Waveguides usually feed high-frequency antennas. In this case, (p. 262, Ref. 2) the attenuators are built starting from a very thin, tapered, resistive card. The attenuator device introduces this card in a section of the slotted guide. The adjustment of the penetration depth in the slot allows controlling the dissipation of power and the desired attenuation. This type of attenuator has a complex attenuation varying with penetration depth and frequency.