We describe the setup for the broadband millimeter/submillimeter characterization of the quasi-optical elements and the dielectric materials commonly used in microwave receivers operated in microwave astronomy. The setup is made of a large aperture (100 mm) Fourier transform spectrometer coupled to a transition edge superconducting detector. The system has been assembled and characterized in different configurations and operation modes for the acquisition of interferograms from various kinds of samples. After the initial test runs, the configuration is now being updated to ensure a broader range of measurements, including reflectance and scattering. We plan to first use this testbed for the characterization of the dielectric materials used in the LSPE/SWIPE experiment, devoted to the study the polarization of the Cosmic Microwave Background.