AM-AM/AM-PM IN A C-BAND TELEMETRY TRANSMITTER USING 16-APSK

Abstract

Due to the economic importance of spectrum allocation, modulation schemes traditionally used in telemetry are being replaced with more spectrally efficient schemes. Amplitude and Phase Shift Keying (APSK) is one modulation scheme being considered for implementation in aeronautical telemetry. However, an APSK modulated signal is vulnerable to nonlinearities of a transmitter’s RF power amplifier (PA). Driving a PA into saturation produces two undesired nonlinearities: amplitude-to-amplitude modulation (AM-AM) and amplitude-to-phase modulation (AMPM). This paper characterizes the PA in a C-Band transmitter using a 16-APSK test signal in terms of these nonlinearities.