Research And Implementation Of High Performance Planar Microstrip Filters

High-performance components are becoming increasingly essential in radio-frequency wireless communication and radar systems.It is no exaggeration to say that filters exist in each high-quality wireless systems and their performance has a great impact on the transmission of the signal in the system.The research and implementation of this paper focuses on the high performance wideband bandpass filter,balanced bandpass filter,dual-band bandpass filter,and dual-band bandstop filter:(1)A new design of wideband bandpass filter based on transversal signal-interaction concepts loaded with open and shorted stubs is proposed.The proposed filter operates at 3 GHz with 3 dB fractional bandwidth of 83.3%.Due to the superposition of signals for two paths,the in-band reflection coefficient is reduced to 15 dB and the out-of-band harmonics are well suppressed to 20 dB.(2)The single-ended and balanced bandpass filters are studied and designed.For the proposed single-ended filter and the differential mode of the proposed balanced filter,two transmission zeros near the passband are realized by using simple stepped-impedance stubs,which enhances the pass-band selectivity of these new filters.The analytical and accurate design equations for transmission poles and zeros of these single-ended and balanced filters are provided based on the scattering-parameters theory.The measured 3 dB fractional bandwidth for single-ended bandpass filter is 79.33%.Over 35 dB insertion loss in the stopband is realized.By inserting open-circuit stubs into the proposed balanced bandpass filter,over 25 dB common-mode suppression is obtained.(3)Simple design structures for dual-band bandpass filter and dual-band bandstop filter with multiple transmission poles and zeros is proposed in this brief.For dual-band bandpass filter,sharp selectivity and high isolation level with eight transmission poles and seven transmission zeros are achieved just by employing three-section coupled lines and three short-circuit stubs.For dual-band bandstop filter,three transmission poles in each stop-band and nine transmission zeros out of bands within 2f0 are realized.The passband return loss and stopband suppression are over 14 dB.In this thesis,the validity of the proposed design is verified by the simulation,fabrication and measurement for the filters.The proposed filters exhibits the advantages including simple structure,excellent pass-band filtering selectivity,deep stop-band rejection,and so on.It can be expected that these filters will be widely used in RF/microwave/millimeter-wave wireless circuits and systems.