Research On High Performance Planar Diplexer For Wireless Communication

With the rapid development of wireless communications industry in recent years,the frequency resource becomes increasingly scarce for wireless communications.To make full use of frequency resource,some new technologies are exploited.However,the use of new technologies requires the support of radio frequency circuits.Therefore,it is of great significance to research RF front-end devices that meet different communication requirements and support different communication methods.As an important part of the communication RF front-end system,the diplexer requires the characteristics of high selectivity,high isolation,and adjustability to adapt to the ever-evolving communication system requirements.Therefore,the diplexer performs various functions.It is of great significance to conduct a comprehensive study.Based on the research work undertaken during my master's degree,this thesis conducted in-depth research on new cross-coupling theory and hybrid electromagnetic coupling theory,and proposed several related high-performance diplexers.The main research contents are as follow:(1)The cross-coupling theory has been deeply studied.Based on the traditional cross-coupling theory,the cross coupling of the source coupling has been further explored to improve the selectivity of the transition band.A diplexer using a high-temperature superconducting technology is proposed.A stub-loaded resonator is used as a common resonator instead of the conventional matching network in the diplexer.Transmission zeroes are introduced through the coupled line to improve the selectivity and isolation of the diplexer.Degree,and analyzed different cross coupling methods.Measured results of fabricated circuit show that the diplexer has a smaller volume,higher isolation,and very low insertion loss.Applying the diplexer to a mobile communication system can improve the system's near-frequency anti-jamming capability,thereby improving spectrum utilization.(2)The hybrid electromagnetic coupling theory is researched.The relationship between hybrid electromagnetic coupling characteristics and transmission is researched,and a highly-divisable tunable diplexer is proposed.The varactor diode characteristics and loading methods are analyzed,various types of loading methods are studied,and the hybrid electromagnetic coupling theory is studied.Two channels of the diplexer are designed with different hybrid coupling properties to generate different transmission zeros to improve the isolation of the diplexer.The loaded varactors achieve the frequency tunability of the diplexer.Applying the diplexer to a cognitive radio system can increase the utilization of the frequency band.(3)The theory of bandwidth stability and the hybrid electromagnetic coupling are analyzed.First,the filter coupling theory is analyzed to analyze the relationship between the coupling coefficient and the external Q value with frequency under the premise of absolute bandwidth stability.Then the hybrid electromagnetic coupling is used to control the change trend of the coupling coefficient between the resonators and the frequency,and a resonator with a controllable slope of the coupling coefficient is designed.Finally,varactor diodes are loaded on the resonator to provide an absolute bandwidth stable tunable bandpass filter.Then an tunable diplexer with absolute bandwidth stability is achieved.The diplexer enhances the passband selectivity by introducing a transmission zero through the source-load coupling,and the diplexer eliminates the inter-resonator coupling control unit,and controls the center frequency in a relatively concise manner while satisfying the absolute bandwidth stability.This study is in line with the practical application of cognitive radio communication systems and further improves the utilization of frequency resources.