Miniaturization Of Multi-band Filter In Wireless Communication System Based On MMR Theory

Multimode resonators(MMR)are currently the main research object of many scholars in the field of multi-pass filters.Compared with other design methods,multimode resonators have the advantages of low insertion loss,small structure size,excellent out-of-band performance,and abundant modes.And thus it is highly favored in achieving multiple pass bands,miniaturization and high performance.However,the commonly used multi-mode resonant structures are mainly half-wavelength SIR,and there is less research on the quarter-wavelength SIR,This dissertation focuses on quarter-wavelength multimode resonators and mainly studies on the following aspects:Firstly,the performance of the basic quarter-wavelength SIR(stepped impedance resonator)structure was analyzed.At the same time,a pair of SIR shared short-circuit vias was used to solve the problem that a single quarter-wavelength SIR could not perform input/output feeding.Based on this,a single frequency filter of 2.4 GHz was designed and simulated by bending and coupling,the return loss(less than 15dB)and insertion loss(less than 0.5dB)performance indicators meet the design requirements.Secondly,the principle of the loaded quarter-wavelength SIR structure is explained in detail and two loading-type filters are constructed.The short-circuit-loaded SIR is interpreted and analyzed using odd-even mode analysis,and the input impedance derivation formula is given for the open-circuit loading type.After comparing the advantages and disadvantages of the two loading filters in the simulation software,the basic SIR structure and the open-loaded model were selected to design a three-way band filter structure.Thirdly,the paper also describes several new quarter-wavelength SIR structures that have been proposed in recent years,deducing the input impedance formula and using embedded methods for multi-pass based on the new quarter-wavelength SIR.The filter structure was tried.Compared with the traditional SIR structure and the new SIR structure,an embedded three-band filter based on the traditional quarter-wavelength SIR was constructed.The filter center frequencies reach 2.4/3.5/5.2 GHz,and the return loss are less than 15 dB and insertion loss less than 0.5dB.Finally,the actual measurement parameters and simulation results confirm each other,The measured parameters are in good agreement with the simulation results,which proves the reliability of the paper's design structure and method.