The Research Of SIR Bandstop Filter

In modern microwave communication systems, with the rapid development in the area of electronic warfare, satellite communication and personal mobile communication, microwave filter as a key component of radio frequency circuit has played an important role. It can be widely used in the system of radar, missile guidance, electronic countermeasures, test instrument. And the merits of communication system are often directly affected by its performance. Meanwhile, due to the development of wireless communication, microwave frequencies are relatively crowded. As well as the requirements of noise, interference, spurious are increasing, the division of frequency band resources is much finer. That's the reason we need to research the band-stop filter which is miniaturization, high performance, low cost and easy to mass production.In order to meet the development of microwave band-stop filter, we analyze the characteristic of band-stop filter based on the structure of step impedance resonator (SIR). In the traditional structure of stripline band-stop filter, the uniform impedance resonators (UIRs) are replaced with SIRs which can reduce the volume and increase the pass-band width. On the basis of these researches, a new structure of dual-band bandstop filter is proposed through frequencies conversion. The coupled stubs are used with cross-section shape, which make the whole structure is more compact and has the advantage of good stopband characteristics. The specific work is as follows:1. The basic structure and characteristics of SIR is researched, and the compact of impedance ratio on resonator characteristic is analyzed.2. A novel SIR structure is applied to design the stripline bandstop filter. The LC coupling is used to design bandstop filter, cross-section structure is used as the mainline and the SIR structure is used as the short line, which replace the traditional quarter-wavelength UIR structure. Finally, a SIR bandstop filter is fabricated and simulated, with the center frequency is 2.45GHz, the stopband width is 270MHz, stopband attenuation is above 70dB, passband insertion loss is below 0.5dB.3. A novel structure of dual-band bandstop filter is designed The SIRs are utilized to implement two parallel connected open stubs with a quarter wavelength long at the respective mid-stopband frequencies to obtain dual-stopband performance. Meanwhile, the coupling stubs are adopted with the cross-section shape. Finally, a dual-band bandstop filter using SIRs while the mid-stopband frequencies respectively at 0.9GHz and 2.4GHz is simulated, with the help of EM simulated software MWO and CST.