A. V. Koudel'nyi and V. G. Chuiko UDC 53.083.8The results are given of developments and investigations of an automated apparatus for calibrating attenuators in the frequency range 10 MHz to 18 GHz for use as working attenuation standards. It is shown that automated apparatus for calibrating microwave wattmeters is suitable for calibrating coaxial fixed and stepped attenuators with an error of lower than +0.02 dB per 10 dB.Calibrated attenuators are convenient as standard devices for measuring amplitude ratios and are employed in the frequency range from tens of kilohertz to hundreds of gigahertz. They are introduced into standards for power, voltage, and other quantities in order to extend their measuring range. It is preferable to use amplitude-ratio standards rather than ratio meters because the cost of a device for establishing (forming) a known signal amplitude ratio by means of a calibrated attenuator is far lower than that of a ratio meter of the same accuracy, and the reliability is higher. Coaxial programmed stepped and fixed attenuators such as the Hewlett Packard series 8490, 8494, and similar have been extensively used in practice. A distinctive feature of fixed and stepped coaxial attenuators is the presence of steps from the series 3, 6, 10, 20, and 30 dB for Russian devices or I0, 20, 40, 50, and 60 dB for foreign devices. Programmed attenuators have steps of 0.1, 1, and 10 dB (for example, type TR Hungarian attenuators or type BM Czech attenuators) or steps arranged as 1-2-4-4 or 10-20-40-40 as for the Hewlett Packard attenuators. Such attenuators are extremely convenient as working standards (standard devices) and comparison standards for calibrating attenuation, and for the comparison of different types of measuring receivers, radio interference meters, group $4 spectrum analyzers, group D 1 heterodyne attenuation meters, group F4 devices for measuring group time delay, group R2 panoramic VSWR meters, group Kh5 noise figure meters, group $2 and $3 devices for measuring amplitude and frequency modulation depths, group $7 and $9 rf oscilloscopes, group V3 rf voltmeters, etc. As a rule working standards of attenuation for coaxial lines, with an error of lower than 0.03 dB per 10 dB are suitable. However the errors of fixed and stepped attenuators given in the catalogs of firms fail to satisfy some of the requirements, although it is known that the instability of attenuators is normally considerably lower than the stated errors. Consequently they can be certified as working standards after careful measurements, as was mentioned in [1].By definition, attenuation is the ratio of the powers at the input and output of an attenuator for the traveling wave regime at its input and output. For attenuators with values below 40 dB it is possible to measure their attenuation by the power ratio method, by definition, using power meters. The schematic diagram shown in Fig. 1 is well known. According to data in [ 1, 2] the minimum error of the power ratio method, resulting from the random errors of the thermistor ...
