The Design Of Corplane Waveguide/Double Interdigital BandPass Filters

In the year 2002, the U.S. Federal Communications Commission (FCC) issued the ultra-wideband technology, business license, the spectrum ranges from 3.1GHz～10.6GHz, ultra-wideband technology began to receive more and more attentions. As an important element to UWB technology, the performance of the filter play the key role..First, this paper introduced a variety of ultra-wideband band-pass filter structure which are presented by some of the domestic and foreign scholars, and discussed the difficulty that we have to face when make the design of UWB band pass filters.we also introduced UWB bandpass filter characteristics of the parameters required, such as return loss, insertion loss and group delay characteristics and so on.Furthermore, this article described the design of broadside-coupled coplanar waveguide (CPW)-UWB microstrip filter, which is consisted by two symmetric microstrip line above the medium and CPW which is at the same side of the floor, due to the presence of the media, there is a large area of overlap between the microstrip line and coplanar waveguide, result to a strong coupling to implement UWB passband. Because of the existence of the step impedance characteristics in the microstrip line, the first three resonant points of the designed UWB bandpass filter evenly distributed in the passband.Finally, the paper analyzed the feature of the unit interdigitalalso, and introduced a new type design of double-interdigitated UWB band pass filter. After adding 4 small loads to the double cross that line parallel to the filter, not only for ultra-wideband passband requirement but also the characteristics of high and low frequencies had also been highly improved, the article also analyzed some of the features of the cell three cross-finger parallel filter, passband group delay is less than 0.25ns, return loss less than 10dB, insertion loss less than 0.5dB.