A new design approach of high efficiency S-band 25 W mixerless power modulator based on high voltage 50V GaN-HEMT technology

In this paper, a novel concept for efficient and wideband, S band - 25W power modulator designed by taking the advantages of high voltage (50V) GaN HEMT technology is reported. The main objective of this study is to demonstrate the interest of merging both amplitude modulation and power amplification functions without the use of mixer in order to get high efficiency performances (>45%). To fully validate this principle, a two-stage power modulator circuit has been fabricated and tested. It delivers an output modulated (AM) power wave to a 50 Ω load and is based on a variable gain control principle with switched saturated states operating always at maximum Power Added Efficiency (PAE). PAE of around 45 % over 400 MHz RF bandwidth is achieved. With a fixed input power (CW) of 19 dBm, >10 dB output power range is obtained corresponding to 15V to 45V drain bias control, with 2.5 W and 25 W RF output powers respectively.