AbstractThe paper describes the measurement of complex permittivity in free space. It is an advanced non-contact method which is used to find the electromagnetic properties of materials. In this case it involves the materials which are used in aviation technology, especially for hardening the avionics against electromagnetic interference. A specialized laboratory workplace equipped with the vector network analyzer ZVA 67 from Rohde and Schwarz was built for the measurement. Initial measurements were performed at high frequencies from 220 to 325GHz on a Teflon sample because of the ease of verifying the results. The high frequency range was achieved by using ZVA-Z325 converters from the same company and the respective antenna systems. This measuring system was used for determining the transmission coefficients. The complex permittivity which characterizes the electromagnetic properties of the material for the above frequency range was found by iterative method programmed in Matlab environment.