Research And Design On The Wideband And Multiband Of Based On The Microstrip Structures

With the phenomenal development of science and technology, wirelesscommunication has been widely used in our life. A lot of new wireless communicationdata services are realized and adopted, Such as GSM, WLAN, WCDMA, WIMAX,Bluetooth and so on. Microwave filter have been promoted a tremendous developmentwith communication industry progress. In order to improve the demand on compatibleof different communication system and sufficient usage of frequency spectrum, thedesign technology of wideband and multiband filter has became the main direction tothe research scholars. Based on the analysis of microstrip structures, such as SuspendedStripline Structure(SSS) and Stepped Impedance Resonators(SIR), wideband andmultiband of microstrip filters are designed. The author’s works mainly consist of:By analyzing the synthetic methods of filter, the coefficient between the resonatorsand the external Q factor are used to design filter. Based on this method, a broadbandinterdigital filter is designed, and the center frequency is1.45GHz, the fractionalbandwidth is48%, the average insertion loss is1dB. By using the same method andtaking advantages of the characteristic of the-type circuit and the SSS, a broadbandSSS filter is presented. Its center frequency is10GHz, the fractional bandwidth is60%,the average insertion loss is1.5dB, and out band rejection at6GHz and14GHz aremore than18dB. By adjusting the spacing between the resonators and keeping thestructure of circuit unchanged to meet the different coupling coefficients, a differentbandwidth of the filter is achieved. Comparing with broadband interdigital filter, theadvantages of SSS is obvious to design the broadband filter and the SSS has aprospective application.Based on the theory of microstrip resonator and using the method of the odd andeven mode to analyze the resonance characteristics of the SIR and T-shaped structure, itis demonstrated by the experiment that the SIR has the characteristics of theminiaturization and the spurious response moving to the high frequency. Then, bytaking advantage of the characteristic of SIR, two novel dual-band open-loop bandpassmicrostrip filters are designed, which are composed of two half-wave SIR with high-impedance short-circuited ends. The center frequency f1, f2are2.55GHz and6.2GHz respectively. The fractional bandwidths are3.8%and3.2%, the two passbandf2/f1>2, and the out band rejection are more than15dB at3GHz and6.5GHz. With theaid of source-load coupling which is employed in the second circuit, extra transmissionzeros can be created. The out band rejection at3GHz and6.5GHz are more than20dB.And, the performance in transition bands is improving. With the introduction of extratransmission zeros does not affect the bandwidths, so the transmission zeros areindependent to design the center frequency and bandwidths. The measured results showgood agreement with the simulation.