The effects of adaptive genetic algorithms (AGAs) and defected ground structures (DGSs) on performance optimization of tapered\r\nmicrostrip filter are investigated. The proposed structure achieves an ultra wide stopband with high attenuation within a small\r\nsurface area, as well as 45% smaller size, in comparison with conventional filters. The parameters of the filter are optimized using\r\nin-home AGA code. In the proposed AGA algorithm, the crossover and mutation probabilities are adaptively changed according\r\nto the value of individual fitness. Then by utilizing the proposed DGS, a compact S-band lowpass filter with ultra-wide spurious\r\nfree window is obtained. The proposed filter achieves an insertion loss of 0.8 dB from DC up to 4 GHz and 21 dB rejection in the\r\nstopband from 4.3 up to 60 GHz. The fabricated and measured results exhibit good agreement with the simulated results. They\r\ndemonstrate that combining AGA and DGS yields best possible response for this group of filters.
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