Abstract: An impregnated thermionic cathode includes a porous matrix of sintered tungsten-alloy particles containing less than six percent iridium and/or other platinum-group metal. The pores of the matrix are impregnated with a temporary process impregnant such as molten copper or an organic monomer, and upon solidification is machined to a desired shape. Thereafter the temporary process impregnant is removed, and the matrix pores again infiltrated with a barium oxide such as molten barium aluminate, or other alkaline earth. A thin, iridium-rich surface activating layer, preferably of about 50% iridium, is then applied to the emitting surface. The diffusion of surface activating iridium is substantially blocked; superior emission and lifetime is provided; and the cathode is relatively low cost and easy to fabricate.