Reliability of SSPA's and TWTA's

Two extensive communication satellite reliability studies were conducted in 1991 and 1993. These studies permitted a direct 'in-orbit' comparison at C-band between a thermionic electron device /spl lsqb/TWT/TWTA/spl rsqb/ and a solid state device /spl lsqb/GaAs MESFET/SSPA/spl rsqb/. Excellent performance, lifetimes and reliabilities for both types of microwave power amplifiers were obtained. However, surprisingly, both studies registered higher failure rates for SSPA's than TWTA's.>