Transmitters using Power Amplifiers

TWT amplifiers have traditionally been used for microwave communications links requiring high power amplifiers. The mean-time-before-failure (MTBF) of traveling wave tube amplifiers (TWTAs) is low compared to solid state power amplifiers and generally limits the communication system performance. The frequency and power capabilities of solid state amplifiers using FETs and IMPATT devices have been advancing rapidly in recent years. Transmitters with higher than 20-W output power and reasonably high power added efficiency are possible at Ka-band due to recent device improvements. Computer simulation results also indicate that FETs can deliver more linear power than a conventional TWT. An important advantage of SSPAs is the reliability of the device itself. This aspect will be discussed in detail. Theoretical calculations show that 30% power added efficiency at the device level can be achieved at Ka-band with state-of-the-art material and fabrication technologies. Some proposed approaches to improve the frequency, power, and efficiency achievable with FET SSPAs in the near future will be discussed.