Design Considerations for GaN based X-Band, High Power and High Isolation SPDT T/R Switch

This paper presents the design considerations for GaN based high power and high isolation single pole double throw (SPDT) switch for X-band applications. The effects of device periphery, off-state parasitic capacitance, gate control voltage, gate control resistance and a method to improve isolation performance is presented. Additionally, a high power and high isolation SPDT switch is also designed using 0.25 μm GaN HEMT process design kit. The reported switch shows insertion loss less than -1.7 dB, isolation better than -38 dB over the entire X-band and isolation of -63 dB at 10.5 GHz. The input and output return loss are better than -18 dB from 8 to 12 GHz. At the same time, it exhibits P₁ dB compression point of 42 dBm. The designed SPDT switch MMIC covers chip area of 1 × 1.95 mm².