Research On The Key Technologies Of Planar Filter Circuits And Devices In Wireless Communication

At present,there is a very urgent demand for channel resource in wireless communication,one channel is often used to transmit signals of multiple paths.In order to avoid signal interference,filter is especially important.From the perspective of easy integration,there is a hope of planar structure and compact size for filters,also,greater demands are placed on the performance of filters by multi-band multi-standard wireless communication.For the purpose of designing planar band-pass filter with high performance and compact size,the design method are studied and discussed in this dissertation,including stub structure and composite right/left hand(CRLH)structure,the main works and innovations are as follows:1.A tri-band bandpass filter works at 2.4GHz,3.5GHz and 5.15 GHz is designed.Two sets of resonators with stubs loaded on their symmetric plane are arranged above and below the feedline,respectively,so the transversal structure is formed and the resonators can be tuned independently.The passband can be adjusted by simultaneously tuning the dimension parameters of the resonators and stubs,so the design freedom is improved.Source-load coupling is introduced to enhance the selectivity and interdigital capacitor is adopted to adjust the internal coupling.Even-odd mode theory is adopted to decompose the structure so the analysis process is simplified.2.The double stub loaded stepped impedance resonator(SIR)is investigated,the equivalent circuit model is established in two passbands and the influence of different impedance ratio on the resonance frequency distribution is analyzed.The method of independently adjusting the external quality factor and the coupling coefficient in two passbands is described with the help of full-wave simulation.A dual-band bandpass filter works at 2.4GHz and 5.35 GHz is fabricated,the accurate adjustment of the parameters is realized without adding any additional network or obviously increasing the circuit area.3.Half wavelength bypass stub is adopted for introducing source-load coupling in the design of bandpass filter with a center frequency of 1.65 GHz,a pair of transmission zeros(TZ)is generated at both sides of the passband by adjusting the dimension of the stub.Defected ground structure(DGS)is also adopted to produce the third TZ.Under the premise of ensuring the compact circuit structure,the out-of-band rejection and frequency selectivity of the filter are greatly improved.The size of the fabricated filter is only 0.29?g×0.26?g,the stopband rejection is better than 50 dB in the range of 3GHz to 4GHz.4.A dual band bandpass filter is formed by loading a complementary split ring resonator(CSRR)in a substrate integrated waveguide(SIW)structure.The lower frequency passband is located below the cutoff frequency of SIW,it is generated based on the evanescent mode of SIW,resulting the decrease of circuit size.In order to enhance the suppression between the two passbands,the DGS structure is etched on both sides of the CSRR.The size of the fabricated filter is only 0.59?g×0.51?g,the 3dB fractional bandwidth of the two passbands is 17.4% and 54.9%,respectively,evidently fit the band characteristics of CRLH structure.The insertion loss is 0.9d B and 1.2d B,respectively,the over-all properties are excellent.5.A quasi planar narrow band bandpass filter with a center frequency of 1 GHz is designed by using double negative cell(DNGC),The spiral resonator contained in the DNGC has a racemic structure which is suitable for miniaturization and almost does not affect the quality factor.The structure of the circuit is analyzed in detail,and the distributed element model and lumped element model are established.The out-of-band rejection is further improved by loading short circuited stubs.The filter has a narrow bandwidth characteristic,the 3dB fractional bandwidth is only 2.2%,and the length is only about 0.17?g,which is reduced by 60% compared with the CSRR filter working at the same frequency.6.A miniaturized ultra wideband bandpass(UWB)filter is designed based on the defect microstrip structure resonator(DMSR).The frequency selectivity and out-of-band rejection is improved by using the interdigital parallel coupled line(IPCL)and CSRR.The fabricated filter is very compact and its size is only 0.51?g×0.12?g,the 3dB fractional bandwidth is up to 129%.After further improvement,the selectivity is greatly improved and the 3dB fractional bandwidth is up to 133%,only with a slight increase in size(0.97?g×0.32?g).