Study And Design Of Microwave Filtering Components

With the phenomenal development in the information engineering, wirelesscommunication has become one of the most popular technologies in this century.Various new wireless communication systems emerge ceaselessly, which havepromoted a tremendous advance in microwave active and passive devices especially formicrowave filter technology. The research work presented in this dissertation focuses onthe design of microwave filtering components. Firstly, a new filter parametersextraction method is proposed in this dissertation, which is based on polynomial fittingand is introduced in order to improve traditional microwave filter simulationoptimization. A modified space mapping algorithm is also presented to accelerate theconvergence process, because the traditional space mapping algorithm is actually notsuitable for microwe filter design.Depending on the efficient optimization method, somekinds of novel filtering components are researched and designed.These new devicesinclude: multi-band filters, multiplexers, balanced filters, balun filters, balanced tounbalanced duplexer, unbalancd to balanced duplexer, filter antenna and oscillatorswhich are designed by utilizing filters. The major work is concluded as following:1. The traditional generalized Chebyshev filter synthesis approach is systematicallystudied as the whole work’s origin. After a new polynomial fitting parametersextraction method is successfully achieved, a modified aggressive space mappingmethod is proposed to overcome the shortcomings that traditional ASM takes along time in parameter extraction process with inconsistent results. Design examlesabout dual-mode filter, microstrip filter and coaxial cavity filter have been proposedto verify the validity of the algorithm.2. The resonance characteristics of the stepped impedance resonators (SIR), short stubloaded resonator (SLR) and square ring loaded resonator (SRLR) are analyzed indetail.The design graphs regarding these resonators are plotted. The designprocedure of microwave dual band filter is also introduced later. Based on theproposed theory, several high performance multiband filters are designed andfabricated.The good agreements between the simulated and measured results verifythe proposed methods.3. Multiplexer optimization synthesis method is studied in detail. To illustrate themultiplexer design procesure a high out-of-band suppression duplexer and fivechannels multiplexer are synthesized and designed. The resonance characteristic ofthe dual stubs loaded resonator is analyzed in detail.Based on the mutilmode resonator, common mode duplexer and triplexer are designed to illustrat theusefully common mode multiplexer design methods.Addtionally, a new multiplxerstructure is proposed by applying defected stepped impedance resonators (DSIR).This new structure features simpler design and more flexible operating frequencychoice compared with the traditional design method.4. The traditional microstrip balanced bandpass filter (BPF) usually has thedisadvanteges such as large size or low common-mode suppression, so a verycompact interdigital coupled resonator, which has the characteristic of strongsuppression to common-mode signals at differential-mode operation frequencyband,is analyzed. By using the novel resonator, a balanced BPF with goodperformance and miniaturization can be achieved. Balun filter is an import balancedcircuit in micriwove communication chain, so two design methods are proposed.One is based on synthesized method and the other one is realized by transforming abalanced filter to be a balun filter. Two design examples are introduced to explainthe idea. Finally, novel and compact balanced to unbalanced duplexer andunbalancd to balanced duplexer are designed to further enhance the balancedcircuits’application in communication system.5. A printed monopole filter antenna is designed by utilizing filter antenna synthesisapproach which is proposed in this thesis. Time domain tuning methord is appliedto guarantee the antenna to perform not only a radiator but also the last resonator ofthe filter. On the overall performance, the filter antenna’s reflection coefficient andgain curve are almost the same as the filter return loss and insertion loss.Lowphase-noise microwave oscillators and wideband voltage-controlled oscillator(VCO) based on microstrip bandpass filters are also proposed. For this type ofoscillator, the passband filter is embedded into the feedback loop to treat as afrequency stabilization element. Instead of designing the oscillator at the groupdelay peak frequency of the filter to achieve a good phase-noise performance,thepeak frequency of the complex quality factor is adopted for oscillator design. Theoscillator designed at the complex quality factor peak frequency improves thephase-noise about10dB as compared with that realized at the group delay peakfrequency. Moreover, by attaching a varactor on each resonator of the comblinefilter, the oscillator can be extended to a wideband VCO.