Nondestructive Measurement of Lossy Materials using the Reflection from an Array of Narrow Series Slots on the Broad Face of a Rectangular Waveguide

The reflection from an array of narrow series slots on the broad face of a rectangular waveguide is used in order to determine the dielectric properties of the medium into which the slots radiate. The relationship linking the reflection coefficient to the complex permittivity is obtained, from the theoretical study of the electromagnetic field in the vicinity of the slots. A system of integral equations is established for an arbitrary set of slots, taking into account both internal and external mutual coupling. The numerical solution is discussed and an optimization procedure for the array is presented, providing a simple relationship over a specified permittivity range. Computed results are compared to experimental values.