40 GHz low noise amplifier

Some of the fundamentals of millimetre wave amplifier design are discussed. Amplifiers, developed by engineers at British Telecom Research Laboratories using GaAs MMIC technology, are described. The designs use 0.3 μm high electron mobility transistor (HEMT) devices, incorporating electron-beam direct-write for the gate strips. The importance of stability analysis has been stressed. The excellent on-wafer gain measurements of the designs have been discussed. The yield of the wafer has been found to be about 50%. The amplifiers provide considerable gain (up to 15 dB) at 39 GHz. With their output power capability, they would be very suitable for use with monolithic oscillators, whose power output is often insufficient to drive monolithic mixers optimally. The noise figure measurements were more disappointing, but this was due to poor device characteristics, and better performance would be expected with lower noise HEMTs. Nevertheless, the excellent gain results obtained so far demonstrate the validity of the BTRL design approach, and provide a sound basis for further development