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| 2. |
- Hammar, Arvid, 1986, et al.
(författare)
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THz smooth-walled spline horn antennas: Design, manufacturing and measurements
- 2016
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Ingår i: 2016 IEEE Antennas and Propagation Society International Symposium, APSURSI 2016, Fajardo, Puerto Rico, 26 June - 1 July 2016. - 1947-1491. - 9781509028863 ; , s. 1341-1342
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Konferensbidrag (refereegranskat)abstract
- We describe a versatile and cost-efficient method for producing smooth-walled spline horn antennas for applications in THz radiometry. Specifically, the development of four different horns for radiometer receiver applications at frequencies 120, 183, 340 and 874 GHz is presented. General methods for efficient optimization of the spline profiles have been developed which enable the horn designs to be tailored to each application. All four designs display high Gaussicity (typically ∼98%). Manufacturing methods based on numerical milling in splitblocks, lathing and drilling have been tested and compared. Milled splitblock horns with integrated receiver circuits (Shottky mixers in this case) allow for lower losses in the receiver system at the expense of higher cross-polarization levels. The radiation pattern of three designs at 183, 340 and 874 GHz have been measured using planar and rotational scanners.
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| 5. |
- Koivisto, Jenni, 1980-
(författare)
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Navigating in the Midst of Uncertainties : Challenges in Disaster Risk Governance in Mozambique
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Disasters cause heavy losses for societies and may quickly erode any development efforts. Consequently, disaster risk reduction (DRR) is an integral part of development work that should be addressed at multiple levels. Global DRR frameworks, scholars and practitioners all advocate disaster risk governance (DRG) strategies that are multi-stakeholder, polycentric and multisectoral. While various substantive knowledge gaps and questions arising from multiple risks and the crosscutting nature of DRR have been relatively well addressed, uncertainties relating to multiple DRR actors operating and collaborating at different scales have gained less attention in previous studies.This thesis investigates the uncertainties in DRG in Mozambique, a low-income country that regularly faces natural hazards. These hazards often cause heavy loss of life and livelihoods and economic damage. The four articles that together constitute this thesis focus on different sets of uncertainties and factors that have constrained or allowed Mozambique to take major steps in this policy area. By exploring strategic and institutional uncertainties related to stakeholder involvement, coordination and policy disputes, this thesis reveals different challenges and opportunities that affect DRR policymaking in Mozambique.This thesis concludes that Mozambique has managed to take important steps in DRR. However, as a consequence of the different challenges to DRR practice in Mozambique, policymaking can be short-sighted and makes slow progress, thus increasing the disconnect between theory, policies and practice. This thesis thus argues that DRG research and practice need to better take into account power-relations; coordination and capacity issues; and responsibilities and transparency across scales, both in Mozambique and elsewhere.
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| 6. |
- Nohrstedt, Daniel, 1974-, et al.
(författare)
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Disaster risk reduction and the limits of truisms : Improving the knowledge and practice interface
- 2022
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Ingår i: International Journal of Disaster Risk Reduction. - : Elsevier. - 2212-4209. ; 67
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Tidskriftsartikel (refereegranskat)abstract
- Action toward strengthened disaster risk reduction (DRR) ideally builds from evidence-based policymaking to inform decisions and priorities. This is a guiding principle for the Sendai Framework for Disaster Risk Reduction (SFDRR), which outlines priorities for action to reduce disaster risk. However, some of these practical guidelines conceal oversimplified or unsubstantiated claims and assumptions, what we refer to as 'truisms', which, if not properly addressed, may jeopardize the long-term goal to reduce disaster risks. Thus far, much DRR research has focused on ways to bridge the gap between science and practice while devoting less attention to the premises that shape the understanding of DRR issues. In this article, written in the spirit of a perspective piece on the state of the DRR field, we utilize the SFDRR as an illustrative case to identify and interrogate ten selected truisms, from across the social and natural sciences, that have been prevalent in shaping DRR research and practice. The ten truisms concern forecasting, loss, conflict, migration, the local level, collaboration, social capital, prevention, policy change, and risk awareness. We discuss central claims associated with each truism, relate those claims to insights in recent DRR scholarship, and end with suggestions for developing the field through advances in conceptualization, measurement, and causal inference.
