Further study on in-situ measurement of complex EM parameters with a flanged open-ended coaxial probe

A measurement system based on open-ended coaxial probe technique is set up to characterize the EM properties of radar-absorbing material situ. Frequency-varying method (FVM), which simultaneously extracts complex EM-parameters, i.e. ε and μ, by intentionally varying the test frequency to obtain two different reflections, is further studied with an emphasis on several key techniques. Criterions for a right order of the interpolation polynomial used to approximate the frequency-dependent EM-parameters; measures to reduce the residual mismatch errors in reflection measurements and to suppress the ambiguities in solving the transcendent equation system are discussed in detail. Several typical radar-absorbing coatings are measured via FVM and the good results validate the feasibility of this in-situ measurement technique.