An improved technique for measuring electromagnetic properties of curved surfaces coating materials with open-ended coaxial line probe

An improved open-ended coaxial probe technique for measuring electromagnetic properties of coating materials with curved surfaces (both convex and concave) is studied. FDTD modeling indicates that the reflection coefficient of the loaded probe is more sensitive to concave surface samples than to those with convex surface. In order to satisfy concave surface materials testings we proposed a technique to improve the measurement accuracy by modifying the standard coaxial probe. A ring patch is added at the end of extended inner conductor throughout the air gap between the probe and the material under test. The performance of the proposed technique is examined. The derived Ε* and μ* of several microwave absorbing materials coated on prototype boxes by using the new probe are relatively in agreement with the published data.