Branch-coupled dual-band attenuator

This invention relates to a branch-coupled dual-band attenuator comprising a substrate and a branch coupler covered on the substrate. The branch coupler comprises a first transmission line, a second transmission line, a third transmission line and a fourth transmission line which are sequentially and vertically surrounded and connected as a rectangle to respectively produce their corresponding characteristic impedances. The branch coupler further comprises a first port, a second port, a third port and a fourth port disposed at the connections of the first transmission line, the second transmission line, the third transmission line and the fourth transmission line, wherein the first port is a signal input port, and the fourth port is a signal output port. Any of the second port and the third port is connected to a resistor in parallel. The middle sections of the first, second, third, and fourth transmission lines are respectively provided with two open circuit ends, and the two open circuit ends of the first,