Fractal microwave filters

In order to meet the ever increasing demand for miniaturization of RF and microwave filters, the suitability of fractal resonators has been examined and a complete design method of miniaturized fractal filters has been developed. It is shown that fractal resonators can significantly be smaller than conventional planar resonators for the same resonant frequency requirements. It is also seen that when increasing the number of fractal iterations, the size of the resonators decreases and the quality factor increases. The design method for miniaturized fractal filters is based on the synthesis of an inline prototype with symmetrical or asymmetrical pseudo-elliptic characteristics and coupling factor simulations using a commercial electromagnetic simulator. Several fractal filters were designed and built using suspended substrate technology. The fabrication was done in house and with the help of a general purpose printed circuit board company. Judging from the quality of the measured filter responses, the fabrication of fractal filters should not be an issue.