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| 9. |
- Nyberg, Daniel, 1980, et al.
(författare)
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Effects of intrinsic radiation Q on mismatch factor of three types of small antennas: single-resonance, gradual-transition and cascaded-resonance types
- 2010
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Ingår i: IET Microwaves, Antennas and Propagation. - : Institution of Engineering and Technology (IET). - 1751-8725 .- 1751-8733. ; 4:1, s. 83-90
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Tidskriftsartikel (refereegranskat)abstract
- Resonators are traditionally characterised by their quality factor Q, which is inversely proportional to the relative bandwidth. Small antennas are often resonant, so they can be characterised by a Q, except for the fact that the correct quality measure of an antenna is the inverse Q, that is the relative bandwidth, rather than Q. Still, it has become common to study fundamental size limitations of small antennas in terms of a so-called radiation Q (or antenna Q). This study explains how this intrinsic radiation Q relates to: (i) the bandwidth-efficiency product of small single-resonance-type antennas, (ii) the gradual cut-off of spherical waves for wideband gradual-transition-type small antennas and (iii) the number of resonances needed to cover a certain frequency band for wideband cascaded-resonance-type small antennas. The study also introduces one intrinsic radiation Q for basic single TE and TM spherical mode sources, and another for combined TE and TM sources.
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| 10. |
- Nyberg, Daniel, 1980
(författare)
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Limitations on efficiency, size and bandwidth of small antennas
- 2008
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The allocated space in a mobile phone for the antennas has become smaller and smaller following the size reduction of the mobile phones themselves and the integration of more functions in them. At the same time new communication systems are being planned where such small antennas also need to be wideband (UWB systems) or have multiple ports (MIMO systems). Therefore, this thesis takes a new and more practical look upon the fundamental size limitations of small antennas.The thesis aims explaining what the limits in radiation Q means in terms of practical bandwidth limitations of three different types of small antennas: single-resonance-type, gradual-transition type and cascaded-resonances-type. Small antennas are often resonant, so when the theoretical bandwidth limitations were formulated it was natural to reuse the formulations and terminology which was used to characterize resonators. The frequency selectivity of resonators is normally expressed by the quality factor Q. That is why the fundamental limitations on antennas are formulated as limitations on radiation Q. The inverse of this quantity represents the relative bandwidth, which is the parameter of interest for antennas. This thesis explains how this radiation Q is related to: 1.The bandwidth-efficiency product of small single-resonance-type antennas.2.The gradual cut-off of spherical waves for wideband gradual-transition-type small antennas.3.The number of resonances needed to cover a certain frequency band for wideband cascaded-resonances-type small antennas. The thesis also introduces one radiation Q for basic single TE and TM spherical mode sources, and another for combined TE and TM sourcesThe thesis also includes some measurements of performance of small MIMO antennas in reverberation chamber.
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| 11. |
- Nyberg, Daniel, 1980, et al.
(författare)
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Radiation Q and radiation efficiency of wideband small antennas and their relation to bandwidth and cut-off of spherical modes
- 2007
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Ingår i: 2nd European Conference on Antennas and Propagation, EuCAP 2007; Edinburgh; United Kingdom; 11 November 2007 through 16 November 2007. - : Institution of Engineering and Technology. - 9780863418426 ; 2007:11961
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Konferensbidrag (refereegranskat)abstract
- Resonators are traditionally characterized by their quality factor Q, which is inversely proportional to the relative bandwidth. Small antennas are often resonant, so they can be characterized by a Q, except for the fact that the correct quality measure of an antenna is rather the inverse Q. i.e. the relative bandwidth. Still, it has become common to study fundamental size limitations of small antennas in terms of a so-called radiation Q (or antenna Q). The paper explains how this intrinsic radiation Q relates to: i) the bandwidth- efficiency product of small single-resonance-type antennas, ii) the gradual cut-off of spherical waves for wideband gradual-transition-type small antennas, and iii) the number of resonances needed to cover a certain frequency band for wideband multiple-resonances-type small antennas. The paper also introduces one intrinsic radiation Q for basic single TE and TM spherical mode sources, and another for combined TE and TM sources.
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| 12. |
- Nyberg, Lars, 1966-, et al.
