A study on reflection coefficient from double layered lossy dielectric by using flanged rectangular waveguide

Knowing the permittivity and permeability of materials is often needed when we design radar absorbers or radomes. Although the resonator method and waveguide method are widely used for microwave measurement, they require one to cut a sample for fitting inner walls, is labor intensive, and it is difficult to obtain accurate measurements especially on higher frequencies because of the occurrence of errors due to the gap between the wall and the sample. In practical measurements of the reflection coefficient it is necessary to consider the error occurrence caused by insufficient contact between the flange and the measured sample. The effect of this insufficient contact is considered by regarding these contacts as an equivalent dielectric layer. We derived the reflection coefficient of the double layered dielectric structure and studied theoretically the effects of the existence of an air or dielectric gap between the flange and a lossy dielectric sheet.