Improved noise characteristics of an X-band helix-TWT combined with a low noise solid state amplifier

Significant reduction of noise figure can be realized by partitioning the high TWT gain about equally between the SSA (solid state amplifier) and the TWT. We report the design study and experimental results of an X-band power amplifier module, consisting of a low-noise SSA and a low-gain helix-TWT. The module consists of the low noise SSA and a low gain TWT. The SSA is a two-stage amplifier where the second stage is configured as a balanced amplifier. The balanced amplifier is designed for achieving a low VSWR and doubling the amplifier power. The active devices of first and second stage amplifiers are a NEC low noise hetero-junction FET and two Mitsubishi power GaAs FETs. The TWT produces a maximum amplified power of 14 W, corresponding to saturated gain of 25.4 dB and efficiency of 21.6 % with a single stage depressed collector.