Research On High-performance Multiband And Wideband Filters

The tremendous adoption of mobile internet and multimedia technology have greatlystimulated the revolution of the wireless communication industry in this century, and it isinevitable to develop multiband and wideband communication systems in the near future tosupport multiple communication standards and high-quality communication. As keycomponents of the communication systems, the research on the multiband and widebandbandpass filters (BPFs) becomes more and more important. Based on the planar microstriptransmission line, this dissertation gives a detail study on the design and implement techniqueof multiband and wideband BPFs, including the multi-band coupling schematics, stub-loadeddual-mode and multi-mode resonators. Besides, the study of differential BPF and antenna,which can be directly integrated with the differential circuits, is also included in thisdissertation. The main innovations of this dissertation can be summarized as follows.(I) The multi-band coupling schematics are proposed to design multi-band BPFs withcontrollable passband frequencies and bandwidths. The multi-band performances areindependently realized by the associated multi-sets of resonators, and each passband has itsown coupling path, viz., the coupling coefficient can be independently determined. Theconventiaonl tapped-line-feed coupling and the coupled-line-feed coupling techniques arecombined in the proposed structure, resulting an independent control of the external qualityfactors. Besides, resonators of embedded layout are adopted to significantly reduce the circuitsize.(II) The multi-stub-loaded multi-mode resonators are presented and applied to the designof high-performance ultrawideband BPFs. Two transmission zeros, which are generated bythe center-loaded stepped-impedance stub, are located at the lower and upper cut-offfrequencies of the passband to supply a high passband selectivity. By using the symmetricalside-loaded stubs, two more modes can be allocated within the passband range and the circuitsize is also reduced. At last, the multiple loaded stubs are utilized to control the distribution ofthe resonant modes as well as that of the transmission zeros, and BPFs with high passbandselectivity and super-wide upper stopband performance can be designed and implemented.(III) The method of the combination of the traditional bandpass and bandstop filters to deisgn wideband differential BPFs is presented. The differential BPF works as a bandpassfilter under differential-mode excitation while as a bandstop filter under common-modeexcitation. To improve the differential passband selectivity, the short-endedparallel-coupled-line stub technique is applied in the differential BPF circuit, and twotransimission zeros are introduced at the lower and upper cut-off frequencies of thedifferential passsband, resulting in a sharper differential passband selectivity while keepingthe circuit size unchanged.(IV) The method to design differential ultrawideband antenna as well as the notch-band ispresented. The differential ultrawideband antenna is designed based on the hybridmicrostrip/slot structure, and the slot in the ground can only be excited underdifferential-mode, thus the differential-mode signal can be radiated and the common-modesignal would be suppressed. Besides, to avoide the interaction with the existed narrow-bandsignal, the differential bandstop filter is reported for the first time and the notch-bandperformance is realized by integrating the proposed differential bandstop filter and thedifferential ultrawideband antenna.