(författare)
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Biological and environmental predictors of heterogeneity in neurocognitive ageing : Evidence from Betula and other longitudinal studies
- 2020
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Ingår i: Ageing Research Reviews. - : Elsevier. - 1568-1637 .- 1872-9649. ; 64
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Forskningsöversikt (refereegranskat)abstract
- Individual differences in cognitive performance increase with advancing age, reflecting marked cognitive changes in some individuals along with little or no change in others. Genetic and lifestyle factors are assumed to influence cognitive performance in aging by affecting the magnitude and extent of age-related brain changes (i.e., brain maintenance or atrophy), as well as the ability to recruit compensatory processes. The purpose of this review is to present findings from the Betula study and other longitudinal studies, with a focus on clarifying the role of key biological and environmental factors assumed to underlie individual differences in brain and cognitive aging. We discuss the vital importance of sampling, analytic methods, consideration of non-ignorable dropout, and related issues for valid conclusions on factors that influence healthy neurocognitive aging.
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| 14. |
- Sobis, Peter, 1978, et al.
(författare)
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SWI 1200/600 GHz highly integrated receiver front-ends
- 2015
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Ingår i: 36th ESA Antenna Workshop on Antennas and RF Systems for Space Science, ESA/ESTEC ,Noordwijk, The Netherlands; 6-9 Oct. 2015. ; session S3.1.2
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Konferensbidrag (refereegranskat)
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| 15. |
- Sobis, Peter, 1978, et al.
(författare)
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Ultra Low Noise 600/1200 GHz and 874 GHz GaAs Schottky Receivers for SWI and ISMAR
- 2016
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Ingår i: Twenty-seventh International Symposium on Space Terahertz Technology (ISSTT).
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Konferensbidrag (refereegranskat)abstract
- Omnisys Instruments is responsible for the 600/1200 GHz broadband front-end receivers and back-end spectrometer hardware for the Submillimeter Wave Instrument (SWI) part of the Jupiter Icy moons Explorer (JUICE) mission, and for the development of the dual-polarization 874 GHz spectrometer channels for the airborne icecloud imager instrument ISMAR. We will present our development of these highly integrated heterodyne receivers which are based on membrane integrated GaAs Schottky diode mixer and multiplier circuit technology, and InP HEMT MMIC LNA technology from Chalmers University of Technology. Preliminary results at room temperature on the 1200 GHz breadboard prototypes show on a typical DSB receiver noise below 3000 K in the 1030 GHz-1220 GHz frequency range with only 1-3 mW of LO power. For the 874 GHz receiver flight modules a record low double sideband noise of 2500 K was obtained with only 2.3 mW of LO pump power. Both the 1200 GHz and 874 GHz subharmonically pumped Schottky mixer designs have been based on the broadband SWI 600 GHz channel mixer design, which had a repeatable receiver noise performance below 1200K with less than 2 mW of pump power at room temperature. All together these results are setting new standards for critical receiver hardware operating at room temperature used in instrumentation for atmospheric research and remote sensing applications.
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| 16. |
- Yang, Jian, 1960, et al.
(författare)
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Impedance matrix of a folded dipole pair under eleven configuration
- 2010
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Ingår i: IET Microwaves, Antennas and Propagation. - : Institution of Engineering and Technology (IET). - 1751-8725 .- 1751-8733. ; 4:6, s. 697-703
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Tidskriftsartikel (refereegranskat)abstract
- A new decade wideband antenna, the Eleven antenna, has been developed during the last years. The basic configuration of Eleven antenna is two parallel dipoles separated by half wavelength above the ground plane, which is referred to as the eleven configuration. In order to cascade the dipoles in log-periodic array for obtaining wideband performance, folded dipoles are often used. The input impedance of shorted folded dipole in free space has been analysed by using two-mode method: a transmission line mode and an antenna mode. In the present study, the impedance matrix of a pair of folded dipoles as a two-port network under the eleven configuration will be analysed by including the mutual coupling among elements of folded dipoles into the two-mode method. As veri. cation, an Eleven antenna with one pair of folded dipoles has been analysed by the present method, modelled in a commercial software - CST MS and manufactured. The results by using the present method agree well with the measured and simulated one.
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