An array of electrically conductive waveguides is made a method including defining slots in broad surfaces of planar dielectric slabs. The surfaces of the slabs, including slots, are metallized. The broad sides of the slabs are juxtaposed, with the slots registered with the planar surfaces of another slab, to form one or more closed waveguides. The waveguides may feed microchips, or act as antennas. The slabs may include electrical conductors andor heat pipes. Heat pipes are made by defining apertures with the dielectric slabs, and introducing wick material into the apertures.