Microstrip patch antenna sensor for measurement of the permittivity of homogeneous dielectric materials

The application of a small air-spaced coaxially fed rectangular microstrip patch antenna as a sensor for the measurement of the permittivity is presented. The models derived for the calculation of the permittivity from the shift in the resonant frequency for solid and liquid materials are described. The models are experimentally verified by measurements on several liquids and solid samples. The results are compared with those obtained using standard techniques, such as coaxial probe and waveguide cell measurements. An error correction technique for the elimination of the systematic error of the measurement is also included. The structure has very good sensitivity particularly for liquids, where the space between the patch and ground plane as well as the space above the patch are filled with the liquid under test. It is well suited for measurement of the complex permittivity of liquids or for monitoring of changes in permittivity values for solid and liquid materials.