| 1. |
- Johansson, Gustav, et al.
(author)
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Picosecond level error detection using PCA in the hardware timing systems for the EISCAT_3D LAAR
- 2010
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In: Radio Science Bulletin. - 1024-4530. ; :333, s. 45-50
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Journal article (peer-reviewed)abstract
- 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.
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| 2. |
- Maaskant, Rob, 1978, et al.
(author)
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Multi-level characteristic basis function method (MLCBFM) for the anaylsis of large antenna arrays
- 2011
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In: Radio Science Bulletin. - 1024-4530. ; 336:3, s. 23-34
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Journal article (peer-reviewed)abstract
- A multi-level version of the Characteristic Basis Function Method (CBFM) is presented for computing the input impedance matrix and radiation patterns of very large antenna arrays. Specifically, we consider the challenging problem of an electrically large subarray that is surrounded by (many) other disjoint subarrays, and solve this problem by employing a two-level Characteristic Basis Function Method. At level zero, Rao-Wilton-Glisson (RWG) basis functions are employed to locally synthesis the surface current. Next, the number of degrees of freedom (DoFs) for the current is reduced at level one by employing the characteristic basis functions (CBFs), each of which is a macro basis function supported by an antenna element, and is a fixed combination of RWG basis functions. Moreover, the characteristic basis functions at level two are supported by subarrays to further reduce the degrees of freedom. This multilevel approach is memory efficient and generates a final reduced matrix equation that can be solved directly, i.e., in-core through standard Gaussian elimination techniques, even though the conventional MoM (Method of Moments) formulation of the same problem may require more than one million RWG basis functions. Numerical examples are presented for various array sizes, including a 25 subarray problem comprised of 64 tapered-slot antennas (TSAs) each. The proposed method demonstrates very good accuracy, numerical efficiency, and a reduced memory storage requirement.
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| 3. |
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| 4. |
- Pellinen-Wannberg, Asta, et al.
(author)
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The impact of high resolution radar on meteor studies: the EISCAT perspective
- 2008
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In: URSI Radio Science Bulletin. - 1024-4530. ; :324, s. 17-28
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Journal article (peer-reviewed)abstract
- Meteors, i.e. meteoroids interacting with the atmosphere, provided a vast amount of knowledge about interplanetary matter already long before the space era. Using what is today known as specular meteor radars (SMR), a great body of data on meteors was accumulated, mainly through recording echoes from the meteor trails. However, due to the specularity requirement and the ceiling effect, this method only detects a subset of the meteor population. By contrast, the High Power Large Aperture (HPLA) radar method can observe head echoes from meteors passing through the radar beam at almost arbitrary aspect angles. The very high power densities available at typical HPLA installations allow millisecond time resolution and spatial resolution in the range of tens of meters to be achieved routinely. In special cases, interference between echoes from two meteors has made it possible to achieve centimetre scale spatial resolution, thus allowing the deduction of an upper limit on the effective target size. Vector quantities such as meteor velocity and deceleration, providing mass and orbit estimates, can be recorded by phased arrays with interferometric capability, as well as by multi-static radars. A case in point is the tri-static EISCAT UHF radar system, which provides a unique capability of monitoring head echoes over a very wide range of aspect angles. A recent analysis of data from the UHF system confirms that head echo targets are essentially spherical in the forward direction. The next generation of HPLA systems is exemplified by the EISCAT_3D multistatic phased array radar concept. We discuss how this system will affect temporal and spatial resolution, sensitivity and rate of statistics in meteor observations.
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| 6. |
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| 7. |
- Wannberg, Gudmund, et al.
(author)
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EISCAT_3D - a next-generation European radar system for upper atmosphere and geospace research
- 2010
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In: Radio Science Bulletin. - 1024-4530. ; :333, s. 75-88
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Journal article (peer-reviewed)abstract
- 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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| 8. |
- Zander, Jens, et al.
(author)
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Opportunistic Secondary Spectrum Access : Opportunities and Limitations
- 2012
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In: Radio Science Bulletin. - 1024-4530. ; :340, s. 29-33
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Journal article (peer-reviewed)abstract
- The dynamic spectrum-sharing technique (“cognitiveradio”), where secondary users opportunistically utilize temporarily or locally unused spectrum, has emerged as a prime candidate technology for relieving the perceived spectrum shortage in the lower frequency bands. Makinga realistic assessment of the amount of spectrum availablefor secondary services was the objective of the EU FP7QUASAR project. In the project, it was found to be fundamentally difficult to reliably determine which part of the spectrum is available. This leads to large safety marginsand to poor spectrum utilization, in general. Furthermore, the business success of future systems depends on thescalability of the secondary-access techniques. Resultsfrom the project indicate that in large-scale deployment,the aggregate interference from the secondary devices isthe key bottleneck. This aggregate interference is difficult for the individual secondary-spectrum user to assess. Inaddition, the vast majority of spectrum opportunities arestrongly dependent on the intended use. They are highly localized in time and space, and not obviously suitable for reliable service provisioning. The exception has been shown to be short-range, indoor communications, where the low transmitter power, walls, and other obstructions successfully provide these margins.
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