The construction has outer (2) and inner dielectric layers which have the same dielectric constant. The layers are formed using normal moulding manufacture layers. A separation is formed between the two layers by domino-shaped spacers. The spacers have wide centre portions (4) which touch each other, and narrower bottom and top layers with holes in the centre. The overall dielectric constant of the spacer taking account of the holes, is equal to the upper and lower layers.
