Research And Design Of Multi-band Microstrip Filters Based On Novel Resonators

Microwave filter is one of the most commonly used critical components in microwave systems.Design of microwave filters with good performance is essential for microwave systems.The development of modern communication system contributes to the progress of microwave systems and microwave filters,and higher requirements are put forward to the microwave filter at the same time.Therefore,microwave filters are moving towards higher performance,smaller size and lower cost.In this paper,the background and current situation of microwave filter are introduced.The significance of microwave filter design is expounded,and the basic theories of microwave filter design are summarized.We focused on the microstrip filter because of its small size and cheap cost.We analyzed the microstrip structure and its transmission line model and summarized common structures and design methods about microstrip filters.On the basis of all above,the following studies were conducted.(1)Based on the study of transmission line theory,a GUI program was wrote using MATLAB for multi-mode resonator designing.Using this program,the position changing of pole can be observed synchronously when the tunable parameters of the resonator is altered.So that,the relationships between poles and parameters are much clearer.This software can be used to calculate resonator’s parameters or to provide references for choosing variables to be constrained.(2)The voltage distribution of the half-wavelength resonator in different modes is studied and the influences of stubs setting on different location are analyzed,and a resonator with three adjustable poles is designed.At the same time,a new defect ground structure with wide stop band characteristic is designed.Using the resonator and the defect ground structure,we proposed a wide stop band dual-band filter.(3)By studying the existing multi-mode resonators,a single stepped-impedance ring loaded resonator is introduced.The resonator’s design reference graph is plotted by selecting appropriate resonator parameters for analysis and calculation.By selecting the appropriate parameters,a compact four-band filter is proposed using the resonators.The stepped-impedance ring loaded resonator generates two transmission poles on each passband of the BPF so that the quad-band BPF can be realized using only one resonator result in a compact size.