Comparison of two post-calibration correction methods for complex permittivity measurement of biological tissues up to 50 GHz

Two correction methods are discussed in this paper to remove residual errors due to the lack of repeatability of coaxial-to-microstrip launchers as part of the TRL calibration procedure. These methods are applied for accurate insertion loss measurement of biological tissues embedded in a two-port microstrip test fixture, from which the tissues' complex permittivity values are extracted for frequencies between 15 and 50 GHz. In the first method, distilled water is used as a calibration standard as part of a two-port calibration procedure. The second method identifies an error transfer function using the difference between simulated and measured insertion loss for distilled water, and then applies it as a correction factor to the measurement results for biological tissues. Both methods are compared in terms of extracting the accurate complex permittivity of brain matter.