Saab Automobile AB

About: Saab Automobile AB is a based out in . It is known for research contribution in the topics: Radar & Antenna (radio). The organization has 760 authors who have published 890 publications receiving 11811 citations.

Phase compensation of rate limiters in JAS 39 Gripen

Abstract: For a modern aerodynamically unstable fighter, like the JAS 39 Gripen, the flight control system (PCS) typically provides 45° phase margin. Therefore rate limiting of control surfaces is an important issue. Software rate limiters are placed on the control servo commands in order to prevent the hydraulic servos from rate limiting. When a rate limiter is saturated, the phase shift drastically reduces the stability margins of the closed loop and increases the risk for pilot-induced oscillation (PIO). This paper describes a novel method for compensating the phase shift of a rate limiter. In contrast to earlier phase compensation methods, this method uses feedback instead of logic or feedforward. Open loop and closed loop properties of the method are discussed. The method gives a drastic improvement on stability margins and reduces PIO tendencies. This is demonstrated on a JAS 39 Gripen example. Phase compensated rate limiters are now used in the JAS 39 Gripen PCS production software. Their effects on closed loop stability and flying qualities are discussed in the paper.

Analysis of elastic structures by matrix transformation with special regard to semimonocoque structures

Abstract: The system of equations for a redundant elastic structure is established by a routine procedure. The work is divided into separate steps, the first being the establishing of the transformation matrix by purely statical analysis. This first step is the only one where knowledge of structure analysis is demanded, all further steps being simple matrix multiplications that can be performed by automatic means such as punched-card machines. The procedure is a modification of G. Kron's method for electric networks. The structure can be analyzed by parts. Subsequent changes in member stiffnesses do not affect the transformation matrix, which can therefore be established once the geometry of the structure is specified. The rest of the work is a simple routine matter. The system of equations obtained is reduced by matrix transformations of a similar kind. The procedure for obtaining the system of equations is illustrated by a simple example.

Device at a radar level gauge

Abstract: A device for gauging the level of a fluid in a container with a microwave signal is described. The device comprises a vertical tube (1) mounted in the container, and a transmitter and a receiver and an electronic unit for determining the level based on the reflex position of the microwave signal. The device is characterized particularly by a calibration device in the form of a polarization means (6, 7) for polarizing the microwave signal in two polarization planes separated from each other and at least one reflecting reactance (10) in the tube (1) arranged to give a substantially stronger reflex of the microwave signal in the first polarization plane than in the second.

Theory of the triple constraint — A conceptual review

Abstract: Projects are generally undertaken because they are part of the plans to meet business needs and charter organizations to new levels of performance. Projects are however constrained by conflicting demands and competing priorities within the project environment. Neglecting to manage these constraints accurately and effectively may be sufficient to condemn a project even if all other project management activities are performed to a high standard of excellence. The aim of this paper is to improve the interpretation of the triple constraint and its dynamics and indicate how this may advance the delivery of project success. An integrated model is proposed to facilitate the strategic management of the triple constraint trade-offs as a function of the project higher purpose.

Comparison of Antenna Measurement Facilities With the DTU-ESA 12 GHz Validation Standard Antenna Within the EU Antenna Centre of Excellence

Abstract: The primary objective of many antenna measurement facilities is to provide a specified high accuracy of the measured data. The validation of an antenna measurement facility is the process of proving that such a specified accuracy can be achieved. Since this constitutes a very challenging task, antenna measurement accuracy has been the subject of much research over many years and a range of useful measures have been introduced. Facility comparisons, together with antenna standards, error budgets, facility accreditations, and measurement procedure standards, constitute an effective measure towards facility validations. This paper documents the results of a comparison between 8 European antenna measurement facilities with a specially designed reference antenna, the DTU-ESA 12 GHz validation standard antenna (VAST-12). The electrical and mechanical properties of the VAST-12 antenna are presented and its three different coordinate systems are defined. The primary objective of the comparison is to obtain experience and results that can serve to develop standards for validation of antenna measurement facilities. The paper focuses on the comparison of the radiation pattern and presents not only the measurement data obtained at the facilities, but also investigates several procedures for comparing these data. This includes various definitions of pattern difference and statistical measures as well as a reference pattern. The comparison took place in 2004-2005 as part of the European Union network of excellence called ACE-Antenna Centre of Excellence.