Flap attenuator

It comprises a thin, disk-shaped attenuation material that extends through a longitudinal slot in the middle of the wider side of the waveguide into the inner space of the waveguide.

The extent of the insertion is variable, and the attenuation can be made approximately linear with the insertion by properly shaping the resistance card.

A shape with as few sharp edges as possible is considered to minimize reflections.

As a rule, semicircular, thin panes are preferred.

[2] In the millimeter wave range, it's possible to achieve up to 40 dB.