piston attenuator

piston attenuator

[′pis·tən ə′ten·yə‚wād·ər]
(electromagnetism)
A microwave attenuator inserted in a waveguide to introduce an amount of attenuation that can be varied by moving an output coupling device along its longitudinal axis.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.