PREAMPLIFIER AND HIGH‐POWER AMPLIFIER

The high‐power amplifier (HPA) amplifies the radio‐frequency signal to a high level for the payload downlink. Before the signal even goes to the HPA, a preamplifier has to boost the signal to a level proper for input to the HPA. The HPA subsystem has the following functions: pre‐distortion to counteract the HPA's nonlinear amplification characteristics, high‐power amplification, and DC power provision. The HPAs are the biggest consumer of satellite DC power for a non‐processing payload. The chapter looks at the variations in subsystem architecture. The traveling‐wave tube amplifier (TWTA) subsystem has a rather wide range of embodiments and terminology to describe them. All traveling wave tubes have small, aperiodic variations in their small‐signal gain and phase responses versus frequency. The solid‐state power amplifier (SSPA) is different from the TWTA subsystem in that the SSPA unit contains the preamplifier, linearizer if any, and DC power supply.