Design And Implementation Of High-Performance Radio Frequency Combiner

RF combiner is an indispensable and important device in modern wireless communication system,widely used in mobile communication system and base station.In recent years,with the continuous development of mobile communication technology,the requirements for the performance indicators of the combiner have been continuously improved,especially the passive intermodulation characteristics of the combiner,which have an increasingly obvious impact on the overall performance of the mobile base station.Based on this,In this thesis,the main design factors affecting the passive intermodulation characteristics of the combiner of the common cavity are studied,and based on this research,two high-performance RF combiners with low loss,high rejection and low intermodulation are designed.Based on the analysis of the type,performance parameters and design method of the combiner,this thesis studies the passive intermodulation characteristics of the combiner based on the coaxial cavity combiner.Through the study of the tuning rod of the resonant cavity of the combiner,the tap structure at both ends,and the electric field,magnetic field or current density of the steps between the cavities,the main design parameters affecting the passive intermodulation of the combiner in the actual design process are analyzed.And a method to reduce passive intermodulation is proposed,and two high-performance RF combiners based on common cavity are designed according to this method.In this thesis,a dual-band combiner is designed.The loss characteristics of the combiner are improved by the common cavity structure at the input and output ends,so that the return loss is lower than-21 d B.At the same time,the center frequency of the two frequency bands is tuned by the tuning rod and kept at 1747.5.MHz and 1842.5MHz,the isolation of the two frequency bands is 108.21 d B and 99.172 d B respectively through the added transmission zero point.Through the design of the tap structure and the tuning of the steps,the third order in the frequency bands of1710MHz-1785 MHz and 1805MHz-1880 MHz The intermodulation values are lower than-175.8d Bc and-174.6d Bc respectively.On the basis of dual frequency combiner,this paper designs a triple frequency combiner based on DCS1800,TD-SCDMA2100 and WLAN2600.Compared with the dual-band combiner,the effects of the tuning rod of the combiner resonator,the tap structures at both ends,and the steps between the cavities on the third-order intermodulation of the combiner are further verified.The three-band combiner designed in this thesis obtains the intermodulation distortion values of the three passbands through processing and actual testing,which are lower than-172.50 d Bc,-169.75 d Bc,and-173.30 d Bc,respectively.To sum up,this thesis studies the structure and design parameters that affect the passive intermodulation characteristics of the common cavity combiner,and designs two RF common cavity combiners based on this research,both of which reach the design indicators and are effectively improved.The passive third-order intermodulation characteristics of the combiner are of great significance for improving the performance of the common cavity combiner and reducing the passive intermodulation characteristics.