With the multiplication of wireless communication applications, spectrum analyzers become universal instruments for signal analysis in the spectral domain. RF spectrum analyzers are generally based on the superheterodyne receiver principle, whose selectivity properties (resolution bandwidth) are determined by filters at the intermediate frequency. The frequency tuning is carried out using the transposition oscillator. Recent devices, notably the “Vector Spectrum Analyzers”, still use the principle of frequency transposition, digitization takes place as soon as the FI (increasingly broadband) and are particularly studied to meet the needs of test and measurement in radiocommunications Digital (3G, WCDMA, WLAN …). All the operations of filtering, FFT, demodulation and analyzes are carried out by digital processing by DSP. Thanks to these increasingly rapid processing methods, the spectrum analyzer has an increasingly “real-time” capacity.