The design of a portable terahertz and subterahertz interferometer, manufactured according to the Martin-Puplett scheme, is presented. The possibility of using film polypropylene polarizers in interferometers of this type has been demonstrated. The provided possibility of using various types of radiation detectors makes it possible to perform measurements in high-performance or high-sensitivity modes. The presented interferometer is proposed to be used to measure the spectra of terahertz and subterahertz radiation produced during the interaction of bunched and continuous beams of charged particles with solid targets.