslinjen. En bra modell kommer inte bara att öka lödningskvalitén och minska antalet kasserade kretskort men kan också även användas för att hitta avvikelser redan i kretskortsdesignen.

  • 6. Johansson, Gustav
    et al.
    Selinder, Johan
    Luleå tekniska universitet.
    Hyyppä, Kalevi
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    DE-Link, an antenna pointing system for stratospheric balloons2005In: ICECS 2005: 12th IEEE International Conference on Electronics, Circuits, and Systems, 2005 : [Gammarth, Tunisia, December 11-14, 2005, Piscataway, N.J: IEEE Communications Society, 2005Conference paper (Refereed)
    Abstract [en]

    The DE-Link attitude determination and pointing system onboard stratospheric balloons provides a low cost, low weight and high accuracy method to increase the efficiency of WLAN communication between balloon and ground station. By determination of the 6-dimensional pose of the balloon gondola in real-time, the WLAN antenna can be pointed toward a known position on the ground. This removes the need for power-consuming omnidirectional antennas. It also gives an improvement in communication speed and reduction of overall weight by the removal of heavy RF power amplifiers. The design uses a combination of GPS receivers, accelerometers and magnetoresistive circuits to determine the absolute attitude and position of the gondola in real-time, and two DC motors to point the antenna in azimuthand elevation directions to compensate for the movements of the gondola. Ground based tests have shown the system to function well with a pointing error of less than ±2 deg.

  • 7.
    Johansson, Jonny
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Borg, Johan
    Larsmark, Mikael
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Lindgren, Tore
    Lundberg Nordenvaad, Magnus
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Business Administration and Industrial Engineering.
    Johansson, Gustav
    Ekman, Jonas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Ståbis, Joel
    Sverige.
    Project: EISCAT 3D2007Other (Other (popular science, discussion, etc.))
  • 8.
    Johansson, Jonny
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Johansson, Gustav
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering.
    Borg, Johan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Larsmark, Mikael
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Lindgren, Tore
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    EISCAT_3D: EISCAT 3D Radar Receiver/Antenna Subsystem Report2009Report (Other academic)
  • 9.
    Stenberg, Gustav
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Advancement of atmospheric research tools2007Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis describes contributions made to improve atmospheric research tools through implementation of modern technologies on existing instruments. The dynamic changes in the atmosphere are ever more evident and the need to monitor them have risen in recent years. To effectively observe these changes, existing atmospheric research tools must be enhanced to provide extended data from different parts of the atmosphere in the form of higher quantity and quality. The computational power of modern electronics are enabling the transition from the analog to the digital realm to progress closer to the physical processes. By doing so, the power of digital signal processing is increasing the capabilities of research tools vastly. New research disciplines that were not achievable in the analog domain are rediscovered and realized in the digital domain. Increased computational power also enables the implementation of more intelligent instrument softwares, allowing applications previously limited to hardware to be implemented in software. The benefit of software realization is, in addition to improved signal processing capabilities, a substantial reduction of upgrade cost, regardless of the reason for the upgrade. In this thesis, it is shown that communication with stratospheric balloons can be improved by implementing an antenna pointing system to provide more bandwidth and range for real-time data acquisition, thus offering more rapid data recovery. This is shown by replacing the existing omni-directional antenna onboard stratospheric balloons with an antenna with a narrower beam, and thereby increase the antenna gain by 260 times. This gain can be used in a trade-off between higher data rates, longer range, and lower weight. It is also shown that by combining the use of band-pass sampling, to reduce data rates, and true time-delay beamforming, realized with FIR-filters, to encapsulate the wide band-width of Incoherent Scatter Radar signals, Large Aperture Array Radars are made feasible. This enables multiple simultaneous beams to be produced, permitting the dynamic behavior of the ionosphere the be recorded through instantaneous observation of multiple volumes of the ionosphere. In consequence of this, the author claims that these improvements lead to increased data quantity and quality, which is the first step toward improved knowledge and understanding of our atmosphere. The importance of that understanding is indisputable; we only have one atmosphere and it affects us all equally.

