This paper aims at giving a derivation of the six electromagnetic field components created by an offset point charge travelling at any speed in a flat chamber, i.e. a two dimensional structure consisting of two infinite parallel plates surrounding a vacuum region. The plates are infinite both horizontally and along the direction of the point charge movement. We study the general case where the two plates are made of several layers of linear materials up to infinity in the vertical direction, with no a priori top-bottom symmetry. We find new results for the electromagnetic fields and impedances, generalizing in particular the so-called "Yokoya factors" that are valid under certain conditions only.