Method for designing low-pass filters with a sharp cut-off

A novel method for designing a compact low-pass filter (LPF) with a sharp cut-off and wide stop-band is presented. In this technique, a simple open-stub microstrip line is printed on top of a substrate and the desired performance is obtained by optimising the shape of the defected ground structure using the genetic algorithm. Details of the design procedure are presented and evaluated through designing two different LPFs. The first LPF is optimised for a 3.5 GHz cut-off frequency and a stop-band up to 10 GHz, whereas the second one is optimised for a 5 GHz cut-off frequency and the stop-band is extended to 16 GHz. Both filters are fabricated and good agreement between simulation and measurement result is obtained. The designed filters have a sharp transition along with a compact size of 25 ?? 20 ?? 0.787 mm³.