A Measurement System For Investigating The Dielectric Properties Of Low-Loss Polymers

Abstract

Polymers with low dielectric losses are largely used in several electromagnetic applications, for example in telecommunications cables, antennas, and microwave devices and components. The interest in studying their dielectric properties has a twofold motivation: (1) a scientific motivation, because the study of polymers is one of the main fields of material science; and (2) an industrial one, because a material with better dielectric characteristics—i.e. lower dielectric losses—is commercially more suitable for the market. The measurement of both dielectric constant and losses is not a straightforward task when dealing with low-loss materials. In this paper we describe a measurement system, based on a revisitation of the well known method of re-entrant cavity, which by a thorough electrical modeling of the sample holder allows absolute measurements to be performed on dielectrics with loss tangent as low as 10−4. The technique is validated on low-loss substrate materials of known characteristics. Measurement examples are reported concerning two fluorinated polymers based on TFE and ECTFE.