Open-ended rectangular waveguides are widely used for microwave and millimeter wave nondestructive testing applications. Applications have included detecting disbonds and delaminations in multilayered composite structures, thickness evaluation of dielectric sheets and coatings on metal substrates, etc. When inspecting a complex multilayered composite structure, made of generally lossy dielectric layers with arbitrary thicknesses and backing, the dielectric properties of a particular layer within the structure is of particular interest, such being health monitoring of structures such as radomes. The same is also true where one may be interested in the thickness or more importantly thickness variation of a particular layer within such structures. An essential tool for estimating the dielectric constant or thickness is an accurate model for simulating reflection coefficient at the aperture of the probing open-ended waveguide. One issue of interest is that radiation from open-ended rectangular waveguides into layered dielectric structures has been considered only when accounting for the dominant waveguide mode. However, when using these models for recalculating dielectric constant or thickness, the results may not be accurate (depending on the measurement requirements). To this end, this paper provides an accurate model for the reflection coefficient which also accounts for the effect of higher-order modes. Finally, the potential of this model for accurately estimating dielectric constant is shown.

Meeting Name

IEEE Instrumentation and Measurement Technology Conference, 2008 (2008: May 12-15, Victoria, BC, Canada)


Electrical and Computer Engineering

Keywords and Phrases

Dielectric constan; Higher-order modes; Open-ended waveguide; Stratified dielectric medium; Thickness; Applications; Ceramic capacitors; Composite coatings; Composite structures; Computer networks; Dielectric properties of solids; Dielectric waveguides; Electromagnetic waves; Energy absorption; Error analysis; Instruments; Measurement theory; Nondestructive examination; Permittivity; Radomes; Rectangular waveguides; Reflection; Structure (composition)

International Standard Book Number (ISBN)


International Standard Serial Number (ISSN)


Document Type

Article - Conference proceedings

Document Version

Final Version

File Type





© 2008 Institute of Electrical and Electronics Engineers (IEEE), All rights reserved.

Publication Date

01 May 2008