A millimetre-wave 6-bit attenuator with high accuracy and low insertion loss by 0.15μm GaAs PHEMT process is presented. A proposed structure is adopted to enhance the attenuation accuracy. A cascade structure is proposed to enhance isolation and compensate the insertion loss. The measurement results show that it has 0.5 dB resolution and 31.5 dB attenuation rage while the return loss is better than -10 dB for all states. The attenuation accuracy is better than 0.5 dB while the RMS attenuation error is less than 0.21 dB. The insertion loss is less than 5.7 dB while the insertion phase shift is less than -6.0°.
