Rotary-vane attenuator with an optical readout

A precision x-band rotary-vane attenuator has been developed that follows its th eoretical cosine squared law of attenuation to within 0.002 dB to a value of 20 dB.The best available attenuation measurement techniques verify this relationship to within th e accuracy of the measurements.From 20 to 50 dB, the deviation from th e theoretical value slowly increases and is fr eq uency dependent.At present, three attenuators of thi s type have been constructed by NBS.Two of th ese attenuators have excell ent attenuation versus frequency characteri sti cs in the 20 to 50 dB ran ge (0.08 dB deviation at 50 dB) while the third has a marked degree of freq uency sen sitivity (0.21 dB at 50 dB).