Design Of Tunable Filter And Reconstruction Research

With rapid development of wireless communication technology,the tunable filter can be applied to limited spectrum resources efficiently and alleviate increasingly scarce situation of the spectrum resources,which has been paid more and more attention by the researchers.The microstrip tunable filter with varactor diode has become a hot spot because of its fast tuning,low cost,and balance of size and performance.In this thesis,a single-band microstrip tunable filter is designed first,and a dual-band tunable filter done as well,which are used varactor diodes as a key skill to achieve tunability.Then a balanced circuit has been used for the suppressing environmental noise interference.It can effectively reduce the size of filter.Finally,a multi-band balanced adjustable filter is designed,which is suitable for the increasingly complex electromagnetic environment and enriches the types of multi-frequency adjustable filters.The outline of the main research contents is described as follows.(?)A single-band tunable filter is designed which is used a technique of T-shaped open-circuit stub loaded open-loop resonator.A tunable dual pass-band is achived with hybrid coupling.The working bands of designed filter is 2.3GHz-2.5GHz and3.4GHz-3.6GHz.This loaded technique has been analyzed to obtain the suitable size of the open-loop resonator and T-shaped open branches.The first passband center frequency of the dual-band pass filter can be adjusted,and with loading the varactor diode at the opening of the split ring resonator.(?)A tunable filter is proposed.Its dual-pass-band centre frequency can be adjusted.By using a stepped impedance resonator,a double-band pass filter is designed with a short-circuit branch and the symmetrically placed open-loop resonator.An open-loop resonator based on electrical coupling is folded to achieve compact size and the better electric performance.We analyze the electrical coupling equivalent circuit and the parity worked model of stepped impedance resonator with a short-circuit branch.The varactor diodes are installed at the end of the stepped impedance resonator and the open-loop.We implement dual centre frequency tunable.(?)A multi-band tunable balanced filter is studied.The working frequency band of it is 2.515GHz-2.675 GHz,3.4GHz-3.6GHz and 4.8GHz-4.9GHz.According to the branch load principle,the electrical length of the branch is appropriately changed by a varactor to achieve frequency adjusted.The common-mode rejection of the balanced tunable filter is achieved by the lumped components added to the symmetry plane,and the parallel coupling line added to the feeder.Finally,a balanced tunable filter is designed,which can be tuable in three frequency bands independently.