Equivalent impedance retrieval of planar surfaces by open resonator technique

The use of an open resonator system with an optimized coupling transition to the feeding waveguide is proposed in this work to accurately characterize the equivalent impedance of planar surfaces from return loss measurements. A modeling circuit derived from a complete modal expansion is adopted to optimize the coupling as well as taking into account for the cavity losses. Two application contexts are considered as validation examples, namely the complex permittivity retrieval of thin substrates and the phase response characterization of microstrip reflectarrays. For both applications, successful K-band experimental results are presented.