One-dimensional unstable resonators with compact output coupling and small magnification factors typical for molecular gas lasers are considered. The properties of the output beams for slab carbon-dioxide lasers with waveguide- unstable cavities have been investigated. It is shown that the losses of similar resonators without side walls depend strongly on the mirrors misalignment, and radiation power fluctuates in a wide range. At the same time, the reflecting ceramics side wall, positioned along the edge of active medium near optical axis allows to stabilize low cavity losses as well as high output power. The change of spatial structure of beams with distance from laser head is studied. It is found that the variations of near-field patterns from uniform distribution caused by diffraction is little affected by the far field radiation divergence. The distances that are necessary for conversion of output beam shape to smoothing-out one-peak profile were determined depending on the uniformity degree of initial distribution. The obtained results can be used in the development of slab gas lasers, when high specific power and good quality of output beam are required.