PURPOSE: To suppress intermodulation noise caused at transmission due to the nonlinear characteristic of a PIN diode phase shifter used for the phased array antenna system for transmission/reception operation.

CONSTITUTION: A transmission/reception branching device 2 is provided on each of element antennas 1 of the phased array antenna system, a transmission band exclusive phase shifter 3 is provided between the transmission/reception branching device 2 and a transmission wave distribution circuit 5, and a reception band exclusive phase shifter 4 is provided between the transmission/ reception branching deice 2 and a reception wave distribution circuit 6, then a bypassed intermodulation noise caused at transmission due to a nonlinear characteristic of the PIN diode phase shifters used for the phased array antenna system into a reception system is suppressed by the transmission/reception branching device 2.