A High Gain GaAs pHEMT Low Noise Amplifier for Ka-Band Active Phase Shifters

A two-stage common source topology, 36 to 38 GHz GaAs pHEMT Low Noise Amplifier (LNA) was designed, fabricated, and tested. This LNA is an essential part of the proposed active phase shifter for soil moisture radiometer phased array antenna. The LNA provides 23 dB gain. A typical noise figure (NF) of 5 dB was measured at 37 GHz. DC power consumption is about 154 mW. The MMIC chip was fabricated by using $0.15 \mu \mathrm{~m}$ GaAs pHEMT process. The total chip area including all the pads and scribe lines is about $1.5 \mathrm{~mm} \times 0.9 \mathrm{~mm}$. Measured gain flatness is about $\pm 1 \mathrm{~dB}$ within $36-38 \mathbf{G H z}$ bandwidth. The high gain, small gain flatness makes this device well suited for the phase shifters in the soil moisture radiometer phased array antenna.