Theory Research And Design Of Novel Multi-mode And Muti-band Bandpass Filter

Microwave bandpass filters have applications in the transmitter and receiver of telecommunication system.It is a very important microwave component which is used to filter the signal from the antenna or modem to remove noise and guarantee the availability and stability of the system.In engineering practice,microwave filters have the types of planar filters,cavity filters,lump-component filters et al.Among these types,microstrip filter is a kind of planar filter with advantage of simplicity of structure,fabrication and integration.So,it has a wide application in engineering.And the design method of microstrip filter is making transformation of lump component filter prototype into microstrip structure.Nowadays,with the development of telecommunication technology,spectrum become a kind of scant resource.So,some systems like wireless local area network start to work at multi-frequency.And multi-mode and multi-band bandpass filter is highly desired.Now these researches are mainly focus on the methods of tri-band filter design,insertion loss reduction,stopband rejection,miniaturization and so on.In this paper,existing methods of multi-mode and multi-band filter are introduced and expanded.And some novel methods are introduced,too.Firstly,a kind of asymmetrical stepped impedance resonator is pointed out its application in dual-band filter design.Then,novel tri-band filters based on cross-coupled resonator and stub-loaded resonator are introduced.And they have good insertion loss and stopband rejection.At last,a miniaturized dual-band filter is designed based on the former three kinds of technologies and defected ground structure.Besides,the methods of equivalent circuit extraction are also studied in this paper and an equivalent circuit of a tri-band bandpass filter is extracted.Moreover,most of the filters in this paper are fabricated and measured,and the measured results agree well with the simulated results.