A Spectrum Analyze Algorithm Without Preselector Based On Fast Fourier Transform

Spectrum is one of the most important features of electric signal.Today,electric signal to be measured is becoming more and more complex,fast and accurate spectrum measurement becomes the target which morden electric measurement system goes after.After adding spectrum analyzer?SA?capability to a vector network analyzer?VNA?,in addition to measuring the S parameter,compression and distortion of the device under test or network,the VNA can perform spectral measurement and spur search simultaneously on all test ports and in-fxture/on-wafer spectrum analysis can benefit from VNA calibration and fxture de-embedding technique.This capability lead to promotion of measurement speed and accuracy,simplification of testment procedure and lower cost,and integration of instruments is becoming tendency.In this paper,a spectrum analysis algorithm without pre-selector based on fast fourier transform?FFT?is put up and optimized,which is based on both domestic and foreign spectrum analysis methods.Furthermore,an experiment on available VNA is conducted to test the feasibility of the algorithm.To solve above problems,the theory of spectrum analysis on VNA is discussed carefully in this paper and a set of spectrum analysis algorithm without pre-selector is designed.In this paper,the method of image signal rejection is mainly discussed to solve problems caused by the structure.Meanwhile,other important questions were discussed.Radio frequency?RF?and intermediate frequency?IF?errors in VNA are analyzed and calibrated to enhance accuracy of the measurement.Parameters,characteristic and range of application of several window function are discussed to reduce spectrum leakage and scalloping loss of FFT.Software-based detector and average method are developed to process raw data.To implement the algorithm,first of all,a MATLAB simulation program and an ADS simulation model are developed.The MATLAB-ADS joint simulation demonstrates the feasibility of the algorithm indirectly.Secondly,to execute the algorithm in a filed test,an experiment platform based on VNA manufactured by the 41^st research institution of CETC was built up and a MATLAB program was developed to control the instrument and execute spectrum analysis.The different functions are modularized to simplify update process in the future.