Abstract: A microwave/millimeter device having a narrow gap between two parallel surfaces of conducting material by using a texture or multilayer structure on one of the surfaces is disclosed. The fields are mainly present inside the gap, and not in the texture or layer structure itself, so the losses are small. The microwave/millimeter wave device further includes one or more conducting elements, such as a metallized ridge or a groove in one of the two surfaces, or a metal strip located in a multilayer structure between the two surfaces. The waves propagate along the conducting elements. At least one of the surfaces is provided with means to prohibit the waves from propagating in other directions between them than along the ridge, groove or strip. At very high frequency, the gap waveguides and gap lines may be realized inside an IC package or inside the chip itself.