Patent ID: 7907032

Claim:
A directional coupler comprising: a substrate; a main line on said substrate and connected at a first end to an input port and at a second end to an output port; a coupled line on said substrate and extending along said main line, said coupled line being connected at a first end to a coupled port and at a second end to an isolated port, said first end of said coupled line and said input port being located at a first side of said directional coupler, said second end of said coupled line and said output port being located at a second side of said directional coupler; and a phase shifter connected at a first end to said isolated port and at a second end to said coupled port, wherein coupling length between said main line and said coupled line is shorter than one-quarter wavelength of the frequency of power transmitted from said input port to said output port, and said phase shifter phase shifts a second reflected wave component such that the second reflected wave component is opposite in phase 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.