Abstract: In this paper,a simple and effective method to extract characteristic impedance and effective relative permittivity of equivalent even transmission line realized by defected ground structure has been presented.Then,the variation of characteristic impedance and effective relative permittivity with frequency of defected ground structure are compared with those of microstrip.Finally,two Chebyshev lowpass filters employed defected ground structure have been designed,fabricated and tested.It shows more than 5dB improvement in maximum stopband attenuation compared to the same designs using microstrip.Moreover,fabrication difficulty for high impedance microstrip has been avoided.