This article describes a novel approach to measure responsivity of a FET-based sub-THz detector using on-wafer probes to directly feed a bare antenna-less detecting device. Thus, the approach eliminates the need to know beforehand the detector’s effective aperture, which can be a source of large variation between responsivity measurements of various FET-based detectors often cited in the literature. It seems that the presented method can be useful at making direct comparisons between responsivity of various devices (e.g., MOSFETs, HEMTs etc.). As a demonstration, the sub-THz responsivity of a pHEMT device fabricated using a commercial GaAs process has been measured in a WR-3 frequency band. Additionally, the results have been compared against data obtained using an alternative approach. The verification method consisted in integrating exactly the same device with a broad-band antenna and a carefully selected high-resistivity silicon lens and comparing its performance with that of a commercial calibrated detector based on Schottky diodes.

An innovative measurement setup for the dielectric characterisation of fibres in a terahertz time-domain spectrometer using an HDPE elliptical lens for coupling into the fibres has been built and validated by measurements of several different types of samples. The setup is based on a commercial all fibre-coupled terahertz time-domain spectrometer. Measurements of the effective refractive index have been conducted on polypropylene-based three-dimensional printing filaments, silica glass rods, and a polytetrafluoroethylene cord of lowered density, covering the frequency range of approximately 100 GHz to 1 THz. The theoretical part of the work includes numerical calculations performed via the finite difference eigenmode method and the characteristic equations of a uniform circular dielectric waveguide for a few guided modes, from which it is clear that primarily the fundamental mode propagates along the fibre. Details on model-based phase corrections, crucial to the accurate determination of the effective refractive index of dispersive fibres, have been presented as well.