Thermoelectric power sensors can now be used as transfer standards, instead of bolometers, in the microcalorimeter technique. This alternative has the technical advantages to be less sensitive to absolute temperature and not downward frequency limited. At INRiM the high frequency power standards are now based on coaxial thermocouples from dc to 34 GHz. Modified commercial thermocouple mounts in 7 mm and 3.5 mm coaxial line are used to realize the national power standard with an accuracy ranging from 0.03 % to 1 % in the mentioned frequency ra nge.

In this paper we present the outcome of the first international comparison in the terahertz frequency range among three different kinds of spectrometers. A Fourier-Transform infrared spectrometer, a Vector Network Analyzer and a Time-Domain Spectrometer have been employed for measuring the complex refractive index of three travelling standards made of selected dielectric materials in order to offer a wide enough range of parameters to be measured. The three spectrometers have been compared in terms of measurement capability and uncertainty.

This paper analyses two possible estimators for the modulus of a complex-valued quantity. The case of uncorrelated and normally distributed real and imaginary parts is treated. The expectations of the two estimators are calculated for varying parameters of the two normal distributions. They are derived analytically, when possible, otherwise numerically by means of Monte Carlo simulations. Studying the statistical behaviour of the two estimators, it can be deduced which represents the best choice, depending on the specific experimental context. The relationship between the second estimator and the maximum likelihood estimator for a Rayleigh distribution is also presented. Examples from the metrological and physical fields are provided in order to compare the considered estimation methods.