Miniaturized fractal rat-race band pass filters

A miniaturized fractal rat-race bandpass filter based on signal-interference technique is presented. The proposed topology uses fractal rat-races operating as transversal filtering sections (TFS). Under signal-interference principle, the filtering action comes through the generation of multiple out-of-band power transmission zeros and constructive in-band signal combinations. The filter is implemented in two stages. Simulated results show that single stage gives an in-band input matching of better than 15 dB and in-band insertion loss of less than 1dB. Roll-off is around 25dB on lower frequency edge. Similarly, double stage filter has an improved in-band matching of better than 19 dB with an insertion loss of 0.9dB and 55 dB roll-off at the lower edge of the passband. The filter exhibits a pass band characteristic from 1.09GHz to 1.88GHz.