  • 10. Stenberg, Gustav
    et al.
    Borg, Johan
    Johansson, Jonny
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Wannberg, Gudmund
    EISCAT Scientific Association, Kiruna.
    Simulation of post-ADC digital beam-forming for large area radar receiver arrays2007In: Proceedings: 2006 International RF and Microwave Conference : September 12 - 14, 2006, Putrajaya, Malaysia / [ed] Zaiki Awang, Piscataway, NJ: IEEE Communications Society, 2007, p. 272-276Conference paper (Refereed)
    Abstract [en]

    In order to provide instantaneous three-dimensional radar measurements spanning the entire vertical extent of the ionosphere, the planned EISCAT 3D incoherent scatter radar system includes multiple receive-only antenna arrays, situated at 90-280 km from the main transmit/receive site. These will employ band-pass sampling at ∼80 MHz, with the input signal spectrum contained in the 6th Nyqvist zone. This paper presents simulations and methods used to investigate use of a post-ADC fractional-sample-delay (FSD) system necessary to perform true time-delay beamforming. To test the feasibility and limitations of the system an extensive simulation tool has been developed. The simulation system is implemented in matlab to provide cross-platform compatibility and can be applied to any similar system. Performance degrading aspects such as noise, jitter, bandwidth and resolution can be included in the simulations. The use of FIR-filters in the base-band of a band-pass sampled signal to apply true time-delay beam-forming is shown to be feasible.

  • 11. Stenberg, Gustav
    et al.
    Lindgren, Tore
    Johansson, Jonny
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    A picosecond accuracy timing system based on L1-only GNSS receivers for a large aperture array radar2008In: Proceedings of the 21th International Technical Meeting of the Satellite Division of the Institute of Navigation: ION GNSS 2008, 2008, p. 112-116Conference paper (Refereed)
    Abstract [en]

    During the development of EISCAT_3D, a Large Aperture Array Radar (LAAR), with direct sampling at each antenna element and constituted of up to 16.000 antenna elements, intended for atmospheric research, the need for a highly accurate timing system was recognized. This paper describes the method and test results of a GNSS based timing system on a 300 m scale formed on L1-only GNSS receivers.Simulations have shown that over a distance of 300 m the maximum allowed total timing jitter is 160 ps. This timing jitter is composed of jitter from the clock distribution, local oscillator, ADC and movement of the antenna phase center due to weather conditions. A reasonable assumption is that at most a third of the total jitter is generated in the clock distribution system, i.e. 50 ps. Such accuracy is impossible to achieve with the traditionally often used non-calibrated cable-based clock distribution system, even heating of clock distribution cables can alter the length of the cables to the extent that too large errors are generated, thus the choice to use a GNSS-based clock distribution system that is unaffected by such effects. Other benefits of building a GNSS timing system include lower cost due to reduced amount of coaxial cable throughout the array and the need for building a continuous cable length calibration system that ensures timing accuracy of the distributed clock system to the necessary levels. By dividing the LAAR into small sub-arrays of 9 elements each, the maximum length of the cables distributing the clock is reduced to 4.5 m which is short enough to be calibrated by length approximation only, assuming that the clock distributed to each sub-array is known. Inserting a GNSS receiver at all of these sub-arrays, to provide a clock reference that is unaffected by changing conditions over the array, each sub-array is now timed to the specified accuracy.In general, a GNSS L1-receiver is rated to produce a clock with an error of less than 50 ns, which is about 1000 times too high. However, unique conditions apply to this GNSS timing system that improvs the accuracy, such as:- A local system, i.e. the maximum distance between two GNSS antennas are 300 m which infer all significant atmospheric errors in this application to be common over the array.- A common highly accurate reference clock is distributed to all receivers, which removes the clock drift errors between the receivers.- Software based selection of satellites used for the timing solution to exclude timing errors from different matrices in the position and timing calculations.- All receivers are stationary which allow long integration times, up to 30 min because the time constant of the cable length change in the reference clock distribution is in that order of magnitudes, to improve accuracy- Phase measurements from one satellite only is sufficient to calculate the timing error between the sub-arrays since the relative position of each receiver is known. - No integer ambiguity solution is necessary, again, since the relative position of the receivers is known and the absolute time difference between the receivers is insignificant, only the phase of the distributed clock is important.Satisfying these conditions decreases the clock error from the GNSS receivers sufficiently to reach the necessary levels of accuracy.Each sub-array contains a Voltage Controlled Oscillator (VCO) in which the distributed clock is reproduced and distributed through a Delay Locked Loop (DLL) to the local GNSS receiver, the radar ADCs and a signal injection system located as close to the radar antennas as possible to calibrate the analogue signal path of the system. The purpose of the DLL is to adjust the phase of the reference clock to be equal throughout the array. This is achieved by creating a closed loop feedback from the GNSS receiver to the DLL and adjusting the phase according to the phase differences in the received satellite signals in respect to a reference GNSS receiver. This reference receiver is a high-end receiver which is used in conjunction with purpose specific software to produce information sent to each of the sub-array receivers necessary to calculate the expected phase of local VCO clock. Compared to the actual phase of the VCO, the DLL can now make the necessary adjustments to the reference clock. The information sent is; satellites to use, Doppler-shift, tracking chip and expected phase. This information allow the sub-array receivers to only be capable of tracking a low number of satellites, no more than 6, and using the tracked phase differences to calculate the expected phase of the local VCO. Thus, full capability receivers are not needed, but instead a Digital Signal Processor (DSP) is used with a GNSS RF-frontend to control the DLL and the Automatic Gain Control (AGC) of the RF-frontend.Test measurements have been performed in a real environment during windy winter conditions, clear weather at -10 C and wind speeds up to 20 m/s in gusts, with three antennas placed randomly, but precisely surveyed, at about 5 m distance from each other placed on a rooftop to simulate the conditions in the EISCAT_3D LAAR. IF data from the antennas were collected during a one hour measurement and then post-processed to calculate the expected phase differences between the antennas. These phase differences provide a direct measurement of the accuracy levels attainable. The test results show that when integrating over 15 min, a total clock distribution jitter of less than 50 ps is achievable with simple calculations that can be implemented into a DSP.

