Signal analysis apparatus and signal analysis method

A signal analysis method for analyzing a measured signal (SRF) of a frequency fRF, the signal analysis method comprising:

• a frequency setting step (S2) of deciding a first intermediate frequency fIF1, a frequency fLO1 of a first local oscillation signal, and a frequency shift amount Δf in accordance with a center frequency fc of the frequency fRF;
• a first local oscillation step (S3) of outputting the first local oscillation signal (SLO1) of the frequency fLO1;
• a first frequency mixing step (S4) of generating a first intermediate frequency signal (SIF1) of the first intermediate frequency fIF1 by performing frequency mixing of the measured signal with the first local oscillation signal, and generating a first spurious signal (SSP1) including a second harmonic component of the measured signal;
• a bandpass step (S5) of a passed center frequency f0 into which the first intermediate frequency signal and the first spurious signal are input;
• a second local oscillation step (S6) of outputting a second local oscillation signal (SLO2) of a frequency fLO2;
• a second frequency mixing step (S7) of generating a second intermediate frequency signal (SIF2) of a second intermediate frequency fIF2 by performing frequency mixing of the first intermediate frequency signal passing through the bandpass step with the second local oscillation signal, and generating a second spurious signal (SSP2) by performing frequency mixing of the first spurious signal passing through the bandpass step with the second local oscillation signal;
• an AD conversion step (S8) of performing AD conversion of the second intermediate frequency signal and the second spurious signal;
• a frequency shift step (S9) of performing frequency shift of the second intermediate frequency signal and the second spurious signal after the AD conversion performed in the AD conversion step by the frequency shift amount Δf on a frequency axis;
• a digital filter step (S10) of a passed bandwidth W in which a second intermediate frequency signal (SIF2′) after the frequency shift performed in the frequency shift step is allowed to pass, and a second spurious signal (SSP2′) after the frequency shift performed in the frequency shift step is removed;
• and
• a signal analysis step (S11) of analyzing the second intermediate frequency signal passing through the digital filter step,
• wherein the first intermediate frequency fIF1 is provided as f0+Δf,
• the second intermediate frequency fIF2 is provided as |f0+Δf−fLO2|,
• a second intermediate frequency fIF2′ of the second intermediate frequency signal after the frequency shift performed in the frequency shift step is provided as |f0−fLO2|,
• the frequency fLO1 is provided as fc+f0+Δf,
• a frequency fSP1 of the first spurious signal is provided as 2×fRF,
• a frequency fSP2 of the second spurious signal is provided as |fSP1−fLO2|,
• a frequency fSP2′ of the second spurious signal after the frequency shift performed in the frequency shift step is provided as |fSP1−fLO2−Δf|, and
• in the frequency setting step, the first intermediate frequency fIF1 and the frequency fLO1 are decided using the frequency shift amount Δf that does not establish a relationship of −W/2≤|fSP1−fLO2−Δf|−fIF2′≤+W/2.