Wideband current shunts are usually used in national metrology institutes to perform AC current measurements. Actually, current shunt standards are commonly calibrated up to 100 kHz using a low frequency approach. The existing traceable measurement methods to characterize current shunt standards are limited in frequency to 100 kHz for current levels above 10 A. This paper describes a theoretical basis of a new high frequency approach based on the use of an impedance matching circuit and a Vector Network Analyzer (VNA). Theoretically, this new method is able to measure and characterize current shunts at frequencies up to 1 MHz.