Latest determination of a coaxial microcalorimeter calibration factor

Abstract

The paper describes the latest analysis made on a 3.5 mm coaxial microcalorimeter, which is the system used by Istituto Nazionale di Ricerca Metrologica to set up the electromagnetic power standard in the frequency band between 1 MHz and 26.5 GHz. The analysis concerns mainly the electro-thermal behavior of the system feeding lines whose performances define the main error component of the microcalorimeter. Previous mathematical models of the system have been updated and the effects on measurement accuracy are shown by comparing new and old measurement datasets at frequency values between 50 MHz and 26 GHz. It results in the fact that the influence of the sensor mismatch on the microcalorimeter calibration factor can be as high as 0.1% and reflects on the effective efficiency value.

Comparison Between Thermoelectric and Bolometric Microwave Power Standards

“…For the thermoelectric case η raw e is given by the ratio e 1 /e 2 and is related to corrected effective efficiency η e by [17] η e = g T η raw For the bolometric case, the relation between η e and η raw e is [16], [19] η e = g B η raw…”

“…Formula (3) holds well up to about 18 GHz, because in this range, thermoelectric power sensors exhibit a very low reflection coefficient T . If this is not the case, a further correction is necessary and term e 1SC has to be multiplied by (1+| T | 2 ) [17].…”

Proposal of a Super-Symmetric Microcalorimeter for Single Step Realization of RF Primary Power Standard

“…In the first step, the power sensor under test is fed alternately with the RF power and the reference power, respectively, and a raw effective efficiency of the power sensor is calculated [4].The second step is necessary to make corrections to the contribution of the microcalorimeter feeding lines. Unfortunately, several problems arise in the calibration step, including microcalorimeter dismount/mount operations, long-term thermal equilibrium, inherent uncontrollable changes in the thermal paths, differences between the power levels adjusted for each step, and very low measured values [1][2][3][4][5].…”

“…The manner in which this system works has been widely discussed in the relevant literature by other researchers [1][2][3] and by us [4][5][6]. However, independent of the technical solution adopted in each laboratory, the effective efficiency of the power sensor used as the calorimetric load can be expressed as the rational function of sensor mount temperatures.…”

Improvements on INRIM Coaxial Microcalorimeter and Outcome of a Model Comparison

“…This voltage is determined by means of the short circuit technique [15], [20], and it has to be halved to take into account the power reflected back by the short circuit. Finally, the term (1 + | S | 2 ) is an additional correction necessary to enhance the accuracy of the power standard when the reflection coefficient S of the power sensor under calibration is not negligible [18].…”