A novel amplitude equalizer is designed based on the band notch characteristic of Defected Ground Structure(DGS). To replace the resonance associated with resistance in traditional amplitude equalizer, two resistances are put into ‘I’ type of DGS. By increasing the width of microstrip line, the characteristic impedance variation effect of DGS is eliminated, so does the bad Voltage Standing Wave Ratio(VSWR). This kind of equalizer is characterized by convenient regulating, ultra wideband, small size, simple structure and easy to processing. 3D electromagnetic simulation results and testing results have proved that this amplitude equalizer can work at 12-40 GHz (Ku to Ka waveband).The Return loss is less than 13.5 dB. The equilibrium quantity can reach 17 dB. The insertion loss is 2.1 dB at sideband. The size is 8 mm×8 mm.