X-band Radar system that has been developed at Universitas Indonesia is a monostatic Radar type, this Radar is using a single antenna for transmitter and receiver. The advantage of this system is cheaper production costs because it only requires one antenna. However one disadvantage of this system is the possibility of the incoming signal which interfere with the signal received by the antenna. To overcome this, we need a device system which has high isolation to suppress interference of electromagnetic waves generated by the transmitter and receiver. Isolation required to suppress interference for a Radar system is ≤ −60 dB and insertion loss ≤ −3 dB. In this research, a design of high isolation system is proposed for the integration of lange coupler design with circulator to get high isolation and better insertion loss. The design of the lange coupler and the high isolation systems were simulated using Advanced Design System (ADS) software. The material used for the coupler is Taconic TLY-5 C1, while the circulator used is a commercial circulator. From the simulation results of the lange coupler, the isolation value at the center frequency 9.4 GHz is −69.63 dB and the insertion loss is −0.03 dB. While the isolation results of high isolation system, obtained the value at the center frequency 9.4 GHz is −72.89 dB and the insertion loss is −0.03 dB. The high isolation system can give higher isolation, therefore this design can be applicable for for monostatic X-band Radar system.