Patent ID: 8289102

Claim:
A directional coupler comprising: a main line located on a substrate, said main line having a first end connected to an input port, and a second end connected to an output port; a coupled line located on said substrate and extending along said main line, said coupled line having a first end located at the same side of said directional coupler as said input port and connected to a coupled port, and a second end located at the same side of said directional coupler as said output port and connected to an isolated port, wherein coupling length between said coupled line and said main line is shorter than one-quarter wavelength of power transmitted from said input port to said output port; a first capacitive element located on said substrate and having a first end connected between said coupled port and said first end of said coupled line, and a second end connected to ground; a second capacitive element located on said substrate and having a first end connected between said isolated port and said second end of said coupled line, and a second end connected to ground; and a phase shifter having a first end connected between said isolated port and said first end of said second capacitive element, and a second end connected between said coupled port and said first end of said first capacitive element, wherein said phase shifter phase shifts a second reflected wave component such that the second reflected wave component is opposite in phase with respect to a first reflected wave component, the second reflected wave component traveling from said output port to said coupled port through said isolated port and said phase shifter, and the first reflected wave component traveling from said output port to said coupled port through said coupled line, and includes an inverting amplifier having a first end connected between said isolated port and said first end of said second capacitive element, and a second end connected between said coupled port and said first end of said first capacitive element.