US Patent 6958630 High-frequency detection method and high-frequency detection circuit

A high frequency detection circuit detects information about a first high frequency power in a high frequency power source device supplying the first high frequency power having a first frequency and a second high frequency power having a second frequency lower than the first frequency to a load. A third high frequency signal that is a mixed signal of a first high frequency signal having the first frequency and a second high frequency signal having the second frequency is detected by a directional coupler. The third high frequency signal is converted to a fourth high frequency signal having a third frequency between the first and second frequencies using a heterodyne system. A progressive wave power of the first frequency is detected based on the fourth high frequency signal.