The performance of a cryogenically cooled X-band amplifier for the geodetic VLBI X-band (8.1-9.0 GHz) is presented. The amplifier incorporates hydrogen passivated InP devices with 0.2×200 μm gate. A comparison of the noise performance with selected commercially available GaAs high electron mobility transistor (HEMT) devices of similar dimensions is presented. The InP amplifier shows lower noise temperature (Tn=4.8 K, NF=0.07 dB) than GaAs, with very low power dissipation (2 mW per stage). This is the first report on the cryogenic noise performance of hydrogen passivated InP HEMT's in this frequency band.
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López-Fernández et al. (1999) studied this question.
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