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  • 1.
    Ekman, Jonas
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Lindgren, Tore
    Wickramanayake, Anura
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering.
    Project: Improved measurements of mining induced ground deformations using GPS and SAR techniques2011Other (Other (popular science, discussion, etc.))
    Abstract [en]

    The LKAB SAR project is implemented to measure the subsidence and terrain deformation around the Kiruna iron ore mine and in the Kiruna city area. The LKAB SAR project has two components. One is the monitoring component in which MDA (main contractor) provides the SAR deformation maps to LKAB and the second is the technology transfer component in where MDA provides theoretical and practical knowledge to LKAB so that LKAB can produce deformation maps by their own. And Cranfield University and Luleå University of technology will carryout the LKAB SAR research. During the SAR project it is expected to use “DInSAR” and “CTM” techniques to measure the deformations. By using DInSAR and CTM techniques, LKAB can achieve the required accuracy levels during the summer season but it is likely that the quality and quantity of the measurements will largely differ during winter season (due to the thick snow cover). Similarly, areas which have thick forest cover will prevent radar waves reaching the ground and because of that it is likely the quality and quantity of the measurements will decrease in such areas during the mid summer period. Therefore LKAB is planning to carry out a research program to improve the SAR measurements.

  • 2.
    Hobbs, Stephen
    et al.
    Cranfield University.
    Wickramanayake, Anura
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Sjöberg, Jonny
    Itasca Consultants AB.
    Lindgren, Tore
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Henschel, Michael
    MDA Geospatial Services.
    Fernando, Priya
    EADS, Astrium.
    SAR inteferometry with seasonally changing snow cover2011Conference paper (Refereed)
    Abstract [en]

    Spaceborne radar interferometry is an established and very powerful method of measuring land subsidence over timescales of weeks to years. It has been demonstrated on natural and urban landscapes and is becoming an operational technique with accuracy better than 1 cm yr-1. The technique generally relies on having scatterers (which reflect the radar signal) which have stable properties over the timescale of interest. In some landscapes these scatterers occur naturally. However, at high latitudes there are particular difficulties because of the strong seasonal variation in the landcover – snow cover in particular can vary dramatically over periods of weeks to months – and the satellite orbits have particular features which are not generally significant at lower latitudes. It is unlikely that natural scatterers will be stable over long periods in these areas. The aim of this project is to develop methods of SAR interferometry suitable for use in landscapes with seasonal snow cover. The project has two themes: (1) improved understanding of SAR imaging at high latitudes and the use of interferometry in such landscapes, and (2) the development of artificial radar targets which can provide the necessary stability for long-term surface deformation monitoring. The sponsor runs a large mining operation at high latitudes. The study has a practical focus and is part of a larger project to provide a mining subsidence monitoring service for the sponsor. The project’s aim is to achieve accurate monitoring of subsidence using radar interferometry at high latitudes. Techniques developed should be suitable for operational use. Test site The experiment test site is centred on the town of Kiruna in northern Sweden (67° 51’ N, 20° 13’ E). The ground is covered with snow (to a depth of 1 m or more) from October to May each year, and so the winter and summer periods have very different land cover properties. The site includes the town of Kiruna, a large mine, and areas of natural sparse forest with mainly birch and some coniferous trees up to several metres tall. Datasets Available Several datasets are available to support the research, these include: • GPS measurements from a network of control points • General weather observations • Mapping data for land cover / land use and topography • SAR images at approximately monthly intervals from 2009 (Radarsat-2, using up to 3 satellite tracks for imaging) • A network of corner reflectors across the test area The core data analysis tool is the MDA software package designed for processing Radarsat images (for both backscatter and interferometric products). The key resource for the research is the time series of high resolution SAR images suitable for interferometric processing, which allows seasonal changes in backscatter to be observed directly. Methodology The project requires a mix of simulation and practical design and fieldwork. The main contributions will be in the area of target specification, design and validation. Achievements to date The project started late in 2009 and the main emphasis so far has been to establish the datasets needed for the research. Radarsat-2 images have been acquired and are being processed to derive interferometric products and to register them to standard projections compatible with each other and ancillary data. Field observations complementing the satellite imaging are also being made. Acknowledgements The project is sponsored in full by the LKAB mining company.The project also benefits from technical advice of MDA.

