Research On High-performance And Miniaturized Radio Frequecncy Filters And Filtering Multifunctional Circuits

In RF front-end system,the RF filter is a key component.Thus,its high performance and miniaturization are significant for improving the performance and reduce the volume of system.In the actual link,it is always cascaded with other functional devices such as balun,power divider,switch and so on.With this cascade architecture,not only bulky volume but also high loss would be resulted.By fusing filter with other functional devices,filtering multifunctional circuit is proved to effectively reduce the circuit size and improve the overall performance.Unfortunately,there are still many theoretical and technical bottlenecks to be broken through for developing filters and filtering multifunctional circuits towards multi-standard and anti-interference.To this end,based on high-Q dielectric resonator(DR)suitable for base station and multilayer low temperature co-fired ceramic(LTCC)technology suitable for terminal,high-performance miniaturized filters and filtering multifunctional circuits are deeply studied in this dissertation.Their innovative design theories for multi-band and anti-interference scenarios are constructed.Consequently,a series of high-performance and miniaturized filters and filtering multifunctional circuits with multi-band and anti-interference characteristics are obtained.The main research work includes:(1)Aiming at the problems of monotonous boundary construction and limited controllable mode in high-Q DR,two types of quad-mode DRs with fully magnetic boundary and hybrid boundary are proposed.Under different boundary conditions,two sets of four modes of the same order are constructed,which are easy to be controlled synchronously and independently.Besides,different excitation schemes are offered for the two types of DRs.Resultantly,good design mediums for high-performance filters and filtering multifunctional circuits are provided.(2)Aiming at the problem of single band of high-performance filter,the multi-band design methods of three kinds of filters are studied,including dual-band duplexer,mechanically reconfigurable filter and electrically reconfigurable filter.Based on the two types of DRs above,the multi-mode transmission and control theories including multi-mode synchronous excitation,separated transmission and independent frequency manipulation are constructed.Among them,for dual-band duplexer,a novel design architecture of sharing input and output quad-mode resonators is proposed.Based on the commonness of multi-mode field distributions,the research on multi-mode synchronous excitation is carried out.According to multi-mode orthogonality,the difficulty in achieving isolation while sharing the output resonator is overcome.Compared with the traditional design,the number of resonators is reduced by 75%.For multi-band reconfiguration,the independent mechanical tuning and electric tuning mechanisms of multi-mode frequencies are deeply investigated,respectively.Then a series of methods of designing high-performance filters with multiple independently reconfigurable bands under mechanical and electric controls are formed.The related research results have published several journal papers in IEEE Transactions on Microwave Theory and Techniques.Aiming at the problem of single band of high-performance filtering multifunctional circuit,the multi-band design methods of two kinds of filtering multifunctional circuits are studied,including filtering switch and balun duplexer.Based on the two types of DRs above,the multi-mode multifunctional theories including multi-mode synchronous coupling switching,synchronous power division and synchronous balanced-to-unbalanced conversion are proposed.Among them,taking the filtering switch as the representative of the filtering multifunctional circuits in TDD systems,the synchronous coupling switching mechanism of the four modes is deeply studied.Then,by using a single DR,a high-performance dual-band filtering switch is realized.The insertion loss is only 0.63 d B for the ON-state and the isolation is better than 41 d B for the OFF-state.Taking the balun duplexer as the representative of filtering multifunctional circuits in FDD systems,the single-ended/balanced input and output mechanisms of multiple modes in DR are researched,respectively.Then a systematic design method suitable for all four kinds of balun duplexers is formed.And a family of balun duplexers with common-mode suppression higher than 50 d B are obtained.The related research results have published in IEEE Transactions on Circuits and Systems I:Regular Papers and won the best student paper award in 2021 IEEE MTT-S International Microwave Workshop Series on Advanced Materials and Processes for RF and THz Applications.Aiming at the problem of harmonic interferences of miniaturized filter and filtering multifunctional circuit,the methods of stopband manipulation and expansion of LTCC filter and filtering multifunctional circuits are studied,including bandstop filter,filtering balun and filtering power divider.Amogn them,for bandstop filter,a novel topology involving internal coupling is proposed.Without increasing the order of resonators,the bandwidth of stopband could be broaden and flexibly controlled.Compared with the traditional design,miniaturization is achieved with the size of only 3.3×2.85×2 mm~3.For filtering balun and filtering power divider,a mathematical synthesis method of wide stopband circuit is proposed based on multi-frequency and multi-port coupling matrix.After physically mapping the coupling matrix by selecting special input,internal and output coupling regions,the harmonic could be eliminated independently without adding extra elements or affecting the passband.Finally,filtering baluns and filtering power divider with stopband up to 4.1 octaves and harmonic suppression higher than 35 d B are realized.The related research results have been authorized a U.S.invention patent and published several journal papers in IEEE Transactions on Circuits and Systems II:Express Briefs.Compared with the traditional designs and other reported designs,the proposed RF filters and filtering multifunctional circuits feature high performance,miniaturization,multi-band and anti-interference,which could promote the developments of the next generation wireless communication systems towards low carbon,high efficiency,intelligent simplicity and multi-network integration.