Complex permittivity multi-frequency measurements for dielectric sheets using a circular disk resonator

An improved complex permittivity measurement method is shown that uses a resonator composed of two circular disks of different radii, where (1) the effective radius of each disk due to the fringing field is estimated by comparing two resonance frequencies and (2) the disks of different radii are used to cancel out conductor loss. The method utilizes a balanced-type circular disk resonator excited at its center through coaxial cables. The basic features of the proposed method are that (1) the perpendicular E-field complex permittivity of a dielectric sheet is measured, (2) only TM0m0 modes having different integer values are selectively excited and (3) multiple frequencies are measured. By using the proposed method, the complex permittivity of polytetrafluoroethylene, polyimide and fiber-reinforced epoxy sheets are measured from 5 GHz to 30 GHz.