  • 12.
    Wannberg, Gudmund
    et al.
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Andersson, H
    EISCAT Scientific Association, Kiruna.
    Behlke, R
    Auroral Observatory, University of Tromsö.
    Belyey, V
    Auroral Observatory, University of Tromsö.
    Bergqvist, Peter
    EISCAT Scientific Association, Kiruna.
    Borg, Johan
    Brekke, A
    Auroral Observatory, University of Tromsö.
    Delsing, Jerker
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Eliasson, L
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Finch, I
    Space Science and Technology Department, Rutherford Appleton Laboratory.
    Grydeland, T
    Auroral Observatory, University of Tromsö.
    Gustavsson, B
    Auroral Observatory, University of Tromsö.
    Häggström, I
    EISCAT Scientific Association, Kiruna.
    Harrison, R.A.
    Space Science and Technology Department, Rutherford Appleton Laboratory.
    Iinatti, T
    EISCAT Scientific Association, Kiruna.
    Johansson, Gustav
    Johansson, Jonny
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Johansson, J
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Hoz, C La
    Auroral Observatory, University of Tromsö.
    Laakso, T
    EISCAT Scientific Association, Kiruna.
    Larsen, R
    EISCAT Scientific Association, Kiruna.
    Larsmark, Mikael
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Lindgren, Tore
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Nordenvaad, Magnus Lundberg
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Markkanen, J
    EISCAT Scientific Association, Kiruna.
    Wolf, I
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    EISCAT_3D - a next-generation European radar system for upper atmosphere and geospace research2010In: Radio Science Bulletin, ISSN 1024-4530, no 332, p. 75-88Article in journal (Refereed)
    Abstract [en]

    The EISCAT Scientifi c Association, together with a number of collaborating institutions, has recently completed a feasibility and design study for an enhanced performance research radar facility to replace the existing EISCAT UHF and VHF systems. This study was supported by EU Sixth-Framework funding. The new radar retains the powerful multi-static geometry of the EISCAT UHF, but will employ phased arrays, direct-sampling receivers, and digital beamforming and beam steering. Design goals include, inter alia, a tenfold improvement in temporal and spatial resolution, an extension of the instantaneous measurement of full-vector ionospheric drift velocities from a single point to the entire altitude range of the radar, and an imaging capability to resolve small-scale structures. Prototype receivers and beamformers are currently being tested on a 48-element, 224 MHz array (the "Demonstrator") erected at the Kiruna EISCAT site, using the EISCAT VHF transmitter as an illuminator.

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