Research And Design Of Multimode Miniaturized Filter

In order to meet the miniaturized development trend of modern communication system,filters are developing toward small volume and low weight.Multimode resonators are widely used to realize compact filter design for their attractive features including inherent compact size and good filtering performance.Multimode filters based on patch resonators or SIW cavities feature compact size and are convenient to connect with other planar circuits,however,their size is usually greater when compared with microstrip resonators and miniaturization degree remains to be improved.Accordingly,three modified resonant structures are utilized herein and several miniaturized bandpass filters are designed,fabricated and measured.Firstly,grounded square patch(GSP)resonators are researched.A GSP resonator is realized by loading metallic vias underneath a patch resonator.This specific geometry introduces an additional mode nominated as LC mode,making the proposed GSP resonator operate below its former fundamental resonate frequency,so the structure becomes more compact.By changing the location of the feedlines,different modes of square GSP resonator are excited,thus single-or dual-band responses can be realized.Slots perturbations are utilized to control bandwidths(BWs)and center frequencies(CFs)of the two filters.In addition,a triple-mode bandpass filter is proposed based on a triangular GSP resonator.Through the metallic vias array and the capacitive-loaded patch,LC mode and TM010 are shifted toward TM110 to form a passband.Moreover,three transmission zeros are generated to strengthen the out-of-band rejection of the filter.Secondly,patch-loaded SIW(PSIW)resonators are investigated and both compact size and high Q-factor are implemented.A narrow-band filter based on LC mode and TM010 is realized by folding a PSIW cavity,although it involves complex stack-up design,the transmission zero near the passband and high Q-factor effectively improve the selectivity of the filter.In addition,a dual-band filter with controllable frequency ratio and BW is proposed exploiting stacked PSIW Cavities,and further miniaturization is accomplished due to the loaded blind holes.Lastly,two-layered grounded patch(TLGP)resonators are studied and two dual-band filters are designed and fabricated.The first dual-band filter is composed of two cascaded triangular TLGPs,CFs can be adjusted by metallic array and coupling coefficients between the two resonators can be controlled through etched slotlines,thus the filter is improved in design flexibility.Another dual-band filter is designed and fabricated based on multimode TLGP resonator and slot perturbations are utilized to control resonant frequencies of six modes.Each passband has three resonant poles,which correspond to the first three resonant modes of the grounded patches on two layers.BWs of the filter are effectively increased and the fabrication cost is reduced since no blind holes are used.