Patent ID: 7176670

Claim:
A method for analyzing a spectrum of an input signal (χ(t)) having at least one line with a center frequency (ω x ) at the center of the line comprising the following steps: zero-mixing the input signal (χ(t)) to produce a base band signal (y(t)) by sweeping a local oscillator frequency (ω s ); filtering the base band signal (z(t)) with a resolution filter to produce a filtered base band signal (y(t); and reconstructing the envelope (E(ω)) of the spectrum of the input signal (χ(t)) by using an estimated amplitude (ŷ x ) at an estimated center frequency ({circumflex over (ω)} x ) of each line of the input signal (χ(t)), wherein only the real component (I) of the base band signal (z(t)) is filtered with the resolution filter and the imaginary component (Q) is generated from the filtered base band signal (y(t)) by performing a Hilbert transform, wherein the amplitude values of the imaginary component (Q) generated by performing the Hilbert transform are corrected by an estimation on the basis of the neighboring amplitude values of the real component (I).