The Clamped Circular Waveguide Method for Microwave Material Characterization

This paper introduces a non-destructive clamped circular waveguide method for the microwave material characterization of sheet-like materials. Utilizing two open-ended circular waveguide probes, a sample can be clamped between them, allowing both transmission and reflection coefficients from the material under test (MUT) to be measured. A unique feature of the clamped circular waveguide method resides in the axially symmetric TE01 operating mode found in the circular waveguides. This mode prevents field coupling and radiation issues seen in the clamped rectangular waveguide method. Additionally, this method addresses several issues present in many microwave measurement methods found in the literature, such as precise sample shaping, limited data from one-port measurements, and meticulous sample placement and alignment. The working theory behind the clamped circular waveguide method is presented in this paper, along with measurements of the complex permittivity of several materials in the 32-40 GHz frequency range.