| Complicated frequency band combination,wider working frequency coverage,tight spectrum resources and etc are the problems encountered by wireless communication tech-nology.The tunable filter is considered to be one of the key components to solve these problems in the future communication system.In addition,filters are one of the main culprits that cause nonlinear phase distortion in wireless communication systems,which conflicts with the high-speed data and high-quality signal transmission of communication systems.Solving the needs of the communication system for the dynamic spectrum al-location function and linear phase performance of the filter is the research theme of this thesis,so research on tunable linear phase filter is carried out.The linear phase filter with tunable center frequency is the research goal of this the-sis,and two requirements are proposed for the linear phase:1.The group delay ripple in each passband is flat,2.The group delay remains constant during the frequency tuning process.There are three parts of the research focus of this thesis,which are introduced below through specific research ideas and content.This thesis expands a novel source-load coupled linear phase filter structure that can improve the performance of the linear phase filter and is compatible with the design of an electrically tunable filter,then the design process and debugging method of source-load coupling linear phase filter are introduced in detail,two source-load coupling linear phase filters with good performance are developed.The measurement results show that the return loss of the fourth order linear phase filter is greater than 16.2dB,and the in-band group delay ripple of more than 60%passband is less than ±0.4ns;the return loss of the sixth order linear phase filter is greater than 17.5dB,the in-band group delay ripple of more than 60%passband is less than ±0.65ns.By analyzing the synthesis method of the source-load coupling filter,the conditions for the group delay of the tunable filter to be kept constant can be established.The circuit model for controlling the coupling parameters established in this thesis is derived from the analysis of the mixed electric and magnetic coupling scheme,and the control method of coupling coefficient and external quality factor of one-half wavelength resonator with single-ended varactor loading is studied through simulation experiments,which provides specific experimental data for reference.According to the structure of source-load coupling linear phase filter and the theory of tunable linear phase filter,the development process of novel tunable linear phase filter is described in detail.In this thesis,the resonator structure and the bias circuit are designed reasonably,the resonator coupling structure and the new input-output coupling structure are proposed to control the coupling parameters to change according to the law,and then a pair of adaptive transmission zeros are introduced through the source-load coupling,a novel high order electrically tuned linear phase filter with constant group delay is devel-oped.The measured responses show that in the tuning range of 16.8%,the insertion loss in the passband of the filter is less than 5.6dB,and return loss is greater than 10.8dB.The group delay characteristics of the filter are basically the same.The group delay fluctua-tion is less than ±0.95ns in the bandwidth range of 60%of each tuning passband,and the group delay fluctuation is less than ±1ns in the whole tuning range,the research results meet the requirements of the index. |
