Modelling And Design Of Filtering Device Used For RF Front-End Of Wireless Communication

The integration of multi-band wireless system is the most popular technique of the modern communication.The filtering device is a critical technology to solve the interference of the multi-band wireless system.The filtering device includes the filter,combiner and filtering antenna（Filtenna）,etc.The equivalent circuit can provide the theoriodical support to design the filtering device,thus the circuit modelling is the basis of designing the filtering device.However,most of the current reaseraches on the circuit modelling focus on the filter synthesis and exctaction of its circuit parameters,there are rare reports on studying removing loading effect of filter efficiently,modelling the equivalent circuit and extracting circuit parameter for conbiner and filtenna.To solve the aformentioned problems,the method to model and design the filtering device used for RF front-end of wireless communication is researched.The reasearches include the method to model the equivalent circuit of filter,combiner,series-fed filtenna and non-resonant filtenna.The specific research results are as follows:1.Proposes a k-means clustering method cooperating with the vector fitting to exactly identify zeros and poles of the filter.The vector fitting is used to approximate the reflection coefficient,and the rational polynomial of reflection coefficient is obtained.Then,the k-means clustering method is utilized to adactively and rapidly identify the zeros and poles caused by the loading effect.Revoming the phase introduced by these zeros and poles,the loading effect is removed,and the network parameters are recovered.Through the improved vector fitting and circuit synthesis method,the equivalent filtering circuit can be exactly modelled by the network parameters.On the basic of the circuit model,the method to analyze the sensitivity of the loading phase and generate the NRN filtering circuit is proposed.Appling the above method,a laser tuning system is designed to automatically tune the dielectric filter.Compared with manual tuning,the tuning efficiency is increased twice,which is a significant improvement for filter tuning.2.Proposes a circuit and mathematical model to reomove the loading admittance of the combiner with common resonantor,resulting in recovering the filter network parameters from the combiner.Then,an algorithm to recover the filter circuit from the combiner is proposed.Based on this method,the extraction of the circuit model of combiner no longer relys on the multi-port network analyzer;only two-port network analyzer is demanded in extracting the equivalent circuit of the filter of combiner,which significantly decrease the cost of test equipment when modelling the equivalent circuit in the combiner.Moreover,through the state space equation,the Y₂₂ and Y₁₂ is proved the key network parameters to exactly model the filter circuit in the combiner.Exploiting the key netwok parameters and the algorithm to recover the fiter circuit in combiner,the dimension of the solved linear equation is reduced by 1/3 at least.Thus,the duration to extract and model the equivalent circuit can be decreased,and the efficiency of processing the algorithm is improved.3.Proposes the equivalent circuit and mathemical model to characterize the N-elements series-fed antenna array,it’s proved that the series-fed antenna array is intrincally equivalent to a second-order bandpass circuit.Then,a method to extract the circuit parameters of the series-fed antenna array is proposed,and the electromagnetic coupling mechanism of the series-fed antenna array is analyzed.Benefited by the extraction method and analysis of coupling mechanism,a third-order series-fed antenna is designed to operate at V2X（Vehicle To Everything）band.Without extra filtering circuit,the series-fed filtering antenna array fully take advantadge of its equivalent filtering circuit.Eventually,the radiation efficiency of the filtering antenna is better than 75%,and the spurious mode radiation is suppressed at least 9 d B.4.Proposed a general circuit model of non-resonant node（NRN）.Analyzing with the mathematical proof,the model can be classified into detuned,capacitance and inductance NRN filtering circuit.Proved by the mathematical deduction,there are only a radiation zero generated by the detune NRN filtering,while a resonance and radiation zero are generated in the capacitance and inductance NRN filtering circuit simultaneously.Further deducing the equation,the relationship between the resonant frequency and radiation zero is found out,then a method to manipulate the resonant frequency and radiation zero is proposed.Based on the above analysis,a capacitance and inductance NRN filtennas are designed for tri-band wireless WIFI router.They are used for the bands 5170-5330 MHz and 5735-5835 MHz,respectively.Realizing the NRN fitering response in the WIFI antennas,the isolation between them is improved by 17 d B,and the throughput of channel operating at 5735-5835 MHz is improved from 150 Mbps to 420 Mbps.In a word,this thesis studys method to extact and model the equivalent circuit of filter and combiner.Based on this method,a laser tuning system is designed to automatically tune the filter.Moreover,this method can be used to conduct the filtenna design too.Realizing the filtering response in the antenna,the isolation between multi-band antennas in vehicle or router is improved.This method can also be extended to design filtering device in the other communication system,resulting in a promising potential.