A lowpass filter with a very sharp transition band using
defected ground structures (DGS) is described. The lowpass filter was
designed by using three dumbbell slots at the ground plane. Two
of those dumbbell slots are the reshaped rectangular and the third
dumbbell slot is an inverted triangle. The lowpass filter designed at
cutoff frequency of 3.0GHz, which is suitable for GSM900, GSM1800
and UMTS applications of the mobile communications. The equivalent
circuits for the proposed lowpass filter and its corresponding LC
parameters are given. The proposed lowpass filter provides a size of
33 × 30mm2, and have good transition band with good performance
in the passband and have wide rejection up to 9.25GHz plus harmonic
suppression in the stopband. Measurements results show good
agreements with the simulated results.