Repeatability of Programmable Waveguide Attenuators at 110-170 GHz and 220-330 GHz

Variable waveguide attenuators are electromechanical components that are used to vary signal levels during RF measurements. Mechanical turn knobs or millimeter screws with a human setting have been used to vary the RF signal level from the attenuator. In particular, waveguide attenuators are needed with modulated signal measurements above 100 GHz frequencies due to the limited output power control ranges of signal generators. One of the requirements of automated measurement systems is that all system components can be programmable with computers. This paper proposes a software programmable approach that controls a mechanical knob turning of the waveguide attenuator. A stepper motor with a step angle of 1.8 degrees was attached to two standard waveguide attenuators. The repeatability analysis of the measurement results showed that the standard deviation of the attenuation variation of the setting can be reduced to 0.05 dB at 110 to 170 GHz and 0.1 dB at 220 to 330 GHz. The proposed method of attaching a stepper motor to the waveguide attenuator enables accurate measurements of the modulated conductive and radiative 6 G signal with a wide dynamic range.