An improved equivalent circuit model of a GaAs FET switch for MMIC phase shifters is proposed that incorporates distributed lines into a lumped-constant equivalent circuit to account for distributed-line effects. The validity of the proposed model is demonstrated by applying a coupled-wave analysis to the FET switch. Comparison of the measured and the simulated phase angles of the S-parameters shows that the improved model gives much bettter accuracy than the lumped-constant model. X-band six-bit MMIC phase shifters designed using the improved model are also described.

This paper describes a monolithic microwave integrated circuit (MMIC) active module with small phase variation and low insertion loss for beamforming network in S-band. The MMIC active module composed of a digital phase shifter, a digital attenuator and a buffer amplifier, has characteristic to control amplitudes and phase shifts by using digital control signals. By using the digital attenuator, the MMIC active module has obtained the excellent performances. This paper also describes the exact on-state resistance of FET switch for designing the digital attenuator.