Dielectric Characterization of Curved Structures Using Flangeless Open-Ended Waveguide Measurement

Open-ended waveguide measurement of layered structures is a well-developed method for determining dielectric and thickness properties of the layers. A full-wave electromagnetic model has been previously developed, which includes the effects of the high-order modes, as a forward model describing the complex reflection properties of layered structures. The open-ended waveguide flange design has also been optimized to closely approximate the electromagnetic assumptions made in the electromagnetic model. However, in certain measurement situations the size of the flange creates gaps between the aperture of the waveguide and the structure being tested. This is often the case for uneven or curved surfaces, which affects the accuracy of dielectric property measurements. This paper presents an empirical method to account for the effect of a flangeless open-ended waveguide probe to enable measurement of curved surfaces and significantly reduce the undesired effect caused by such gaps.