Research Of Embedded Tri-band Microstrip Filter

The wireless communication industry develops rapidly since the21stcentury.With the existence and application of WCDMA, WIMAX and WLAN, the singlechannel signal cannot meet the needs of modern communication system and it will bereplaced by multi-channel signal gradually. Filter, a significant part of the RFcommunication system, should be designed into multiband filter.Aiming at the request, we study the tri-band bandpass filter and propose theembedded structure to realize the tri-band filter in this paper. Compared with the filterwith traditional structures, such as series-parallel filters, coupling matrix synthesis andmulti-mode resonance, the filter with embedded structure has a small size, and is easyto design, and we need not to consider the coupling coefficient between two differentbands.We have designed two kinds of tri-band filter in this paper. In chapter four, thetri-band filter is realized based on embedded SIR(Stepped-Impedance-Resonators)structure. Firstly, we design three pairs of SIR with the shape of C, and each pair ofSIR is equal to a filter with a proper center frequency. Secondly, we embed the smallersize SIR which controls high center frequency into the bigger size SIR which controlsthe low center frequency. After three times of attempts, the tri-band filter is realizedand its center frequencies are2.4/3.5/5.2GHz. In chapter five, we design a tri-bandfilter by embedding two bandstop filters into a broadband bandpass filter. The mainsolution is that we load the bandstop elements on the coupling elements of bandpassfilter so that we can split the band of ultra-band bandpass filter into three bands. Finally,a tri-band filter with the center frequencies2.4/3.8/5.2GHz is realized and simulated byADS. Therefore this method proves effective and feasible.