Research On Multi-port Front-end Technique For SDR Receiver

With the rapid development of communication technology,the demand for quantity and quality of communication products is increasing.The increasing of quantity requires for a wider communication bandwidth,while the improving of the quality requires for more advanced communication techniques and optimization methods to guarantee.Conventional communication devices rely on hardware to achieve its performance,which brings many problems,such as the 4complex equipment structure,complex operations and high price.Therefore,there is an urgent need for new technology to change the existing state.Software-defined radio(SDR)is proposed to break the rule that realization of communication function between devices only relies on hardware.The SDR technology is widely used in many applications,especially the proposing of SDR receiver attracted more attention.In order to implement the high performance of SDR receiver,it is necessary to design a RF front-end with high quality in the receiverThe front-end of multi-port SDR receiver has many advantages,such as wide bandwidth,simple and efficient integration of Monolithic Microwave Integrated Circuit(MMIC).The six-port junction is a typical structure in multi-port technology.Scholars have done a lot of research work on this technology and designed many six-port junction circuits with novel structure and good performance.However,the bandwidth of six-port junction still can be improved.In order to extend the bandwidth and satisfy the need of project,two broadband six-port junction circuits are designed which cover the frequency ranges of 2.5GHz-10GHz and 6GHz-18GHz respectively.The bandwidth of the front-end in SDR receiver has been further improved by the six-port technology.The main works of the thesis are listed as follow:1?The principle of multi-port sensing and its mathematical model are described,and the theory of signal demodulation based on six-port junction is analyzed in detail,which provides the theoretical basis for the design of six-port junction circuit.2?An optimized six-port junction circuit which has good performance in 2.5GHz?10GHz is designed.Firstly,the Wilkinson power divider with 7 sections which works in 2.5GHz-11.5GHz and the cross and series coupler with 9 sections which works in 2GHz-12GHz are designed by the method of increasing the number of their sections.Secondly,the six-port junction circuit is designed by connecting a power divider and three couplers which are designed above.The simulation results show that the design of the six-port circuit has good performance in a wide frequency range.3?Another broadband six-port junction circuit is designed which works in 6GHz?18GHz.Firstly,a bifacial and out-phase power divider is designed by the structure of microstrip and slotline.Secondly,a combination design method is proposed by increasing the number of sections and optimizing the shape of coupled microstrip line.Then a microstrip-slot coupler with better performance is designed.Finally,the six-port junction circuit which connected by the bifacial and out-phase power divider and the microstrip-slot coupler is designed and has good simulation result.The circuit board is completed and the measured performance is worse than simulation performance because of the precision of circuit making.It can basically satisfy the actual requirements.4?The power detecting and calibration technology are described.The characteristics of square-law in diode will disappear in high power signal.Then non-linear calibration technology of the detector circuit is also studied in this thesis.