What refers to the motion of the antenna axis (of the beam) as the radar looks for an aircraft?

The term that refers to the motion of the antenna axis, or the beam, as the radar searches for an aircraft is indeed associated with "scanning method." Scanning methods are employed in radar systems to effectively cover a specific area and detect targets like aircraft. The antenna may rotate or change position in a predetermined pattern to maximize coverage and ensure that it can detect incoming signals from various directions.

Different scanning methods can significantly affect detection capabilities, including how quickly and accurately an aircraft can be located. This dynamic movement allows the radar system to interrogate a broader spatial area, which enhances tracking efficiency and effectiveness.

The other terms relate to different aspects of radar technology but do not specifically denote the motion of the antenna beam searching for targets. For example, tracking describes the subsequent following of a detected target, propagation refers to the way radar waves travel through different mediums, and refractive index pertains to the bending of electromagnetic waves, which influences radar performance but does not directly define antenna motion. Hence, the focus on scanning method specifically highlights the process by which radar actively seeks out aircraft.