Beam steering originates from antenna design and adaptive array processing [1, 2, 3], and is mainly focused in this direction [4, 5, 6]. In the early days, it was used in radio soundingRadio sounding [7]. At millimeter waves, mechanical rotation with fixed beams remains practice [8]. It makes it difficult to find references, as direction finding is challenging. The digital revolution and subspace [9] methods have surpassed this approach. Monopulse radarMonopulse radar is one example [2]. A wide range of literature exists across various domains. In this chapter, we focus on the spatial filtering method.