The Research And Design Of Microstrip Ultre Wideband Band Pass Filter

Since 2002, the United States Federal Communications Commission(FCC) issued that the 3.1GHz-10.6GHz band can be used as commercial, Ultra-Wideband wireless communication began to receive wider attention and get rapid development. Relying on the advantages of large capacity of space, high power consumption, fast transmission rate, high gain, well safety performance, powerful penetrating power, strong multipath resolution and so on, the Ultra-wideband(UWB) band pass filter becomes a new communications technology, which is full of huge potential for development. Microwave filter as the indispensable component of microwave system can not only be used to avoid the receiver interference outside the frequency band signal, but limit the radiation of a high-power transmitter in the defined frequency band,which performance can influence the quality of the whole system.In this paper,after researching and analyzing the microwave filter,which is the key part of the UWB system,there several kinds of filter’s design ways that can get the features of high selectivity, wide stopband suppression and compact structure are being put forward. The specific innovative contents are as follows.At first, on the basis of the research status, what the the paper do is research for the existing structure of UWB filters, analyze the basic principle and filter characteristics in order to compare the advantages of them and provide trains of design thoughts and then put forward to the basic theory of filter design, especially the ways of how to implement the single reactive element and resonant circuit in microstrip circuit, which laid a theoretical foundation for the latter filter design.According to the result of analysis, there are three kinds of UWB filters designed out. The first adopt the way of using wide stopband low-pass filter with cut-off frequency 10.6GHz cascade with a miniaturization high-pass filter with cut-off frequency 3.1GHz, in which, the low-pass filter is loaded with unilateral triangular and trapezoidal section stepped impedance while the high-pass filter using the optimal distribution structure. In the low-pass filter, in order to broad stopband to achieve the suppression of at least 27 GHz, the DGS structure is used in the groundside. For high-pass filter, in order to decrease the huge size, there choose to fold the main transmission line to a semi-circle. This structure owns the characteristics of well performance in the passband, far enough suppression in stopband and large structure, which can’t meet the requirement of miniaturization. The second filter is designed by the three mode resonator loading with more symmetrical fan shapes stepped impedance in the center, which has compact structure, small volume, well properties in passband but narrow stopband suppression. The last suspended stripline UWB filer in the vigorous use of the specific double coupling structure. Because of the bend stub adding in both side, the cross coupling will generate to make the sideband more steep. This kind of filter not only performs well in passband, but has minute size. What’s more, the suppression in stopband is broader than other general filters.