  • 3.
    Isoz, Oscar
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Akos, Dennis
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering.
    Lindgren, Tore
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Sun, Chih-Cheng
    National Cheng Kung University.
    Jan, Shau-Shiun
    National Cheng Kung University.
    Assessment of GPS L1/Galileo E1 interference monitoring system for the airport environment2011In: Proceedings of the 23rd international technical meeting of the Satellite Division of the Institute of Navigation, ION GNSS 2011: Sept. 19 - 23, 2011, Oregon Convention Cener, Portland, Oregon, Manassas, Va: Inst. of Navigation , 2011, Vol. 3, p. 1920-1930Conference paper (Refereed)
    Abstract [en]

    How does the GPS Ll spectrum look like at a commercial airport? How frequently do radio frequency interference (RFI) incidents occur? To answer this, the GPS Ll/Galileo El band was monitored at two different airports for an extended period of time. The monitor stations continuously recorded the noise level using the automatic gain control (AGC) in the frontend. Also, the raw intermediate frequency (IF) signal was recorded at regular intervals as well as when the AGC level dropped below a certain threshold. In this paper the analysis of long-term measurements of the spectrum and AGC level at Luleå Airport outside Luleå, Sweden, and Kaohsiung International Airport in Kaohsiung City, Taiwan, is presented. The results shows that RFI incidents did occur at both airports, although more frequent at Kaohsiung International Airport. The measurements also show that the AGC level is useful in systems monitoring the RFI environment. Importantly, the measured data could be utilized for analyses toward the future introduction of GBAS for civil aviation authorities.

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  • 4.
    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.))
  • 5.
    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)
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    FULLTEXT01
  • 6.
    Kvarnström, Björn
    et al.
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Business Administration and Industrial Engineering.
    Lindgren, Tore
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Ekman, Jonas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Monte Carlo simulation of an radio frequency identification system with moving transponders using the partial element equivalent circuit method2010In: IET Microwaves, Antennas & Propagation, ISSN 1751-8725, E-ISSN 1751-8733, Vol. 4, no 12, p. 2069-2076Article in journal (Refereed)
    Abstract [en]

    When designing an radio frequency identification system it is important to take both the position and the movement of the transponders into account. In this study, a simulation method that enables the description of a complete RFID system including moving and rotating transponders as well as a complex, industrial environment is presented. By using the partial element equivalent circuit method to calculate the magnetic field generated by the reader antenna and describing the transponders using a magnetic dipole, it is possible to use the Monte Carlo method to describe the dynamic behaviour of the complete system. The method is used in this study to describe the difference in performance between two different reader antennas and these results are also compared to measurements of similar systems operating in an industrial environment. The difference in performance between the two systems is similar in both the simulations and the measurements. A small discrepancy was seen between the results from the simulations and the measurements which is for the most part because of the limited read rate of the RFID systems used in the measurements.

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  • 7.
    Lindgren, Tore
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    A partial element equivalent circuit (PEEC) and numerical electromagnetics code (NEC) interface toolbox for Matlab2010Report (Other academic)
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  • 8.
    Lindgren, Tore
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Algorithm development for multistatic GNSS radar technology2007Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Bistatic GNSS radar has received increased attention in recent years within both the radar and the GNSS communities. Its major advantages are that it has complete earth coverage and that more information is available due to the geometric diversity of the transmitters. Also, the receiver in a multistatic radar system does not have to transmit a signal which enables development of low power and low cost equipment. This thesis describes contributions made to multistatic GNSS radar algorithms for surface characterization and object detection. By analyzing the strength and shape of the reflected signal's waveform properties of the surface and the height above ground can be determined. In addition to this primary reflection, transient secondary reflections can be found in bistatic GNSS radar data. These are due to reflections in buildings and other structures only when the geometry between the GNSS satellite, measurement platform, and the reflecting body is correct. An algorithm to detect these reflections and determine the location of the reflecting object has been developed and tested experimentally. Previously, significant effort has been put into develop the synthetic aperture radar (SAR) theory to include the bistatic situation. These algorithms are here developed further into a more generic multistatic GNSS SAR system for surface characterization. This is done by using range and doppler processing techniques on signals transmitted by multiple satellites to determine the angular dependence of the surface reflectivity. The developed algorithm have also been tested experimentally.

