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Avoiding ambiguity in beamspace processing

In direction finding of narrow-band signals using antenna arrays with a large number of elements, the so-called beamspace matrix is often used to project the measurements into a lower dimension subspace. This reduces computation time and allows for parallel processing. On the other hand, beamspace preprocessing may introduce ambiguity, i.e., spurious estimated directions. We show that when the null space of the beamspace matrix is suitably designed, ambiguity within any sector of interest can be avoided.