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Abstract. A technique of direction finding is proposed, which can be applied to the magnetic-dipole type source located in the conductive ground. To distinguish a weak ULF source signal from the natural noise a network of multicomponent magnetometers is supposed to be used. The data obtained by the ground-based stations is processed in such a way that a set of partial derivatives of the magnetic perturbations due to the source are found. Comparing these derivatives with theoretical formulae makes it possible, in principle, to find the ULF source parameters such as the distance and amplitude. Averaging the data and a special procedure are proposed in order to exclude random fluctuations in the magnetic moment orientation and to avoid hydrogeological and other local factors.

In modern electronic warfare systems there is a need for direction-finding of transmitters using waveforms for military stealth communication. In this paper, a correlation-based method is investigated utilizing the phase of the cross spectral density to estimate the time-difference-of-arrival from a two-channel digital receiver. A least squares method is reviewed, and its performance is investigated by theoretical analysisand by Monte-Carlo simulations. Proper Cramér-Raobounds are derived. It is shown that the method is statistically efficient for flat spectrum signals. The method is found to be a promising method for use against military communication in an electronic warfare direction-finding system. ; QC 20111102

Radiofrequency (RF) interference threatens the functionality of systems that increasingly underpin the daily function of modern society. In recent years there have been multiple incidents of intentional RF spectrum denial using terrestrial interference sources. Because RF based systems are used in safety-of-life applications in both military and civilian contexts, there is need for systems that can quickly locate these interference sources. In order to meet this need, the Air Force Research Laboratory Weapons Directorate is sponsoring the following research to support systems that will be able to quickly geolocate RF interferers using passive angle-of-arrival estimation to triangulate interference sources. This research studies the performance of angle-of arrival (AoA) estimation algorithms for an existing uniform linear antenna array. Four algorithms are presented, they are phase-shift beamforming, Capon or Minimum Variance Distortionless Response (MVDR) beamforming, the Multiple Signal Identification and Classification (MUSIC) algorithm, and one instantiation of a Maximum Likelihood Estimation (MLE) algorithm. A modeling and simulation environment using MATLAB™ is developed and the performance of each algorithm is simulated as implemented on a uniform linear array. Performance is characterized under various non-ideal conditions.

A remotely switched null-peak network for combining RF signals from dual antenna arrays used for
radio direction finding and animal tracking is described. The design is based on a balanced 50-Ohm coaxial
bridge, which provides a difference (null) and summed (peak) output from two parallel antennas to the
receiver. Reed relays activated through the receiver cable permit the network to be switched between
peak or null modes of operation from the receiver, without the need for long dual cable runs from the
antenna. The bridge presents a nominal 50-Ohm impedance at all terminals.