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  • 9.
    Lindgren, Tore
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Characterization problems in radio measurement systems2009Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Radio measurement systems may have their performance significantly degraded due to environmental factors such as multipath, weather effects, and mechanical displacements. Characterization of these effects are therefore important in order to ensure functionality of the system. The characterization itself may also be the purpose of the system. This thesis contributes to the answer to the question of how to assess the effect of the environment on the propagation and reception of radio waves for three different applications.Traditionally the functionality of a radio measurement system has been assessed using either simulations assuming ideal conditions (e.g. free space) or measurements under controlled circumstances. There is no doubt that both these approaches are very useful when designing antennas and related hardware. In many applications it is also sufficient to assume ideal conditions and only use an a priori characterization. The applications considered in this thesis all operates in an environment that can be considered to be challenging. In these cases the environment needs to be taken into account in the design process of the system. Both simulations and measurement methods have been considered. The combination of electromagnetic simulation methods, such as the method of moments (MOM) or the partial element equivalent circuit (PEEC) method, with statistical methods, such as the Monte Carlo method, have been given special attention. The measurement systems considered, both for determining the performance of antennas and for detection of objects and transponders, are all assessed from a "challenging environment" point of view.The three application considered are multistatic radar using global navigation satellite systems (GNSS), measurement systems for antenna arrays in noisy conditions, and simulation of RFID systems with moving transponders. In the multistatic radar the focus is on detecting signals reflected in directions other than that of the primary reflection. The results shows that detecting these signals is possible even with the low signal levels involved. This is especially the case when reflecting objects are present which could scatter the signal in a specular way. By using the equivalent electric current method it is possible to estimate the complex far-field radiation pattern of antenna arrays even when the signals used have a low signal-to-noise ratio (SNR). This has been shown using simulation of a large antenna array and with measurements using a small array for GNSS receivers. When designing RFID systems it is important to be able to estimate the performance in terms of number of detected transponders with all movements of the transponders taken into account. This is possible by using a very simple model of the transponders (e.g. a magnetic dipole) in which case only one electromagnetic simulation is needed. This enables the use of the Monte Carlo method to take the random movements of the transponders into account using a low number of computations. The use of the PEEC method further enables a combined simulation of both the electromagnetic properties of the reader antenna and the electric functionality of the receiver circuit.Although the considered application are very different the obtained solutions are in many ways general. The fact that even the weak signals reflected in non-specular directions in a multi-static GNSS radar can be detected can be used in any application involving multi-path propagation or stray signals. The equivalent electric current method have here been considered for two radically different antenna arrays operating in a low SNR environment. Although the simulation approach chosen for the RFID simulations rely heavily on the simple magnetic dipole method it would work with any antenna at any frequency as long as the model of the antenna is sufficiently simple.

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  • 10.
    Lindgren, Tore
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Tradeoff between complexity and performance in measurement systems for large antenna arrays2011Conference paper (Refereed)
    Abstract [en]

    n this paper different calibration methods for large antenna arrays subject to random errors in position and phase are compared. The results shows that the gain loss is reduced when more sophisticated calibration systems are used while the beam is broadned if the position error is measured using one probe.

  • 11.
    Lindgren, Tore
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Akos, Dennis
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering.
    A multistatic GNSS synthetic aperture radar for surface characterization2008In: IEEE Transactions on Geoscience and Remote Sensing, ISSN 0196-2892, E-ISSN 1558-0644, Vol. 46, no 8, p. 2249-2253Article in journal (Refereed)
    Abstract [en]

    Bistatic global navigation satellite system (GNSS) radar has received increased attention in recent years within both the radar and GNSS communities. In this paper, the traditional bistatic GNSS radar and bistatic synthetic aperture radar (SAR) concepts are fused into a more generic multistatic GNSS SAR system for surface characterization. This is done by using the range and Doppler processing techniques on signals transmitted by multiple satellites to determine the angular dependence of the surface reflectivity. The method has also been tested experimentally, and the results are presented.

