This paper discusses the electronically scanning characteristics of a Leaky-Wave Antenna by means of controlling the real part of the leaky-mode complex longitudinal propagation constant at a fixed frequency. The structure is based on a standard rectangular waveguide section with a series of slots cut along its broad wall and loaded with a transversely-magnetized ferrite slab parallel to the narrow wall and extending along the full height of the guide. The beam steering in this configuration is achieved by a combination of two mechanisms namely the variation of the internal magnetization of the ferrite slab and its position. A rigorous theoretical analysis of the electromagnetic field propagating inside the loaded waveguide is followed. By numerically solving the transcendental equation for the leaky-mode phase constant of such LWA the associated propagating modes can be obtained. A parametric analysis of the permeability tensor and the position of the slab shows a ∼50° beam deflection from near broadside toward ± endfire direction. The relevant radiation patterns are also calculated proving the scanning performance of the antenna. A good input match (<-30dB) was observed for the different positions of the ferrite slab.