Swedish Defence Research Agency

About: Swedish Defence Research Agency is a government organization based out in Stockholm, Sweden. It is known for research contribution in the topics: Radar & Synthetic aperture radar. The organization has 1413 authors who have published 2731 publications receiving 56083 citations. The organization is also known as: Totalförsvarets forskningsinstitut.

A 10-GW Pulsed Power Supply for HPM Sources

Abstract: A research activity involving the detailed consideration of novel high voltage transformers (HVTs) for pulsed-power applications has recently begun at Loughborough University (LU). Although the main goal is the demonstration of a compact and lightweight unit employing magnetic self insulation under vacuum conditions, the initial stage of the work is directed towards the development of a conventional air-cored HVT as a main component in a compact power supply for HPM sources. In cooperation with the Swedish Defence Research Agency (FOI), the power supply has been tested with a HPM source of the vircator type. The power source for the system uses a 70 kJ/25 kV capacitor bank and an exploding wire array to generate a 150 kV voltage pulse in the primary circuit of the HVT. A pressurised SF6 spark gap in the secondary circuit sharpens the high-voltage output, so that pulses approaching 500 kV and with a rise time below 100 ns are generated on a 20 Omega high-power resistor. The peak power produced by the power supply is in excess of 10 GW. Measurements provided by various diagnostic techniques are analysed with the aid of a detailed numerical code. Experimental results are presented from final testing of the system, where a reflex triode vircator replaces the 20 Omega resistor. Measurements made of the microwave emission using free-field sensors are presented for various electrode configurations. Comments are made with the microwave emission from the same vircator powered by a Marx generator at FOI.

Three-dimensional laser radar modeling

Abstract: Laser radars have the unique capability to give intensity and full 3-D images of an object. Doppler lidars can give velocity and vibration characteristics of an objects. These systems have many civilian and military applications such as terrain modelling, depth sounding, object detection and classification as well as object positioning. In order to derive the signal waveform from the object one has to account for the laser pulse time characteristics, media effects such as the atmospheric attenuation and turbulence effects or scattering properties, the target shape and reflection (BRDF), speckle noise together with the receiver and background noise. Finally the type of waveform processing (peak detection, leading edge etc.) is needed to model the sensor output to be compared with observations. We have developed a computer model which models performance of a 3-D laser radar. We will give examples of signal waveforms generated from model different targets calculated by integrating the laser beam profile in space and time over the target including reflection characteristics during different speckle and turbulence conditions. The result will be of help when designing and using new laser radar systems. The importance of different type of signal processing of the waveform in order to fulfil performance goals will be shown.

Underwater communication link with iterative equalization

Abstract: In this paper an acoustic underwater communication link is presented. The channel has severe inter symbol interference, which is dealt with by an iterative linear equalizer and a Turbo code. Experiments has been performed in the Baltic Sea using a 4QAM signal with bandwidth 4 kHz at a center frequency of 12 kHz. The raw data rate is 8 kbit/s but after reduction for error correction coding the net bit rate is 2.88 kbit/s. With a source level of 180 dB re. 1mu/Pa @ 1m and a single hydrophone receiver, a reliable communication is shown up to a distance of 60 km. Very important for a successful decoding is the initial synchronization, which also is discussed

On MILES based on flux‐limiting algorithms

Abstract: Non-classical large eddy simulation (LES) approaches based on using the unfiltered flow equations instead of the filtered ones have been the subject of considerable interest during the last decade. In the monotonically integrated LES (MILES) approach, flux-limiting schemes are used to emulate the characteristic turbulent flow features in the high-wave number end of the inertial subrange region. Mathematical and physical aspects of implicit sub grid scale modelling using nonlinear flux-limiters are conveniently addressed using the modified LES-equation formalism. In this study, the performance of MILES is demonstrated as a function of the flux-limiting scheme in selected representative case studies

Definition on SAR image quality measurements for UWB SAR

Abstract: Analyses in this study show that measurements under currently used definitions on SAR image quality measurement may be unsuitable for UWB SAR. The main objective of this paper is therefore to propose a definition based on the shape of a single point target in a SAR image which is more suitable for UWB SAR. We use both real and simulated data based on the airborne UWB low frequency SAR CARABAS-II in experiments. The time-domain algorithm Global Backprojection (GBP) is selected for the image formation in this study.