Research And Design Of The Rf Front-end Of Portable Spectrum Analyzer Based On Planar Integration Technology

Nowadays with the development of communication technologies,more and more spectrum analyzers are required for outdoor work.Portable spectrum analyzer has become a research area with large market demand.The thesis focuses on designing the RF front-end of the portable spectrum analyzer with an operating frequency of 9 kHz to 3 GHz.The main work of the thesis includes:Firstly,the background and the current researches of the portable spectrum analyzer are introduced.The advantages and disadvantages of those technologies are classified and analyzed.Compared to those technologies,high-intermediate-frequency heterodyne structure is applied in the RF front-end of spectrum analyzer.Secondly,the system scheme is determined according to the technical requirements of the RF signal chain.With the superheterodyne structure and the high Q Substrate Integrated Waveguide(SIW)intermediate frequency filters,the RF front-end presents high signal selectivity,high dynamic range,and high spur reduction characteristics.The whole module is designed as a six-layer microwave Printed Circuit Board(PCB),which isolates the signal layer,the power layer and the radio frequency circuit.The multi-layer structure has good electromagnetic compatibility and saves the area.The local oscillator adopts high-performance voltage controlled oscillator(VCO),instead of single wideband oscillator,in which miniaturization is reached and performance is guaranteed.With the help of the combined simulation of HFSS and ADS,the design of the SIW band pass filter,the radial microstrip stub filter are completed.Finally,the thesis finishes the test of the RF front-end and gives the test results.The return loss of receiving end is lower than-20 dBm,the sensitivity is up to-102 dBm,the spur reduction in the passband is more than 70 dBc,the phase noise of the third intermediate frequency is better than-95 dBc/Hz @ 10 kHz.The 1 dB compression point is greater than-2 dBm.And the IP3 is greater than 7 dBm.It can be seen from the results that the requirements of the RF front-end in the spectrum analyzer is met.The RF front-end in this thesis uses high Q SIW filter and high-performance VCO and finishes the design of miniaturization which performs as good as the desktop spectrum analyzers.Compared with commercial products of the same frequency band,the RF front-end in this thesis has better phase noise performance,and costs only one-tenth.The front-end can be used for affordable portable spectrum analyzer with the characteristics of simple structure,low cost and good performance.And is meaningful for the new generation of portable spectrum analyzer.