In the system of TT&C, the RF signal into IF signalby the multistage frequency conversion, the traditional frequency conversion structure is complex, the isolation between RF port and LO port is small. For these defects of the traditional mixer, this paper designs a sixport mixer structure consisting of a passive sixport junction, a squarelaw detector, and a differential amplifier, its work center frequency is 2.25 GHz. Firstly, the structure and frequency conversion principle of sixport mixer are analyzed,the sixport junction and sixport mixer were simulated by ADS software.The simulation shows that the sixport junction has good isolation and phase transmission characteristics, sixport mixer with low conversion loss, large dynamic range and low required local oscillator power. So the use of sixport mixer to replace the traditional mixer structure has some advantages with a simple structure.