Design Of Lowpass And Dual-Band Band-pass Filter Based On SISL

As one of the important components in the wireless communication system,the radio frequency filters select signals within assigned bandwidth and block useless signals in the RF front-end,building important conditions for high-quality signal transmission.Therefore,the design of high-performance filters has always been a research hotspot for scholars at home and abroad.There are many structures to implement filters to suit the needs of different applications.Substrate Integrated Suspended Line(SISL),as a novel type of transmission line structure,has the advantages of self-packaging,low loss,and easy integration,and thus has great research value.Based on the SISL platform,this paper studies on lowpass and dual-band bandpass filter,and the main content is concluded as follows:1.Design of SISL wide stopband lowpass filter based on transformed radial stub:The transformed radial stub is selected as the main resonator of the filter.The even-and odd-mode equivalent circuits are used to analyze it,and the solutions of the transmission zeros and poles of the structure are solved graphically.In order to further improve the roll-off rate and stopband rejection of the filter,stepped impedance resonators and open stubs are cascaded.Finally,a SISL lowpass filter with six transmission zeros,low insertion loss,and wide stopband is realized.2.Design of SISL dual-band bandpass filter based on dual-path coupling topology:A SISL dual-path coupling topology for dual-passband response is proposed,which simultaneously uses both single-and dual-mode resonators.The single-mode resonators ensure that the two passbands’ bandwidths can be independently determined,while the dual-mode resonators not only reduce the required resonators,but also eliminate the need for additional input/output matching circuits.The signals propagate along the two physical paths in the topology to form cross-coupling in each passband,generating multiple transmission zeros along with 0° feed structure.Based on this topology,third-order and fourth-order dual-passband bandpass filters applied on two5 G communication bands and using all FR4 substrate are designed.The mechanism of the transmission zeros is analyzed in detail,and the design procedures of filter are given.The measured results show that the designed dual-passband bandpass filters have high band-to-band isolation and out-of-band rejection,as well as the advantages of low cost and self-packaging.3.Loss reduction techniques and design of switchable filter: The main sources of the insertion losses of the designed dual-band bandpass filters are analyzed,and doublemetal layers and pattern substrate are used to reduce the losses.The measured results show that the insertion losses of the two passbands have been significantly improved;By adding PIN diodes at suitable positions in the fourth-order dual-passband bandpass filter,this paper further designs a switchable filter with four filtering modes,and all the four modes exhibit good filtering responses.