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    FULLTEXT01
  • 12.
    Lindgren, Tore
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Akos, Dennis
    Non-specular point reflections in GNSS bistatic radar2006Conference paper (Refereed)
    Abstract [en]

    In this paper the impact of using different measurement platforms with different qualities is discussed. Data collected during three different measurement campaigns were used in this study. The data collected over Iowa, USA, in July, 2005, which were from a low flying airplane (low altitude and high dynamics), a data set collected from a stratospheric balloon outside Boulder, USA, in April, 2006 (high altitude, low dynamics), and a data set collected at the Boulder Atmospheric Observatory (BAO) outside Boulder, USA, in April, 2006 (low altitude, stationary).

  • 13.
    Lindgren, Tore
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Backén, Staffan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Akos, Dennis
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering.
    Estimation of the complex far-field of an antenna array using live GNSS signals and the equivalent electric current method2009In: Proceedings of the 13th IAIN World Congress, Stockholm, 27-30 October 2009, Nordic Institute of Navigation , 2009Conference paper (Refereed)
    Abstract [en]

    When using antenna arrays with GNSS receivers both the gain and the phase of the far-field radiation pattern may be distorted due to coupling effects. This problem can often be characterized in the design process of the antenna or by measurements in a measurement range. This is, however, not always possible and it is then necessary to characterize the antenna using live measurements. In this paper the equivalent electric current method is used to estimate the gain and phase of the far-field of an antenna array for a GPS receiver. In the method, the complex far-field pattern of an antenna is estimated using the distribution of the electric current, which is described using suitable basis functions. The method was evaluated using data collected by a 7-element GPS antenna array. The results show agreement between the model and measured results.

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  • 14.
    Lindgren, Tore
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Borg, Johan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    A measurement system for the position and phase errors of the elements in an antenna array subject to mutual coupling2012In: International Journal of Antennas and Propagation, ISSN 1687-5869, E-ISSN 1687-5877, Vol. 2012, article id 526121Article in journal (Refereed)
    Abstract [en]

    When deploying large antenna arrays in arctic environments, a local measurement system may be necessary in order to ensure control over the position and phase of the individual antenna elements. In this paper, a method of estimating the position and phase of each individual antenna element in the presence of mutual coupling is presented. It uses both measurements of the scattering matrix in the array and measurements of the electric field using a minimum of four probes located in the near field of the array. Simulations show that the method gives accurate results even in the presence of noise in the measurements. The geometry of the probe-array system affects the performance significantly.

  • 15.
    Lindgren, Tore
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Ekman, Jonas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Design and evaluation of RFID systems using the partial element equivalent circuit method2008In: Proceedings of the International Symposium on Antenna and Propagation: ISAP 2008, Chinese Microwave Association , 2008Conference paper (Refereed)
    Abstract [en]

    Systems based on radio frequency identification (RFID) techniques are finding new markets and uses. For maximal readability, RFID-systems have to be tailored to its specific environment. In this paper, the partial element equivalent circuit (PEEC) method is used to analyze an RFID-system with reader, tag, and additional electronic circuitry. The results show how the method can be used to match antennas with discrete, external components and study the backscattered energy from the tag. The simulations are very fast which allows for studying multiple locations of the tag in order to tailor the RFID-system.

  • 16.
    Lindgren, Tore
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Ekman, Jonas
    Performance of a Yagi antenna during snowfall2008In: Proceedings of the International Symposium on Antenna and Propagation: ISAP 2008, Chinese Microwave Association , 2008Conference paper (Refereed)
    Abstract [en]

    Precipitation in the form of snow could severely degrade the performance of the planned EISCAT_3D radar antenna array. In this paper the performance of the antenna elements, crossed yagi antennas, is studied using both simulations and measurements. The results shows that during snowfall the performance of the antenna is degraded, and under severe conditions the antenna becomes non-operational. To guarantee operability of the system, the effect of snow cover should be taken into account when designing the final antenna.

