This paper describes a novel method of characterizing complex permittivity using a complementary frequency selective surface (CFSS). The CFSS provides a passband behavior and the change in the passband when a material under test (MUT) is placed adjacent to the CFSS has been used for retrieving of the complex permittivity of the MUT. The complex permittivity of the MUT are determined based on the measured bandpass resonant frequency and insertion loss of the CFSS with the MUT. This is an amplitude-only method where phase measurements are not required. This technique offers a convenient, fast, low-cost and nondestructive measurement that is not restricted by the sample size or shape.
