Research And Implementation Of QPSK RF Direct Modulator

The transmission of lots of data in the process of development of the satellite remote sensing is a problem that must be solved.As a result,the modulator is the key part of the satellite.QPSK(Quadrature Phase Shift Keying)direct modulation is a advanced modulation approach which has strong anti-interference,faster transmission rate,high reliability.Therefore it is widely used at home and abroad.Due to the limitation of the machining accuracy and the processing craft on microstrip substrate,the technique of QPSK RF direct modulator was begun very late in our country,and the technology in this field is relatively backward.It is necessary to research about the modulator.Besides,the thesis does in-depth research from my own practical work.I believe that the research about the technique of QPSK RF direct modulator is important in engineering application.First,the thesis introduces the working principle of QPSK direct modulator,and it is detailed analysis about the performance index of the modulator.Then the thesis simulates and models the characteristics of Lange Bridge,Willkisin and microwave filter step by step.According to the implements modeling and simulation,layout file and put into production.At last,a lot of electric performance tests have been done on the actual object.The size of the direct modulator is 73mm×45mm×19mm.Through the test of the actual object,this thesis analyzes the measured results and compared with the results of simulation.After the modulator were assembled,each module was debugged..Especially,these key electric performances such as I/Q amplitude and phase imbalance have been focused on.Because the debugging on I/Q amplitude and phase imbalance is a key and difficult problem,we do lots of work,such as we debug the module with the indium.According to the test results on the actual object.We can draw a conclusion from the test data that the VSWR of input/output is less than 1.2 and group delay ripple is not larger than 5ns,and these reach a good level.The phase imbalance improves from 4.0oto 2.69 o,and the amplitude imbalance improves from 1.0dB to 0.31 dB.Test and simulation results verify that our design approach is reasonable and accurate.