Traditionally, RF measurements of materials have been dominated by the paradigm of taking witness samples into the laboratory. This is because of the historically large size of both the microwave analyzer equipment and the fixturing. Recent technological developments in both compact spot probes and compact microwave analyzers are now enabling a dramatic shift in this paradigm. This article discussed the concept of a hand- held reflectometer system for measurement of microwave relevant materials. The technology described here integrates the microwave analyzer and sensor, thereby eliminating the need for RF cables.
A second recent technology improvement that has also advanced the design of new materials measurement fixtures is advanced computational electromagnetic simulation. High accuracy modeling techniques combined with ever faster computers allow new measurement fixture designs. In the past, fixtures were designed so that they could be modeled with simplified analytical equations. Now fixtures can be designed without this constraint. Additionally, numerical simulations can be used to convert measured parameters directly into the desired intrinsic material properties.
This article showed an example of such a system, which uses a computed look-up table to do this material property inversion at VHF and UHF frequencies. Because of this, newer engineered composites such as meta- materials can be characterized. In general, the described system provides a new capability for measuring effective dielectric properties on materials that are both anisotropic and inhomogeneous.
From these measurement system examples, it is evident that the advances of i) miniaturized VNAs and ii) CEM based design and inversion provide critical enabling technologies for the creation of new materials measurement systems. From this, the microwave industry can expect to see new measurement devices and methods, with capabilities that were not previously attainable with conventional techniques.
