Investigation Of Novel Microwave Filtering Circuits Based On Quarter Wavelength Resonator

Due to the rapid development of wireless communication technology,the spectrum resources become more intense and the operating frequency of various services become relatively concentrated.The filtering circuits are widely used because of frequency selection characteristics.Due to the periodical resonance characteristics of transmission line resonator structure,the filtering circuits using resonators always suffer from harmonic and thus interferes with the entire communication system.Therefore,harmonic suppression and wide stopband has attracted much attention.In addition,for a complete communication system,it generally contains multiple services.Setting up a set of filtering circuits for each service will increase the cost of the system,which is contrary to the development trend in the miniaturization of microwave systems.Therefore,high-performance dual-frequency even multi-frequency filtering circuits will inevitably become a research hotspot.This thesis briefly introduces the background and research significance of microstrip filtering circuits,and investigates the current research status of harmonic suppression filters and dual-band filters.The basic theory of microwave filtering circuit and the current design method of filtering circuit are given.A variety of microwave filtering with engineering value circuits are designed and implemented.The resonant characteristics of a quarter-wave resonator(including stepped-impedance resonator)were analyzed by basic theory,formula derivation,and computer simulation.The effects of different parameters on the resonant modes were studied.For the first time,the voltage-null point of the third harmonic of stepped-impedance resonator with different physical parameter is obtained by theoretical calculation.Second,this paper proposed a new type of feeding method.Good harmonic suppression can be achieved by orthogonally coupling the feeding line at the voltage-null point of the harmonic.With the proposed feeding method,four single-ended bandpass filters with harmonic suppression are designed.Combined with this feeding method and coupled-line theory,this paper also presents a design of a balanced bandpass filter with wide stopbands on differential mode and common mode.Last but not the least,by loading shunt stubs at the voltage-null point of the resonator's third harmonic,stub-loaded resonators can be constructed,the third and the fifth frequencies of which can be controlled independently.For millimeter wave application,a millimeter wave dual band bandpass filter whose frequencies and bandwidths can be controlled independently is designed based on the stub-loaded resonator and low temperature co-fired ceramic.The microwave filtering circuit studied in this paper and its design can provide important technical support for the stable operation of the communication system.