Design Of High-performance Filter Based On Microstrip Line

For the past few years, with the leap-forward development of communication techniques, the developments of communication modes are diversities and multi-modes.Within the limited spectrum resources, spectrum is becoming more and more crowded.Available frequency space assigned to different communication systems is becoming narrow; moveover, the modern wireless communication technology also towards the direction of miniaturization and high performance, gradually. And highly integrated development is also the trend of the time. Therefore, as an important passive components in communication system, the development and research of filter is very significant. Multi-mode development of communication system present more and more stringent requirements for filter performance. Especially in the wireless data services,such as GSM、WLAN、WCDMA、WIMAX、Bluetooth, and put forward a higher requirement for compatibility between the spectrum, spectrum utilization and requirement of small size, high selectivity, low insertion loss, low power consumption but also the restraint outside the band. So the ultra wideband bandpass filter and multi-band bandpass filter become the main direction of scholars’ study, and this article mainly introduce ultra-wideband bandpass filters and multiband bandpass filters. Main research of this article can be generalized as:First of all, we make an careful earnest study and summary at related research achievements at home and abroad, obtain the research focus and the present situation of ultra-wideband bandpass filter and multiband bandpass filter. And then, the technical index of filter, the design method and basic theory of resonator are introduced,moveover introduce the synthesis method of ultra-wideband filter, multiband filter and several kinds of common resonators. And make a detail introduction about the design fundamental of ultra-wideband filter multiband bandpass filter.Second, we analyze how to design ultra-wideband filter on the basis of multi-mode resonator. Frequency characteristics of the multi-mode resonator are introduced, and then design two ultra-wideband bandpass filters based on multi-mode resonator applied to the Indoor UWB Systems, the center frequency and bandwidth of the two filter are6.75/6.8 GHz, 7.5/7.8 GHz, respectively. Through introducing inductive coupling and capacitive coupling in the input and output structure to generate the transmission zeros,in addition, the transmission zero position can be dominated through revising the amount of inductive coupling or capacitive coupling to achieve high-selectivity. The simulation and experimental results agree well.Finally, how to design multiband bandpass filter is introduced. Two novel compact high-selectivity microstrip triband bandpass filters are designed. The first one is applied to GSM/WiMAX/WLAN, to achieve high-selectivity a nonuniform coupled-line with two U-folded shapes on one line is proposed. The second filter is applied to WiMAX/WLAN based on two asymmetric λ/4 resonator pairs.