A device for application in the high frequency field and a method for forming a photonic band-gap structure are provided. The device being mountable on a primary substrate for forming the device. The device being formed by forming conformal coplanar waveguide metallizations on surface areas of two substrates, connecting the conformal coplanar waveguide metallizations of the two substrates, and structured back-etching of the two substrates, starting at surface areas of the two substrates that are opposite the coplanar waveguide metallizations.