Balanced bandpass filter with intrinsic common mode suppression using slot coupled lines and microstrip loading lines

摘要

In this paper, a novel balanced filter based on slot coupled lines with microstrip loading lines are proposed. The filter can intrinsically suppress the common mode noise without specially designed. Besides, this kind of filter can achieve much smaller bandwidth than other slot-line-based filter, which is more popular in the practical application. On the other hand, due to the loading lines near the slot coupled line, the length of the slot line can be reduced compared to the previous design, which can further reduce the area. The demonstration filter with central at 2.73 GHz and 36 % bandwidth are shown in this paper. The size of the filter is 0.25 (λg*λg). The minimum insertion loss is 1.7 dB and the common mode suppression is more than 50 dB in the pass band and more than 32 dB below 10 GHz, which is quite strong compared to the published balanced filter.