Patent ID: 7904038

Claim:
An output monitor circuit of a radio-frequency circuit which monitors a radio-frequency (RF) signal of wavelength λ that is output from a radio-frequency circuit, comprising: an output line formed on a substrate, wherein the output line inputs the radio frequency signal from an RF input end, and transmits the radio frequency signal to an RF output end; a coupling line of a length less than λ /4 formed on the substrate and that faces and couples with the output line; a terminating resistor placed on the substrate and connecting one end of the coupling line that is located on a side of the RF input end of the output line and a grounding line on the substrate; a detection circuit placed on the substrate and which detects a radio-frequency signal derived from the coupling line, to produce a monitor signal; and a back flow blocking circuit which blocks signal components back flowing from the RF output side toward the output line in a portion where there is no coupling between the output line and the coupling line.