Spectrum analyzer is a versatile electronic measuring instruments to study on electrical signal spectrum structure, which is applied to the measurement of the signal distortion, modulation, spectral purity and frequency stability and it also can be used to measure the amplifier and filter of the circuit system. It can also be called frequency-domain oscilloscope, trace oscilloscope, harmonic analyzer, frequency analyzer, etc. Modern spectrum analyzer can display the results of the analysis in digital or analog mode. If the instrument internal adopt digital circuits and microprocessors, it can be with storage and computing functions.