Study On Theory And Application Of Multifunctional And Reconfigurable Filter Technology In Integrated Electronic System

With the rapid development of wireless communication technology,various communication standards are proposed for civilian communication targeting different application scenarios.This requires the communication devices can adapt different standards of communication schemes.Besides,wireless communication technology also plays an important role in the battle field.Modern electronic warfare requires the combat platform to accommodate various electronic systems such as communication system and radar system.However,the electronic systems are isolated to each other,which leads the whole system to be complex and expensive.To solve this problem,the idea of integrated electronic system is put forward.By tuning the working frequency and reconfiguring the working mode of some modules in the RF(radio frequency)front-end,different electronic systems can be integrated,leading to a compact and cost-effective system.Microwave filter is one of the core components in the electronic system and it is widely used in the RF front-end.Reconfigurable filter can be used to replace the filter bank to reduce the size of the system.Besides,the integrated electronic system can flexibly switch between different working modes with the help of reconfigurable filter.Multifunctional filter,such as filtering phase shifter and filtering power divider,can be used in the system to further reduce the size and lower the fabrication cost of the system.To realize integrated electronic system,the technology of reconfigurable filter must be studied first.This dissertation focused on the theory and technology of the reconfigurable filter.In this dissertation,a new method of coupling matrix synthesis method is given and various kinds of multifunctional reconfigurable filter is proposed,including reconfigurable filtering phase shifter,reconfigurable phase-shifting diplexer,reconfigurable balun filter,reconfigurable single ended to balanced filtering power divider,reconfigurable reflectionless balanced filter and reconfigurable bandstop filter.The content of this dissertation includes the following four parts:1.To address the problem of low system integration due to the independent use of phase shifters and filters in the RF systems,a design method of filtering phase shifter is proposed.Based on filter coupling matrix theory,the relationship between the amplitude response and the phase response of the filter is studied first,the corresponding mathematical model is established,and a method for obtaining the coupling matrix with specified phase and amplitude responses is proposed.Then,by studying the intrinsic relationship between the specific elements of the filter coupling matrix and the transmission phase of the filter,a method to expand the phase tuning range of the filtering phase shifter is proposed.The experimental results demonstrate that the transmission phase of the filter can be freely controlled within the passband tuning range of 0.65GHz-0.86 GHz.Furthermore,to solve the problem that the coupling coefficient with frequencydependent characteristics are inconvenient to control during the tuning process of the filtering phase shfiter,a novel coupling matrix synthesis method is proposed.Based on the characteristics of frequency-dependent coupling structure,a coupling matrix representation combined with the values of certain circuit components is given,and the corresponding optimization method to obtain the desired coupling matrix is studied.In this way,the transmission phase of the filter can be flexibly controlled without the need to tune the magnetic coupling between resonators.The experimental results demonstrate that the designed circuit can achieve a phase tuning range greater than 175° within the passband tuning range of 0.6GHz-0.71 GHz.Besides,in the process of operating frequency and transmission phase adjustment,additional transmission zeros are introduced by the frequency-dependent coupling structure,which can greatly improve the selectivity of the filter.Then the design method of filtering phase shifter based on portloaded non-resonant node is studied,and the design method of duplexer with specified frequency and phase response is proposed.2.To address the problem of low system integration due to the discrete use of filters,power dividers and baluns in the current RF system,a multi-functional reconfigurable single-ended-to-balanced filter design method is proposed.Based on the analysis method of multi-port microwave network,the characteristic of a symmetrical five-port network is studied first.The response of the symmetrical network under even and odd mode excitation in different working modes are analyzed and the corresponding conclusions are given.A circuit structure is then proposed.By adjusting the equivalent electrical length of the resonator,tuning the coupling coefficient between the resonators and changing the port termination condition,the conditions required in different operating modes can be met.The experimental results demonstrate that the circuit can be switched between different operating modes,including single/dual passband balun filter mode,single/dual passband single ended to balanced filter mode.In each working mode,the passband center frequency of the circuit can be freely controlled.3.To address the problem that the reflected out-of-band signal of the filter can cause instability of the nonlinear circuit in the system,a design method of reconfigurable reflectionless balanced filter is proposed.Based on the working principle of the balanced circuit,the characteristics of the four-port balanced filter under odd and even mode excitation is studied first.The relationship between the port input impedance and the operating frequency is then analyzed.A novel lossy absorption network is proposed which can be directly terminated at the input and output ports of the filter.Reflectionless characteristics for both the common mode and differential mode signal can be achieved using the proposed method.The experimental results demonstrate that the passband center frequency of the designed first-order reconfigurable reflectionless filter can be tuned from 1.6GHz to 1.9GHz.The return loss of the filter under differential mode excitation is better than 9.5d B from DC to 3.5 times of the center frequency.The return loss of the filter under common mode excitation is better than 10 d B from DC to 2.3GHz.Furthermore,to increase the selectivity of the filter,a design method for reflectionless filter with arbitrary order is proposed.The experimental results demonstrate that the designed first-order,second-order,and third-order balanced filter all have wideband reflectionless characteristics for both common-mode and differential-mode signal,which agrees well with theoretical expectations.4.To achieve adaptive suppression of interference signal in the integrated RF front-end system,a design method of ultra-wideband reconfigurable bandstop filter is studied.Based on the working principle of bandstop filter,different filter topologies suitable for different frequency bands is studied first.To address the problem that the size of the distributed circuit is too small and it is inconvenient to implement the circuit in the high frequency band,a method to improve the operating frequency of the circuit is proposed.Furthermore,the automatic control method of the module is studied.two reconfigurable bandstop filter modules were fabricated.The experimental results demonstrate that the frequency tuning ranges of the two band-stop filters can cover 0.1GHz-3GHz and 2GHz-18 GHz,respectively.Besides,automatic frequency control is achieved for both the two modules.