Research On Planar Tunable Filter And The Applications In Other Passive Circuits

With the large-scale integration and unification of the wireless components and circuits,the requirement for the modern wireless devices becomes more and more stringent,which expects that one wireless system or one wireless device can work for different functions and operate at different frequency bands.Thus,the multi-band wireless system and the associated devices were developed.However,how to address the interference from the different operation bands or operation frequencies in the current wireless system is still a challenge.Thus far,the tunable bandpass filter(BPF)is the best solution,since it has the ability to significantly reduce the system size and improve the performance of the multi-band communication system.The tunable filters have been widely employed in microwave test system,FM transceiver,wide-band RADAR,MEC etc..Whereas,it has to be admitted that many drawbacks hindered their widespread application.For instance,how to realize miniaturization and planarization of the circuit,simplification of the design and control,decrease the loss,increase the reliability and add more tunable parameters are urgent demands.Therefore,this dissertation makes the effort to solve them.The author lists the contributions of this dissertation as follow.1.As the promising basic structures of the tunable filters,a series of novel frequency-fixed BPFs with different functions and electrical-tuning potential are proposed,which will be extended to the electrical-tunable filters in the future research.At first,the author proposes a highly selective dual-band BPF based on electric-magnetic(E-M)mixed coupling technology,which is capable of independently controlling positions of the transmission zero(TZ).Secondly,the author proposes a resonator-loaded resonator(RLR)and the corresponding design theory,which can be applied to multi-band BPF design.A dual-band BPF and a tri-band BPF are implemented.Thirdly,the author proposes two highly flexible and very compact lumped BPFs.One of them achieves the wide passband and very wide upper stopband with good rejection level,and the other is the two-pole BPF with four controllable TZs.Fourthly,the author proposes a design approach for highly selective substrate integrated waveguide(SIW)BPF with two TZs using E-M mixed coupling.The SIW BPF operates at readily-tunable TEM mode.Finally,the author proposes a transversal filter design approach to yield the band-pass response in which the number of the TZs is more than that of the transmission poles.2.Based on the commonly applicable frequency-fixed BPF synthesis,the author proposes a unified synthesis methodology for the transversal filter for the first time,which can be utilized to guide the multimode-resonator-based tunable filter design.The methodology addresses the difficulty of the non-one-to-one correspondence between the coupling matrix and the tunable BPF responses.Accordingly,the author presents a two-order planar prototype and its physical layout based on strip-line and commercial diodes.The agreements among theoretical,simulation and measurement responses validate the proposed methodology.Uniquely,the extra merits such as the switchable passband and stopband tunability further extend the application perspective.3.The author proposes a simple,two varactor-loaded and synchronously-tuned dual?mode resonator and its stepped-impedance version,of which the two resonances are synchronously controlled by a bias.Meanwhile,the space between two resonances can be specified resulting in the fact that the constant,increasing,or decreasing bandwidth(BW)are readily predefined.The stepped-impedance version improves the frequency tuning range,extends the stopband BW,and reduces the circuit size.Four frequency agile BPFs(FA-BPFs)with constant,decreasing,and increasing BW are engineered and the experimental results verify the proposed theory.Finally,the switchable dual-/single-band FA-BPF is proposed with the ability of the independent passband control to achieve entire 2G/3G/4G spectrum coverage.It is the widest tuning range dual-band tunable filter ever reported to the best of the author's knowledge.4.Aiming at the single-mode resonator-based coupled tunable filter,this paper proposes a new general synthesis methodology using element-variable coupling matrix.Also,author also proposes the fully canonical four-order filter model,and analyze its feasibility of the constant BW FA-BPF in theory.To realize the theoretical model in practice,the novel synchronously-tuned resonator is proposed.This resonator allows the E-coupling and M-coupling,while the coupling coefficient value and variation tendency can be predefined.For demonstration,three four-order FA-BPFs are implemented to achieve four-pole four TZ response with electric-coupling-dominated path and magnetic-coupling-path.The experiment results validate the design theory.The four-order FA-BPF with constant BW is reported for the first time.5.The author proposes a coupling matrix-based filtering power divider(PD)and its design method.Paper establishes the theoretical model based on the filter coupling matrix,and validates its ideal power dividing and port isolation.Coupled feeding BPF and coupling matrix can be applied to the proposed filtering PD synthesis and design.To practically validate the model,a single-band two-order PD with two TZs,a single-band four-order PD with four TZs,a dual-band PD with four TZs,an unequal two-pole PD with two TZs,an equal two-pole frequency-agile PD with two TZs and an unequal two-pole frequency-agile PD with two TZs are presented.The very good experimental results of all the measured PDs demonstrate the proposed method can be used to design two/high-order,single/multi-band,equal/unequal,frequency-fixed/frequency-tunable filtering PD.