| In the information age with rapid development,information exchange has become the most basic needs of human society.The applications of wireless communication appear everywhere.The whole world is connected by a variety of different radio signals.In different application scenarios,the transmission signal has different communication standards,frequency range and modulation schemes for transmitting efficiently.For example with the 5th generation mobile communication technology(5G)proposing,the existing equipment will not be able to satisfy this new communication standard,and thus have to upgrade hardware and pay a higher price.The RF receiver based on Software Defined Radio(SDR)technology can receive and demodulate the signals with different standards,frequency range and modulation schemes by changing the software parameters in different scenarios,without adjust the hardware structure.It is an important research direction of the RF receiver.Multi-port technology can transform the RF signal into baseband signal directly,and then the baseband signal will be digitized.Since it can satisfy the design goals of the SDR,the research on the multi-port direct conversion receiver will have important practical significance.This thesis analyzes the principle of multi-port microwave network structure,and analyzes the modulation and demodulation principle of the six-port microwave network structure emphatically.Designed and implemented two different six-port junctions.The first six-port junction with monolayer microstrip line structure has a frequency range from 1.8GHz to 3.1GHz.Its bandwidth is improved by open stub.The other six-port junction extends the number of sections,and changes the position of open stub in the coupler,then a six-port junction with size saving and a frequency range from 6.5GHz to 10GHz has been designed.The six-port junctions have good amplitude and phase characteristics with simulation.Finally,the circuit board is made and tested,the result shows that the performance of six-port junction is good as expected.Secondly,this thesis analyzes and compares the characteristics of different kind of receivers.Compared to superheterodyne receiver.direct conversion receiver has simple structure and can be easily integrated and has no mirror frequency interference.The direct conversion receiver based on multi-port technology can transform the RF signal into baseband signal directly with schottky diode detector by utilizing the feature that the output signals of multi-port network structure consists of amplitude and phase information of input signals.Then research and design a new transceiver system based on six-port technology which uses variable terminal load to achieve direct microwave band QAM modulation.It greatly simplifies the hardware system and has good reception performance.Finally,the calibration techniques of multi-port direct conversion receiver were studied.The devices,equipment and system can be calibrated in software layer by calibration techniques,and the performance and accuracy can be improved without changing the hardware.Studied the calibration method of six-port junction a new linear calibration method based on QPSK signal and a new nonlinear calibration method for schottky diode are proposed,and the demodulated accuracy of received signal has been improved. |
