Research On Key Technologies Of Miniaturized Ultra-wideband Filter

In recent years,ultra-wideband(UWB)filters have received increasing attention.With the development of short-range wireless communication technologies such as ultra-wideband technology,ultra-wideband filters are required to achieve high performance while maintaining a simple and compact structure as well as an easy-to-use process.The current ultra-wideband filters have a large size,low out-of-band suppression,low passband characteristics and other shortcomings.Therefore,the design of miniaturized highperformance ultra-wideband filters is particularly significant.With the aim of miniaturizing ultrawideband filters,an ultrawideband filter with notched bands,an ultrawideband filter with a wide rejection band,and a multi-passband filter are investigated in depth in this dissertation.An ultra-wideband filter utilizing low-temperature co-fired ceramic technology(LTCC)is also studied.The research scope and novel findings of the dissertation are as follows:1.To reduce signal interference in the ultra-wideband,an ultra-wideband filter with multiple notched bands is proposed.First,an ultra-wideband filter with higher selectivity was designed by constructing a modified multimode resonator with multiple uniform stubs loaded with a dumbbell-shaped stepped impedance resonance.It was modeled using HESS simulation and tested with a vector network analyzer(E8363B).The test results show that the fractional bandwidth reaches 127%and the selectivity reaches 0.939.Compared to traditional multimode resonators,their fractional bandwidth increases by 10%and selectivity increases by 0.018.Then,using this multimode resonator,an ultra-wideband filter with a quintple notched-band is proposed by loading a closed-loop C-shaped resonator,embedding L-shaped stub lines,and etching Hilbert fractal structure.It is not only eliminates the interference of five communication frequency bands in the ultra-wideband range but also uses the embedded stub line and etching fractal structure technology to realize the miniaturized filter.The simulation and measurement results show that the proposed filters with notched-band have a large number of notched bands and high selectivity.2.Aiming at limited stopband rejection in ultra-wideband filters,an ultra-wideband filter with wide stopband rejection is proposed to improve the spurious passband.An ultrawideband with low insertion loss and wide fractional bandwidth was designed by adopting a rectangular ring resonator-loaded stubs and a tri-section stepped-impedance resonator.Taking advantage of the good reflection characteristics of the funnel-shaped resonator,the out-of-band rejection of the upper stopband was improved by loading the funnel-shaped resonator directly below the stub line.The designed ultra-wideband filter was tested using a vector network analyzer(N5247B).The measured results show that its central frequency is 5.84 GHz and the upper stopband rejection frequency can be up to 25.72 GHz at 20 dB attenuation,which is 4.4 times that of the passband central frequency.The circuit size is only 0.13λg×0.92λg.Compared to existing funnel shaped resonators,their fractional bandwidth has been increased by 18.57%,and the upper stopband suppression has also been significantly improved.Thus,the ultra-wideband filter effectively solves the problem of limited stopband rejection while broadening the passband bandwidth.3.Aiming at narrow bandwidths and insufficient number of passbands in multi-band bandpass filters,a bandpass filter with multi-band characteristics is proposed.First,a miniaturized wideband quint-band filter was realized by embedding a three-stage gradual quad-section stepped-impedance resonator inside a regular octagon.Next,a miniaturized wideband sext-band filter was designed by embedding a tri-section stepped-impedance resonator inside a symmetric L-shaped stub.Because this sext-band filter is optimized with multiple open stubs,it adopts multiple open stubs,which not only improves the performance of the filter but also moves the center frequency of the passband to the low-frequency end and reduces the size of the filter.A vector network analyzer(E5071C)was used to test the wideband sext-band filter.The sext-band filter can cover GPS,LTE,WLAN and other communication frequency bands,and its size is only 0.15λg ×0.16λg.The filter has a simple and compact structure,and it can achieve a larger number of passbands with fewer resonators and has a wider passband.4.To improve the integrated filter design,the ultrawideband filter and a wideband filter with high out-of-band rejection characteristics utilizing the LTCC technology are proposed.First,a three-layer ultrawideband filter with a simple structure was designed using the LTCC process.The filter is based on a tri-section stepped impedance resonator and achieves ultrawideband characteristics through a mixed electromagnetic coupling technique.The HFSS simulation results show that the fractional bandwidth of the filter is 88%.To improve the stopband rejection performance,a seven-layer wideband filter was designed using the LTCC process.A seven-layer wideband filter with a high rejection was designed by folding broadside-coupled line-loaded uniform impedance stubs.The HFSS simulation results indicate a central frequency of 3.38 GHz and an upper stopband rejection frequency of up to 8.14 GHz,which is 2.4 times the central frequency.