Linear, Efficient Multi-Carrier Envelope Tracking Power Amplifiers with Frequency Hopping for Phased Arrays

Abstract

An efficient, multi-carrier envelope tracking power amplifier system for next generation phased array applications, capable of frequency hopping over 500 MHz of bandwidth on four RF power amplifiers simultaneously from a single FPGA is presented with performance results. The band-limited Adagio envelope shaping technique enables multi-carrier envelope tracking to enhance RF power amplifier efficiency, while novel digital pre-distortion algorithms that generate multi-waveform models were developed to enhance linearity over wide bandwidths. Crest factor reduction algorithms were used to reduce the high PAPR that is a consequence of wide bandwidth multi-carrier signals. To validate the high efficiency and linearity of this parallelized system while frequency hopping, a combination of four different types of waveform signals, each containing two to four carriers spread across 500 MHz of bandwidth and independently frequency hopping, were tested on four separate ETPA elements simultaneously. Each of the four sub-systems demonstrated post digital pre-distortion results for spectral regrowth of better than -35 dBc, drain efficiency better than 35%, gain of 8 dB to 12 dB, and average output powers of 40 dBm to 43 dBm.