  • 17.
    Lindgren, Tore
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Ekman, Jonas
    Backén, Staffan
    A measurement system for the complex far-field of physically large antenna arrays under noisy conditions utilizing the equivalent electric current method2010In: IEEE Transactions on Antennas and Propagation, ISSN 0018-926X, E-ISSN 1558-2221, Vol. 58, no 10, p. 3205-3211Article in journal (Refereed)
    Abstract [en]

    Precipitation in the form of snow or rain could severely degrade the performance of large antenna arrays, in particular if knowledge about the beam shape and pointing direction in absolute numbers is necessary. In this paper, a method of estimating the far-field of each individual antenna element using the equivalent electric current approach is presented. Both a least squares estimator and a Kalman filter was used to solve the resulting system of equation and their performance was compared. Simulation results shows that the estimated far-field for one antenna element is very accurate if there is no noise on the signal. During noisier conditions the Kalman filter gives less noisy results while the systematic errors are slightly larger compared to the least squares estimator.

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  • 18.
    Lindgren, Tore
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Soutodeh, Omid
    Kildal, Per-Simon
    Study of cluster of hard horns feeding an offset multi-beam reflector antenna for dual band operation at 20/30 GHz2004In: 2004 digest: IEEE Antennas and Propagation Society international symposium : June 20 - 25, 2004, Monterey, California; held in conjunction with USNC/URSI National Radio Science Meeting, Piscataway, NJ: IEEE Communications Society, 2004, Vol. 3, p. 3015-3018Conference paper (Refereed)
    Abstract [en]

    The study of a multibeam reflector antenna system with hard horn feeds is extended to include the defocusing effects encountered in the actual cluster. This is done by using the ARECIBO code, a reflector program for analysis of multi-reflector antennas. There are many different analysis models for offset reflectors implemented in ARECIBO. The one used for the present study is aperture integration after Fourier series expansion of the aperture field. This is fast and accurate within main beam and first sidelobes, but it is of course slow compared to the BOR model.

  • 19.
    Lindgren, Tore
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Vinande, Eric
    University of Colorado, Boulder.
    Akos, Dennis
    Masters, Dallas
    University of Colorado, Boulder.
    Axelrad, Penina
    University of Colorado, Boulder.
    Measurement of backscattered GPS signals2006In: Position, Location, and Navigation Symposium, IEEE Communications Society, 2006, p. 664-669Conference paper (Refereed)
    Abstract [en]

    This paper describes a technique utilizing GPS ground reflections (GPS bistatic radar) to detect objects with a significant radar cross section located on the surface of the earth. GPS bistatic radar has been shown to be effective as a radar altimeter and for characterization of the reflection surface but has thus far not been shown to be effective for object detection. The technique uses ground reflections with longer path delay than the shortest path specular reflection. Data was collected using a COTS software receiver and post-processed using an in-house tool. Regions with ground reflections were overlayed on aerial imagery to identify possible sources.

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  • 20.
    Norton, Amanda
    et al.
    University of Colorado, Boulder.
    Lindgren, Tore
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Akos, Dennis
    A study of bistatic GNSS radar2006In: GIS development: Asia Pacific edition, Vol. 10, no 6Article in journal (Other (popular science, discussion, etc.))
    Abstract [en]

    One of the more recent areas of GNSS research of increasing popularity is the study of reflected GNSS signals. This will enable the use of GNSS as a passive radar system that can be used as an alternative to radar altimetry and for ground feature characterization. Of interest is also the possibility to use GNSS signals for object detection. The advantage of using GNSS signals as a passive radar system is that it has complete earth coverage. The signals are, however, weak and the computational load associated with the analysis is heavy.

  • 21.
    Sotoudeh, Omid
    et al.
    Chalmers University of Technology.
    Kildal, Per-Simon
    Chalmers University of Technology.
    Ingvarsson, Per
    Saab Ericsson Space.
    Lindgren, Tore
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Fast and accurate parametric studies of alternative feeds for offset multibeam antennas by assuming rotationally symmetric geometries (BOR1 modelling)2003In: Proceedings of ESA Antenna Technical Workshop on Satellite, Antenna Modelling and Design Tool, 2003, p. 255-261Conference paper (Other academic)
  • 22. 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.

  • 23.
    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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