Saab Automobile AB

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

An algorithm for adaptive predistortion of certain time-varying nonlinear high-power amplifiers

Abstract: An extended Kalman filter (EKF) is proposed for adaptive precompensation of time-varying nonlinear distortion caused by high-power amplifiers (HPA) such as traveling wave tube (TWT) amplifiers frequently used in for instance, radar transmitters. In many applications, a means for adaptive predistortion is essential in order to reduce out-of band transmission. The proposed scheme is based on a nonlinear Wiener model for identification of the HPA characteristics and a predistorter with a Hammerstein-type structure. The usefulness of the proposed scheme is illustrated by means of a numerical example. In particular, it is shown that suppression of nonlinear distortion, introduced by a typical Ku-band TWT amplifier, in the order of 25-30 dB can be achieved. Furthermore, the performance of the EKF is compared to that of the recursive prediction error method (RPEM) and the stochastic gradient algorithm (LMS).

An Efficient Solution to the Factorized Geometrical Autofocus Problem

Abstract: This paper describes a new search strategy within the scope of factorized geometrical autofocus (FGA) and synthetic-aperture-radar processing. The FGA algorithm is a fast factorized back-projection formulation with six adjustable geometry parameters. By tuning the flight track step by step and maximizing focus quality by means of an object function, a sharp image is formed. We propose an efficient two-stage approach for the geometrical variation. The first stage is a low-order (few parameters) parallel search procedure involving small image areas. The second stage then combines the local hypotheses into one global autofocus solution, without the use of images. This method has been applied successfully on ultrawideband CARABAS II data. Errors due to a constant acceleration are superposed on the measured track prior to processing, giving a 6-D autofocus problem. Image results, including resolution, peak-to-sidelobe ratio and magnitude values for point-like targets, finally confirm the validity of the strategy. The results also verify the prediction that there are several satisfying autofocus solutions for the same radar data.

System and method in a radar level gauging system

Abstract: The present invention relates to the field of radar level gauging systems, in which a level of a surface of a product stored in a container is measured. The gauging system comprises: a radar level gauge arranged above the surface of the product which is arranged to transmit a microwave signal towards the product surface and receive a reflected microwave signal from the product surface; a calculation unit arranged to determine a measured value of the product level based upon the received signal; means for comparing the measured value of the product level with a predetermined value; and a second level gauge arranged closed to the bottom of the container and arranged to determine the product level when the measured value is below the predetermined value.