HF attenuation

For HF attenuation measurement, the working group has highly precise measuring set-ups of the coaxial and waveguide type for frequencies of up to 40 GHz under operation, most of which work on the principle of the power ratio method. Basically, a d.c. power substitution method is concerned here which consists in measuring the HF power with and without the attenuator to be tested, using a self-adjusting bolometer bridge and determining the attenuation from the power ratio.

The attenuation of coaxial attenuators up to 100 dB for frequencies up to 26.5 GHz (up to 120 dB for frequencies up to 1.2 GHz) and of waveguide attenuators up to 60 dB (for frequencies of 8.2 GHz to 18 GHz) is determined, using an HF series substitution set-up, by comparison with cascaded calibrated attenuation transfer standards.

Standard measuring setup for HF attenuation

Due to the mismatch between signal generator and measuring receiver, an additional uncertainty contribution occurs in all attenuation measurements. Independent of the measuring method applied, for each measuring frequency the insertion point must be matched to the characteristic line impedance by means of suitable tuners, a reflectometer being used for control. Only in this way the smallest possible measurement uncertainty is guaranteed. Attenuation measurements with higher uncertainty can be carried out with a commercial attenuation measuring set-up or a network analyser; both instruments are traced to the attenuation measuring set-ups described above.

Measurement and calibration capabilities for HF attenuation

Literature relating to HF attenuation