A novel fractal geometry for harmonic suppression in parallel coupled-line microstrip bandpass filter

In this paper, we present novel fractal geometry for suppression of second, third and fourth harmonics in parallel coupled-line microstrip bandpass filter (PCLM-BPF). This new fractal geometry is obtained by finding the best shape for fractal generator curve using genetic algorithm. The PCML-BPF design is initiated using a classical methodology and is finalized by modification of the line-edges with the new fractal geometry. Therefore it is easy to design and fabricate this kind of filter. To validate this novel geometry, third-order Butterworth bandpass filter have been designed and fabricated at 2.5 GHz with a 10% fractional bandwidth on RO3003 substrate. The numerical and experimental result of this new geometry, confirms that there is 5 dB more decrease on second, 18 dB on third and equal decrease on forth harmonic compared to Koch fractal geometry and about 45 dB on 2^nd, 12 dB on 3^rd and 32 dB on 4^th in comparison with the conventional filter. Unlike the Koch fractal geometry which increases the magnitude of the third harmonic even than conventional filter our new fractal geometry decreases the magnitude of this harmonic.