The measurements of the characteristics of an artificial mains network (AMN) are always affected by an AC-coaxial adapter connecting an impedance measuring equipment to the AMN. The present paper theoretically investigates the influences of the adapter on the measured AMN S-parameters in terms of the mode S-parameters. As a result, it proposes a correction method for eliminating the adapter influences in order to reveal the true AMN characteristics. The experimental measurements using two adapters of considerably different characteristics prove that the proposed method can yield almost the same estimates of the AMN impedance.