Abstract: The waveguide is constructed with a specially designed laminate which comprises multiple plies of a graphite-epoxy composite. Thermal compensation is achieved by orienting the graphite fibers in the various plies in selected directions. Graphite fiber has a negative coefficient of thermal expansion while epoxy has a positive coefficient of thermal expansion. At least one ply in the laminate has longitudinally oriented graphite fibers while a second ply has transversely oriented fibers. Third and fourth plies, intermediate of the first and second plies, have graphite fibers which are oriented at selected angles relative to the longitudinal and transverse plies. The angles of orientation of the graphite fibers in the intermediate plies are selected by use of an equation and a set of curves relating the temperature characteristics of the laminate to fiber angle, once the width of the waveguide and the free-space wavelength of the signal propagated in the waveguide are known.